This section of the JOURNAL OF AGRONOMICEDUCATION began with Volume 2, and it is meant as aconvenient place for the reader to browse. Publishers sendus copies of books, and we persuade experts to review them.We also write short descriptions of some books and listothers. The number of cooperating publishers and review-ers is increasing. The bookload is heavier in the text andtechnical areas than in education. We believe that the bal-ance will shift as publishers in the education field learn ofthe Journal.

This section is directed more to the scientist-teacherthan to the teacher-scientist. The reader would do well torecommend books here to students only after determiningtheir level and applicability. The reviews definitely willserve as a convenient guide. The listing of books and thebrief descriptions, which were staff-written, are an effort togive the specialist an opportunity to alter course content ascurrent book literature is generated in subspecialties.

Do we recommend every book reviewed, described, andlisted? No. Bookshelf is neither testing lab nor academy.We just obtain new books, find reviewers, write descriptions,and list books. We have a single case to report with a "bad"book. Charles Roland, of Mayo Clinic, thinks that "bad"books should be reviewed. In our case, we asked a recog-nized authority to review a rather specialized book. He de-clined to write a "bad" book review. A second expert saidthe book would not serve the student well. We decided notto list the book.

Our selection this time is quite large. Even our formerEditor, who recommended the foundation of Bookshelf, hasreviewed an education book, and this year’s harvest of cropproduction volumes is especially high, maybe because of theemphasis on intensive agriculture. A couple of global viewscomplement the selection of books on specialized subjects.

AN INTRODUCTION TO CROP PHYSIOLOGY--F. L.Milthrope and ]. Moorby, Cambridge University Press,London. 292 p. Hardback, $11.95; paperback, $5.95.

The book is well written and illustrated, and is conciseand logical in its presentation. A quantitative treatment ofthe subject of crop growth and development is a majorpoint of emphasis of the book. The author’s statement setsthe tone for this approach

Having obtained sufficient qualitative appreciation ofthe various components of the system, it is then pos-sible to measure them and relate each to the other.This involves finding suitable relationships betweenthe magnitude of a process and the variables whichdetermine if, of putting these together in such a waythat the magnitude in any stated set of circumstancescan be predicted, and of then assessing the interplay

between the different component processes so thatthe behavior of the whole can be predicted.

The quantitative relationships among the various physio-logical processes are, of necessity, considered in mathemati-cal equations. A knowledge of differential and integralcalculus is essential for an understanding of many sectionsof this book. Some background in soil chemistry andphysics would be helpful because of the emphasis in certainparts of the book.

The book provides an up-to-date treatment of the topicscovered, but at a somewhat elementary level. The selectionof topics is good, but there are significant omissions whichare noted for each chapter. The book appears to be a goodtext for a course in crop growth or physiology, assumingadequate prerequisites of math and plant physiology, andsome familiarity of micrometerology and soil science. Theexamples utilized in the book emphasize perennial foragesand small grains, with rather limited treatment given tocorn, soybeans, and other major crops in the U. S. A limitednumber of references (primarily books) are cited at the endof each chapter. A brief analysis of each chapter follows:

Chapter 1 presents the philosophy and organization ofthe book with a brief outline of growth and differentiationof plants.

Chapter 2 The environment. The soil environment andthe aerial environment are the two major topics covered inthis chapter. Good coverage of mineral nutrient availabilityin soil is given, especially in the area of ion movement toplant roots. Soil water, atmosphere, temperature, andstructure are covered in a rather brief fashion. The "aerialenvironment" consists principally of radiation and its utiliza-tion by crop canopies. The scope of this treatment is ade-quate for an introductory crop physiology text. Thischapter suffers from a failure to consider other major en-vironmental factors that affect plant growth such as tem-perature, light duration including photoperiodism, and en-vironmental stress conditions.

Chapter 3 The supply and use of water. Water absorp-tion by roots and loss from the leaf canopy comprise themajor portions of this chapter. The treatment is quantita-tive in nature with numerous equations expressing themetabolic and physical processes involved in water absorp-tion and loss from leaf canopies. There is little coverage ofcellular water relations and water use efficiency by plants.

Chapter 5 Photosynthesis and respiration. Good cover-age of topics including the physics of CO2 diffusion into theleaf and photochemical aspects of photosynthesis. Environ-mental affects on photosynthesis including light, tempera-ture, water, minerals, and CO2 concentration are brieflycovered. Rather thorough coverage of photosynthesis andrespiration of plant communities makes this one of the bet-ter chapters in the book.

Chapter 6 Germination and seedling emergence. Seeddormancy, water uptake, and metabolism are rather brieflytreated, but major points in these areas are mentioned andexamples provided. Bud initiation and growth in vegetativeorgans provides an interesting section to this chapter. En-vironmental affects on germination, including temperature,water, and depth of seeding comprise the remainder of thechapter. Major deficits of this chapter are the omission of

107

108 BOOKSHELF

the role of growth regulators in seed germination, vernaliza-tion, and the too-brief treatment of the biochemistry andmetabolism in seed germination.

Chapter 7 Vegetative growth. Generation of cells, tis-sues, and their differentiation into leaves, stems, and rootscomprise the major part of this chapter. Numerous figurestrace the development of these organs over time and reflectthe quantitative changes taking place. Mathematical analysisof vegetative growth is developed to a limited extent in thischapter. A major deficiency of this chapter is the lack oftreatment of plant growth regulators in plant differentiationand photomorphogenesis.

Chapter 8 Flowering and fruit growth. Anatomical andmorphological descriptions of the differentiation and growthof flowers and stems constitute a major portion of thischapter. Quantitative and qualitative changes in these or-gans over time are illustrated through several graphs pre-senting a rather comprehensive picture of the developmentand growth of the flower and fruit. The rather considerableinvolvement of phytochrome(s) and photoperiodism floral initiation is only briefly touched upon and the area ofmaturation of the grain is almost entirely absent.

Chapter 9 Some aspects of overall growth and its modifi-cation. The quantification and mathematical analysis ofgrowth and "growth analysis" provide a significant portionof this chapter. Dry matter production and nutrient ac-cumulation with ontogenety of the plant organ and environ-mental influences provide the other area of emphasis to thischapter. Coverage of these two topics is very good andnumerous illustrations provide for ready grasp of the in-formation. An interesting section on spatial relationshipsof crops and their quantitative relationships provide a goodinsight into plant growth and development under increasingpopulation pressure. This chapter is one of the highlights ofthe book.

Chapter 10 The predict.lon of responses. Model buildingto predict crop productivity given inputs of crop growth anddevelopment, environmental parameters, and to a limiteddegree crop genotype are discussed in this chapter. Al-though the ideas presented are intriguing, too little informa-tion is presented to provide the reader with sufficient in-sight to fire his imagination into the possibilities of modelbuilding.

I found the book generally suitable to fill a gap in thearea of crop growth and crop physiology without a heavybiochemical emphasis which is characteristic of plant physi-ology texts.--L. H. Smith, Department of Agronomy andPlant Genetics, University of Minnesota, St. Paul, MN 55101.

methods for measuring photosynthesis. It includes a dis-cussion of the process of photosynthesis itself and a discus-sion of how methods are related to the aim of the study,the type of equipment available, and the labor required tomake particular measurements. The remaining chapters in-clude discussion of principles and design of gasometricmethods; the design and use of infrared analyzers for CO2and of other physical analyzers for CO2 and 02; and theuse of manometric, volumetric, chemical and isotopic meth-ods to measure CO2. Other chapters discuss photorespira-tion, radiation, stomatal apertures, diffusive resistance, leaftemperatures, chlorophyll, and growth analysis and ap-propriate methods to measure them. All chapters have ex-perienced, reputable authors. Each chapter has an ex-tensive’, up-to-date reference list. The manual comes in hardcover and is printed on high quality paper. The authors ofthe chapters are to be commended for the quality of theindividual chapters; the editors have drawn these chapterstogether in an effective manner to make a complete andintegrated volume. The reader will find this volume to be aconvenient and authoritative source for information on anyof the topics listdd above. The manual is not merely a de-scription of methods; rather the subject matter of eachtopic is reviewed as well. An attempt is made to bring orderto nomenclature and to help the reader understand whycertain terms (and certain types of measurements) are inap-propriate in various situations. Thus, it should be a usefulreference for the teacher, the student, and the researcher.The chapters are intepretive and, therefore, carry the bias ofthe individual authors; this fact is inevitable since nostandard interpretation or nomenclature exist. Nevertheless,the stature of the authors, the extensive literature citations,and the quality of editing result in a document which has ahigh degree of acceptability. The volume, if widely read,could add much to the exactness of general usage and ofliterature presentations on topics related to photosynthesis,some of which (radiant energy measurement and expression,for example) are widely abused in present plant science ex-perimentation and literature.--Dale N. Moss, Professor ofCrop Physiology, Department of Agronomy and PlantGenetics, University of Minnesota, St. Paul, MN 55101.

WEED CONTROL HANDBOOK, VOLUME 2, RECOM-MENDATIONS--J. Fryer and R. Makepeace. BlackwellScientific Publications, Oxford, England. Distributed inthe U. S. by F. A. Davis Company, 1915 Arch Street,Philadelphia, PA 19103. 1972. 7th Ed. 424 p. Hard-back, $16.00.

PLANT PHOTOSYNTHETIC PRODUCTION. Manual ofMethods--Z. Sesthk, J. Catsk~ and P. G. Jarvi~ (Eds.).Dr. W. Junk, N. U., The Hague. 1971. 818 p. 175Dutch Guilders.

This manual is based on a Czech predecessor published in1966. All of the chapters have been rewritten and expandedand the present version contains 19 chapters on separatetopics with contributions from 35 authors from 10 coun-tries. The introductory chapter is a discussion of suitable

The British Crop Protection Council first issued the WeedControl Handbook in 1958. It consists of two volumes.Basic principles about weeds and their control with em-phasis on chemical control are covered in Volume 1. Herbi-cide recommendations is the subject of Volume 2, now inits seventh edition. Plant growth regulators are covered forthe first time in this new edition. Volume 2 no longer willbe revised every 2 years as done previously. Increasedpublication costs and a wealth of well-established weed con-trol recommendations make it impractical to do so. This

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974

edition will not be replaced or revised for at least 3 to 4years. The text of the seventh edition has been completelyrevised and much of it rewritten. Numerous new recom-mendations have been included. Each recommendation hasbeen cleared for safety to humans, domestic animals, andwildlife under Great Britain’s Ministry of Agriculture,Fisheries and Food. Readers in the United States must keepin mind that the recommendations are valid for crops grownin Great Britain and Northern Ireland. Each chapter hasbeen written by a team of specialists from universities, in-dustry and official organizations. Some 55 contributors, allspecialists on the use of herbicides and plant growth regula-tors, provided the information for this new edition. Thechapter on plant growth regulators covers general informa-tion, recommendations, and technical data and is relevantto both volumes of the handbook. The metric system isused throughout this edition. A handy, loose conversiontable is provided with the book and another is included inthe appendix. The BSI-approved common chemical namesare used for the nomenclature of herbicides. Names ap-proved by the Weed Science Society of America have beenadopted where BSI-approved names do not exist.--Larry W.Mitich, Extension Agronomist, North Dakota State Univer-sity, Fargo.

SOIL ORGANIC MATTER AND ITS ROLE IN CROPPRODUCTION--F. E. Allison. American Elsevier Sci-entific Publishing Company, Inc., New York. 1973.637p. $52.00.

This is a truly outstanding and timely book that willhave wide appeal to all agronomists. It is anticipated thatextensive use will be made of the book as a reference textin graduate and undergraeluate courses in soil science. Al-though major emphasis is given to the more practical aspectsof soil organic matter, the volume contains a wealth of in-formation of interest to the research specialist. The bookrepresents the final contribution in the remarkable careerof Dr. Allison and is a fitting monument of his life’s work.Essentially, the book covers soil organic matter in its broad-est sense, which is a reflection of the authors breadth ofknowledge on the subject. Dr. Allison has brought togetherin a single volume his years of experience in the fields ofsoil organic matter, soil microbiology, and nitrogen trans-formations. Opposing viewpoints are presented fairly andimpartially, but, in the end, Dr. Allison selects the optionwhich in his considered judgment is correct, and he does sowithout imposing his interpretation on the reader. Teach-ers, students, researchers, and extension workers will ap-preciate Dr. Allison’s refreshing writing style and ability toarouse interest. A possible shortcoming of the book is apaucity of illustrations. The volume consists of 30 well-written chapters arranged into 7 sections. The first section,represented by a single chapter, includes a thought-provok-ing essay on agricultural practices throughout the centuries.Subsequent sections are:

The Soil and Living Matter In It Chapters 2 to 5Formation and Nature of Organi~

Matter In Mineral Soils Chapters 6 to 9

109

Sources and Possible Fate ofNitrogen In Mineral Soils Chapters 10 to 13

Functions and Effects of OrganicMatter In Mineral Soils Chapters 14 to 19

Some Organic Matter and CropManagement Problems InMineral Soils Chapters 20 to 28

Organic Soils Chapters 29 to 30The various chapters explain in layman terms the forma-

tion and nature of soil organic matter, its dynamic function,influence on physical, chemical, and biological processes,gains and losses of soil nitrogen, management problems in-volving mulching and green manures, and organic mattermaintenance. Topics of special interest for the environ-mantalist include Chapter 13 (Loss of Nitrogen from Soils),Chapter 26 (Growing Crops on Subsoils and Mine Spoils),Chapter 27 (Organic Matter and Soil Conservation), andChapter 28 (Organic Farming). Other highlights of the bookinclude Chapter 16 on soil aggregation and root develop-ment, Chapter 18 on phytotoxic substances, and Chapter19 on plant disease control. The nature of the book is suchthat many readers will not read all sections with equal en-thusiasm but everyone will find material of interest. Be-cause of the wide range of topics considered, extensivecoverage of any individual item was not possible. The re-search specialist will recognize deficiencies, but this is to beexpected in abook of this type. References cited in the textare generally appropriate although many deserving paperswere missed. The book is printed on high quality paper andis relatively free of errors. Only its high price ($52.00) willkeep the volume from the bookshelves of many scientists,educators, and students.--F. J. Stevenson, Department ofAgronomy, University of Illinois, Urbana-Champaign, IL61.801.

WORLD FOOD PRODUCTION, DEMAND AND TRADE--Leroy L. Blakeslee, Earl O. Heady and Charles F. Fram-ingham. Iowa State University Press, Ames, IA 50010.417 p.

The purpose of this book as stated by the authors is "toproject food production and demand in terms of majorvariables and trends reflected in the recent past" (pp. 17-18). The book is presented in three parts. Part I discussesthe historical perceptions of the world food problem as wellas the methodology applied in the study. Part II presentsprojected production and demand for major food comomodifies up to year 2000 in 96 countries. Furthermore,this part discusses the implications of new production tech-nology and public policy. Finally, part III discusses inter-national trade in cereals, fertilizers, and phosphate rock.

The authors conclude that the world food situation isnot likely to deteriorate during the next three decades, as-suming free trade in foods. It should be noted that the dataseries used in the study terminates in 1970. Hence the re-duction in food production during the last 2 years is notrepresented in the projections. The projections suggest thatlarge food deficits are likely to develop in most of Africaand West Asia if past production trends are continued.

110 BOOKSHELF

Furthermore, Latin America as a whole is expected to bedeficient in food by year 2000. On the other hand, thestudy predicts considerable food surpluses in North Americaand Oceania.

It should be noted that the terms "deficits" and "sur-plus" refer to the difference between projected productionand effective demand, and not production versus nutritionalrequirements. Because of lack of purchasing power amonglarge portions of the population in most developing coun-tries, fulfillment of effective demand would not assure ful-fillment of nutritional requirements by any standard. In-creasing purchasing power among low income groups couldgreatly increase food demands, hence expand the gap be-tween production and demand in developing countries, thenet result being drastic increases in food prices.

The importance of population control in assuring suf-ficient food for the world population is emphasized by theauthors. Current rates of population growth must be severe-ly reduced if sufficient food is to be assured. The so-calledGreen Revolution, even if successful, is only a stop-gapmeasure unless population trends are drastically reduced.

No attempt is made to include in the projections the im-pact of recent break-throughs in agricultural productiontechnology. As noted by the authors, the study attemptsto "evaluate the consequences of a continuation of recenttrends" (p. 29). Hence, its real value for future decision-making on agricultural development refers to its ability topoint out where corrective public policy measures areneeded. This reviewer does not attempt to evaluate themethodology used in predicting the trends.

In Chapter 11 on "Outlook under the Green Revolutionand Government Policy" the authors suggest that if knowl-edge of more productive and profitable inputs is generatedand communicated broadly, farmers everywhere will makerapid progress in applying them. Unfortunately it isn’t thatsimple. How do we reach the other 50 to 75% of the farm-ers? There is much evidence that the gap is widening. Whathappens to 7 out of 8 children born on the small farm butwho cannot continue to make their living there?

The book provides a useful contribution to the data baseon the world food vs. population situation and will un-doubtedly help us to better understand these related prob-lems and how to deal with them in the future.

The reviewer is grateful to Drs. P. P. Andersen andAlberto Valdes, Agricultural Economists on the CentroInternational de Agricultura Tropical (CIAT) staff, whocontributed to this review.--U. J. Grant, Director General,CIAT, Call, Colombia.

FORAGES: The Science of Grassland Agriculture--Mau.riceE. Heath, Darrel S. Metcalfe, and Robert F. Barnes (Eds.).3rd ed. Iowa State University Press, Ames, Iowa. 1973.755p. $18.95.

This book is the basic text in the United States forcourses in the forage crops and should remain so. It iscomprehensive in scope and thus adaptable to a widevariety of instructional needs. It is, as well, a useful refer-

ence for most scientists and applied agronomists concernedwith the forage crops. Many animal industries people willalso find it of value. Arranged in four general subject mat-ter parts, the book covers forages and a productive agricul-ture, forage grasses and legumes, forage production practice,and forage utilization. Any of these, with reasonable ampli-fication, could be the subject matter of a separate book.The text continues the increasingly common practice ofbeing compiled rather than authored by a single writer. Assuch, it has the strengths not ordinarily found in textbooks.The 96 authors have provided expert handling of subjectmatter of each chapter and subject matter is current, thoughconstrained by the obvious limits imposed in keeping thebook to manageable size. Compiling this textbook, evenwith the planned approach employed in developing it, is notwithout some drawbacks. There is not the continuity thatwould flow from the pen of a single author, and coverageof a subject tends to stand apart from that provided byothers. One drawback is the use of the metric systemthroughout. While the reviewer recognizes that thissystem’s use will be mandated in the future, he argues thatthe usage is out of step with common current usage in thefield. Obviously the data reported have all been laboriouslyconverted to the metric system but the reader must convertback to the English system to use or interpret the informa-tion. Remarkably little discussion is given to corn as a for-age crop. The importance of this crop for forage shouldjustify at least a chapter in the book. The book is well-illustrated and well-referencecl. It is remarkably free oferrors. Expression generally is clear, but occasionally ob-scured as authors have labored to keep length of chapterswithin bounds. This limiting of discussion occasionally re-quires some prior knowledge for full understanding of thesubject matter discussed.--Walter W. Washko, Departmentof Plant Science, The University of Connecticut, Storrs, CT06968.

CORN. ITS ORIGIN, EVOLUTION, AND IMPROVE-MENT-Paul C. Mangelsdorf. Harvard University Press.Cambridge, Mass. 1974. 262p. $20.00

In this interesting book, the author brings together andsynthesizes much of the previously published informationdealing with the origin, evolution, and improvement ofcorn.

Dr. Mangelsdorf has spent nearly half a century tryingto unravel the mystery of the origin and evolution of corn,and he effectively tells the story as he sees it. Not all sci-entists who have worked on the origin and evolution of corncompletely agree with Dr. Mangelsdorf’s theories that cul-tivated maize originated from a wild corn similar to podcorn, that teosinte is a derivative of a hybrid between maizeand Tripsacum, and that modern corn varieties are the resultof introgression of teosinte or Tripsacum germplasm or bothinto maize germplasm. The author attempts to point outwhere disagreements exist and indicates why he thinks hisconclusions are valid.

This book is not only a story of corn but of people andcivilizations associated with the origin, evolution, and

JOURNAL OF AGRONOMIC

domestication of corn. Much of the evidence upon whichthe author bases his conclusions comes from archeologicalinvestigations in the once inhabited caves in Mexico andSouthwestern USA. He draws on evidence from prehistoricart forms from ancient civilizations in Mexico and Peru.Fossil pollen discovered in drill cores taken more than 200feet below Mexico City was analyzed and entered into theconclusions reached.

The book is recommended reading for anyone interestedin corn breeding and genetics or in the origin and evolutionof corn. Most plant breeders would profit from reading thisfascinating story.

The genetic studies involving maize and its closest rela-tives teosinte and Tripsacum, and the author’s attempts toreconstruct an ancestral form of corn are presented in aninteresting fashion. The last two chapters present an ex-cellent summary of the findings regarding the nature ofheterosis and discuss some of the modern breeding tech-niques. Unfortunately full-sib reciprocal recurrent selection,which appears to be one of the most promising new breed-ing methods for simultaneous production of new hybridsalong with population improvement is not mentioned. How-ever, he does mention reciprocal recurrent selection asoriginally conceived by Comstock, and his coworkers.

In utilizing exotic germplasm, the author proposes thatexisting inbred lines should be crossed to exotic germplasmfollowed by backcrossing to the line once or twice prior toselling to develop an improved line for use in hybrids. Hedoes not suggest incorporation of exotic germplasm intoadapted segregating populations and the use of recurrentselection procedures to improve such populations prior toinbreeding and the development of new inbred lines. Hissuggested precedure will undoubtedly give favorable resultsmore quickly, but the latter should not be overlooked froma long-term point of view.--C. O. Gardner, Department ofAgronomy, University of Nebraska, Lincoln, NE 68503.

EDUCATION, VOL. 3, DECEMBER 1974 111

CROP PRODUCTION--Harold D. Hughes and Darrel S.Metcalfe. The Macmillan Company, New York. 1972.627 p.

This text, a third edition, is well designed for a beginningcourse in the production of field crops.

The first 19 of the total of 42 chapters are devoted togeneral crop production, including history, distribution,statistics, environment, crop-plant botany, seeds, moistureand soil relationships, tillage, crop rotation, and crop im-provement. Five later chapters cover general forage crops,hay, pastures, silage, and crop enemies, respectively. Cornis discussed in three chapters, and sorghums, soybeans, andalfalfa are treated in single chapters. The remaining 12chapters cover groups of two or more related-purpose crops.Chapter 8, entitled Science and Agricultural Research in-cludes historical features, organization, methods, objectives,and the value and financing of the research. Summarizeddata on crop water use and plowing depths in various ex-periments are tabulated in other chapters. With only 308pages devoted to specific Crops, the discussion of manycrops is extremely brief. Several minor domestic crops in-cluding lentils, pigeon peas, triticale, and sainfoin are notmentioned. The length of the book is adequate for a one-term crops course, but its value as a specific crop referenceis somewhat limited. Fortunately, many books and broadreference articles, in addition to those cited in the text, arelisted at the end of several chapters.--John H. Martin, De-partment of Agronomic Crop Science, Oregon State Uni-versity, Corvallis

CROP PRODUCTION--R. J. Delorit, L. J. Grueb, and H. L.Ahlgren. Prentice-Hall, Inc., Englewood Cliffs, N. J.4th Ed. 744 p. $9.95.

STORAGE OF CEREAL GRAINS PRODUCTS--Clyde M.Christensen. American Association of Cereal Chemists,Inc., St. Paul, MN. 1974. 549 p.

The first second edition of the book was published in1954. It is one of a series of monographs sponsored by theAmerican Association of Cereal Chemists. The new editionis largely a new book to present advances in the last 20years.

SUN, SOIL, AND SURVIVAL--Kermit C. Berger. TheUniversity of Oklahoma Press, Publishing Division of theUniversity, at Norman, OK. 1972. 371 p. $7.95

This book was copyrighted in 1965 by MacMillan andCompany and assigned to the University of Oklahoma Pressin 1972. It is an updated version of "Introductory Soils."The book has the simple mission of "introducing, in theclearest language possible, the basic fa~ts of plant nutritionand plant requirements."

The fourth edition of Crop Production offers those whoteach an initial crops course another text from which tochoose. Seven years have passed since the third edition,and the authors have, with the addition of the chapter onTurfgrass, brought into a beginning crops book this very im-portant aspect in our lives. The chapters of this book areorganized along lines somewhat similar to other contemporoary texts in crop production. The importance of food pro-duction for a hungry world as well as essentials of plantclassification are covered in the initial chapter. ’A chapteris devoted to the means by which seeds germinate, plantsgrow and develop. The cereals are discussed in individualchapters. Notable by their absence, no mention is made ofeither the millets or triticale in this section. Flax and pota-toes are discussed in individual chapters. The authors sug-gest that study of the forage legumes begin with the alfalfachapter. They have discussed certain cultural practicescommon to most of the forage legumes in the alfalfa chapterand have largely omitted discussion of these practices in thechapters dealing with other legumes. Illustrations, most ofwhich were furnished by the USDA, SCS, or commercialmachinery manufacturers, are of generally high quality andadd to the readability of the book. Helpful study questions

BOOKSHELF

are provided at the end of each chapter. The questions havebeen revised somewhat from the previous editions. Thereare some rather glaring omissions in the text. As previouslymentioned, millet and triticale are completely omitted. Theopportunity to control loose smut of wheat and barley bychemical means is not mentioned. Oilseed crops other thanflax and soybeans might well have been included in a chap-ter prior to the discussion of forage crops. The book mightbe useful in high school agricuIture programs or as a text inan undergraduate crops course.--V. E. Youngman, AssociateProfessor of Agronomy, Colorado State University, FortCollins.

"--We must ask ourselves what the world truly needs.--We must unhesitatingly accept that we have to deal

with a poor, not a rich world.--We must see to it that the global surpluses of food

and feed--not merely some bread grain-go towardalleviating hunger and malnutrition rather than towardproviding frills for the festive table of the already wellnourished."

The author offers under "Main Elements in a World Pro-gram" 11 focal points for a global crash program. Thischallenging book should be required reading for all Ameri-cans.--Samuel M. Weisberg, Executive Director, League forInternational Food Education, Washington, D. C. 20036.

FOCAL POINTS--GeorgBorgstrom. MacMillan PublishingCompany, Inc., New York. 1973. 320p. $8.95.

Focal Points, as the title suggests, concentrates on thoseideas that the author believes in need of top priority con-sideration if catastrophic food crises are to be avoided inthe near future. The author successfully conveys a sense ofoverwhelming urgency to act intelligently. He points outwith much realism the global limitations of arable land,water, and climate, which impose a statute of limitationson scientific effort to increase food production. He deline-ates that overriding importance of population control butalso points out that achieving population control must re-main a long-term objective. Exemplifying with Mexico,Java, Egypt, the Caribbean, Pakistan, and Bangladesh, hepoints out the severe limitations to increased food produc-tion in these areas and the existing damage to the environ-ment from overpopulation, ill-considered irrigation pro-jects, deforestation, and population transfers. A major con-clusion is that these countries as they now stand simply can-not provide food to sustain expected population increase.He points out the limitations of the "green revolution"--that it requires extensive use of chemical fertilizers and ir-rigation. Both of these are usualIy not available to thepoorest farmers for economic reasons. Thus, the gulf be-tween the affluent farmer and the subsistence farmer growsgreater. Turning to supposed "potential (areas)" for provid-ing food for an ever-increasing world population, he evalu-ates Canada as having a very limited real potential in partbecause of limitations of climate and water supply. In thecase of Argentina, he concedes a large potential for provid-ing more legumes and bread grains for Latin America exists,provided it turns away from providing Europe with meatand feed corn. New Zealand is evaluated and the conclusiondrawn that a much larger population than at present can besustained there. But that New Zealand cannot, in additionto this, remain a prime supplier of global food needs. Onlythe United States and Canada are acknowledged by theauthor as net providers of food of any real significance tothe world. The concluding section of this challenging bookis entitled "For the Seventies: A New Strategy." This sec-tion offers a searching analysis of what the author believeshas been wrong with past efforts to relieve hunger. Notleast is his belief there has been a gross underestimation ofthe dimensions of the problem and therefore inadequate,piecemeal efforts to cope with it. Dr. Borgstrom states:

PHYSICAL ASPECTS OF SOIL WATER AND SALTS INECOSYSTEMS, Ecological Studies, Vol. 4--A. Hadas, D.Swartzendruber, P. E. Rijtema, M. Fuchs, and B. Yaron(Ed.). Springer Verlag, New York. 1973. 460 $38.60.

From Aug. 19 to Sept. 4, 1971 a symposium entitled"Soil Water Physics and Technology" was held in Rehovot,Israel. Commissions I (Soil Physics) and VI (Soil Tech-nology) of the International Society of Soil Science co-sponsored the symposium and the Israeli Soil Science So-ciety organized it. This book is a collection of papers pre-sented at that scientific meeting.

Subjects covered in the book include physical phenom-ena of soil-water-plant systems associated with the move-ment and retention of water in soil, requirements of plantsfor soil-water, and salt accumulation in soil. Both theoreti-cal and practical aspects of these phenomena are discussed.Papers presented at the symposium and published in thebook were organized into three major sections: I. Waterstatus and flow in soils, II. Evapotranspiration and crop-water requirements, and III. Salinity control. Concise sum-maries of remarks and discussions from the symposium arepresented at the end of each section and provide valuableadditions to the book.

The first part of section I is devoted to water movementin soils and 11 papers are included. The physics of infiltra-tion into soil are reviewed, and experimental data are pre-sented for infiltration into uniform and nonuniform soils.Of particular interest is an analytical infiltration modeldeveloped to incorporate the influence of movement andcompressibility within the air phase upon flow in the waterphase of the soil. Also, an approximate analytical modeldeveloped to predict drainage of an initially water-saturatedsoil column showed good agreement with experimental re-sults for a sand. In still another study theoretical and ex-perimental data were compared in an analysis of soil watermovement toward seed and seedlings prior to emergence.

The second part of section I deals with energy of soilwater and soil-water interactions. Nine papers range in sub-jects such as the existence of a continuous, unfrozen waterphase that separates ice from the mineral or organic matrixin frozen soils, the influence of adsorbed cations uponphysical properties of soil, experimental determinations ofelectrical streaming potential during water flow in a soil

JOURNAL OF AGRONOMIC

column, theoretical treatment of a nonindependent domainconcept of hysteresis of soil water, a comparison of fieldand laboratory determinations of field capacity, and the in-fluence of raindrop impact upon soil crust formation.

The first part of section II includes nine papers related toevaporation from soils and plants, and seven papers are in-cluded under the subject of crop-water requirements in asecond part. Topics presented include experimental de-terminations of evaporation and evapotranspiration fromsoil as influenced by microclimate and macroclimate, anevaluation of methods for estimating evapotranspiration,numerical simulation of water flow in a simplified soil-water-plant system, prediction of heat flow in a bare soil byan analytical model, irrigation management, and water re-quirements for such crops as apples, citrus, tea, and corn.

Salinity control is presented in the third section of thebook. Eight papers are presented on topics of nitrate up-take by test plants as controlled by concentration or by ac-tivity in the growth media, simulated and experimentalanalyses of salt movement in irrigated soils, response ofspecific crops to salinity of soil and irrigation water, andreclamation of alkali and sodic soils.

In summary, this book has limited use as a textbooksince it is comprised of research reports on a wide range oftopics under the overall subject of physical phenomena ofecosystems associated with water and salts in the soil. How-ever, it should prove to be a valuable reference book foragricultural scientists who have an active interest in physicalaspects of soil-water-plant systems. The quality of researchreported in papers within this book varies from marginal tovery good. The best and most original papers would appearto be those reported under the subject of water movementin soils.--Robert S. Mansetl, Soil Science Department,University of Florida, Gainesville, FL 32611.

EDUCATION, VOL. 3, DECEMBER 1974 113

of the text, he will find occasional attempts by the authorsto bring out the ecological implications of their particularareas of seed research specialization. The authors have leftto the reader and his background the task of tying the vari-ous subject matter areas into the complex of interactingecological factors involved in the processes of producing an-other seed. Dr. Rorison, in Chapter 27 entitled "SeedEcology--Present and Future," points out that the papershave been largely concerned with seed physiology as seenthrough the eyes of crop physiologists, biochemists, andpathologists. He brings forth in a brief summary form theimplications of the previous papers as they relate to seedecology now and in the future, a nearly impossible task fora few short pages. The physiological and biochemicalaspects of viability, dormancy, germination, and maturity ofthe seed were discussed in many of the chapters. Seedmigration from the parent plant, an important ecologicalfunction, was scarcely covered in the text. Readers willneed a good background in cellular seed biology, bio-chemistry, genetics, agronomy and plant pathology. As atextbook for a course on seed physiology, this book couldbe considered for advanced students at a graduate level. Forthose interested in seed technology with a desire for an ex-cellent source of data and/or reference, this book offersmany outstanding contributions on international researchefforts. Several approaches offering new challenges to seedresearch were interwoven throughout the several chapterswith concepts and approaches of long standing. It appearsthat the symposium planners and/or publishers were caughtup with the popularity of the term "ecology" in efforts tospur the interest in a most timely and informative text.This should not limit the usefulness of the book in that itprovides a major contribution to the literature on the sub-ject of seed technology, but it fails to live up to its title,Seed Ecology.-William L. Colville, Chairman, AgronomyDivision, University of Georgia, Athens, GA 30602.

SEED ECOLOGY--W. Heydecker. (Ed.). Penn State Univer-sity Press, University Park, PA. 1973. 578 p. $27.50.

The publishers state on the inside jacket cover of thebook, "The dual purpose of this is to provide an insight intothe mechanisms of adaptation, survival, germination, andseedling establishment, and an appreciation of their limita-tions. The points of view considered are not only those ofthe plant ecologists, but also the geneticists, plant bio-chemists, plant physiologists, seed technologists, soil physi-cists, agronomists and agricultural engineers. The inter-disciplinary approach of ’Seed Ecology’ is intended to pro-duce a balanced picture of the complex relationship whichexists between seeds and their environment and, as such,will provide a major contribution to literature on this sub-ject." Seed Ecology is a compilation of papers tSresentedby internationally recognized authorities on several aspectsof seed science. Dr. Heydecker, in Chapter 1, sets the stagefor an ecological study of the seed and its environment. Thereader expecting to find a treatise on seed ecology in theclassical ecological sense is likely to be disappointed. De-pending upon the reader’s definition of "ecology," he willfind few chapters dealing directly with the subject matter ofecology. As the reader progresses through the 27 chapters

ENVIRONMENTAL QUALITY AND THE CITIZEN, ATeaching Guide for Adult Education Courses Related tothe Environment-Bernard L. Clausen and Ross L. lver-son. Soil Conservation Society of America, 7515 North-east Ankeny Rd., Ankeny, IA 50021. 1973. 40 p.$2.00.

The authors state their objective as helping people be-come more informed and thoughtful citizens in regard toenvironmental affairs. Ten class sessions are divided intoobjectives, background information, teaching activity, andreferences. The teaching activity section provides think-type class exercises. This booklet is not for the professionalenvironmentalist or for the person who wants to becomean "expert." It is not intended to be a text (the authors dosuggest a text to accompany the course), but rather an out-line for the instructor to relate to current local environ-mental problems. A special committee for the Soil Con-servation Society of America compiled a bibliographydivided into subject categories, e.g., forests, water, agricul-ture, law, etc. This arrangement will prove useful to peopleinterested in further reading or a particular area of environ-mental study.--MED.

114 BOOKSHELF

TOPSOIL AND CIVILIZATION--Vernon Gill Carter andTom Dale. University of Oklahoma Press, PublishingDivision of the University at Norman. June 1974. 292p. $7.95-cloth, $2.95-paper.

The first edition of this book was published in 1955. Ithas been out of print for some time. This version was pub-lished because of the continued interest in the book. TheSoil Conservation Service is acknowledged for illustrationsand documentary assistance in the preparation of this book.

MEASURING INSTRUCTIONAL INTENT--Robert F.Mager. Fearon Publishers, Belmont, CA 94002. 1973.159 p. Paperback $3.25.

This book is a logical sequel to Mager’s well known book:"Preparing Instructional Objectives." The purpose of thislatest publication is to match the examination or testingwith the objective so that a perfect score in the exam wouldalso mean that the objective had been achieved. The bookis prepared in a programmed learning style with the samehumor, interest, and compelling diction that characterizedMager’s writing. Adherence to the principles outlined herein the preparation of examinations would eliminate muchof the frustration and anguish suffered by dedicated andwell prepared students.--B. R. Bertramson, WashingtonState University, Pullman.

9 years. In the United States, attempts at this type of hand-book appear annually in several states. There is constantfear that obsolescence will overtake these volumes beforethe ink has dried. A chapter on application equipment,operation, calibration, and maintenance leads to one onsafety and then to the chronological evolvement of regula-tory "schemes". There is, one finds, still a place in thisprocess for voluntary compliance. Years ago the Britishestablished guidelines for worker safety including safe re-entry periods, protective clothing for various operations,and the rinsing of empty containers. Several chapters dealwith pest control arranged by crop including one lengthyand comprehensive chapter on glasshouse crops. Pests ofmajor importance have a three-asterisk designation, those oflesser importance two or one. There are abbreviations toremember or refer back to and the serial listing of diseaseorganisms and pesticide recommendations takes a practicedeye to follow but its all there and page space is well con-served. This is not a handbook to read at one sitting. It is areference, and a basic Primer for its biology and chemistry.As with most handbooks only the entries about crops onegrows would be of particular importance. So belabored areagriculturalists in the United States with real and imaginedthreats of certain pesticides, it comes as an added pleasureto discover that the British still permit and recommendsome of the highly persistent of pesticides including DDT,BHC, and the mercury. Perhaps the British here again dis-play their cooler heads in the face of increased panic andprotestation.-Joseph Capizzi, Entomology Department,Oregon State University, Corvallis.

INSECTICIDE AND FUNGICIDE HANDBOOK . . . forcrop protection--Hubert Martin (Ed.). Blackwell Sci-entific Publications, Osney Mead, Oxford, Great Britain.1972. 4th Ed. Distributed in the U. S. by E. A. DavisCompany, 1915 Arch Street, Philadelphia, PA 19103.415p. $15.00.

The stated purpose of this handbook is to offer thegrower and agricultural advisor information on the correctuse of pesticides and, as well, refinements in methods ofcrop protection. The handbook succeeds in its intendedgoal and, along the way, reveals an integrated and sensibleapproach to the use of chemicals, to safety requirements,and necessary, but only necessary regulatory matters.Where this total system may be compared with that promul-gated in the United States the Old World hands have theupper hand. Put together by British authorities on pestcontrol (British Crop Protection Council), this 4th editionintroduces the reader to pertinent biological considerationsand follows with an alphabetical review of insecticides andfungicides. The handbooks’ appendix treats the propertiesof these same pesticides but this time organized by chemicalclass. It is written by and for the British and so one may beamused or perplexed by terminology or language at times.It speaks of "sulphur shy" crops and "winter washes." Oneparticular bafflement will suffice. "Blighted potato tubersdiscarded at reddling near clamp sites." Still, these are minorirritations at worst. There is much to enjoy and appreciate.Realize, for example, that this is just the fourth revision in

BIOLOGICAL NOMENCLATURE--Charles Jeffrey. Crane,Russak & Company, Inc., 347 Madison Avenue, NewYork, NY 10017. February, 1974. $6.75.

This is part of the Special Topics in Biology Series. In69 pages, the book is described as "an explanatory treat-ment of the nomenclature of all groups of organisms...forthose who, through interest or necessity, have to deal withthe scientific names of living things and fossils." The topicscovered include systematic background, names, and codes,scien/tific names, principles of text nomenclature, and othertaxonomic subjects.

PEDOLOGY, WEATHERING, AND GEOMORPHOLOG-ICAL RESEARCH--Peter W. Birkeland. Oxford Univer-sity Press, New York. 1974. 285 p. $11.00.

This book is based on a soils course taught by its authorfor graduate students and undergraduate seniors at theUniversity of Colorado where he is Professor of GeologicalSciences. Major emphasis is on pedology and weatheringwhile references to geomorphological research are primarilyrestricted to soils and landforms of Quaternary deposits inthe United States. Unfortunately, excellent soils-geomor-phology research in the southeastern United States, New

JOURNAL OF AGRONOMIC

Zealand, and Australia are ignored. The preface to the bookindicated that this may have been the author’s choice.

Chapter 1 covers the soil profile, horizon nomenclature,and soil characteristics. The author suggests some modifica-tions in traditional hQrizon nomenclature such as "K" forCaCO3 impregnated (roughly equivalent to petrocalcic)horizons and "E" for albic and/or A2 horizons. The nextchapter (2) briefly discusses the U. S. Soil Taxonomy.Chapter 3 treats physical and chemical weathering processesand Chapter 4 discusses the products of Weathering.Chapter 5 covers processes responsible for the developmentof soil profiles.

A lucid, well organized treatment of the five soil-formingfactors in Chapters 6 through 11 is the highlight of Dr.Birkeland’s book. The material in these chapters is a wel-come additional approach to the presentation of this highlyimportant topic in soil genesis. In the final chapter (12)the author provides examples in the use of soils inQuaternary stratigraphic studies.

Illustrations are profuse and of uniform excellent quali-ty. The author has taken the trouble to graphically portraytabular data from the literature. Two appendices are in-cluded which treat data necessary for describing a soil pro-file and climatic conditions in the United States. The bookcan serve as an excellent supplementary text for an ad-vanced undergraduate course in soil genesis, classification,and morphology--Frank G. Calhoun, Department of SoilScience, University of Florida, Gainesville, FL 32611.

AGRICULTURAL GENETICS. Selected Topics--RomMoav (Ed.). National Council for Research and Develop-ment, Israel. 1973. 352 p. Paperback.

This book is based on proceedings of the AdvancedSeminar on Agricultural Genetics for Latin America held inMaracay, Venezuela, on .October 19-29, 1969 under theauspices of the Governments of Venezuela and of Israel. Agroup photograph, names, titles, and addresses of the 48participants from 18 countries, general conclusions andrecommendations for the improvement of genetic andbreeding research effort in the Latin American countries incollaboration with Israel precede 19 "up-dated" technicalpapers. Fourteen papers are from Israel, two from Argen-tina, and one each from Brazil, Italy, and Trinidad. Thetopics represent genetic and breeding research on agricul-tural plants and animals of economic importance to Israeland Latin American countries. Besides, general theoreticalor review articles, genetics and breeding of four agriculturalplants (cucurnis, castor bean, peanut, and cacao plant),and three animals (dairy cattle, chicken, and carp) are pre-sented in separate papers.

"Recent Studies on Heterosis" by E. Patemia~i reviewsthe practice and theory of hybrid corn improvement re-search. Four papers by R. Frankel provide a general reviewof male sterility and self-incompatibility mechanisms inplants and their use in hybrid seed production. One papereach on Cucumis breeding and genetic sex types by E.Galun, Theobroma cacoa L. (self-incompatibility as an out-breeding mechanism) by B. G. D. Bartley and F. W. Cope,

EDUCATION, VOL. 3, DECEMBER 1974 115

’Evolution of the Genus Arachis’ by A. Krapovickas, castorbean breeding (sex inheritance and hybrid seed production)by D. Atsmon, cattle breeding for meat and milk by M.Soller and R. Bar-Anan, broiler breeding by M. Soller andR. Moav, carp breeding by R. Moav and G. W. Wohlfarth,and breeding for drought resistance in field crops by D.Atsmon review the authors’ research on their respectivetopics. Two papers-’Gene-pools for Plant Breeding’ by D.Zohary, and ’Conservation of the Genetic Resources ofLatin America’ by Lee;n, emphasize the conservation anduse of genetic variability for the improvement of agriculturalplants and animals. One paper each by A. Ashri and E. A.Favret review basic and applied aspects of induced muta-tions and their use in genetic and breeding research. A paperby M. Soller explains the Britten-Davidson model for generegulation in higher plant cells. The concluding paper byRom Moav on ’Economic Evaluation of Genetic Differ-ences’ includes three lectures on agricultural economicsrelevant to various breeding stocks and their use in the im-provement of cattle, poultry, and other farm animals.

The book has excellent reviews on related topics of malesterility, self-incompatibility and sex inheritance mechan-isms and their manipulation in plant breeding.-S. S. Maan,Department of Agronomy, North Dakota State University,Fargo.

AUDIO TUTORIAL SYSTEMS--Detroy E. Green and D.G. Woolley. Burgess Publishing Company, 426 SouthSixth Street, Minneapolis, MN 55415. 1970. $6.75.

This book utilizes the personalized learning and narratedtutorial systems ("PLANTS"), which has been reported the JOURNAL OF AGRONOMIC EDUCATION. It is de-signed for a self-learning situation. The book is spiral-bound and numbered within groups. The contents are givenby catalog number, i.e., the titles being Crop PlantAnatomy, Crop Plant Classification and Identification;Crop Physiology; Climate, Soils, Soil Water, Tillage, andSeeding; Seed Quality, Plant Breeding; Weeds; Insects; CropDiseases; and Crop Harvesting and Storage. The typicalstudent study guide (crop plant anatomy) has the followingsections:

I. The Plant CellII. Seed and Seedling Anatomy

A. Corn seed anatomyB. Corn seedling (The section includes questions

such as "Why does the dent corn dent?")C. Soybean seed anatomyD. Soybean seedling

III. Grass and Legume InflorescenceA. Parts of a grass floretB. Grass spikelet

IV. Inflorescence TypesV. Parts of a Legume FlowerVI. Plant Stems

A. Functions of StemsB. Stem anatomyC. Modified stems

VII. Plant LeavesVIII. Plant Roots

116 BOOKSHELF

BIOLOGY DATA BOOK, SECOND EDITION, VOLUMESI AND II--Philip L. Airman and Dorothy S. Dittmer.Federation of American Societies for ExperimentalBiology, 9650 Rockville Pike, Bethesda, MD 20014.1973. $30.00 each volume, $75.00 the set of 3.

These tomes include every conceivable type of biologicaldata. Volume I covers genetics and cytology, reproduction,development and growth, properties of biological sub-stances, materials and methods and nine appendixes. Vol-ume II includes biological regulators and taxins, environ-ment and survival parasitism, sensory and neutobiology,scientific names and common names. Volume III is in theprocess. That volume will include nutrition, digestion, andexcretion; metabolism; respiration and circulatory; andblood and other body fluids. About 2,200 life scientistsanalyzed 40,000 scientific reports to make possible thepublication of these reference guides. They are truly a mas-sive undertaking. The three-volume set will include 1,800pages.

PLANT SCIENCE--Jules Janick, Robert W. Schery, FrankW. Woods, and Vernon W. Ruttan. W.H. Freeman andCompany, 660 Market Street, San Francisco, CA 94101.740p. 1974. $14.50.

This edition includes two new chapters, "AgriculturePollution and the Environment" and "The Organization ofAgricultural Research Systems." Other material on changesthat the field has undergone since 1969 are also included.

portant ions such as nitrate and phosphate. It is stated thatchemical fertilization lowers the nutritional value of cropsand that insecticides may seriously affect the function ofsoil organisms. Both of these statements are surely subjectto challenge. A more general criticism of this book is thatthe authors go into considerable detail on some topics in agiven subject matter area and essentially ignore other topicsof equal importance.

Despite the above comments, the book does provide anadequate overall view of environmental pollution problems.Subject matter is up to date and relevant to today’s prob-lems. An ample number of figures and tables are providedthroughout the book and the reading is relatively easy andfast. This text will serve as a good teaching instrument forthe instructor of an introductory environmental sciencecourse.--D. A. Graetz, Department of Soil Science, Univer-sity of Florida, Gainesville, FL 32611.

ADVANCES IN AGRONOMY--N. C. Brady, Editor. Pre-pared under the auspices of the American Society ofAgronomy. Vol. 25. Academic Press, New York. 400p. 1973.

The eight chapters in this book cover advances in Phos-phorus in Runoff and Stream; Crimson Clover; Zero Tillage;The Genetic Control of Flowering and Growth in Sorghum;Ion Absorption by Plant Roots; Lodging in Wheat and Oats;The Phenomenon, its Causes, and Preventive Measures;Genesis and Management of Acid Sulfate Soils; and MaltingBarley in the United States.

ENVIRONMENTAL SCIENCE--Amos Turk, JonathanTurk, Janet T. Wittes, and Robert Wittes. W. B. Saund-ers Company, Philadelphia. 1974. 563 p.

This book is designed as a text for a semester collegelevel course dealing with environmental concerns. A widerange of topics are covered beginning with a discussion onbasic ecological principles, followed by discussions on en-vironmental pollutants and ending with a chapter on socialand economic issues in environmental studies. Thirteenchapters are included covering the following subjects:ecology of natural systems; human adaptation to environ-mental change; extinction of species; growth of humanpopulations; energy; agricultural systems; control of pestsand weeds; radioactive pollutants; air pollution; waterpollution; solid wastes; noise; and social, legal, and econom-ic aspects of environmental degradation. Problems at theend of each chapter are designed to alert the student to theenvironmental implications of the chapter.

The student hoping to get a good background on agri-cultural sources of pollution will be disappointed and willbe given an incomplete and potentially misleading pictureof the subject. For example, humus is stressed withoutmentioning other components of the soil and calcium is usedas the example to illustrate leaching of ions without mention-ing cation exchange or other more environmentally im-

NEW BOOKS FROM THE SOCIETIES

DRAINAGE FOR AGRICULTURE--Jan van Schilfgaarde,editor. Agronomy Monograph 17. ASA publication,Madison, Wis. 1974. 736 p. Active members $13.Others $16.

The science of drainage has changed drastically in thelast generation, necessitating the publication of this latestAgronomy Monograph. This book brings together currentinformation on field practice design and construction tech-niques and the relationship between drainage and other vari-ables in agricultural produc.tion. The principles includedhere should be helpful to anyone involved in water man-agement.

SEVENTY GENERATIONS OF SELECTION FOR OILAND PROTEIN IN MAIZE--J. W. Dudley, editor.CSSA publication, Madison, Wis. 1974. 212 p. Activemembers $7.50. Others $10.

Continuous selection over 10 generations is a uniqueexperiment in breeding and selection in a food and fieldcrop. Reports and analyses of this ongoing experiment,

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974

started in 1896 and continuing today, make up the heart ofthis historically-oriented discussion; should be interestingto plant breeders and researchers alike.

A NEW LOOK AT ENERGY SOURCES--D. E. McCloud,editor. ASA Special Publication 22. Madison, Wis.1974. 50 p. Paperback. Free while the present supplylasts.

This special publication looks at a problem that will con-front society indefinitely-energy. Composed of four papersfrom the ASA Annual Meeting in 19’73, "A New Look atEne.rgy Sources" explores existing and future resource sup-plies and their use. The authors emphasize the need forintelligent energy planning for the future, the dangers ofoverdependence on fuels in farming, and uses of agriculturalwaste to produce energy supplies.

117

tions covering toxic constituents and nutritive values of newcrop cultivars. This publication contains papers given byfield and horticultural bceeders, industry representativesand the FDA at a special symposium dealing with the newGRAS (generally recognized as safe) regulation.

OILSEED CROPS FOR TODAY’SWright and J. R. Wilcox, editors.Madison, Wis. Inprocess. Paper.

SOCIETY--L. NealCSSA publication,

Oilseed crops as energy converters relate uniquely toenergy needs for today’s society by concentrating renewableenergy. This publication discusses the potentials of oilseed

crops for food and industrial uses are exp.anding. Bothyield and quality can be improved with environmental andcultural changes according to the editors.

PESTICIDES IN SOIL AND WATER--W. D. Guenzi, editor.SSSA publication, Madison, Wis. 1974. 576 p.

Pesticides in Soil and Water is an up-to-date account of acontroversial problem in today’s agriculture. This 16-chapter book contains a comprehensive review and evalu-ation of information concerning pesticide transformation insoil and water.

PROCEEDINGS FROM THE SECOND INTERNATIONALTURFGRASS CONFERENCE--E. C. Roberts, editor.ASA, CSSA publication, Madison, Wis. 1974. 600 p.+

SYSTEMS ANALYSIS IN FORAGE CROPS PRODUC-TION AND UTILIZATION--R. W. Van Keuren, editor.CSSA Publication, Madison, Wis. 1975.

The objective of this special publication is to show theneed for systems analysis to integrate the complex relationsinvolved in forage production and utilization. The authorspoint to the need for a multi-discipline approach withagronomists, animal and dairy scientists, agricultural engi-neers and economists cooperating. The development andpotential results of this approach are discussed.

AUDIOVISUAL NOTES

This book, the result of a 1973 symposium, contains 71papers followed by discussions of current practical informa-tion on sports turfgrass production in both warm and coolclimates. It includes key concepts for turfgrass managementin the 1970’s--breeding, fertilization, disease, insect andweed control.

HISTOSOLS, THEIR CHARACTERISTICS, CLASSIFICA-TION, AND USE--A. R. Aandahl, editor. SSSASpecial Publication 6. SSSA publication, Madison, Wis.1974. 152 p.

This book grew out of a 1972 ASA symposium present-ing current knowledge of organic soils, a subject totally re-organized after 1965. Ten papers present discussions ofHistosol properties, testing, laboratory analysis, use andmanagement.

S-2 Division Slide Set

A slide set, ’ Cation Exchange Properties in Soils," is avail-able from the Soil Science Society of America.

The slide set is designed to provide background informa-tion on the sources of negative charges effective for absorp-tion and desorption of cations. The slides and narrative arenot meant to be all-inclusive, but may be used to supple-ment or complement the user’s own material.

The set, consisting of 45 slides, was prepared and de-veloped by a committee headed by E. O. McLean of PurdueUniversity. Other committee members included MurrayDawson of Oregon State University, Henry D. Foth of Mich-igan State University, and A. L. Page of the University ofCalifornia, Riverside.

The cost of the slides including an 8-page narrative is$15 for domestic orders and $16 for orders outside of theUnited States.

THE EFFECT OF FDA REGULATIONS (GRAS) PLANT BREEDING AND PROCESSING--C. H. Hanson,editor. CSSA Special Publication 5. CSSA publication,Madison, Wis. 1974. Paper.

Plant scientists and processors were concerned with theeffects of the 1971 Food and Drug Administration regula-

Board of Education

The Newsletter "Engineering Outlook," published by theUniversity of Illinois, reported in June 1974 a new systemfor classroom interaction over long distances. The College

118 BOOKSHELF

of Engineering is using this Bell Laboratories system, a Re-mote Blackboard. It looks like an ordinary blackboard butit is pressure-sensitive and specially designed to transmitwhatever is written on it over a telephone communicationnetwork. Microphones transmitting over the same networkare used by the instructor as he teaches--allowing both lec-ture and written explanations to be conveyed to a receivingcenter. What the instructor has written on the blackboardappears on a television set and the words can be broadcastover a speaker on a conference telephone set. Microphonescan be also made available at the desks of students. Univer-sity of Illinois has set up receiving centers at Rockford,Freeport, and Rock Island, Illinois. The system allows fortwo-way communication. Receiving centers can have, inaddition to their television sets and speakers a blackboardand a microphone for asking and answering questions orillustrating and solving problems. In the 6 months of test-ing, the University of Illinois has begun to make several sug-gestions for improving the practicality of the boards forteaching. Testing will continue for about one more year.The boards are expected to be available for renting by thepublic after that.

OTHER NEW BOOKS RECEIVED

were places to discuss and topics to discuss. There are a fewpictures of what happened to Horton and views of chores,leisure, and winter on the farm. This piece of nostalgia willbe interesting to people who experienced those days orthose who have heard about, them.

Library Guides and Information Tools

AGRINDEX: Experimental Issue and AGRINDEX:Supplementary Information. Food and Agriculture Or-ganization of the United Nations. AGRI$ CoordinatingCentre, FAO, Via delle Terme di Carcalla, 00100 Rome,Italy.

This is an experimental issue published by the FAO.AGRIS, as it is called, is an attempt to provide a compre-hensive current awareness service in all fields of interest toFAO consisting of a current bibliography in printed formand magnetic tape. The index consists of 513 pages ofentries consisting of the author, title, corporate entry,language, journal title, etc., of current research articles. Itcontains several indexes, including author and corporatebody.

General

FARM TOWN, A MEMOIR OF THE 1930’s-J. W. Mc-Manigal and Grant Heilman. The Stephen Greene Press,Brattleboro, VT 05301. 1974. $12.95ocloth, $7.95-paper.

Photographs in this book were taken by J. W. McManigalaround his hometown of Horton, Kansas, between 1935and 1940. Its 96 pages are mostly photographs of the farmscene in the 1930’s. Back then, spring was a time of comingalive; haying, threshing, corn picking, were a part of thedaily scene and downtown, the sale, the fair, and politics

ASHER’S GUIDE TO BOTANICAL PERIODICALS--A.Asher & Co. B. V., Amsterdam, The Netherlands. 1973.(15 three-weekly volume) Dfl. 550,--.

This is a publication similar to Current Contents. It ispublished in The NetherIands and is a current reference forbotany and allied subjects. Periodicals covered are listed inthe Table of Contents alphabetically. Relevant titles of agiven issue’s contents are then printed under the periodicalname. A subject index includes scientific plant names,names of plant communities, and names of botanists. Anauthor index is also provided.

5UPPLEI ENT

Basic laboratory studies in plant and soil sciences

R. P. Patterson and M. G. CookI

PREFACE

At a time of rapidly expandingpopulation and shrinking land areasuitable for agriculture, one of ourmost urgent needs is to utilize effec-tively our limited, and in most casesnonrenewable, resources for efficientfood and fiber production. Educatorsare becoming increasingly aware of thestrong enthusiasm of students at alllevels for participation in projects orexperiments which relate to humanneeds.

This supplement has been preparedfor high school and introductory col-lege-level students. It contains de-scriptions of activities that are adapta-ble as individual student projects forscience fairs and other science ex-hibits. The materials may be used aslaboratory exercises in introductoryplant science and earth science coursesin many educational institutions, in-cluding community colleges and tech-nical institutes. The investigations aredesigr~ed to acquaint students with twoimportant living systems surroundingthem-soils and plants.

These exercises were selected tointroduce the student to fundamentalprinciples underlying soil and plant be-havior. Each exercise has been de-

1Associate professor, Crop Science De-partment and Professor, Soil Science Depart-ment, North Carolina State UniversityRaleigh, respectively.

scribed in sufficient detail such thatthe student can understand the prin-ciples involved and complete the in-vestigation with minimal assistancefrom the instructor. Selected refer-ences have been provided to enablethe interested student to probe thesubject matter area more deeply.

The introductory material consistsof a discussion of the proper techniquefor selecting a topic, planning, design,ing, and conducting the experiment,and for interpretation, summarization,and presentation of the experimentalresults. In section I, 10 basic plantgrowth experiments are described, andsection II describes 10 basic experi-ments relating to the field of soil sci-ence. Glossaries of botanical namesfor plant species and chemical namesfor pesticides used in the exercises areprovided after Section II.

This supplement was prepared bythe Teaching Improvement Committeeof the Resident Education Division ofthe American Society of Agronomy.The authors are indebted to many in-dividuals for their assistance in thiswork, and want especially to thankB. A. Buchanan, S. R. Chapman, D. A.Emery, W. J. Flocker, J. R. George,Roger Higgs, D. A. Miller, D. F. Post,T. A. Ruehr, J. W. Schafer, and D. D.Wolf.

This supplement is our first attemptto prepare a reference source for thepurposes indicated. Thus, the authors

welcome comments and suggestionsfrom teachers and students that willimprove later revisions of the supple-ment.

HOW TO CONDUCT THE EXPERIMENTIntroduction

During the course of this investiga-tion you are going to learn that thestudy of the soil and the plants is afascinating experience. Since plantsare the sources of almost all of ourfood, it is natural to wonder howplants grow and develop, what effectthe environment has on crop produc-tivity, and how various soil properties,such as particle size and chemicalmakeup, influence the growth ofplants.

Once you actually get involved inconducting your experiment, and be-gin to get a feeling for how soil and/orplant systems behave, you may be-come interested in exploring a particu-lar part of your subject in greaterdepth. This is how the plant or soilscientist makes progress. He will firstconduct a preliminary experiment togive him some basic information aboutthe subject he has chosen to investi-gate. Then he will use the results ofthis first experiment as a guide to theplanning of a second experiment. Thescientist continues in this manner untilhe has answered the question heoriginally asked.

119

120 SUPPLEMENT: BASIC LABORATORY STUDIES

Selection of Topic

Selecting a suitable topic to investi-gate may be the most important de-cision you will make. Considerationshould be given to your abiliites, theamount of space and materials a par-ticular project will require, and mostimportantly, how enthusiastic you areabout investigating a particular idea.

Time spent discussing your idea withteachers will be time well spent. Also,do some reading on the topic tentative-ly selected to investigate. Be sure totake thorough notes on importantpoints and on the source of your in-formation.

There probably will be specificpoints that need to be discussed withyour teacher before a final decision ismade on a topic. Your discussions andultimate choice of topic will be muchbetter if some preliminary reading onthe subject has been done. Aboveall, find out what others have doneand written on the subject.

Be certain that you are being realis-tic about the chosen topic. Is thetopic practical for you? Are you goingto be able to get the materials neededto conduct your experiment properly?Once convinced that you really wantto work on the project and that youhave the means to do it, you are readyto go to work,

Planning the Experiment

Once the topic has been selected,decide what questions you want toanswer concerning the problem. Makea list of the questions to be answered.Try to keep the number of questionssmall (2 or 3), so that your projectdoes not become so complicated thatyou lose sight of your fundamentalobjectives.

It is a good idea to prepare a briefstatement of the goals, or objectives,of your study. Indicate why or howyou feel this study is important to sci-ence. This material should be includedin the introduction of your written re-port.

Designing the Experiment

This part of your study, deciding onthe experimental plan and procedure,

is crucial to success. It is importantthat you use a testing procedure thatwill enable you to answer the questionsasked. So often a good experimentalidea is doomed to failure because theright scientific procedure was not em-ployed.

The key to success is to design yourexperiment in such a way that the test-ing procedure includes a plan to con-trol adequately the factor or factorsbeing tested. If your design is good,you can be reasonably confident thatobservations (data, or results) will the treatments imposed.

It is often necessary to test proce-dures by running a preliminary experi-ment, or possibly more than one. Thisis a time for patience. Be certain thatyour experimental design is a good onebefore collecting your data. Once youhave settled on a satisfactory proce-dure, record the materials and methodsused in preforming the experiment in anotebook. It is important to recordevery step in detail. Be complete tosuch an extent that someone elsewould be able to read your report andperform the experiment just as youwill have done.

All treatments included in the ex-periment should be replicated, or re-peated, several times. This is impor-tant if you are to be able to analyzedata meaningfully. If necessary, con-sult your instructor on the use of theappropriate experimental design.

One important point that could beeasily overlooked is the necessity forincluding controls in your experiment.Of course you want to test the effectof your variable (or treatment) on ex-perimental materials. For example, ifyou want to test the effect of plant-water stress on crop growth, you wouldarrange for some plants to grow underconditions of soil 1,oisture deficiency.However, for comparison purposes,you need to know how these plantsgrow when all the environmental con-ditions are the same except that theplants are not under a water stress.This can readily be accomplished bykeeping a set of similar plants ade-quately supplied with water (controls),and otherwise growing under the sameenvironmental conditions as thestressed plants.

Finally, be sure that your time

schedule for conducting your experi-ment is realistic. Write down a timeschedule for conducting all phases ofyour experiment, and check with theinstructor to make certain that you areallowing enough time to completeyour experiment on schedule.

Conducting the Experiment

You are now ready to apply the ex-perimental procedure, to make allnecessary measurements and observa-tions, and to record them carefully ina notebook. All data gathered shouldbe recorded in a precise, neat, andeasily understood manner.

Use data forms and books whereverpossible, so that your data can be or-ganized into graphic and t’abular form.Keeping your data well organized willenable you to understand results muchbetter. Each set of data should bedated and titled properly.

All observations, including problemsthat may occur with your procedure,should be promptly noted. Sometimesa note made of an unusual observationor occurrence will help explain resultsof a deviating nature later on. Remem-ber that if you wait too long beforenoting observations in a book, an im-portant point might be forgotten. Asis the case with your procedure, resultsshould be sufficiently clear and organ-ized so that they can be easily under-stood by someone else.

Presentation and Interpretation ofExperimental Results

This step is the real "meat" of yourexperiment. What do your resultsmean? Make a comparison betweencontrols and treatments. Arrangingdata properly can be most helpful inmaking the various comparisons neededto satisfy the objectives of your study.The proper use of charts, tables, andgraphs are helpful in interpreting data.

After thinking about your data,discuss results with your instructor, in-dicating what you think to be theirsignificance. What outstanding con-clusions and inferences can be drawnfrom your data? Relate the conclu-sions of your limited study to the find-ings of others. What are the implica-tions of your findings to modern agri-cultural production?

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 121

Be careful not to read more into thedata than is actually there. Be open-minded about interpreting data. Ifyour results did not turn out as youthought they should, do not be dis-couraged. This frequently happens toprofessional scientists. If your datado not agree with your original theory,it may mean that your hypothesis waswrong, or experimental errors duringthe conduct of your experiment led tofaulty data.

In any case, it is unwise to draw toostrong a conclusion from data obtainedfrom one trial of the experiment. Byrepeating the experiment (more thanonce if necessary) you become moreskillful in procedures. If you duplicateyour results with repeated trials usingthe same experimental procedure, youcan be more confident of your tech-nical ability and data.

Summarization of Data

It is wise to prepare a short synopsis,or summary, of the experimental re-sults and the important conclusionsdrawn as a result of your experiment.This practice helps to clarify yourthinking concerning observations inview of original objectives. It is ameans of communicating your findingsto other people.

SECTION I.

PLANT GROWTH EXERCISES

Exercise 1

Photosynthetic Differences Among Plants

The basic source of food for all ani-mals, including man, is green plants.All of humanity obtains the energyand nutrients needed for growth, de-velopment and sustenance either byeating plants directly, or by eating ani-mals that have eaten plants (or otheranimals).

Through the process of photosyn-thesis, green plants are able to "cap-ture" some of the radiant energy ofthe sun and use it to bond togethersmall molecules into the large organicmolecules that are characteristic ofliving organisms. Thus, photosynthesisis the process by which plants producethe materials which enable them togrow, develop, and produce seed. Thephotosynthetic rate varies widely a-mong species. Many plants of tropicalorigin such as corn (Zea mays L.) andgrain sorghum (Sorghum vulgare Pers.)have relatively high photosyntheticrates under high light irradiation whenother growth factors are not limiting.Other plants, such as grasses of tem-perate origin and most dicots, such assoybeans (Glycine max Merrill) haverelatively low photosynthetic rates,even under very high light intensities.

Under conditions of high light ir-radiation (order of 4000 to 5000lumens per square meter) plants whichmaintain relatively high photosynthet-ic rates (50 to 60 mg CO2 fixed persquare decimeter leaf surface per hour,or the rate of conversion of CO2 toplant dry matter), are said to be "ef-ficient". Plants under similar condi-tions which fix carbon at low rates (20to 20 mg CO~ dm-2 hour-a) are said tobe "inefficient".

Plants growing in a field are con-tinually competing with one anotherfor the available water, light, nutrients,and space. The plant which is mostefficient, i.e., is able to do the best jobof competing for these growth factors,is the one which will be able to growbest. One reason why certain weedyplant species are able tO grow so wellin many crops is that they are able to

compete favorably for these importantgrowth factors.

The technique which this experi-ment utilizes is based on the fact thatspecies of the two groups (efficient andinefficient) react differently to CO2stress, or to low levels of CO2 supply.Efficient species have very low CO~compensation concentrations (theequilibrium CO~ concentration for il-luminated leaves in a closed system, orthe atmospheric CO~ concentration atwhich CO2 uptake in photosynthesisequals CO2 output in respiration), infact near 0 ppm CO2. Inefficientspecies have much higher COz com-pensation concentrations, usually from50 to 60 ppm COz or higher. In otherwords, efficient plants are able to uti-lize the available CO~ supply muchmore effectively than are inefficientplants.

This experiment shows clearly thestriking physiological differences whichoccur among plant species.

Objective: To illustrate differences in photo-synthetic capacity among various crop andweed species.Materials: acrylic plastic (or a narrow, tall

fish aquarium)acrylic plastic solvent (or window glass to

co ver aquarium )nutrient solution (see exercise 2, or obtain

from dilution of a complete liquid con-centration found in most garden supplyshops.)

fluorescent lamps (30-watt, cool-white)crop species-see proceduresand (fine)trays or small pots

Procedure

Construct a transparent chamber ofacrylic plastic as shown in the follow-ing drawing:

~ ~top. ~::::::::7::-_-_:::: ::.-_::

base

The chamber consists of two parts,a base or a trough and a top. Bothparts are constructed such that a clear-ance of about 5 cm will exist all around

122 SUPPLEMENT: BASIC LABORATORY STUDIES

the chamber. A convenient dhambersize is 1.5 meters long, 1.5 meterswide, and 1 meter high. The baseshould be about 5 cm high.

Trays or pots of test plants selectedfrom the lists of high or low efficiencyincluded in this section are placed onthe base, and the top is fitted intoplace. The chamber is then filled withnutrient solution (see exercise 2) to depth of 5 cm to form an airtight sealbetween the base and the top and tosupply the plants with nutrients.

The plants should be grown in sandbecause soil, which contains organicmatter will release CO2 under the ex-isting warm temperature and high hu-midity conditions. The CO2 producedwould be utilized by all the plants inthe chamber, thus delaying death ofthe inefficient plants.

It is important that the chamber beconstructed and remain airtight. Other-wise CO~ from outside the chamberwill enter and lengthen the time re-quired to obtain the desired effect. Ifan aquarium is used, use grease on thewindow glass to create an air seal.

There is a simple way to determinewhether a closed environment has beensuccessfully established, and thus toinsure that a low CO2 concentrationwill develop inside the chamber. Thisprocedure involves a visual monitoringof the CO~ doncentration inside thechamber, and can be accomplished byplacing about 25 ml of indicator solu-tion in an Erlenmeyer flask and plac-ing the flask under the cover with theplants when closing the container atthe beginning of the test. The indi-cator solution is made with 10 ml ofsodium bicarbonate solution (5 × 10 4M) containing 1 ml universal indicatorper 250 ml (Fisher Scientific Supply).The final pH of bicarbonate solutionis related to the CO~ concentration inthe closed environment when at equi-librium. Plants such as soybeans (lowefficiency plant), which are known tocompensate at about 50 ppm, producea green color and those such as corn(high efficiency plant), known to com-pensate at 0 to 5 ppm, produce a bluecolor (Tregunna et al., 1970).

Continuous illumination is providedby 6 to 12 four-foot, 30-watt cool-white fluorescent lamps placed 5 cm

above the chamber top. The tempera-ture of the chamber interior should beno hotter than 35C. To check thetemperature, place a thermometer withits base wrapped in aluminum foil in-side the chamber.

Among the species which can besatisfactorily studied in this chamberare;

High-Efficiency Plants

Corn

SorghumSugarcanePigweed, redrootBermudagrassBarnyard grassLarge crabgrassFoxtail milletYellow foxtailJohnsongrassProso milletPurple nutsedgeBahiagrassRussian thistle

Low-Efficiency Plants

SoybeansRiceWheatTobaccoSpinachOrchard grassSugarbeetsCottonSunflowerLambsquarterLettuceItalian ryegrassOatsBarleyKentucky bluegrass

There is a wide range in degree ofefficiency among the species in each ofthese groups. In other words, classifi-cation of plant species on the basis ofdegree of competitiveness, or efficien-cy, is both relative and somewhatarbitrary.

In about 3 to 5 days some of the in-efficient species should begin to showa chlorosis, or yellowing, of the leaves.In a few more days they will begin to

die. The efficient plants, on the otherhand, not only will remain alive byutilizing the CO2 respired by the inef-fident ones, but will resume normalgrowth when the top is removed.

For comparison purposes it is wiseto grow some control plants outsidethe chamber, but otherwise exposedto the same environment as the plantsinside the chamber.

On a daily basis, starting with thefirst day, keep a record of the appear-ance of the plants. Note which plantsand plant parts begin to show signs ofCO2 stress first. After all the inef-ficient plants have succumbed, removethe top and observe the recovery of allplants in air.

Interpretation

When efficient and inefficient plantswere placed together in the closedchamber, the resulting CO~ equilibriumconcentration was below the CO2 com-pensation concentration of the inef-ficient plants. These inefficient plantsrespired enough CO2 to permit survival(and usually growth) of the efficientplants. Eventually the inefficientplants respire so much carbon thatthey begin to die. Any plants remain-ing alive in this closed system wouldhave a low CO~ compensation concen-tration, and thus should have an ef-ficient photosynthetic apparatus.

Plants which fix CO~ at high rates

have an initial advantage which makesthem either potentially high-yieldingcrop plants or serious weed pests.Notice that many common weedspecies are able to fix CO~ at highrates. When this capability is com-bined with characteristics such as rapidgrowth of rhizomes and stolons, or theproduction of a large number or easilydisseminated seeds (which is the casefor many weedy species), the resultusually is a competitive plant.

Scientists are presently using thistechnique to look for efficient in-dividual plants within an inefficientspecies. The hope is that if more ef-ficient individuals can be found, theycan be used as parents in a breedingprogram to increase significantly theyield of that particular inefficient

species. So far, progress has not beenachieved in this endeavor.

A variation of this experiment wouldbe to grow different varieties of a crop,such as soybeans, and see if you canfind differences in the efficiency ofutilization of CO2 among the individualplants.

Ref ereT~¢es

Tregunna, E. B., B. N. Smith, J. A. Berry,and W.J.S. Downton. 1.970. CanadianJ. Bot. 48:1209-1214.

A dditio nal R ea dings

Black,C. C., T. M. Chen, and R. H. Brown.I969. Biochemical basis for plant com-petition. Weed Science 17:338-344.

Menz, K. M., D. N. Moss, R. Q. Cannell, andW. A. Brun. 1969. Screening forphotosynthetic efficiency. Crop Sci.9:692-694.

Moss,D. N., and L. H. Smith. 1972. A sim-ple classroom demonstration of differ-ences in photosynthetic capacity amongspecies. J. Agron. Educ. 1 : 16-17.

Exercise 2

The Nutrient Requirements of Plants

All green ~lants require several ofthe more than one hundred elementsfound in the earth’s crust. The re-quired elements are called essentialmineral elements, for without them theplant cannot develop properly. Eachessential element plays a particular rolein the plant’s development, and if thatelement is either lacking or present ininadequate quantity, the plant doesnot grow normally, and a characteristicdeficiency, symptom will appear. Thenutrient elements must be present inthe proper balance if " satisfactorygrowth is to result. The essential plantnutrient elements are given.

Essential Plan t Nu trien t Elem en ts

Life-supporting elements-hydrogen,oxygen, and carbon-90 to 95% of allplant substance is due to these ele-ments, which come from the air (Cand O) and water (H).

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 123

The primary nutrients--nitrogen,phosphorus, and potassium-are neededby crops in relatively large amounts.

The secondary nutrients--calcium,magnesium, and sulfur--are needed byplants, but in smaller amounts.

Micronutrient elements - boron,manganese, copper, zinc, iron, molyb-denum, chlorine-required by plants invery small quantities, are just as neces-sary to the plants well-being as are theother essential elements. Research isbeing conducted to determine whetheradditional elements are necessary forplant growth.

Objective: To verify the essentiality of vari-ous elements for corn (Zea mays L.), andto determine their characteristic nutrientdeficiency symp toms.

Materials: distilled waterchemical compounds (see Procedure section)sand (washed with HCI, see Procedure)corn seed (other test plants can be used, but

ira legume is used, be sure to inoculatethe seed with the proper strain ofbacteria)

pots .24 liter (one-half pint) capacitythin plastic film

Procedure

All steps are to be carried out usingdistilled water and materials washed indistilled water. To avoid contamina-tion, the sand to be used should be aspure as possible, preferably pure quartzsand, and should be washed with hydro-chloric acid (1 volume of concentratedHC1 diluted with 10 volumes of tapwater). Allow the sand-acid mixtureto stand for a few minutes. Then pouroff the acid and wash the sand several

times with tap water until the washwater appears quite clear. Then rinsethe sand several times with distilledwater.

Line a clean pot with a layer ofplastic film. Punch a hole in the filmto correspond with the drainage holesof the pots and lightly place a plug ofglass wool over the holes. Fill the potto within about 2.5 cm of the top withwashed quartz sand and plant fourseeds per pot (2.5 cm deep for corn).

Prepare 1 liter of each deficiencysolution you want to test, using theamounts of stock solutions indicatedin Table 1. For example, to preparea complete nutrient solution, use 5 mlof stock solution A, 5 ml of stock solu-tion B, 2 ml of stock solution C, 1 mleach of stock solution D, I, and J, andpour these solutions into 985 ml ofdistilled water. Use extreme care notto contaminate either the stock solu-tions or nutrient solutions.

Prepare the stock solutions as indi-cated in Table 2. Always use cleanglassware and be careful not to con-taminate the bottles of chemicals withdirty spatulas or by interchanging thereagent bottle lids. Weigh the chemi-cals accurately on a balance having asensitivity of -+ 0.01 g.

Adjust the acidity (pH) of each nu-trient solution to about pH 6 with

dilute HC1 and dilute NaOH and in-dicator paper.

Label the nutrient solution contain-er and the corresponding pot. Care-fully pour 25 ml of the appropriatenutrient solution in the pot, takingcare not to pour the solution on theplants if you can avoid it. Repeat atregular intervals, being careful not tolet the sand become dry. Increase the

Table I. Stock solutions for essential element deficiencies.

Deficient Stock solution

element A B C D E F G I-I I J Water

mlComplete 5 . 5 2 1

K 7.5 -- 2 50 --P 7.5 -- 2 -- 20

Ca --- 15 2 1 ....N --- ~- 0. 5 50 20

Mg 5 5 --- I -- I0S 5 5 -~- 1 ....

Fe 5 5 2 j 1 ....

--- l 1 985--- 1 1 938.... 1 1 968.... 1 1 980200 - 1 1 727.... I I 977--- 2 1 1 985--- 1 986

124 SUPPLEMENT: BASIC LABORATORY STUDIES

Table 2. Preparation of stock solutions.

Stocksolution Compotmd

Dissolvein

ml Water

A Ca(NO3 )2 ¯ 4H20

B KNO3C MgSO4 . 7H20

D KH2 PO4E Ca(H2 PO4 ). H20F K~ SO4G CaSO4. 2H~ O

H Mg(NO~ )2 ¯ 6H~

I Contains per liter: I. 81gMnCl2.4H~ O2.86 g H3 BO30. 22gZnSO4.7H200. 08gCuSO4. 5H20

0. 09gH2 MoO4.H20Ferric Tartrate, A 0. 25% solution.Iron chelates may be used

11.7 50

5. 0 50

5.0 20

1.4 10

1.0 400

5. 2 601.0 500

2, 5 10

amount of nutrient solution added perpot as the plants mature. To insurethat enough solution is added eachtime, always add solution until it justbegins to drain from the bottom of thepot. Be sure to prepare additionalnutrient solution when your supplyruns low. Do not be placed in the posi-tion of not having nutrient solutionwhen your plants need it.

When the plants are about 5 cm tall,thin to the same number of plants ineach pot. The plants should be grow-ing in a greenhouse or other environ-ment suitable for plant growth.

Once a week the pots .should beflushed with an excess of distilledwater and fresh nutrient solution ap-plied immediately. If the wrong solu-tion is mistakenly added to a pot, thatpot should be flushed quickly with alarge volume of distilled water, andthen the correct solution applied im-mediately. Keep all pots and solutioncontainers properly labeled. Colorcoding (identifying solutions and potsof a given treatment with a particularcolor of tape, paint, etc.) will help tokeep errors from occurring.

Maintain a daily record on observa-tions of color changes of leaves at thetop, midportion, and bottom of eachplant, signs of necrotic (dead) spots leave~, malformation of growing tips,

and any other visual signs of abnormalgrowth.

Measurements that can be made in-cludez (1) plant height increase perday or week; (2) total fresh (green)weight of plant tops and roots (minussand) produced in a given time inter-val; (3) dry matter produced (dry tis-sue for 24 hours at 75C in oven), and(4) root observations on fresh roottissue. Observe the root tips, or apices,especially in the case of the calciumdeficient plants.

Contrast growth and overall appear-ance of nutrient deficient plants withthat of plants growing in the presenceof a complete nutrient solution (con-trol plants).

Interpretation

Try to account for differences ingrowth and appearance of plants(especially coloration) on the basis your knowledge of the role of mineralnutrition in plant metabolism. Healthyleaves shine with a rich dark greencolor.

You should be able to observe thefollowing nutridnt deficiency symp-toms on corn leaves.

Nitrogen deficiency: Yellow greencolor; distinctly slow and dwarfedgrowth; browning of leaves which

starts at the bottom of the plant, andproceeding upward; browning starts attip of bottom leaves and proceedsdown the center of the midrib.

Phosphorus deficiency: Purplishleaves, stems, and branches; slowgrowth and maturity; small, slenderstalk.

Potassium deficiency: Mottling,spotting, streaking, or curling of leaves,starting on lower levels; lower leavesbrown on margins and tips; browningstarts at tip of leaf and proceeds downfrom the edge, usually leaving the mid-rib green; poor root development (lead-ing to lodging, or falling down of olderplants eventually).

Calcium deficiency: Leaves havewrinkled appearance, with light greenbands along margins, young leaves mayremain folded, or become "hooked"in appearance and die back at the tipsand along the margins; short and high-ly branched roots.

Magnesium deficiency: Whitishstrips along the veins, and often apurplish color on the underside of thelower leaves.

Sulfur deficiency: Young leaveslight green in color and have even light-er veins; spotting of leaves; short,slender stalks; slow, stunted growth.

Iron deficiency: Leaves have pale-yellowish color and a general striping,especially in young tissue.

Additional Readings

Clark, R. B. 1970. Effects of mineral nutri-ent levels on the inorganic compositionand growth of corn (Zea mays L.). OhioAgr. Res. Develop. Center Research Circu-lar 181. Wooster, Ohio.

Hageman, R. H., D. Flesher,J. J. Wabol, andD. H. Storck. 1961. An improved nutri-ent culture technique for growing cornunder greenhouse conditions. Agron. J.53:175-180.

Hewitt, E.J. 1952. Sand and water culturemethods used in the study of plant nutri-tion. Bradley and Son Ltd., Reading,England.

Hoagland, D. R., and D. I. Arnon. 1950.The water culture method for growingplants without soil. Calif. Agr. Exp. Sta.Circular 347.

National Plant Food Institute. 1967. Ourland and its care. 1700 K Street, N. W.,Washington, D. C. 20006.

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 125

Exercise 3

Plant Response to Water Stress

One of the most important growthfactors limiting crop yields is watersupply. Not all crop plants are able toutilize a given amount of availablewater to the same degree. Water useefficiency, defined as ~he grams ofwater required to produce one gram ofdry matter, is an important considera-tion in evaluating the water require-ment of crops and weeds.

Crops which can make efficient useof water may be expected to yieldmore in periods of moisture stress(drought) than those which can not.Weeds which use water efficiently area more serious threat to crops duringperiods of drought. The water require-ments for certain crop and weed speciesare given in Table 3 (Shantz andPiemeisel, 1927).

In general, crops and weeds whichhave high yield capacities and competi-tive abilities have water requirementslower than that of nonefficient plants(i.e., plants which have low COx fixa-tion, or photosynthetic, rates, and thushave lower yield capacities). Noticethe low water requirements of many ofour most serious weed species. This inpart explains their strong competitiveability in many crop production sys-tems. Also notice that the food plantsvary considerably in their efficiency ofwater utilization. This kind of in-formation helps farmers decide whichcrops to plant in areas that tend to beeither wet or dry during the growingseason.

With adequate supplies of availablewater suitable for an expanding agri-cultural production becoming less andless available, it is important that cropscienti6ts become increasingly familiarwith the water needs oi ~ our cropplants. Considerable research is under-way at present to learn more about thebehavior of many of our importantcrops when they are subjected to waterstress.

Objective: To study the behavior of cropsand ~eeds during and following waterstress.

Table 3. Water requirement (g of waterrequired to produce I g of dry matter) forcrop and weed species grown at Akron,Colorado (Shantz and Piemeisel, 1927).

Efficient Water

species requirement

prostrate pigweed 260proso millet 267common purslane 281foxtail millet 285Sorghum species 304Sudangrass 305redroot pigweed 305Russian Thistle 314blue gramagrass 338corn 349

Nonefficient Waterspecies requirement

cocklebur 415barley 518cabbage 518wheat 557cotton 568cowpeas 569potato 575watermelon 577oats 583sunflower 623rye 634crimson clover 636lambsquarter 658prostrate knotweed 678crested wheatgrass 678cucumber 686common bean 700turnip 714alfalfa 844common ragweed 9 ’. 2smooth bromegrass 977

Materials: selected crops and weeds (seeTable 3)

plastic pots (20 cm is suitable)vermicufitesandnutrient solution (see experiment 2,

Tables I and 2)balance (4-decimal place is desirable)cheeseclothsmall tray

Procedure

Fill plastic pots with a mixture oftwo parts by volume of vermiculiteand one part of sand. Select plants ofinterest from the list given above (in-

clude plants having low and high waterrequirements). For each species, plantabout 6 seeds (about 2 cm deep for fairly large seed, like corn, and about0.5 to 1.0 cm deep for. a smaller seed,like alfalfa.) If legume seed are planted,be sure to inoculate the seed and]orpotting medium with the proper strainof bacteria. When the plants are about15 cm tail, remove all the plants fromthe pot except the healthiest one (i.e.,thin to one good plant/pot). Theplants should be grown in a greenhouse,or other suitable growing environment.

Except when subjecting the plantsto water stress, water the pots once aday (preferably early in the morning)with nutrient solution for the first 3weeks, and twice a day thereafter (earlymorning and mid to late afternoon pre-ferably). Once a week flush each potwith an excess of tap or distilled waterto remove salts which may have ac-cumulated in the rooting zone. Im-mediately after flushing with water re-supply the pots with nutrient solution.

When the plants are about 6 weeksold (or when they appear to be vigor-ous, well-established seedlings), with-hold nutrient solution (and water)from certain of the plants. Continuesupplying with nutrient solution andflushing other pots, so that you willhave some control plants (for compari-son purposes) that never undergo water stress. It is best not to establishthe moisture treatments until the rootsfor each species have completely oc-cupied the pots. Otherwise, differencesin root systems could be a factor inthis experiment.

Allow the water stress to developfor 7 to 10 days, or until the plantsappear to be fairly severely stressed.Then rewater the stressed plants, andcontinue watering all plants for a fewdays (recovery period).

During the entire period of stressand recovery, make notes of your ob-servations of changes in the appearanceof the plants. Note especially whichplants begin wilting first, and the ex-tent to which they recover from thestress during the night (you will needto observe your plants early in themorning, at midday, and in the lateafternoon to do this). Also note whichplant parts begin wilting first, and

126 SUPPLEMENT: BASIC LABORATORY STUDIES

which are last to show signs of wilting.Look for changes in the color of theplants, especially the leaves. Make acomplete record of the daily changesthat you see, from the beginning ofthe stress period to the end of the re-covery period.

In order to quantitate observations,you will need to make certain measure-ments. Leaf segments (choose leavesin the mid-portion of the plant) about2.5 cm in length (or discs 2.5 cm indiameter, or smaller as leaf size dic-tates) should be cut from near themiddle of the leaves, weighed, and thenplaced on top of several thicknesses(about 1 cm thick) of cheesecloth,which is laying in a tray. Cover the tis-sue with a thin layer (about two thick-nesses) of cheesecloth, and then addwater to the tray until the water levelis about 0.50 cm beneath the tissue.Maintain the water in the tray at thislevel. A cross-sectional view of thisarrangement is as follows:

Plot the data for this measurementas follows for each species:

50

WaterSaturationDeficit

1 X (= 15 to 20)

time, days

Interpretation

Your observations and measure-ments of water deficit should pointout marked differences among plantswith regard to their responses to waterstress and recovery following relief ofthe stress. Water deficit is one indexof the water status of plants growingunder a given water stress circumstance.

compare varieties of a particular plantspecies with respect to their droughttolerance. Plant breeders and geneti-cists are especially interested in learn-ing how different plants of a particularspecies respond to water stress, as thisinformation is of value in the selectionof particular varieties for their breed-ing programs.

References

Shantz, H. L., and L. N. Piemeisel. 1927.The water requirements of plants atAkron, Colorado. J. Agr. Res. 34:1093-1189.

A dditio nal Readings

Garman, W. H. (ed.) 1964. Water--essentialresource. Plant Food Rev. 10(2): 1-16.

Garman, W. H. (ed.) 1968. Water and agri-culture. Plant Food Rev. 14(1):1-16.

Sanchez-Diaz, M. F., and P.J. Kramer. 1971.Behavior of corn and sorghum underwater stress and during recovery. PlantPhysiol. 48:613-616.

/ ~ cheeseclothtray---~k~ /t ~ ~ (2 layers)

Layers of cheesecloth leaf tissue (lying above 1 cm layer(1 cm thick) of cheesecloth and

below thinner layer)

The leaf samples are kept in thisposition for 4 hours, until equilibriumis attained (or until the samples nolonger absorb water). The cells of theleaf sample then have absorbed asmuch water as they are capable of ab-sorbing, and thus have achieved a stateof "maximum turgot". The "turgidweight" is then obtained (after gentlyblotting free water from the surfaces),and after drying for 24 hours at 85C,the dry weight is obtained. All weigh-ing should be made to four decimalpoints if possible. The water satura-tion deficit is then calculated as fol-lows:

Water deficit

__ turgid wt - initial wt × 100turgid wt - oven-dry wt

The lower the deficit, the less is the

degree of stress in that leaf. By plot-ting curves for deficit vs days of stressand recovery for several plants in thesame figure, you will be able to com-pare the behavior of these plants towater stress under similar environ-mental conditions. By plotti~ag datafor the controls in the same figure,you can evaluate the effect of thestress treatment on a particular crop.When all your data are plotted, see ifyour results agree with what would beexpected from the table in the intro-duction to this exercise. Generally itis found that drought-resistant plants(those having a relatively low water re-quirement) show a smaller decrease inwater content for a given increase inleaf water stress than do those whichare less drought-resistant.

Plant scientists use methods similarto the ones used in this exercise to

Exercise 4

Chemical Interactions Among Plants

Plants are known to produce chemi-cais which can influence the growth ofadjacent plants. In recent years, cropphysiologists and ecologists have at-tempted to learn more about themechanism involved in this chemicalinteraction. Several of the chemicalsresponsible for the interaction havebeen identified, and progress has beenmade in understanding precisely how achemical produced in one plant can af-fect the growth of an adjacent plant.

Johnsongrass [Sorghum halepense(L.) Pers.] is aweedy species which hasbeen found to interact chemically withadjacent plants by producing chemicalswhich affect the growth and develop-ment of the other plants. This vigor-ous-growing weed is a serious pest inmany farming areas of the UnitedStates. Thus plant scientists are study-ing this weed intensively, hoping tolearn more about its behavior so thatits growth may be more effectivelycontrolled.

Recently it has been learned thatjohnsongrass interferes with germina-

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 127

tion and seedling development of cer-tain plant species by production ofchemicals in above- and below-groundplant parts. These chemicals inhibitthe growth of plants in the immediatevicinity of the johnsongrass plants. Inthis way the competitive ability of thisweedy species is increased.

Crop ecologists have learned muchabout plant interactions in natural en-vironments in recent years. The par-ticular type of plant interaction towhich this experiment relates is calledallelopathy, and is defined as the pro-cess in which a plant releases into theenvironment a chemical compoundwhich inhibits the growth of anotherplant in the same or neighboringhabitat. As would be expected, thisallelopathic interaction is a strong forcein the process of natural selectionspecies.

Objective: To determine the effect ofjohnsongrass leaf and rhizome extracts onseed germination and seedling growth ofseveral plant species.

Materials: johnsongrass plants (either col-lect from field or grow from seed)

homogenizerwhatman No. I filter paperbuchner funnelside-arm filter flaskpetri dishesnutrient solutiontest tubes (100 ml), or similar containerdrying oven (not essential)test species (johnsongrass, corn, soybeans,

sudangrass, crabgrass, wheat, barley,millet, pigweed, bromegrass, bristle-grass, and lambsquarter

Procedure

Prepare extracts by boiling 10 gfresh weight of johnsongrass leaves andof rhizomes (underground stems) for5 min in 100 ml of distilled water.Grind in a waring blender (or suitablehomogenizer) for 10 min, allow tostand for 30 min, and filter throughwhatman No. 1 paper with buchnerfunnel. Bring the volume of the ex-tract up to 100 ml with distilled water.

Inhibition of seed germination. Twohundred seeds of each of the testspecies are germinated at room tem-perature (about 24C) for 5 days in the

dark in petri dishes on filter papersaturated with a solution consisting ofa 1:5 ratio of a complete nutrient solu-tion (see Exercise 2, Table 1 and 2) rhizome or leaf extract of johnson-grass.

Always include controls in your ex-periment. The controls are preparedby substituting distilled water for theextracts in the above procedure.

Inhibition of seedling growth. Seed-lings of the test species of plants aregrown in quartz sand for 2 weeks in acomplete nutrient solution. Thentransfer the seedlings to 100 ml testtubes (or other suitable containers)containing a 1:5 ratio of nutrient solu-tion to plant extract. Allow the seed-lings to grow for 10 days in an environ-ment suitable for good plant growth.A growth chamber utilizing a photo-period of 16 hours at 27C, and a nighttemperature of 20C, would be ideal.Controls should be included, using a1:5 ratio of nutrient solution to dis-tilled water under the same conditions.

Results

Inhibition of seed germination. De-termine the percentage of germinationof all seeds in each treatment by usingthe following formula:

Number of seeds germinated × 100200 seeds used initially

germination.

Arrange your data according to theformat of the following table:

Percentage germination of seeds grownin rhizome or leaf extracts of johnson-grass for 5 days

rhizome leafPlant control extract extract

Inhibition of seedling growth. De-termine the oven-dry weight (dried at70C for 48 hours) of the seedlings ofall species tested. If an oven is notavailable, determine the fresh weightafter blotting the tissue as dry as pos-sible with toweling. Arrange the datain the following manner:

Effect of rhizome and leaf extracts onseedling growth

Plant

oven-dry weight, mg

rhizome leafcontrol extract extract

Interpretation

The data were obtained to gain in-formation concerning the effects ofjohnsongrass on germination and seed-ling growth of certain crop species.Extraction of the leaf and rhizometissue removed chemicals that have aninfluence on plant growth and develop-ment. The main plant growth inhibi-tors extracted in both leaves and rhi-zomes are chlorogenic acid, p-coumaricacid, and p-hydroxybenzaldehyde.

Under natural conditions, as therhizomes grow in the soil, these chem-icals are exuded (elaborated) into thesoil by the rhizomes, and thus caninteract with other plants growing inthe vicinity of the johnsongrass rhi-zomes. Also, rainwater which strikesthe leaves leaches some of the inhibi-tory chemicals from the leaves andplaces these chemicals in the soil.

As your data should show, plantspecies differ in the degree of whichthese chemicals inhibit germinationand seedling growth. From results,you will be able to draw some conclu-sions as to the extent of inhibitorychemical activity ofjohnsongrass plantparts on each of the test species. Foreach species, was germination or seed-ling growth most affected? Also,which source of extracted chemicals,leaf or rhizome, appeared to have thegreater effect on germination andseedling growth?

As a variation of this project, youcould select another weedy plant, anduse either the same or other testspecies.

Further Studies on This Subject

The interested student could com-pare the effects of each inhibitorycompound (chl6rogenic acid, p-cou-marie acid, and p-hydroxybenzalde-hyde usually is found to be the mostprominent inhibitor present, and also

128 SUPPLEMENT: BASIC LABORATORY STUDIES

the most persistent at different seasonsof the year. The inhibitors present inthe extracts can be identified if thestudent has some ability in chemistry.The techniques for these experimentsare outlined in the paper by Abdul-Wahab and Rice (1967). This studycould actually be conducted in soil toevaluate natural field conditions.

References

Abdul-Wahab, A. S., and E. L. Rice. 1967.Plant inhibition by johnsongrass and itspossible significance in old-field succes-sion. Bull. Torrey Bot. Club 94:486-497.

A dditio hal Readings

B6rner, H. 1960. Liberation of organic sub-stances from higher plants and their rolein the soil sickness problem. Bot. Rev.26:393-424.

Griimmer, G. 1961. The role of toxic sub-stances in the interrelationships betweenhigher plants. In Mechanisms in biologicalcompetition. Syrup. Soc. Exp. Biol. 15:219-228. Academic Press, N. Y.

Hamilton, K. C., and K. P. Buchholtz. 1955.Effects of rhizomes of quackgrass (Agro-phyron repens) and shading on the seed-ling development of weedy species. Ecol-ogy 26:304-308.

Exercise 5

Nitrogen Fixation by Legumes

The four most abundant elements inplant tissue are carbon, hydrogen, oxy-gen and nitrogen. Nitrogen is theonly one of these four which is com-monly found to limit plant growth.Nitrogen is crucial to life for severalreasons, one being that it is a keycomponent of protein.

The air we breathe is primarily amixture of nitrogen and oxygen gases.About 78% by volume is pure nitrogenin a free, or uncombined state (pureN2 gas). Every hectare of land surfacehas about 77,280 metric tons of freeN2 above it. Free nitrogen, as such,cannot be utilized by green plants. Tobecome available, it must be combinedwith other elements. The process bywhich gaseous nitrogen is convertedinto forms which plants can utilize iscalled nitrogen fixation.

Nitrogen fixation may occur bylightning (electrical discharges in theatmosphere); by various chemical re-actions from industrial processes; andby several species of micro-organismsliving in the soil, in plant tissues, andin fresh and salt water.

Nitrogen-fixed organisms over theearth are thought to be responsible forthe fixation of something in theneighborhood of 100 million tons ofnitrogen each year. This represents agreater amount of nitrogen than thatavailable from all other sources, includ-ing commercial nitrogen-containingfertilizers. It is clear that as fertilizernitrogen needs continue to rise, asagronomists strive to increase foodproduction, and as fossil fuels availablefor manufacturing fertilizer nitrogenbecome less available, scientists mustlearn more about the important pro-cess of biological nitrogen fixation.

Farmers can utilize atmosphericnitrogen for their legume crops byinoculating the legume seed with theproper strain of bacterial culture be-fore the seeds are planted. Legumecrops are important sources of proteinfor human and animal nutrition.

Soon after the legume seedling be-gins to grow, nitrogen-fixing bacteriainvade root hairs of the plant. Onceinside the root hair, the bacteria mul-tiply in large numbers. A growth calleda nodule forms on the root as a resultof this interaction of bacteria and roothairs. The bacteria live inside thesenodules and a partnership, or symbioticrelationship, is established. Symbiosisis the living together in intimate as-sociation of two dissimilar organismsfor their mutual benefit. The legumeplant furnishes energy which the bac-teria use to change the free nitrogen ofthe atmosphere into a form that theplant can use to produce its proteinand other nitrogen-containing organiccompounds. The nitrogen is thus saidto be "fixed". Neither the legume northe bacteria can change gaseous nitro-gen to a combined (and thus useable)form on its own. However, each canlive independently in the s0il byutilizing combined forms of soil nitro-gen.

Two forms of organisms are capableof fixing nitrogen, symbiotic forms andnonsymbiotic, or free-living, forms.

Because of their importance of cropnutrition, agronomists have studiedprimarily the symbiotic forms. Free-living forms can assimilate nitrogen gaswithout entering into symbiosis withany other organism, but this method offixation is much less important to cropproduction than symbiotic fixation interms of the amount of nitrogen fixed.

The organism which fixes gaseousnitrogen symbiotically in nodules onlegume roots is a bacterium of thegenus Rhizobiurn. The reason whyRhizobium symbiosis is restricted tolegumes is unclear.

In order for nitrogen fixation tooccur, the legume and bacterial strainmust be compatible. Not every strainof bacteria is capable of fixing nitrogenin a given legume. The legumes fallinto eight cross-inoculation ,groups.Examples of important legumes ineach group are given below. In addi-tion to the seven listed, there is aspecific strain group listed in Erdman(1959).

Cross-

inoculationGroup Crop

Alfalfa alfalfa, sweet cloverClover red, white, alsike, and

crimson cloverCowpea peanuts, lima beans,

cowpeas, annuallespedezas, kudzu,and sericia

Pea and garden peas, sweetvetch peas, and vetch

Soybean soybeansBean garden beans and

pinto beansLupine lupines

Effectiveness of the legume-bacteriasymbiosis in fixing nitrogen dependson many factors. Some factors affecteach partner separately, and some fac-tors affect them together. Some im-portant factors are as follows:

1) Kind of legume-Species andvarieties differ in their response torhizobia, and thus influence the num-ber, rate of for~nation, and effective-ness of nodules.

2) Physical environmental factors(temperature, moisture, etc.)--Bothcrop and bacteria have optimum grow-

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 129

ing conditions, and if either the soil oraerial environment is not optimal, theeffectiveness of the symbiosis is re-duced.

3) Fertility and pH status of soil-The presence of a large quantity ofcombined nitrogen (NO3--N, for ex-ample) in the soil will suppress nodula-tibn and nitrogen fixation. The soilmust not be too low in pH (too acid),or growth of bacteria (as well aslegumes) is suppressed. If soil condi-tions are such that nutrient elements(especially molybdenum) required forgrowth are present in insufficientquantities, fixation will be restricted.Molybdenum is specifically requiredby the enzyme system involved innitrogen fixation. Thus, molybdenumis required by both the bacteria andthe plant.

If a particular legume crop has beengrown successfully on a given fieldevery so often for the past severalyears, inoculation of the seed with theproper bacterial culture may not benecessary because the bacteria existfrom previous crop years. If there isany question, it is always a wise invest-ment of time and money to inoculatethe seed. If the soil is too acid (per-haps due to the added lime not havinghad time to react) or if the soil isthought to be low in molybdenum,then molybdenum should be mixedwith the seed at the time of inocula-tion.

Objective: To evaluate the influence oflegume seed inoculation on the growth oflegumes and legume-grass mixtures.

Materials: desired legume and grass seed(examples are given in the exerciseintroduction)

proper bacteria strainspots (20 cm is ideal)sandnutrient solution (see Exercise 2, Table

and 2)soil from an area which has not been limed

and fertilized in recent years

Procedure

First, select the legume plants tostudy (white clover, peas, garden bea.~s,and soybeans are good choices). Inoc-ulate seed of these plants with the ap-

propriate bacteria culture obtainedfrom a reputable farm service center-observe the following precautions:

use the right inoculant for eachlegume,

make sure expiration date for theinoculant has not passed.

keep commercial culture in cool,dark place until used (remember,culture contains living bacteria):

follow directions and mix culturewell with seed.

plant seed within 24 hours afterinoculation, or reinoculate.

firm soil around seed and keep seed-bed moist.

Prepare a series of pots containingthe following:

Treatment Description

1 sand, complete nutrientsolution

sand, nutrient solution lack-ing only nitrogen

soil, limed and unfertilizedsoil, limed and fertilized

with phosphorus, andpotassium (but nonitrogen)

soil, limed and fertilizedwith nitrogen, phos-phorus and potassium

soil, unlimed and fertilizedwith potassium and phos-phorus (but no nitrogen)

A sample of the soil should be sub-mitted to a qualified soil testing labo-ratory (frequently the state college ofagriculture can provide this service)and amounts of agricultural lime andfertilizer added in accordance with theresults of these tests.

Inoculated legume seed (of the de-sired species) should be planted in onecomplete set of the pots (consisting ofeach of the six treatments) and un-inoculated seed planted in anothercomplete set. In addition, a 50:50mixture (by seed number) of legume-grass combination should be plantedin a third complete set of the pots.The legume seed in the legume-grassmixture should not be inoculated.

It may be difficult for some studentsto prepare the various soil treatments(treatments 3 through 6). If so, thisexperiment can be very satisfactorilycompleted (and the project objectives

attained) by using only treatments and 2. To prepare the appropriate nu-trient solutions, the student shouldfollow the instructions in Exercise 2,Table 1 and 2.

With regard to the legu~ne-grass mix-ture, rescue, orchardgrass, and wheatare grasses that would be good choicesfor seeding with legumes such as theclovers, !espedeza, beans, and peas.

After 5 to 6 weeks of growth, recordthe following information:

1) Height of plants (both compon-ents in case of mixtures).

2) Dry weight of plants.3) Color of leaves of growing plants

on a weekly basis.4) Location and extent (number)

of nodulation on legume roots-note the internal color of nod-ules.

In terpre ta tion

Legume plants growing either with-out effective nodules on their roots orwithout adequate soil nitrogen willsoon show a yellowing of the leaves,which is indicative of nitrogen de-ficiency (note description of nitrogendeficiency symptoms in Exercise 2).Nitrogen-deficient crops cannot com-pete well in a field environment andare soon crowded out by the morevigorous-growingweeds. If the legumeis adequately supplied with nitrogen,such as is the case if the nodules arehealthy, the plants will be dark greenin color, grow vigorously, crowd outthe weeds, and produce a high yield.

Legumes can have nodules on theroots and still not grow well. Thepresence of nodules does not insurebenefit. For the plants to be well-inoculated, the nodules must be ef-fective. Effective nodules are large andare clustered arounxt the main (tap)root of the plant. Ineffective nodulesare small, and tend to be scatteredthroughout the root system. Effectivenodules also have a dark red "beef-steak" color on the inside. Ineffectivenodules are anemic-looking, white, orgray on the inside. It is not uncom-mon to find b~th types on the sameplant under field conditions.

The nitrogen produced by an effec-tively nodulated legume may be usedby a grass growing in association with

130 SUPPLEMENT:BASIC LABORATORY STUDIES

the legume. The nitrogen used by thegrass can come from nitrogen-contain-ing compounds (such as amino acids)excreted by the legume roots, or fromnitrogen released from decompositionof nodules and roots sloughed off thelegume roots. There is considerableevidence that legume-grass mixtures aremore efficient than nitrogen-fertilizedgrass for economic feed production forlivestock. In every case where legumeroots are effectively nodulated, a por-tion of the fixed nitrogen is returnedto the land as manure, and thus resultsin soil improvement.

Nitrogen nutrition of crops is close-ly connected to plant protein produc-tion. As time passes, the shortage ofprotein in the world becomes more andmore critical. It is evident that proteinfrom plant sources is a key to solvinghunger problems. Also, nitrogen ferti-lizers are becoming increasingly ex-pensive, and are simply not availablein much of the world. Thus the im-portance of nitrogen fixation as ameans of providing nitrogen for leg-umes, and for legume-grass combina-tions, is readily understood.

References

Erdman, L. W. 1959. Legume inoculation--whatitis. What it does. Farmers Bul. No.

2003, U. S. Department of Agriculture,Supt. of Documents, U.S. Government

Printing Office. Washington, D. C.

Additional Readings

Alexander, M. 1961. Introduction to soilmicrobiology. John Wiley and Sons, Inc.New York.

Burton, J. C. 1965. The Rhizobium-legumeassociation in microbiology and soil fer-tility. Oregon State University Press.Corvallis.

Nutman, P. S. 1965. Symbiotic nitrogenfixation. In W. V. Bartholomew and F.E. Clark (ed.) Soil nitrogen. Agronomy10:363-379. Amer. Soc. of Agron.,Madison, Wis.

Exercise 6

Chemical Weed Control in Plants

Weeds are unwanted plants. A plantis considered aweed if it interferes withman’s utilization of land and water re-sources. Many kinds of weeds arecontinually competing with crop plantsfor the available light, water, carbondioxide, nutrient elements, and space.Weed competition is a major factor af-fecting the yield and quality of ourcrops. Some weeds are poisonous tolivestock, and others are directly noxi-ous to man. Weeds harbor insect anddisease-causing organisms, clog irriga-tion and drainage canals, interfere withnavigation, allow for deterioration ofbuildings and machinery, and are un-desirable along roads, right-of-ways,and similar settings. For all these rea-sons, agricultural scientists are con-tinually striving to develop means ofeffectively controlling weeds. Muchprogress has been made, but as the de-mand for food and fiber intensifies,greater success in effectively combat-ing weeds will be necessary.

Scientists have developed a numberof methods of controlling weeds.These include (1) preventive measure(using weed-free seed, clean farmequipment, proper animal manure, andirrigation water management), (2)physicafmethods [tillage, mowing, cut-ting, flooding, dredging, draining,chaining (dragging heavy chains acrosscanal bottoms), flaming, and mulch-ing], (3) biological methods (usingnatural enemies, such as parasitesrpredators, and pathogens), (4) habitatmanagement (environmental manipula-tion), and (5) chemi.cal control (use herbicides).

Often, a combination of weed con-trol methods can be utilized, and thissystematic concept, or "weed-manage-ment system," is the approach weedscientists are presently using in theirattempts to control serious weed pests.However, at the present time chemi-cals, usually in conjunction with time-ly cultivation, are the most effectivemeans of controlling weeds in crops.In recent years, the use of herbicidesin certain circumstances has beencriticized. Unquestionably, the user

needs to be fully responsible in termsof environmental protection.

This experiment demonstrates thatchemicals can be used effectively tocontrol weeds, even in cropping situa-tions where serious weed pests aregrowing.

Objective: To evaluate the effectiveness ofherbicides for weed control in selectedcropping systems.

Materials: six wooden flats (pots can beused)

soil (fertile and limed, to adjust soil pH ifnecessary)

corn, soybean, alfalfa, wheat, cocklebur,and fescue seed

herbicides (atrazine, DNBP salt, and2,4-DB)

protective equipment for spraying (oldclothes, gloves, safety glasses, andface mask)

simple sprayer for applying herbicidesolutions-a sprayer is needed thatwill enable the operator to direct theherbicide solution on the plants.

Procedure

Plant one row of corn, one row ofsoybeans, one row of alfalfa, and onerow of wheat in each of six flats. Plant-ing densities for corn and soybeansshould be 1 seed/10 cm, and for alfalfaand wheat 1 seed/3 cm. Plantingdepths for corn and soybeans shouldbe about 2.5 cm, and for alfalfa andwheat about 0.5 to 1.0 cm.

In four of the flats cocklebur seedshould be heavily interseeded in one-half of each flat and fescue seed seededin the other one-half of each flat (weedseeding at right angles of crop rows).

Two of the flats will serve as con-trois (no herbicides added). One con-trol flat will contain crops and weedsand the other control flat crops alone.

Apply atrazine, DNBP salt, and 2,4-DB, as sprays, 5 weeks after the cropsare planted. Apply herbicides over allthe foliage at the rates recommendedon the label of the herbicide container.Use protective equipment (old clothes,gloves, safety glasses, and face mask)while spraying.

Examine the response to spraying(and control flats) every few days for

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 131

a period of 3 weeks and record thefollowing data each time:

1) Height of crop and weeds.2) Number of leaves on crop and

weeds.3) Injury (yellowing, or chlorosis,

and browning, or necrosis).Always make comparisons and con-

trasts with the controls. A good wayto organize these data would be to cal-culate a ratio of sprayed treatments tocontr61s for each observation.

If the student wishes, other crops,weeds, and herbicides could be testedusing the above technique. The vegeta-ble crops provide interesting experi-mental material for chemical weed con-trol studies.

Interpretation

Atrazine is a herbicide which is usedextensively for weed control in corn.It is absorbed by both leaves and roots,and is translocated throughout theplant. Atrazine is thought to kill sus-ceptible plants by interferring withphotosynthesis. The chemical is quick-ly broken down into harmless productswhen absorbed by corn roots andleaves. Plants that are susceptible toatrazine either do not decompose it, ordecompose it at such a slow rate thatthe plant is killed.

The salt of DNBP is also selective inits toxicity to plants. Therefore, it canbe used to kill young wee,ds growingin corn, soybeans, small grain, alfalfa,clovers, peas, and peanuts. However,if DNBP salt is applied at too high arate, it behaves as a "contact" herbi-cide. That is, it will kill any vegetationwith which it comes in contact. PureDNBP (not the salt) is very toxic growing plants, so it is used as a generalcontact herbicide. Paraquat is anotherexample of a commonly used contactherbicide. When it is desirable to killthe above-ground parts of existingvegetation in an area, pure DNBP andparaquat are good choices.

The herbicide 2,4-DB is often usedwhen broadleaf weed control in leg-umes is desirable. Control of broad-leaf weeds such as cocklebur in leg-umes such as soybeans is very impor-tant because these weeds are often-times a serious pest in legume crops.

In such a situation farmers cannot usethe usual broadleaf herbicides, such as2,4-D, because the 2,4-D would alsokill the soybean plants. 2,4-D is a veryeffective chemical for controlling manybroadleaf plants. After 2,4-DB hasbeen absorbed by the plant, it is con-verted into 2,4-D. Many legumes havethe ability to convert 2,4-DB into2,4-D very slowly. In these plants, theconcentration of 2,4oD at any one timeis never great enough to cause seriousplant injury. Most other plants makethe conversion of 2,4-D rather rapidly,providing a concentration of 2,4-D highenough to kill the plant. Therefore,the legume plants escape injury andmost weeds are killed.

From data you should be able todraw conclusions as to the relative ef-fectiveness of these herbicides forweed control in the four test crops.Looking at the controls alone, rankthese crops in their ability to competewith weeds.

A dditio hal Readings

Klingman, G. C. 1961. Weed control: As ascience. John Wiley and Sons, Inc., NewYork.

LeGrand, F. E. and S. E. Allred. 1966. Safeand effective chemical weed control.Oklahoma State University ExtensionCircular E-760. Stillwater, Oklahoma.

Muzik, T.J. 1970. Weed biology and con-trol. McGraw-Hill Book Co., New York.

Weed Science Society of America. 1967.Herbicide Handbook. W. F. HhmphreyPress, Inc., Geneva, New York.

Exercise 7

Sediment Control Through Proper Cropand Land Management

A pollutant has been defined as aresource out of place. Sediment, ournation’s largest single water pollutantby far, has a twofold effect on the en-vironment. It depletes the land re-sources from which it comes, and itreduces the quality of the water re-source in which it is deposited. Aboutone-half of all sediment originates onagricultural land, so agriculture has amajor role to play in maintaining en-

vironmental quality. Rapidly chang-ing land use patterns, both on farmsand in urban areas, require improvedpractices if sediment damage is to bereduced and environmental quality en-hanced.

Sediment becomes an importantpollutant when it fills reservoirs, lakes,and ponds and clogs stream channels;andwhen it settles on productive land,destroys aquatic life, creates turbidity,and impairs water distribution systems.Sediment may also carry other pollu-tants, such as plant nutrients, pesti-cides, toxic metals, and perhaps bac-teria and viruses.

Sediment carries physical, chemical,and biological materials, all of whichcontribute to pollution of the environ-ment. In addition, deposition of sedi-ment in reservoirs for water storage isbecoming a serious economic problem.In view of the fact that good reservoirsites are becoming scarce, preservationof existing reservoir capacity is critical.When new reservoir sites are no longeravailable, sediment will have to be re-moved from existing reservoirs, if theadvantages of water storage and floodcontrol are to be realized. The cost ofremoving the sediment which accumu-lates annually in U. S. reservoirs, as-suming it could be done, it estimatedat about one billion dollars (Glymphand Storey, 1967).

With improved technology, and bya wiser use of our crop and land re-sources, control of sediment to a lowand manageable level can be attained.This exercise illustrates an importantprinciple that must be followed if pol-lution of our water by sediment is tobe minimized.

Objective: To evaluate the effect of wisecrop and land management on ground waterand stream water quality.Materials: 2 wooden flats .(0. 75 m by 1.0

by 0.25 m)16 l-liter beakers (or similar con tainers)tubingco tton45.4 kg of friable, well-granulated garden soil1,000 grams of a 16-16-16 fertilizer (percent

N - percent P20s - percent K20)heavy plasticbrace and bit, or electric drill and wood bitsfescue and corn seedsmall quantity of algae (from a farm pond)

132 SUPPLEMENT: BASIC LABORATORY STUDIES

Procedure

Build two large wooden flats, eachhaving the following dimensions: 0.75m by 1.0 m by 0.25 m. Elevate theflats by attaching 20 cm legs at oneend and 10 cm legs ~t the other end.Divide one of the flats into two equalparts by placing aboard lengthwise inthe flat. Then line the inside walls andbottom of each flat with heavy plasticsuch that the flats will hold water.Next bore four holes at the lower endof each flat at the point where the bot-tom board meets the end board. Spacethe holes about the same distance apartalong the bottom of the end board.Place a small quantity of fine gravel onthe inside of each hole to keep soilfrom escaping. Place a length of cop-per tubing in each of the bored holes,flange the end, and make the connec-tions watertight with a waterproofsealer. Attach flexible tubing to thecopper tubing and lead each into a 1liter beaker. The arrangement issketched below.

begins to dry out. Try to apply thewater uniformly across each flat. Besure to water the bare flat each time(and with the same amount of water)the planted flat is watered.

After the plants have grown forabout 5 weeks, place the l-liter beak-ers in position and collect the waterdraining through the soil over a periodof 3 weeks. During the collectionperiod, the flats should be wateredseveral times.

At the completion of the collectionperiod the contents of the beakersshould be stirred thoroughly to insurethat the sediment is uniformly sus-pended in the beakers. Immediatelypour 100 ml of suspension from eachbeaker into a bared container, evapo-rate the contents to dryness, and re-weigh the containers plus contents.The following relationship will apply:

weight of beaker and dry solids

- weight of beaker alone

= weight of dry solids.

Mix thoroughly 100 grams of a 16-16-16 (percent N - percent P2Os percent K20) fertilizer analysis with45.4 kg of well-granulated, friablegarden soil. Place one-half of the soil-fertilizer mixture in each of the twoflats, and pack the soil firmly.

In one-half of the soil in one flat (a0.33 m by 1 m section) plant a thickbroadcast seeding of fescue seed (about0.50 to 1.0 cm deep) and in the otherone-half plant corn seed on the con-tour (parallel to the ends of the flat(about 2.5 cm deep and about 10 cmapart in the row). Firm the soil aroundeach kind of seed. Do not plant anyseed in the second flat.

Moisten the soil in both flats using asprinkler attached to a garden hose.After the seedlings have emerged, con-tinue watering the plants as the soil

The dry solids consist of soil andfertilizer salts which were dissolved inthe water and soil particles (mostlyclay- and silt-sized particles) whichwere suspended in the water.

Place the l-liter beakers containingthe remainder of the suspension underfairly strong light and place equivalentweights of algae (very small quantitiesare satisfactory) in each beaker. Allowthe algae to grow for 1 month. Peri-odically shake the suspensions well (atleast once daily). At the end of month remove the algae, blot dry, andobtain the fresh weight of the algae ineach beaker with a fish net of a knownweight.

Throughout the experiment noticethe physical features of the soil,especially the tendency toward ero-sion, in both flats.

Interpretation

Sediment and its nutrient load arethe primary hazards to water quality.It has been estimated that 3.6 billionmetric tons of sediment wash into U.S. waterways each year (Wadleigh,1968). In the neighborhood of 2.7million metric tons of nitrogen and 1.8million metric tons of phosphoruswash into our waterways annually.

A certain fraction of the nitrogenand phosphorus in sediment becomesavailable to aquatic life, especiallyalgae. As the algae grow, oxygen dis-solved in the water is consumed by thealgae, leading to less oxygen availablefor fish, and ultimately to eutrophica-tion of the body of water. Availabledata suggests that little fertilizer phos-phorus leaches through the soil or runsoff as inorganic phosphate in solution,but it can wash off as phosphate ad-sorbed on sediment (Taylor, 1967).Fertilizer nitrogen, being much morewater soluble than fertilizer phosphor-us, is readily leached through the soiland into waterways.

There is ample evidence that sedi-ment and nutrient losses are less fromland in meadow, or grass sod, thanfrom land in corn or soybeans (Stolten-berg and White, 1953). However,whatever the vegetative cover, fertiliza-tion would be expected to improveplant growth, and runoff and erosionmay be reduced more than enough tobalance the enrichment. Thus, the neteffect could be a substantially lowernutrient loss where fertilizers producemore vegetative cover and plant resi-dues.

Another consideration is that ferti-lizers substantially reduce our landneeds for crop production. By usingadequate fertilizer on our better land,where erosion hazards are minimal, wemay be able to retire our poorer landto permanent grass or tree cover, thusgreatly reducing the amount of landexposed to erosion and the accom-panying loss of nutrients.

Thus it may be seen that when com-mercial fertilizers are judiciously usedin the proper alrrounts, water qualitycan actually be improved. Clearlyoveruse or misuse of fertilizers maylead to deterioration of water quality,

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 133

but to not use enough fertilizer formaximum crop growth would beequally hazardous to water quality.Indeed, a strong argument can be madefor using even higher rates of fertiliza-tion where crop yields can be increasedwithout creating a pollution hazard.More land could then be returned tocontinuous vegetation until later whenit might be needed to produce foodand fiber. Using this technique, youwill be able to compare various crop-ping systems with respect to their sedi-ment and nutrient runoff potential.

References

Glymph, L. M. and H. C. Storey. 1967.Sediment--Its consequences and control.Pub. 85. Amer. Ass. Advan. Sci.,Washing-ton, D. C. p. 205-220.

Stoltenberg, N. L. and J. L. White. 1953.Selective loss of plant nutrients by ero-sion. Soil Sci. Soc. Amer. Proc. 17:406-410.

Taylor, A.W. 1967. Phosphorus and waterpollution. J. Soil Water Conser. 22:228-231.

Wadleigh, C.H. 1968. Wastes in relation toagriculture and forestry. Misc. Pub. No.1065. U. S. Department of Agriculture,Washington, D.C. 112 pp.

Additional Readings

Soil Conservation Society of America. 1971.A primer on agricultural pollution. 7515Northeast Ankey Road, Ankeny, IA50021.

Exercise 8

Herbicide Effectiveness and Volatility

Many factors influence herbicide ef-fectiveness. Some of these factors re-late to properties of the herbicide,some to characteristics of the environ-ment, and some to plant processes.Usually, these factors interact underfield conditions in a very complexmanner to determine effectiveness of aparticular herbicidal application.

Herbicides have different selectiv-ities (differential effects on differentplants) because they have differentmolecular configurations. This molec-ular structure difference causes varia-tions in chemical and physical proper-

ties of the molecule, which in turnmodifies its biological activity.

Dominant environmental factorsthat affect herbicidal effectiveness aretemperature, rainfall or overhead ir-rigation, and soil type.

A given plant species may or maynot be injured by a specific herbicide,depending on its genetic make-up, age,rate of growth, morphology (shape),and physiology.

The volatility of a herbicide is oneimportant herbicidal property whichdetermines its effectiveness. All chem-icals have a vapor pressure, which is ameasure of the ease by which mole-cules of the substance escape from thesurface. The evaporation of water isan example of volatilization. Gasolineis much more volatile than water.Vaporization of a moth ball is an ex-ample of volatilization of a solid(called sublimation). At a given pres-sure, vaporization of both liquids andsolids increases as temperature rises.

Herbicides are generally volatile, andwhen they are sprayed on leaf surfacesor soil surfaces will evaporate, to agreater or lesser degree depending onthe properties of the herbicide. Inmany cases the chemical properties ofthe herbicide which cause it to bevolatile are the same properties whichcause it to be an effective weed killer.The volatile gases which evaporate maydrift to susceptible plants, includingdesirable crop plants, and be quitedamaging.

This exercise focuses attention onthe volatility properties of several im-portant herbicides, and demonstratesthe danger of desirable vegetation ofcareless application of these materials.

Objective: 1) To observe the effects ofvolatility differences due to chemicalformulation or type of herbicides.2) To evaluate the relative hazard of severalherbicides due to the possibility of vapordrifting onto adjacent vegetation.Materials: the Herbicides trifluralin, EPTC,

Dinoseb (Dinitro, or DNBP), 2,4-Damine, and 2,4-D ester

balance7 beakers, 250 mlgraduated cylinders, 100 mllabelsmixed plant populations, or potted speci-

mens such as wheat, oats, barley, garden

beans, clovers, cotton, broccoli, tomatoes,garden peas

Fume tents (see procedure)

Procedure

Assemble 6 fume tents as follows:cover "A" frames, saw horses, or tentframes with clear plastic, making sureto make all seams airtight with tape.Place the tents near a window, or agood light source.

Place a complete set of the testplants inside the fume tents. For bestresults, use plants that are 2 to 2V2weeks old.

Observing all label safety precau-tions, including wearing gloves andprotective clothing, place 200 ml ofeach of the five herbicides listed underMaterials in a labeled beaker. Set onebeaker of chemical in the approximatecenter of each fume tent and seal offeach tent completely. The sixth tentshould not contain any chemical, andwill serve as a control. During a 1-week period observe the plants daily,noting any changes that occur in color,shape, or distortion of tissue.

After 7 days of exposure, removethe beakers, again observing cautionwhen handling the chemicals. Recordthe milliliters of chemical remaining,milliliters evaporated, and percentevaporated.

Remove the fume tents, and make acomplete record of plant injury symp-toms. Examine the plants for changesin color and shape of plant parts.Some of your plants will developtwisted or malformed leaves, stems,and roots.

Make weekly observations of plantinjury symptoms for an additional 3weeks.

Throughout the course of the study,make comparisons of the treated testplants with the control plants.

Interpretation

Treflan and EPTC are fairly volatileherbicides which are normally appliedto the soil and are translocatedthroughout the plant. The rather highvolatility of these chemicals will resultin some leaf tip burning of youngmonocots (such as barley and wheat)

134 SUPPLEMENT: BASIC LABORATORY STUDIES

and dicots (such as beans, clover, andcotton). The dicots would be moreheavily damaged then the monocots.

Dinoseb is a volatile chemical thatkills vegetative tissue on contact. Sinceit kills by contact, it will burn offplant tops without much .affectingroot systems, except by repeated ap-plications. All plant foliage (monocotsand dicots) with which the vaporscome in contact will be damaged.

Broadleaf plants in general are verysusceptible to both 2,4-D amine and2,4-D ester, and grasses as a rule arequite tolerant to these chemicals.

However, the ester formulation of2,4-D is very volatile and the amineformulation has low volatility. Thus2,4-D ester would be expected to bemore damaging to the broadleaf plantsunder the fume hood than would2,4-D amine.

2,4-D is used extensively for broad-leaf weed control in many crop man-agement situations. Whatever the use,be it in the field or in the home yard,if valuable broadleaf plants are in thevicinity (or downwind), of the targetbroadleaf weed, 2,4-D amine shouldbe used, and due caution observed.

The age of a plant often determinesits resistance to a particular herbicide.In general, young plants are easier tokill than older plants. You could readi-ly demonstrate this by placing someolder plants in your fume hoods along-side the younger plants.

The growing points of monocots(grasses, like oats and barley) are lo-cated at the base of the plant or be-neath the soil surface when the plantsare young, and thus are protectedfrom contact-type herbicides by thesurrounding leaves. Any contact sprayremaining on the leaves may injurethe exposed leaves but will not con-tact growing points. Thus, grasses cangrow out of this kind of damage. Bycontrast, broadleaf plants (such as cot-ton, peas, beans, and tomatoes) haveexposed growing points at the tips ofthe shoots and in leaf axils. With thistype of plant, the contact herbicideactually strikes the growing point.

Additional Readings

Ashton, F. M. Principles of selective weedcontrol. 1971. Agrichemical Age 14(1):8-12.

Klingman, G.C. 1961. Weed control: As ascience. John Wiley and Sons, Inc., NewYork.

Muzik, T.J. 1970. Weed biology and con-trol. McGraw-Hill Book Co., New York.

Exercise 9

Crop Improvement Through Plant Breeding

From the beginnings of agricultureman has strived to improve the plantsthat provide his food. Crop improve-ment has taken many forms over theyears. Man has improved the environ-ment in which crops are produced.He has learned how to fertilize andlime the soil, control serious pests, andimprove the water supply to his crops.He has become a better manager of allhis farm resources. He is doing a bet-ter job of carrying out all the produc-tion operations (planting, fertilizing,controlling weeds, harvesting, etc.) atthe right time, or on the correctsch6dule. However, one of the mostimportant factors determining the suc-cess of his production operation is thekind of crop seed he plants. Every seedof a particular crop has a given po-tential for yield and quality, and thefarmer’s success depends in large meas-ure on whether he has planted theseed having the highest yield potentialfor his particular location. If a seedhas high yield potential for a given lo-cation, it is said to be adapted to thatparticular environment.

The plant breeder has the responsi-bility of changing the heredity, orgenetic make-up, of a plant so that itis better adapted to a particular en-vironment, and thus would have ahigher yield potential. There was atime when plant breeders had to relyentirely on their skill and judgement inselecting superior plant types. Skilland judgement are still an integral partof plant breeding, but scientific knowl-edge in this field has advanced rapidlyin recent years, and today the plantbreeder has many basic scientific prin-ciples to guide him.

Plant breeders have been successfulin influencing many plant characteris-tics in addition to yield and quality.Some of these are drought, disease, and

insect resistance; maturity; and winterhardiness. Successful plant breedersusually work as members of a team,combining their knowledge with thatof scientists in disciplines such asgenetics, statistics, physiology, bio-chemistry, entomology , and plantpathology.

This exercise will demonstrate onetechnique plant breeders utilize intransferring genetic information fromone plant to another, and thus in-fluencing the characteristics of theplant.

Objective: To illustrate the transfer ofgenetic information from one plant to an-other bv the process of crossing.

Materials: seed of a yellow corn varietyseed of a white corn variety (with a maturi-

ty similar to that of the yellow cornvariety)

fertile garden soil (well-fertilized land andlimed)

pots (at least 0.25 m)

Pro cedure

Plant four seeds of the yellowhybrid 2.5 cm deep in the soil in eachof two pots. Do the same for thewhite hybrid. Place the pots in an en-vironment suitable for growing corn,such as agreenhouse. For best growth,the plants should have at least 10 to12 hours of sunlight daily. Keep theplants well-watered. When the plantsare about 8 cm tall, thin to the onemost healthy plant in each pot.

When the tassels (male flowers) justbegin to emerge from the top of theplants, place a large transparent bagover the tassel area, add attach it firm-ly to the plants. Place small paper bagsover the ear shoot (female flowers) each plant, and fasten tightly to theplant at the base of the ear shoot.

About 4 days after pollen has begunto be shed from the white variety,shake the bag and tassel to collect pol-len in the bag. Gently remove the bagfrom the tassel of the white variety,remove the bag covering the ear shootof the yellow variety and place the bagcontaining the pollen over the ear shootof the yellow variety. Be careful notto spill the pollen. Holding the bagtightly against the base of the ear

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 135

shoot, shake the bag well to scatter thepollen onto all the silks. Secure thebag on the ear shoot to keep out allother pollen. You have now cross-pollinated these two varieties.

Next, cross-pollinate in the otherdirection, using these same two plants.

Using one of the remaining p6ts,and using the above technique, transferpollen from a tassel to the ear shootof the same plant. This is a self-pollination procedure.

Make very careful notes on all thatyou have done.

When the ears have matured on thestalks, harvest them, and allow themto dry in a dry, well-ventilated placeuntil their weights do not change.Keep the proper label on each ear.

When dry, shell the ears, and recordthe shade of yellow for each ear foreach direction of cross. Count thenumber of kernels from each ear thatappears to have a distinct color.

Interpretation

Each plant has genetic characteris-tics which cause it to be different fromevery other plant. Some of these char-acteristics are desirable, and some areundesirable. When a plant breeder seesa desirable characteristic in a particularplant that is of interest to him, he willfertilize the female flower with pollenfrom another plant having a specificneeded quality.

Corn is a good test plant to use toillustrate the procedure of cross-ferti-lization because it has imperfect flow-ers (is monoecious). AIthough it is bit more tedious, crossings can readilybe made between plants having flow-ers that are perfect, that is, which haveboth male and female parts on thesame flower.

Additional Readings

Frey, K.J. 1971. Improving crop yieldsthrough plant breeding. In Moving offthe yield plateau. Publ. No. 20. Amer.Soc. of Agron., Madison, Wis.

Hughes, H. D. and D. S. Metcalfe. 1972.Crop Production. Macmillan, New York.

Exercise 10

Air Pollution and Crop Growth

Pollutants of many different typesare present in the air, and some ofthese pollutants are known to have adamaging effect on plants. Most aerialpollutants are the result of energy con-versions which occur in industrial pro-cesses and in the combustion of fuelby various forms of transportation.Among the products of energy con-version which enter the atmosphere,and which might injure vegetation, arecarbon monoxide, sulfur dioxide, sul-furic acid, hydrogen sulfide, nitricoxide, nitrogen dioxides, hydrogenfluoride, ethylene, ozone, aldehydes,soot, and hydrocarbons.

The major reason for the impor-tance of the nitrogen oxides as pollu-tants is their participation in photo-chemical reactions which produceozone and the peroxyacyl nitrates(PANs), two highly phytotoxic (toxicto plants) oxidants. When stomates ofleaves are open, these materials willdiffuse into the interior of the leavesand, due to their strong oxidizing prop-erties, will be damaging to the proteinof leaf cells. The available evidencesuggests that a primary physiologicaleffect of these kinds of pollutants(strong oxidants) may be to suppressplant respiration (an inhibition ofoxidative phosphorylation in mito-chondria). Actually, the precisemechanism by which most pollutantsdamage vegetation is largely unknown.

This exercise will demonstrate theresponse of several important cropplants to air pollutants.

Objective: To evaluate the response of cropplants to aerial pollutants.

Materials: exposure chambertext crops (soybeans, cotton, tobacco, corn,

Romaine lettuce, etc.)-tobacco makes anexcellent test crop, because it is sensitiveto many kinds of pollutents

sulfur dioxide, nitric oxide, nitrogen diox-ides, ozone (if available)

balloons

Procedure

The chamber constructed for use inExercise 1 makes an ideal exposurechamber. Holes will need to be boredin the walls to serve as inlet and outlet

ports for the gases. Select the gasesand crops you want to test.

All the gases listed under Materialsare commercially available in smallcylinders, including ozone. However,ozone is quite expensive, and thepurity of the commercial product islow. If you do not have access to anozone generator, it might be best tonot include this gas. A simple ap-paratus for generating ozone can beconstructed in the laboratory (Crakerand Manning, 1973). Ozone is a com-mon pollutant under certain conditions(such as following an electrical storm),and when sensitive crops (such as to-bacco) are growing in the area. How-ever, you can have a good project byutilizing some of the other gases men-tioned, even if ozone is not availableto you.

You should determine the approxi-mate dosage, or volume of gas in yourchamber, to produce the pollutant ef-fect. This can readily be done by fill-ing a balloon with a specific gas to aconstant diameter, or circumference.After filling the balloon to the known-volume level, that volume of gas shouldbe expelled into the exposure chamber.

You should so some preliminary ex-perimenting to determine the optimumconditions necessary to get a pollutanteffect. The gases you use will vary inthe dosage required to produce an ef-fect. Also, the age and general healthof test plants, among other factors,will influence the required dosage.

Make careful notes of all your ob-servations, both during the prelimi-nary testing period and during the ac-tual experimental run. Look especial-ly for lesions, color changes, and dis-tortions of younger and older leaves,and for premature senescence, or aging,of older leaves, especially those whichhave extensive lesions on them.

As a variation of this project, youmay want to investigate some of thefactors which influence the extent ofinjury to crops from aerial pollutants.

At all times when handling thesegases, observe extreme caution, andfollow carefully the directions, accom-panying the cylinders.

Interpretation

Many factors determine the extentof damage of a particular pollutant to

136 SUPPLEMENT: BASIC LABORATORY STUDIES

a given crop. The degree of responsevaries from species to species and fromvariety to variety within a given species.Other factors involved include extentof development and maturity of thespecies, cultural environment (especial-ly the general nutritional status of theplants), and meteorological conditions(especially humidity and temperature).Of course, the concentration of theaerial pollutant is a primary factor indetermining how injurious it is tovegetation.

In general, each plant type can becategorized as being either sensitive,intermediate, or resistant to a particu-lar pollutant under a fixed set of en-vironmental conditions. However, as arule, when any plant is growing understress in its environment (such as mag-nesium deficiency in the soil), it willbe more sensitive to the phytopollu-tant. Moreover, since the path of pol-lutant entry into the plant is common-ly through stomates in leaves, environ-mental conditions which lead to open-ing of stomates (such as high light in-tensity and fairly low carbon dioxideconcentration) will usually intensifythe severity of damage to the vegeta-tion.

Plants can be preconditioned to altertheir response to phytopollutants. Pre-treating plants by supplying a 22-hourphotoperiod (22 hours of light fol-lowed by 2 hours of dark on a repeat-ing cycle) sometimes will protect thoseplants from ozone damage, for ex-ample. Temperature preconditioningalso has an effect. An interesting vari-ation of this experiment would be tosee what preconditioning treatmentswould reduce the severity of damageto a particular pollutant.

References

Cra.ker, L. E. and W. J. Manning. 1973.Demonstrating ozone injury on plants. J.Agron. Ed. 2:23-24.

A dditio hal R eadings

Heck, W. w.,J. A. Dunning, and H. Johnson.Design’ of a simple plant exposure cham-ber. National Center for Air PollutionControl Publication APTD-68-6, U. S. De-partment of Health, Education and Wel-fare. Cincinnati, Ohio.

Heck, W. W., F. L. Fox, C. S. Brandt, and

A. A. Dunning. 1969. Tobacco, a sensi-tive monitor for photochemical air pollu-tion. National Air Pollution Control Ad-ministration Publication No. AP-55, U. S.Department of Health, Education andWelfare. Cincinnati, Ohio.

Jacobson,J. S. and A. C. Hill. 1970. Recog-nition of air pollution injury to vegeta-tion: A pictorial atlas. Air Pollution Con-trol Association, Pittsburgh, Pennsylvania.

MacDowall, F. D. H. and A. F. W. Cole.1971. Threshold and synergistic damageto tobacco by ozone and sulfur dioxide.In Atmospheric environment. PergamonPress, Great Britain.

Tso, T.C. 1972. Physiological disorder:Pollutant effects. 1972. p. 106-110.In Physiology and biochemistry of tobac-co plants. Dowden, Hutchinson, & Ross,Inc. Stroudsburg, Pa.

SECTION II

SOIL SCIENCE EXERCISES

Exercise 1

The Soil as a Natural Body

What is soil? Soil, in its broad sense,refers to all of the unconsolidated ma-terial occupying the earth’s surfacewhich provides a natural medium forplant growth. An individual soil, how-ever, is a three-dimensional body withrecognizable boundaries. We describethis individual as a natural body be-cause it has properties resulting fromthe interaction of natural processessuch as weathering, leaching (loss ofnutrients by water moving through thesoil), and organic matter development.

The soil-forming factors are climate,organisms, parent material, slope, andtime. Climate (rainfall and tempera-ture) affects weathering rate, leachinglosses, nutrient supply, and organicmatter buildup. Macroorganisms(trees, grass, worms, etc.) influenceleaching and accumulation of organicmatter. Microorganisms (protozoa,bacteria, etc.) affect organic matterdecay and biochemical reactions. Par-ent material is important because it isthe source material (rocks and miner-als) that undergoes alteration to formsoil. Soil properties often reflect thenature of the parent material. Slopeinfluences the thickness of the soil,organic matter accumulation, and soildevelopment because it affects the

amount of leaching and erosion. Timerefers to the duration and intensity ofinteraction by the other factors.

Objective: To describe the soil in terms ofits features and properties, and relate thosecharacteristics to natural processes.

Materials: topsoil from grass pasturetopsoil from forest siteroad cut or pit (if available)2 X 2 colored slides (optional)IOX magnifying glass (optional)

Procedure

1. Examine a handful of soil from agrass pasture and one from a forest site.

a. Study the organic fraction.The roots, leaves, stems, insects, andearthworms--both living and.dead-represent the active organic matter.The dark coIored material which hasdecayed so that its original form is notrecognizable is called humus.

Organic matter improves soil by in-creasing aeration and water storage.Nitrogen, phosphorus, sulfur, and othernutrients which are a part of the or-ganic matter are liberated slowlythrough microbial decay for use byplants. Organic matter is maintainedby incorporating crop residues and ma-nure within the soil.

h. Observe the mineral fraction.Many different sizes of particles arepresent. (A 10X magnifying hand lenshelps show the distinction in particlesize.) The largest mineral fragmentsaregravel. The smaller visible particlesare grains of sand. They feel grittywhen rubbed between the thumb andforefinger.

Silt is intermediate in size betweensand and clay. Hardly any of the in-dividual silt particles can be seen withthe naked eye but they can be de-tected by their floury, nonsticky feel.Silt may weather chemically to releasenutrients for plant growth. Silt, alongwith sand, forms the framework of thesoil when bound together by clay andorganic matter.

Clay is very finely divided micro-scopic material, which is plastic whenwet. Clay has a tremendous surfacearea for holding water which causessoil to swell, shrink, and be sticky.CIay surfaces are active chemically and

adsorb nutrients such as calcium, mag-nesium, and potassium. Thus, loss ofthese elements by leaching is reduced.Nutrients adsorbed on clay surfaces areavailable to plants.

The relative amounts of sand, silt,and clay in a soil determine the texture(relative coarseness or fineness) of thesoil. Texture affects the ease of tillage,water percolation and nutrient reten-tion. Soils are classified in soil classesaccording to the proportions of sand,silt, and clay.

2. Examine a road cut or a pit ex-cavated to a depth of 60 to 90 cm.(If a field site is not available, the stu-dent may obtain excellent 2 × 2 slidesfrom colleges where soil science istaught to illustrate the concepts in-tended in this exercise.)

a. Observe the layering whichcan be distinguished by color (andtexture, if observed in the field). Eachlayer is called a horizon. The presenceof several sharply defined horizons sug-gests an advanced stage of soil develop-ment. Such soils are classified as ma-ture or old and they have three groupsof horizons, namely: The surface ortopsoil; the subsoil; and the parentmaterial. Young soils do not have welldeveloped horizons. A cross sectionof soil from the surface down to andincluding the underlying parent ma-terial is known as a soil profile.

b. Follow plant root develop-ment into the deeper soil layers. Deeprooted trees allow water to carry or-ganic acids from decaying leaves downthrough the soil. This makes the top-soil acid and gray. Shallower rootedgrasses concentrate basic elements e.g.,calcium and magnesium, in the surfaceand form a dark colored fertile soil.Most soils have either timber or prairieas native vegetation.

Soil depth determines the suitabilityof different crops. The water holdingcapacity and fertility of the deeperlayers are associated with drought re-sistance and soil productivity.

Results

As the soil is studied, record in-formation and remarks on the datasheet.

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 137

Horizon boundaries

DATA SHEET

Horizon properties

Draw in horizon boundaries and desig-nate topsoil, subsoil, and parentmaterial.

Designate color, coarseness, roots,etc.

3O

.~60

90

120

The nature of the soil forming factors responsible for the formation of this soil are:

Climate Slope

Native Vegetation Time (Age)

Parent Material

REMARKS:

Interpretation

There are literally thousands of dif-ferent soils because the soil-formingfactors may be combined in many,many ways. Each combination pro-duces a specific kind of soil. True, thevariation within any one of the fivefactors listed in the data sheet may bevery slight, e.g. a few degrees changein temperature, but it will be enoughto produce a different soil.

Many soil properties can be pre-dicted just by knowing somethingabout the five soil-forming factors.Thus, a typical soil in the Midwest will

be dark-colored and fertile due to anutrient-rich parent material; cool,moist climate; level slope; grass vegeta-tion; and youthful age. In contrast, atypical soil in the Southeast will belight-colored and infertile due to a nu-trient-deficient parent material; warm-er, moist climate; variable slope; treevegetation; and old age.

Source

H. S. Jacobs, R. M. Reed, S. J. Thien, andL. V. Withee (ed.). 1964. Soils labora-tory exercise source book. Amer. Soc. ofAgron., Madison, WI.

138 SUPPLEMENT: BASIC LABORATOPY STUDIES

Exercise 2

Soil Texture

Soil particles vary greatly in size.Soil scientists classify soil particles intosand, silt, and clay. Starting with thefinest, clay particles are smaller than0.002 mm in diameter. Some are sosmall that ordinary microscopes do notshow them. Silt particles are from0.002 to 0.05 mm in diameter. Sandranges from 0.05 to 2.0 mm. Particleslarger than 2.0 mm are called gravel orstones. The relative amounts of sand,silt, and clay in a soil describe its tex-ture. Most soils, as found in nature,contain mixtures of sand, silt, and clayin many different proportions. To ar-range these many different possibilitiesinto meaningful groups, we have 12texture classes that contain all possi-bilities. These 12 classes are shown onthe texture triangle (Fig. 1).

Objective: To determine the percentages ofsand, silt, and clay in a soil and relate theparticle size distribution to soil properties.

Materials: topsoil and subsoil (200 g. ofeach) from the same soil site

distilled waterCalgon® or Calgonite® (sodium hexameta-

phosphate)2 containers, approximately 500 ml capacit~ruler (metric)balanceblender or mixer (optional)

Procedure

1. Add 50 g of soil to 1/2 liter dis-tilled water in a container with a lid,e.g., a canning jar.

2. Add 1A teaspoon of sodiumhexametaphosphate (Calgo.n® or Cal-gonite®) and shake the mixture.

3. Record the height of the sus-pension in the container, mix the con-tents vigorously, carefully place thecontainer where it will not be moved,and record the time.

4. The rate of fall for sand particlesis 0.036 cm/sec. Divide the height ofthe sus.pension (cm) by the rate of fall(cm/sec) to determine when all the

IO

PERCENT SAND

Fig. I. Guide for textural classification. The use of the texture triangle can be illustrated bythe example: 55% clay, 32% silt, and 13% sand is a clay. Note that all three percentage lines(dotted lines) intersect at a point in the region marked clay.

sand has fallen. For example, if thedepth of the suspension is 10 cm,

l0t(sand) - .036 - 277.5 sec = 4.6 min.

10t(silt)- .00036 27778 sec

= 7 hours 43 min.

5. When the sand has settled, pouroff the silt and clay into another con-tainer.

6. Shake up the sand portion againwith distilled water, let settle, and pouroff the silt and clay. It may be neces-sary to do this two or three times toremove all the silt and clay.

7. Separate the clay from the silt byallowing the silt particles to settle outand repeating the separation procedureuntil almost all the clay is removed.(Use the settling time for silt fromyour calculation in step 4.)

8. Dry the sand, silt, and clay andweigh each.

Results

1. Calculate the percentages ofsand, silt, and clay in the soil.

2. Determine the soil texture usingthe texture triangle (Fig. 1).

In terpre ta tio n

Size of soil particles is important.The amount of open space betweenthe particles has a lot to do with howeasily water moves through a soil andhow much water it will hold. Toomuch clay, in proportion to silt andsand, causes a soil to take in watervery slowly. Such a soil also gives upits water to plants slowly. These soilsare sticky when wet. Textures includ-ing the name ’loam’ refer to soils thathave a favorable proportion of sand,silt, and clay. Air and water relationsare best in these soils.

Size of soil particles is importantfor other reasons, too. It affects theease of working the soil, that crops canbe grown, and the efficiency of certainfertilizers. Sandy soils that have nofine clay or silt particles filling thepore space cannot hold as much mois-

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 139

ture since there is less surface area forthe water to cling to and the pores areso large that the weight of the watercauses much of it to.run down and outof the soil. For this reason, mediumand coarse sands and sandy soils low inclay, are known as droughty soils-crops cannot live long in them withoutvery frequent rains.

Exercise 3

Soil Density and Pore Space

One of the most obvious propertiesof a soil is its mass or weight. In thisexercise we are dealing with the bulkdensity (sometimes called volumeweight), which is the dry weight of unit volume of soil in its natural stateof compaction (uncompressed and in-cluding pore spaces). Bulk density ismuch more important than particledensity, which is the dry weight of thesoil solids only (compressed and notincluding pore space).

again. Read the volume of soil in thecylinder.

c. Weigh each cylinder plus soil.2. Pore Space

a. Fill two 100 ml cylinders tothe 70 ml mark with tap water.

b. Slowly pour exactly 50 ml ofdry sandy soil in one; 50 ml of dryclay soil in the other.

c. Stir the mixture with a stirringrod and let stand 5 min to allow the airto escape.

d. Record the final volume of thesoil-water suspension. Make yourreading at the top of the liquid. Thevolume of the soil-water mixture willbe less than the soil volume and watervolume added separately because muchof the water goes into the pore spaceof the soil.

Results

1. Densitya. Calculate the density of each

soil as’. grams soilvolume soil

sirable as they generally indicate favor-able physical properties for plantgrowth. Densities below 1.3 are as-sociated with clayey soils; densitiesabove 1.5 are associated with sandysoils or soils that are highly compacted.

Bulk density is related to porespace-the higher the density, thelower the total pore space. Totalporosity is important for moisturestorage and aeration since as one in-creases the other decreases. Good soilsneed both large and small pores. Thelarge pores permit water to passthrough and aeration to take place.Small pores are needed to retain waterduring long dry periods.

Source

H. S. Jacobs, R. M. Reed, S. J. Thien, andL. V. Withee (ed.). 1964. Soils labora-tory exercise source book. Amer. Soc. ofAgron., Madison, WI.

Exercise 4

Temperature

Objective: To measure the density of soft(including the pore space) and relate thequantity of pore space to soil texture.

Materials: a sandy soil and a clay soil (Asandy soil feels gritty when rubbed be-tween the fingers; a clay so//reefssticky when moistened and rubbedbetween the fingers.)

100 ml graduate cylindersbalancewatersieve or screen (10-mesh or finer)

Procedure

1. Densitya. Weigh two 100 ml graduate

cylinders. Fill one cylinder one-fourthfull with dry sandy soil (10-mesh orfiner); the other with dry clay soil.Simulate natural soil packing by care-fully tapping the cylinder five timesfrom a height of 2.5 cm onto a card-board box or several thicknesses ofpaper towels.

b. Fill the cylinder ¾ full withsoil and pack again. Finally fill thecylinder to the 100 ml mark and pack

Soil Density

Sandy

Clay

b. Explain the difference indensity values obtained.

2. Pore Spacea. Calculate the percent pore

space in each soil: (Soil volume water volume) - (mixture volume) pore space volume.

b. Explain the differences in porespace values obtained.

Pore space volumeSoil volume

X 100

= percent total pore space.

In terpre ta tio n

Bulk density is a good indicator ofsoil physical conditions. Bulk densitiesbetween 1.3 - 1.5 g/ml are most de-

Soil temperature is important in de-termining the productivity and use ofsoils. Temperatures of field soils varywidely depending on their location,depth, and seasonal conditions. Tem-perature fluctuations are greatest atthe surface and decrease in magnitudeat lower depths. Crop plants growand develop in the changing micro-climate near the soil surface.

Objective: To demonstrate that soils differin rate of "’warming up’" due to their mois-ture contents.

Materials: topsoil3 thermometers (0 -50 C 3 pans about 10 cm deep

Procedure

1. Fill one pan with soil and soak itwith water. Fill another pan with drysoil and add just enough water so thatthe soil is moist throughout.

2. Place a thermometer on its sidein each rail and incline it just enoughto bury the bulb 0.5 cm beneath thesurface of the soil. Pack the soil slight-

140 SUPPLEMENT: BASIC LABORATORY STUDIES

ly to insure good contact of the ther-mometer bulb with the soil.

3. Record the temperature in eachsoil for threedays at designated timeintervals (at least six readings a day)between 6 a.m. and 6 p.m.

Results:

1. Record the temperature in eachsoil in the table below.

ent color; the effect of particle sizecan be demonstrated by selecting asandy soil and a clay soil.

Source

H. S. Jacobs, R. M. Reed, S.J. Thien, andL. V. Withee (ed.). 1964. Soils labora-tory exercise source book. Amer. Soc.of Agron., Madison, WI.

Hours Wet Soil Moist Soil .Dry Soil

Temperature

2. Plot a graph of temperatureversus time for each soil.

Temperature,Degrees

Wet Soil.-Moist Soil ............Dry Soil ...............

0 Time, Hours

Interpretation

The observed fluctuations in soiltemperature are related to moisturecontent. Water requires about 5 timesmore heat to raise the temperaturethan does dry soil. Therefore, wetsoils require more energy to heat thandry soils. Because of the higher water-holding capacity, black soils (high or-ganic matter) are colder than light-colored soils and warm up more slow-ly even though black soil absorbs themost heat.

Soil temperature affects numeroussoil and plant activities. These includeroot deve!opment, seed germination,nitrogen reactions, and organic matterdecay, to name just a few.

There are a number of variations tothis exercise the student may desire totry in addition to or in place of thisone. For example, the effect of soilcolor on temperature can be demon-strated by selecting two soils of differ-

Exercise 5

Percolation Test to MeasureSoil Permeability

Permeability is the quality of a soilthat enables water to move through it.Generally the most desirable soils arethose that permit rapid movement ofexcess water through the soil but thathave the capacity to retain water inthe small pores for long periods oftime. Many soils are impermeable-water passes through too slowly--orexcessively permeable-water passesthrough too rapidly. This downwardmovement of water through a soil iscalled p erco la tion.

Objective: To measure the rate of watermovement through soils in order to estimatesoil suitability for various uses.

Materials: a sandy soil (gritty feel) and heavy clay soil (sticky feel)

post hole digger or spadeknife or sharp instrumentwatergravel or coarse sandstopwatch or other timing device

Procedure

1. Select two soil sites in the field.One should be sandy to a depth ofmore than 1.0 m; the other should beclayey at the 1.0 m depth. If it is im-practical to have natural field sites, thisexercise can be done in the laboratoryby packing two plastic tubes with thesoil materials and adding water to thetops of the columns.

2. Dig or bore a hole, with hori-zontal dimensions of from 10 to 30cm and vertical sides, to a depth of atleast 1.0 m.

3. Carefully scratch the bottom andsides of the hole with a knife blade orsharp pointed instrument in order toremove any smeared soil surfaces andto provide a natural surface soil intowhich water may percolate. Removeall loose material from the hole. Add5 cm of coarse sand or fine gravel tothe bottom of the hole to maintainuniform conditions.

4. Carefully add clear water to thehole to a minimum depth of 30 cmover the gravel. By adding water ifnecessary, keep water in the hole forat least 4 hours, and preferably over-night. Allow the soil to swell over-night. This saturation procedure in-sures that the soil is given the oppor-tunity to swell and approach the con-dition that it will be in during thewettest season of the year. Thus thetest will give comparable results in thesame soil whether made in a dry or awet season.

In sandy soils containing little or noclay the swelling procedure is not es-sential and the test may be made asdescribed under item 5c, after thewater from one filling of the hole has

completely seeped away.5. With the exception of sandy soils,

percolation rate measurements shall bemade on the day following the pro-cedure described under item 4.

a. If water remains in the testhole after the overnight swelling peri-od, adjust the depth to approximately15 cm over the gravel. From a fixedreference point measure the drop inwater level over a 30 min period. Thisdrop is used to calculate the percola-tion rate.

b. If no water remains in the holeafter the overnight swelling period,add clear water to bring the depth ofwater in the hole to approximately15 cm over the gravel. From a fixedreference point measure the drop inwater level at approximately 30 minintervals for 4 hours, refilling 15 cmover the gravel as necessary. The dropthat occurs during the final 30 minperiod is used to calculate the percola-tion rate. The drops during priorperiods provide information for possi-ble modification of the procedure tosuit local circumstances.

c. In sandy soils (or other soils in

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 14"1

which the first 15 cm of water seepsaway in less than 30 min, after theovernight swelling period) the timeinterval between measurements shallbe taken as 10 min and the test runfor 1 hour. The drop that occurs dur-ing the final 10 min is used to calculatethe percolation rate.

Results

1. Calculate the permeability ofwater through each soil and expressthe rate as minutes per centimeter.

2. Using the following table, howmuch absorption area would be re-quired for a septic tank to handleadequately the effluent from a fourbedroom home?

EffectivePercolation Absorption

Rate Area Required

min]cm of water m2/bedroom

1 52.0 84.0 107.5 12.5

10 1520 20

Note: Effective absorption area is thearea (in square meters) of tile drainagesystem for a septic tank to functionproperly and is based on the numberof bedrooms in a home.

In terpre ta tio n

In field soils percolating water oftencarries with it nutrients and other sub-stances. This process is called leaching.The materials in solution may be car-ried deeper in the soil, or out intostreams. Soil productivity often is re,duced as a result of leaching and thematerials being leached sometimescause pollution problems in rivers andstreams.

In urban areas soil permeability isbecoming more and more important inselecting sites for homes and other in-stallations. For example, in the designof a subsurface sewage disposal systemit is of utmost importance to deter-mine whether the soil is suitable forabsorbing the septic tank effluent.

The percolation rate of the soil mustbe acceptable without interferencesfrom a high ground water table or im-pervious rock or clay formations belowthe septic tank field.

Source

North Carolina Board of Health, Bulletin519. Raleigh, NC

Exercise 6

Electrical Properties of Clay

One of the most fascinating proper-ties of almost all soils is that they areelectrically charged, usually negativelycharged. The negative charges in soilsarise from the clay and organic matter.The positively charged ions that areattracted to the negatively charged sur-faces in soils, and thus balance thecharge, are called cations. The processwhereby positively charged ions re-place and exchange each other on thesurfaces of the clay and organic par-ticles is called cation exchange. Thisexchange is reversible and accounts forcations being exchanged between thesolid and liquid phases of the soil.

The capacity of soil to hold cationsis termed the cation exchange capacityand is expressed in terms of: milli-equivalents per 100 grams of soil. Onemilliequivalent of calcium per 100grams of soil is equal to 400 poundsof calcium per acre. This amount ofcalcium is contained in 1000 poundsof pure limestone. Soils vary widely intheir cation exchange capacities, from0 to 50 milliequivalents per 100 grams.

Objective: To demonstrate that clay has anet negative charge.

Materials: clay soil, or just the clay itself ifthe clay was separated in the Soil Textureexercise (A clay soil can be identified ashaving a sticky feel when it is moistenedand rubbed between the fingers)

"B" batteries, 45 voltEosin Y dye (negative)Methylene blue dye (positive)funnelsfilter paperNote: The cost of the dyes is about $3.50/

25 g. Several other dyes are suitable ifthese are unavailable. Your high schoolchemistry teacher should be able toprovide ass/stance.

Procedure

1. Use of battery circuit.a. Mix the clay soil in water to

form a watery paste.b. Hook together several 45 volt

’B’ batteries to get 90 volts and runwires from the + and - battery termi-nals into the clay paste. (You don’tneed 90 volts but it makes the demon-stration more rapid and dramatic.)

c. After a few minutes, removethe wires from the paste and note thecollection of clay on one of the wires.

2. Use of colored dyes.a. Prepare dilute solutions of

eosin and of methylene blue (approxi-mately 0.1% solutions of each).

b. Fit two funnels with filterpaper and place a small quantity ofthe clay soil in each funnel.

c. Pour the eosin solution slowlyinto one of the funnels (Be sure thedye goes through the soil, not downthe sides of the filter paper.) Note thecolor of the solution after it comesthrough the filter.

d. Add methylene blue in likemanner to the other funnel and ob-serve the color of the filtered solution.

e. Mix some eosin and methyleneblue together-you should get a horridpurple color. Pass the mixed solutionthrough the soil and observe the colorof the solution coming out.

Results

1. Which pole attracted the clayparticles?

2. What kind of charge, + or -, ison the clay?

3. Record the colors of the filteredsolutions when the dyes were used:

Dye

EosinMethylene

Blue

Mixture

OriginalColor

Orange

Blue

Purple

Color ofFiltered Solution

142 SUPPLEMENT: BASIC LABORATORY STUDIES

Eosin is negatively charged (an anion);methylene blue is positively charged(a cation). With this knowledge, ex-plain what happened in the demon-stration.

Interpretation

The cation exchange properties ofsoils influence plant nutrition and thedesirability of a soil as a growth medi-um in a number of ways. Cation ex-change has been described as secondonly to photosynthesis in importanceas a natural process. It is important insupplying nutrients to plants and theprinciple of cation exchange underliesthe fertilization and liming of soils.The important plant nutrient ele-ments-potassium, calcium, magnesi-um, iron, manganese, copper, and zincare all cations. Many chemicals whichreach the soil are cations, e.g., somepesticides, and these cations enter intothe cation exchange process.

Sol~rcc

Dr. J. L. Ahlrichs, Purdue University.

Exercise 7

Soil Acidity and Liming

A soil is acid when there are morehydrogen ions present than hydroxylions in the soil liquid phase. A soil isneutral when the soil solution containsequal amounts of hydrogen and hy-droxyl ions. Acidity is usually ex-pressed by a number called pH. ThepH scale goes from 0-14. At pH 7.0,the medium is neutral; below 7.0, acid.;above 7.0, alkaline.

In high rainfall areas, the alkalineelements e.g., calcium, magnesium,potassium--are displaced by the acidicelements, hydrogen and aluminum.To reduce the acidity, aIkaline eIe-ments are added back to the system inthe form of lime, e.g., calcium carbon-ate. The calcium replaces the acidichydrogen and aluminum that are pres-ent. Large quantities of lime are usual-ly added to neutralize the acidity onthe clay and organic particles in addi-

tion to neutralizing the free acidity inthe liquid phase.

Objective: To measure the pH of soil and toidentify the chemical elements responsiblefor bringing about pH changes in soils.

Materials: Sample of topsoil carefully takenfrom the top 15 cm of soil with a soiltube or a clean spade (several samplesmay be studied depending on the timeavailable)

aluminum chloride (AICI3)calcium carbonate (CaCO3)hydrochloric acid (HCl)distilled waterspot plate (or commercially available

procelain sample holder)indicator solutions (see Table 4)pH meter (optional)

Pro cedure

1. pH determinationa. Place enough soil on the spot

plate to fill the hole about one-thirdfull.

b. Add enough indicator dye(select one from Table 4 with a broadpH range) to moisten the soil com-pletely and get a slight excess.

c. Stir well and let stand for 2 to3 min.

d. Using a stirring rod, draw outa thin layer of the soil solution andcompare its color with the color chartfor that particular indicator.

e. To check your reading, selectanother indicator (one with a narrowpH range) and follow the above pro-cedure.

f. If a pH meter is available, takea pH reading as follows: Mix 10 g ofsoil with 20 ml distilled water. Allowto stand 5 rain with occasional stirring.Insert the electrodes into the soil sus-pension and, while swirling the sus-pension, read the pH.

2. Aluminum as a source of aciditya. Pour about 30 ml of distilled

water into a beaker and measure thepH with an appropriate indicator (orpH meter).

b. Add four or five drops of 1NAIC13 to the water and again measurethe pH.

3. Neutralization of Acid withCaCO3

a. Place a small amount of CaCO~in one of the wells on a spot plate.

b. Add dropwise a few drops of1N HCI and note the visible bubbling(effervescence).

4. Adjustment of soil pHa. Add about 5 g CaCO~ to 5 kg

of soil and mix thoroughly.b. Add enough water to the mix

to barely moisten the soil but not wetit.

c. Place a small amount of thesoil in a spot plate and determine thepH as in procedure 1.

Resul~

1. What was the pH of the soil usingthe indicator dye? With pH meter, ifused?

2. What was the effect on pH whenAICI~ was added to the water?

Medium pH

Water

Water +A1CI~

3. Describe the chemical reactionthat occurred when HC1 was added toCaC03.

4. Compare the pH of the soil afterliming with that before liming,

Table 4. Common indicator dyes*

Indicator pH range Color change

Bromcresol green 4. 4- 6.0 red to yellowChlorphenol red 4.0- 6.6 yellow to redBromthymol blue 5.0- 7.5 yellow to bluePhenol red 6.6- 8. 2 yellow to red

* Color charts and the above indicators are available from the LamotteChemical Products Company, Chestertown, Maryland,

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 143

Soil pH Before pH After

Interpretation

Soil pH has a pronounced effect onthe types of plants that grow natural-ly, or that can be grown with fertilizerand lime. For example, berries growbest on acid soils where alfalfa, sweetclover, and sugarbeets would not growat all; they grow better on neutral toalkaline soil.

Changes in acidity greatly influenceplant growth. The effects are mostoften indirect rather than direct. WhenpH changes, the proportion of acidicto alkaline elements is modified; bac-terial activity is affected; and the avail-ability of nutrient elements may beincreased or decreased.

Exercise 8

Soil Nematodes

Nematodes, threadworms, or eel-worms (as they are commonly called)are very abundant in the soil. Veryoften they are present in large amountsand of many varieties. These organ-isms are round and spindle-like in formwith one end usually spear shaped orpointed. They are almost entirelymicroscopic.

Most of the nematodes live on deadorganic material, other nematodes, orsmall soil organisms. However, certainnematodes are parasites (live off ofliving organisms) and attack the rootsystems of higher plants.

Objective: To separate nematodes from thesoil samples, examine them, and comparethe number of nematodes in various kindso f soils.

Materials: plastic bags for soil samplesrubber bandsbeakers, one per soil sample

three soil samples suspected of containingnematodes

sieve, I mm meshsieve, 2 mm meshnumber 20 bolting silkglass marking crayonpipette (fine tip)microscope slides and cover slipsmonocular microscope

Pro cedure

1. Obtain soil samples from threedifferent places in which plants aregrowing and evidence of nematodedamage is present. Samples from adepth of 10 to 20 cm are better thanthose from the surface. Place the soilsamples in plastic bags, fasten withrubber bands and identify as to loca-tion of source.

2. Mix 1 kg of each soil samplewith warm water (35C) in a beaker.Use enough water so that the mixtureof soil and water is in the liquid state.Stir the mixture and pour through the2 mm sieve. This step removes mostof the large debris.

3. Pour the filtrate through the 1mm sieve. This removes more of thedebris.

4. Pour the filtrate through a pieceof Number 20 bolting silk. The silkcatches the nematodes and allows thefiner debris to pass through.

5. Transfer the strained nematodesand debris to a beaker of warm water,agitate, and decant as soon as the heavysand particles settle out.. Repeat ifnecessary¯

6. Add more warm water, agitate,and allow to stand for from 2 to 4 min.At this time the nematodes will sinkto the bottom. Pour off the muddywater. The residue will contain mostof the nematodes with a minimum offine debris.

7. Tilt the beaker and pick off adrop of water with the nematodes init with the fine pipette. Place the dropof liquid on a clean microscope slideand cover with a cover slip. Examineunder low power and make a drawingon a clean sheet of paper of what yousee in a field. Count the number ofnematodes in five different fields andcalculate the average for a single field.

8. Record the average of each type

of soil along side of the location.Make some observations as to the num-ber of nematodes in different typesand locations of soils.

Interpretation

Parasitic nematodes are importantbecause they find it easy to penetrateplant tissue. The roots of practicallyall plants are susceptible, and the dam-age done is often very great, esepciallyto fruit and vegetable crops grown insouthern U. S. Even in greenhouses,nematodes may become a serious pest.Often they are difficult to control;thus, a nematode infection is a seriousmatter.

Source

Jenkins, W. J. and J. N. Sasser. 1960.Nematology--Fundamentals and recent

advances with emphasis on plant parasiticand soil forms. The University of North

Carolina Press, 480 pp.

Exercise 9

Soil Microorganisms

The upper few centimeters of mosttopsoils are literally teeming withmicroorganisms. There may be asmany as one billion microorganismsper gram of soil under optimum condi-tions. Though unseen with the nakedeye, these tiny organisms are necessaryfor soil to be truly soil.

The microbial population of the soilis made up of five major groups: bac-teria, actinomycetes, fungi, algae, andprotozoa. Bacteria are the mostabundant group, usually more numer-ous than the other four combined.

Objective: To demonstrate the occurrenceand quan tity of microorganisms in soils.

Materials: topsoilsterile pipettes (An autoclave or pressure

cooker is needed for sterilization in thisexercise. If a pressure cooker is used,proper precautions should be followed.)

7 sterile petri dishes7 tubes of nutrient starch plating agar1 bottle containing 100 ml sterile water

144 SUPPLEMENT: BASIC LABORATORY STUDIES

4 tubes containing 9 ml sterile waterbiological microscope (optional)

Procedure

1. Pulverize a small portion of eachsoil sample.

2. Transfer a 1 g sample to the bot-tle containing 100 ml of sterile waterand shake vigorously for about fiveminutes.

3. Make serial dilutions as high as1:1,000,000 by transferring 1 ml ofwater from the 100 ml bottle into oneof the four tubes containing 9 mlsterile water with the aid of a pipetteand mixing thoroughly. One ml is ob-tained from this tube with anothersterile pipette, transferred to a secondtube and mixed thoroughly. Repeatby transferring 1 ml from the secondtube to the third tube and from thethird tube to the fourth tube.

4. Using a sterile pipette, transfer 1ml of the solution from the first tubeto a sterile petri dish. Use a separatepetri dish for each tube.

5. Transfer the nutrient agar fromfour tubes to the four petri dishes con-taining the microorganisms. You mayneed assistance from your Biologyteacher in preparing the agar.

6. Incubate at room temperature.7. Observe after 2 days and again

after 7 days.8. Optional: If a microscope is

available, examine the microbial col-onies in more detail, e.g., size, shape,etc.

Results

1. Record the number, size, andcolor of the different colonies of or-ganisms you observe in the petri dishes.

2. With the aid of your instructor.and]or a textbook, classify the micro-organisms as to bacteria or fungi.

In terpre ta rio n

Microorganisms have a great bearingon the soil as a medium for plantgrowth. Bacteria, actinomycetes, andfungi are agents of decay and thus areeffective in decomposing organic mat-ter. When these microorganisms de-compose organic material, the majorwaste produced is carbon dioxide gas.

In the atmosphere above the surfaceof a hectare, there is approximately44.8 metric tons of carbon dioxide.The living organisms in a hectare offertile soil return that much carbondioxide to the atmosphere in 1 year.Microbes thus have an essential part inthe carbon cycle in nature.

Microorganisms participate in manydifferent ways in the nitrogen cycle innature. Nitrogen stored in the soil isalmost entirely organic nitrogen. Bac-teria are responsible for converting theorganic nitrogen to inorganic formsavailable to p/ants.

Microbes also affect the availabilityof various minerals. Iron, manganese,and sulfur are transformed from un-available to available forms by microbi-al oxidations and reductions. For ex-ample, soils contain microorganismswhich produce antibiotics similar tothe antibiotics used in medicine. How-ever, it should be pointed out that thesoil harbors pathogens which causeplant diseases. Also certain ones maytie up mineral nutrients and reducetheir availability to plants.

Exercise 10

Fertilizer Nutrient Demonstration with Corn

Many of our soils are deficient incertain essential elements to producean adequate quantity and quality offood and/or fiber. Some kind of ferti-lizer is usually needed. Most plantsneed about 15 chemical elements. Ofthese, 4 are usually in short supply and1 or 2 are scarce enough to requiresome attention. The four major ele-ments are calcium, nitrogen, phosphor-us, and potassium. Some of the othersknown as trace elements, such as cop-per, zinc, or molybdenum, may be de-ficient in some special case.

Nitrogen, phosphorus, and potas-sium are so commonly used in com-mercial fertilizers that their percentageis always noted on the fertilizer bag inthe same order. For example, a 3-9-18 fertilizer is one that contains 3%nitrogen (N), 9% phosphorus (P2Os),and 18% potassium (K20).

Soils can be tested to determinewhat elements they need. When the

needed fertilizers are added a goodcrop can be expected, if there isenough rainfall and other conditionsare favorable. Contact the agriculturalextension agent in your county forfurther information about soil tests.

Objective: To observe the effects of nitro-gen, phosphorus, and potassium on thegrowth of corn when the elements areadded individually and in combinations.

Materials: Ten 4 liter metal containers (Igal metal cans)

Soil (approximately 60 kg) from an erodedarea or from land which has been inten-sively cropped with little or no fertiliza-tion

25 ml container (~ pint jar) of each fertilizerbelow:Nitrogen: Ammonium nitrate (NH4N03),

33.5-0-0 grade or Ammonium sulfate((NH4)2S04), 21-0-0 grade

Phosphorus: Superphosphate(Ca(H2P04)2) , 0-20-0 or 0-45-0grade

Potassium: Potassium Chloride (KCI),0-0-60 grade or Potassium sulfate(K2S04), 0-0-50 grade

0.6 cm mesh screening nailed to wood framefor screening soil (No t necessary if soilcrumbles easily)

100 or more kernels of hybrid seed corn

Procedure for Soil

1. Crush and screen the soil, whenair dry but still somewhat moist,through 0.6 cm screening and mixthoroughly before placing into themetal cans. Fill nine cans to within1.5 cm of the top of the can. This jobshould be done in the fall and the cansset away until needed.

Procedure for Planting Time

1. The cans should be planted 4weeks before a full explanation of theresults can be seen. Observations onthe growth and deficiency symptomsof the plants can then be continued foranother 2 weeks.

2. The design of the demonstrationis as follows:

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974 145

a. Check-no fertilizerb. Nitrogen alonec. Phosphorus aloned. Potassium alonee. Nitrogen plus phosphorusf. Nitrogen plus potassiumg. Phosphorus plus potassiumh. Nitrogen plus phosphorus plus

potassiumThe above design requires weighing

out four individual amounts of eachfertilizer nutrient described in the nextstep. Place these amounts on labeledpapers or paper cups, combining nu-trients where specified.

3. Weigh out the individual fertilizernutrients on a balance which should beavailable in your high school chemistrylab.

a. Nitrogen: 0.7 g of (33.5-0-0)or 1.12 g (21-0-0)

b. Phosphorus: 0.55 g of (0-20-0) or 0.25 g of (0-45-0)

c. Potassium: 0.18 g of (0-0-60)or 0.22 g of (0-0-50)

These amounts are equal to 179 kgof N (nitrogen), 38.2 kg of P (phos-phorus) or (89.6 kg of P2Os), and 73.9kg of K (potassium) or (89.6 kg K20) per hectare (2,240,000 kg ofsoil).

4. Remove 5 cm of soil from eachof the eight containers, level off thesoil in the can, and space-plant 10 cornseeds close to the outside edge of thecan. Pour the fertilizer nutrient mix-ture into the center of the circle ofseeds and replace the soil that was re-moved. Label the cans so that youcan identify each fertilizer treatment.

Seed and fertilizer placement shouldbe as follows:

~SeedSFertilizer

5. To determine amount of waterto put into the planted containers, takethe extra can of soil and pour a vol-ume of water into it equal to one-fifththe volume of soil in the can. Use theremaining empty can to obtain thisone-fifth measure.

6. Water the seeded containers.The water should wet the soil com-pletely but not to the extent that freewater stands in the bottom of the can.Do not punch holes into any of thecans since any water movement out ofthe cans will carry away nutrients.

7. Place the containers 15 to 30 cmfrom a window. Good daylight plusartificial light from the classroom dur-ing dark days is necessary for goodgrowth of the corn plants.

8. Thin plants to the same number(7 or 8) per can 1 week after emer-gence. Add water only when the soilsurface becomes dry. Do no.t waterexcessively. Allow plants to grow un-til they are 30 to 60 cm tall.

Results

1. Identify deficiency symptoms asthey show up.

2. Note the effects of each nutrientalone and in combination with others.Balance in nutrition should be evident.

3. Compare all containers contain-ing the same nutrient. Observe whichadditional nutrient is causing addedgrowth.

Interpretation

Nitrogen stimulates the growth ofleaves and stems and gives the plant adark green color. Nitrogen can alsobe added in the form of ammoniumnitrate or ammonium sulfate if it isneeded quickly. Certain plants cantake nitrogen from the air but manyimportant crop plants, such as corn,do not have this ability.

Phosphorus is essential to the de-velopment of plant seeds as well asother parts of the plant. It can beadded in the form of superphosphate-a fertilizer made from ground rockphosphate treated with acids. It alsocan be added in the form of bone mealor can be obtained from some of thebyproducts of steel manufacture.

Potassium is needed by plants togrow strong stems. Potassium ferti-lizers are made from potash salts ob-tained from potash mines, and fromother sources.

For a more thorough .discussion ofessential nutrients see Section I, Ex-ercise 2.

146 SUPPLEMENT: BASIC LABORATORY STUDIES

Glossary of botanical names of plant species used in the exercises

Species Botanical name

alfalfabahiagrassbarleybarnyard grassbeans, common

gardenlimapinto

bermudagrassbluegrass, Kentuckybristlegrassbroccolibromegrass, smoothcabbageclover, alsike

crimsonredwhite

cockleburcorncottoncowpeascrabgrass, largecucumberrescuegrama, blue]ohnsongrassknotweed, prostratekudzulambsquarterlespedezalettuce, romainelupinesmillet, foxtailmillet, yellowmillet, prosooatsorchardgrasspeanutpeas, garden

sweetpigweed, prostrate

redrootpotatopurple nutsedgepurslaneragweed, commonriceryeryegrass, Italiansericiasorghum speciessoybeanspinach

Medicago sativa L.Paspalum notatum FliiggeHordeum vulgate L.Echinochloa crusgalli L. Beauv.Phaseolus vulgaris L.P. vulgaris L.P. limensis L.P. vulgaris L.Cynodon dactylon L. Pers.Poa pratensis L.Setaria sp.Brassica oleracea var. botrytisBromus inermis Leyss.Brassica oleracea var. capitata L.Trzfolium hybridum L.T. incarnatum L.T. pratense L.T. repens L.Xanthium pennsylvanicum Wallr.Zea mays L.Gossypium hirsutum L.Vigna sinensis Endl. "Dig#aria sanguinalis L. Scop.Cucumis sativus L.Festuca sp.Bouteloua gracilisSorghum halepense (L.) Pers.Polygonum avicularePuerariaChenopodium album L.Lespedeza sp.Lactuca sativaLupinus sp.Setaria italica (L.) Beauv.S. glauca L.Panicum miliaceum L.Avena sativa L.Dactylis glomerata L.Arachis hypogaeaPisum sativumP. sativumAxyris sp. L.Amaranthus retroflexus L.Solanum tuberosum L.Cyperus rotundus L.Portulaca oleracea L.Ambrosia artemisiaefolia L.Oryza sativa L.Secale cereale L.Lolium rnultiflorum Lain.

Sorghum vulgate spp. Pers.Glycine max L. MerrillSpinacea oleracca L.

sudangrasssugarbeetsugarcanesunflowersweet cloverthistle, Russiantobaccotomatoturnipvetchwatermelonwheatwheatgrass, crested

JOURNAL OF AGRONOMIC EDUCATION, VOL. 3, DECEMBER 1974

Sorghum sudanense (Piper) Stapf.Beta vulgaris L.Saccharum officinarum L.Helianthus annus L.Melilotus sp.Salsola kali L.Nicotiana tabacum L.L ycopersicon esculentumBrassica napus L.Vicia sp.Citrullus vulgaris Schrad.Triticum aestivum L.Agropyron desertorum Fisch.

147

Glossary of chemical names of pesticides used in exercises.

Pesticide Chemical name

atrazinedinoseb, DNBP salt2,4-D2,4-DBEPTCparaquatTreflan®, trifluralin

2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine2-sec-butyl-4,6-dinitrophenol(2,4-dichlorophenoxy) acetic acid4-(2,4-dichlorophenoxy) butyric acidS-ethyl dipropylthiocarbamate1,1 -dxmethyl-4,4 -blpyr~dtm~um ionot,~,~-Trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine

Jou rnal of

rono mic ducationFub|ished by the American Society of Agronomy

677 South Segoe Road Madison, Wisconsin 53711