interactions of landscape ecology, planning and design

Landscape and Urban Planning, 2 1 ( 199 1) 3-11 Elsevier Science Publishers B.V., Amsterdam

3

s of landsca e ecology, planning and design

Frank B. Galley” and Juan Bellotb*’ alnstitute of Ecology and School of Environmental Design, University of Georgia, Athens, GA 3062, L7SA

bInstitute of Mediterranean Agronomy, Zaragoza, Spain

(Accepted 10 October 1990)

ABSTRACT

Golley, F.B. and Bellot, J., 199 1. Interactions of landscape ecology, planning and design. Landscape Urban Plann., 2 1: 3- 11.

Landscape ecology provides planners and designers with two kinds of information. First, landscape ecology describes the structure of the physical and biological environment at a scale that is practical for humans. Second, landscape ecology describes dynamic processes in time and space, and explores the ways in which structures shape processes. An understanding of processes allows us to extrapolate patterns into the future and, therefore, to plan and to predict the consequences of design. Building a strong connection between landscape ecology, planning and design requires special training and experience. The Institute of Mediterranean Agronomy of Zaragoza, Spain, which is part of the International Center of Higher Studies in Mediterranean Agronomy, Paris, has been teaching courses on rural planning and the environment for over 12 years. This course experience, and the research associated with it, provides an example of how these separate disciplines can be integrated.

Landscape ecology is a curious mixture of subjects and reflects a complex set of motiva- tions for interactive work. It expresses a variety of points of view, which we can list as follows.

( 1) Spatial scale is an important variable, a truism of geography.

(2 ) Physical structure, in Anne Spirn’s ( 1989) terms, the “deep structure”, provides the foundation for all landscape processes.

( 3 ) Design features of landscape elements, such as their shape and connections, may be as important as their mass, and the qluantity of physical resources they contain.

(4) Landscape processes involve flows of air and water and the chemicals which compose

‘Present address: Depto. C.A.R.N., University of Alicante, Alicante, Spain.

them, movements of organisms and transport of materials by humans, movement of humans, and movements of concepts and beliefs.

( 5 ) Biological and cultural life generates a continual variety of behaviors which are selected by the biological, cultural and physical environment. The unrestrained expression of biological and cultural variety is chaotic. Or- der and pattern is obtained through the ecological interaction of biota and environment. But, in this exchange, environment is also changed. Thus, in time we may observe a shifting landscape pattern.

Theoretical landscape ecology investigates these patterns and processes, their origin, and how they influence each other. Applied landscape ecology uses our understanding of patterns and processes to solve environmental problems which have a spatial component, and to plan how landscapes should be organized in the future. For this reason, there is a close re-

0169~2046/9 l/$03.50 0 199 1 Elsevier Science Publishers B.V. All rights reserved.

4 F.B. GOLLEY AND J. BELLOT

lationship between landscape ecology and planning and design. We can move back and forth from one to the other, with landscape ecology providing information to the planner- designer, and the planned and designed landscapes serving as field experiments to test hy- potheses for the landscape ecologist.

EDUCATION IN LAN SCAPE ECOLOGY AND PLANNING

In order to achieve this ideal connection between landscape ecology and design, the prac- titioner needs a special educational experience, in which a method of interaction and integration is employed. There are relatively few institutions which focus on training students to integrate landscape eco!ogy and planning and design. One such institution, however, is the Institute of Mediterranean Agronomy of Zaragoza, Spain, which has op- erated a course on rural planning and the environment for about 12 years. The Institute is part of the International Center of Higher Studies of Mediterranean Agronomy, with its headquarters in Paris and training centers at Montpellier (France), Bari (Italy) and Las Canas (Greece). Discussion of the organization and objectives of this course will help clar- ify the ways in which education can be focused on the interaction of e ecology and planning.

The object of the Center and Instituie is to provide advanced, postgraduate training in appropriate subjects to agriculturally oriented professionals in Mediterranean countries. The students are often professionals who take leave from their research institution or experiment station to receive advanced instruction at the Institute.

The rural planning course lasts for 9 months and is usually attended by 20-30 students, with degrees in agronomy, biology, geography, and landscape architecture. The course is fuil-time and is considered to be equivalent to fulfil the course requirements for the Masters degree in

an American state university. Selected students may continue research work and present a thesis to the faculty for the Masters of Sci- ence degree. The course has been coordinated by Frank Galley and administrated by Juan Bellot, under the overall direction of the Insti- tute Director, Miguel Valls. Faculty and staff come from the United States, Spain, Ger- many, Belgium, the United Kingdom, France and Italy.

The rural planning course is divided into three sections: a foundation section, a methods section, and a practical section. The class is usually divided into three teams, which are selected by the coordinator and administrator so that fields of expertise and experience are mixed up and each team has similar skills. After a 2 week introduction, these teams are given a region and a problem to address over the entire course. The regions are typically a municipio (a small political unit analogous to an American county) of the Autonomous Region of Aragon, the location of the Institute. Prcb- lems vary widely I’rom year to year. Last year we asked each team to reduce cereal production of the municipio by 20%, the target set by the Agricultural Ministers of the EEC in Brus- sels, but not to reduce income per farmer, or cause migration from the municipio, or de- stroy the environment. Thus, students had to search for alternative sources of production, evaluate their impact in terms of income, pop- ulation and environment, and then plan alternative land use in the municipio. Students de- vote the entire final third of the course to this project and present their results formally before a jury at the end of the term.

The foundation portion of the course is designed to provide all students with a grounding in four key topics. Our motto is that rural planning from a landscape ecology perspective may be compared to a stool that rests on four legs. These legs are physical geography, ecology, rural sociology, and regional economics. We find that all students have expertise in at least one of these areas, but no student has expertise in

INTERACTIONS OF LANDSCAPE ECOLOGY. PLANNING AND DESIGN 5

all the areas. Our objective is to give all students an introduction to the concepts of the disciplines that are rele /ant to planning, a common nomenclature, and some experience with the literature. Students are given field exercises, seminars and opportunities for discussion, as well as time for personal study.

The physt$al geography section concentrates on the origin of land forms, the Earth heat balance, and climate and hydrology. Practical exercises include experience with cartography, aerial photography, and analysis of remote- sensed images. The ecology section focuses on the factors controlling primary organic production, development and maintenance of soils, major biogeochemical cycles, and the maintenance of biologica.! Aver&y. The rural sociology section is concerned with the patterns of social organization and the decision systems that regulate productivity and the environment. Social organization may involve the origin and evolution of land use patterns, urban areas and villages, and transportation. The section on economies introduces the students to the patterns of rural production, economic controls of these patterns, regional accounting systems, cost-benefit analysis, and shadow pricing of environmental factors.

The second third of the course is devoted ?o methodology. Students are introduced to methods of systems analysis, environmental impact assessment, landscape design, and soil- water planning. Integration of all parts of the course is through a simple, conceptual systems analytic approach. The approach is introduced in the first week’s introduction to the course, and each foundation section contributes to it. In the methods section, systems analysis is ac- tually practiced, with students being trained in the appropriate mathematics and being given hands-on experience with modeling and pro- gramming. The objectives are to teach landscape spatial analysis and the ways to account for flows across landscape cells, and the integration of landscape properties within defined spatial areas.

The lectures and exercises on environmental impact assessment consider methods to evaluate non-market values and to weigh their im- portance, methods to compare multiple impacts, including social impacts, and environmental-economic-social trade-offs. The landscape design section focuses on the methods used in design and planning, the integration of diverse forms of information on maps and drawings, and the administrative controls to various land uses. Finally, the lectures on soil-water planning address patterns of resource allocation in arid Mediterranean climates, irrigation schemes, and soil reclama- tion projects.

In addition to the foundation and methodo- logical lectures and exercises, students also hear a few other special lectures and seminars on such topics as change in agricultural technology, rural industrialization, tourism, and biological conservation.

During the first two parts of the course, the students are also initiating their practical work which will occupy them full-time in the final term. For example, during the foundation lectures, students are beginning to inventory their regions. These inventories frequently result in maps of land forms, soils, vegetation and land use. Usually the students visit the areas, dis- cuss their project with rural administrators and farmers, and begin to build contacts for later work.

Talus, the rural planning course gives the students an intensive exposure to a large set of concepts and technical terms and methods, and requires that they absorb these and apply them to a specific complex problem. The integration of the information is through the practical problem-solving exercise of planning in a specific municipio. Final presentations usually result in a 2OO-page report, dozens of maps and drawings, and a two-hour lecture and discussion before a jury of professors. Students corn-- pleting this course are presented with a certifi- cate by the Institute.

Over the past 5 years, two to five students

F.B. GOLLEY AND J. BELLOT

have continued their training by carrying out research for their MS degree on an irrigated landscape near the Institute each year. This has resulted in nine theses and several published reports. It has also served as a study site for the class and as an example of a systems approach to landscape ecology and rural planning. That is, the research has fed back to the course in a mutually beneficial manner. In the next section of this paper we will describe the study and present some of its results to illustrate our method of landscape analysis, and to show how research of students and faculty relates directly to training the new generation in modern in- tegrative concepts, as well as solving specific problems in the environment.

The attention of our landscape ecological in- vestigators has focused on a 5256 ha area called La Violada. This area is part of a large irrigation project, initiated in the 194Os, which COL

lects water from watersheds in the Pyrenees Mountains, stores it in a complex of rescr- voirs, and distributes it across northern Ara- gon and neighboring regions. The La Violada project receives water from the Monegros Canal and dischar allego River, which enters the Ebro River and the Mediterranean Sea (Fig. 1). La Violada is divided into about 700 farms. Farmers live in three villages and obtain their supplies and sell their products through an agricultural cooperative.

La Violada was constructed in a geological depression which originally v-as occupied by intermittent saline lakes and marshes. The geological formations are composed of in- terbedded strata of gypsum, marl, calcite, and similar sedimentary rocks. These strata have been mixed in the construction of field ter- races so that the soils of a field are relatively homogeneous and frequently contain pieces of sedimentary rock. The project is bordered by

Pollgono de la Wolada

Fig. 1. The locality of La Violada irrigated landscape in Spain (upper left ), the Autonomous Region of Aragon (upper right ), and its relation to the Rio Gallego and the Rio Ebro.

water canals, which lead to each field by a sub- sidiary network of canals. Each field is drained by tiles which lead to the drainage network. All drains ultimately lead to an exit ditch which leaves the project (Fig. 2 ) .

La Violada is located in a dry subhumid Mediterranean climate with a strong continen- tal influence. Precipitation from 1955 to 1977 averaged 493 mm annually, and is character- ized by irregular torrential storms. The basin is underlain by a layer of clay which is im- permeable. Hydrological studies have shown that the basin is closed (Tanji, 1977; Aragues et al., 1986).

We are attracted to this area partly because the basin could be treated as a watershed, and because earlier studies had shown that the basin produced large amounts of saline drainage

INTERACTIONS OF LANDSCAPE ECOLOGY, PLANNING AND DXSIGN 7

from the cooperative. Data for each field were used to calculate the dynamics of the whole landscape. These data on the internal dynamics could then be related to the hydrologic performance of the entire basin, which is monitored continuously by the irrigation agency.

Thus, the La Violada landscape analysis is a systems study in which the fields are indepen- dent of each other, each fie!d fed by and drained of water individually. The landscape performance is the sum of the field performance, as there is little, if any, interaction between fields. The questions posed were: ( 1) how is the biogeochemistry of each field con- trolled by the type of crop and by management; (2) what are tire energy and economic inputs and gains for each crop, and how do these interact with the biogeochemistry of the fields?

The results of these studies have been re-

Fig. 2. A schematic diagram of La Violada irrigated landscape, showing the location of canals (---), drains, ( + ), and the network of roads (-).

water (Albert0 et al., 1986). The salts in this water pollute the Gallego and Ebro Rivers, and are derived by dissolution of the gypsum and other sedimentary rocks. The objectives of our landscape ecology project were to document the biogeochemical flows across the landscape, determine the major controls on these flows, and suggest ways of reducing saline pollution.

The landscape was treated as a collection of farm fields growing five different crops. Cur- rently, maize is the principal crop ( 2392 ha ) , followed by irrigated barley (7 18 ha), wheat (206 ha), and a!falfa (483 ha). Part of the landscape is unable to be irrigated, and on this area mainly barley is grown (900 ha). Ran- dom samples of soils and crops in fields repre- senting each land use type (each crop) were taken seasonally using standard methods (Cerezo, 1987; Esquizabel, 1987; A: xzqueta, 1988; Trebol, 1988). Entrance water and drainage water were collected and analyzed for chemical content. Energy requirements for production and harvest of each crop were de- termined by direct observation and question- naires to farmers (Campillo, 1987). Eco- nomic data were collected from farmers and

ported in several formats (Bellot and Golley, 1989; Golley et al., 1990), and a full analysis of the project is being prepared for publica- tion. Here we will present an overview of the results, stressing performance of crops in relation to the overall basin performance.

The landscape as a whole loses large quantities of salts in the drainage water (Table 1). Most water is supplied by irrigation, and more than half of the water input appears in the

TABLE 1

Annual balance of water and selected chemicals on La Violada landscape

Water Selected chemicals ( kg ha- ’ ) (mm)

Ca S Na N K

Input Rainfall 452 7 b 4 2 3 Irrigation 1045 816 174 220 18 62 Later flow 76 3 - I - - Fertilizer - 29i 71

Total I573 826 180 225 312 136 output

Evapotranspiration 674 - - - - - Grain 38 - - 163 57 Drainage 900 4366 3886 579 66 73

Total I574 4404 3886 579 229 130

F.B. GOLLEY AND J. BELLOT

TABLE 4

8

TABLE 2

System yields Land-use application

crop Yield Value Average yield (Mt ha- ’ ) (Mt ha-‘) ($ ha-‘)

Spain Georgia, USA

Alfalfa 13 3 Maize 12 1392 7 4 Wheat 6 690 2 1 Barley 5 355 2 2

Maize Wheat Barley Alfalfa

Water Nitrogen (m” ha-‘) (kg ha-‘)

11332 431 4037 153 4000 173

50000 88

TABLE 5 TABLE 3

Annual balance of calcium and nitrogen on maize and wheat fields of the La Violada irrigated landscape (kg ha- ’ )

Calcium Nitrogen

Maize Wheat Maize Wheat

Innut 951 339 273 169 Plant uptake 73 20 189 146 Output in harvest 23 3 138 110 Return to soil 50 17 51 36 Out to drainage 3611 1590 54 24

drains. CI c*mical input of elements associated with the u:rrestrial surface, such as calcium, sulfur and sodium, occur in relatively large amounts in irrigation water, as these waters are collected on semi-arid watersheds. However, the drainage water contains quantities three to twenty times larger t ts. These salts are derived by dissolution of the gypsum and other lithic constituents in the soils. Nitrogen and potassium levels in the drainage water are also elevated. These elements come from fer- tilizers. Crop yield on the landscape is substan- tial (Table 2 ), and the economic return is relatively large.

The overall dynamics of the basin is calcu- lated as the sum of the dynamics of each indi- vidual field. The crops on these fields behave differently. For example, we can compare the annual performance of wheat and maize (Ta- ble 3 ). Maize receives twice the nitrogen and three times the calcium received by wheat. There is a greater uptake of calcium by maize, but uptake of nitrogen is approximately simi-

Economic control ($ Mt-’ )

World price change

1981 1986 Ratio

Maize 152 116 0.76 Wheat 177 i 15 0.64 Barley 115 71 0.62

lar in the two crops. Outputs are slightly larger for maize, with the exception of calcium in drainage water. The levels of calcium in drains from maize fields are twice those from wheat fields. The discrepancy between input and output of nitrogen is accounted for by denitrifica- tion in these irrigated soils (Ryden and Lund, 1980). These data illustrate the biogeochemical patterns of the crops, each one of which dif- fers from the others. The overall applications of water and nitrogen fertilizer for all crws are shown in Table 4. Alfalfa produces five to six cuttings per year and requires the most water. Maize requires the largest quantities of fertilizer.

Clearly, the La Violada landscape exhibits a complex biogeochemistry, which is regulated by the area1 extent of the crops and by the management decisiuns relating to water use and fertilizer application. The land-use pattern and the management associated with each pattern are important controls of the biogeochemistry of the system. What factors regulate the land-use pattern?

In 1989 a study of the landscape pattern showed that 19% of the area was in maize, 58%

INTERACTIONS OF LANDSCAPE ECOLOGY, PLANNING AND DESIGN 9

in grains, and 2 1% in alfalfa. In contrast, in 1986, 62% was in maize, 24% in grains, and 12% in alfalfa. The shift to maize production, away from grain and alfalfa, is partly a re- sponse to differential declines in world crop prices (Table 5 ). The decline in the price of maize has been less than that of wheat and barley (unfortunately, we do not have compara- ble data for alfalfa). In addition, the costs to farmers to produce maize has increased at a slower rate than the costs of grain production. The consequence of these economic relation- ships has been a shift toward an economic ad- vantage of maize production, and the farmers on the La Violada landscape have responded to this economic environment.

These patterns explain why land use has changed on the iandscape. They do not explain why farmers use the observed quantities of water and fertilizer inputs. To understand these patterns we have compared the economic inputs and outputs of a crop with the energy inputs and outputs. Energy analysis is an accepted accounting system in agriculture. and it allows a more direct measure of environmental costs and benefits (Flu& and Baird, 1980 ). In this instance we monitored all the inputs and outputs from samples of fields, measuring the number of hours of labor, energy use of ma-

TABLE 6

Economic inputs lada. Spain ( pta 1

and outputs for maize and wheat at La Vio-

Inputs, Wheat Mairc

Swds 8500 I 3000 1 ~rttlrrcr. at seeding 1 jSO0 27369 I-ertilizcr. side dressing 1 1250 I8964 Herbicide 3000 3432 Insecticide 0 770

Flld 4992 7680 lrrigalion water 1150 3000 Seeding 2000 3000 Harvesting 7500 7500 Total costs 53892 84715 lncomc from gram 130000 212500 Ralio (income to cost ) 2.4 1 2.5 I

T.:.SLE 7

Growing season mean energy input and output from a field of wheat and maize on the irrigated La Violada polygon, Spain (MJ ha-‘: 4.2 MJ= 1000 kcal)

Component Wheat Maize

Natural inputs Solar radiation 37338600 44730000 Irrigation water and precipitation 18322 29535 Seeds 4075 405 Human labor 37 81

Fossil fuel inputs Nitrogen fertilizer 12240 34456 Fuel 4304 6707 Machinery (sequestered) 1189 1849 Phosphorus fertilizer 1219 1988 Drying and storing crop 741 9397 Potassium fertilizer 262 1278 Pesticides 304 151

Total inputs (excl. solar) 42693 86387 outputs

Harvested product 105031 218252 Drainage water 308 701 Evapotranspiration 18295 33472

chinery, the energy embodied in fertilizer, irrigation water, and so on.

The economic and energy accounts are too detailed to present here. Therefore, we will only illustrate the patterns by comparing maize with wheat. The economic accounts (Table 6) show that the income and costs of maize production are almost twice those of wheat, but that the ratio of income to cost is approximately the same. Fertilizer comprises the largest propor- tion of expenditure for both crops.

In contrast, the energy accounts show that the largest amounts of energy are associated with irrigation water and nitrogen fertilizer inputs (Table 7 ) if we ignore the solar radiation input that dwarfs all the other energy fluxes. The discrepancy between the economic and energy accounts is concerned with the value of water. Clearly, water is undervalued ecsnomi- tally and farmers are not motivated to con- serve water. A possible mechanism to reduce water use and pollution output would be to change the price of water. Water comprises about 40% of the energy inputs, excluding SO-

10 F.B. GOLLEY AND J. BELLOT

lar energy, and is only about 2% of the total economic cost. Change in water price would shift the economics of the crops and possibly cause a change in land use, as well as result in the institution of water-conserving technology. The price of water and other inputs is really information which the farmer uses as a guide in crop management. Basically, free water means that the farmer has no information on water as part of the management equation. It should be noted that these costs do not include the costs of the pollution and the costs of the construction of the irrigation system.

What can we learn from these examples? First, landscape ecology provides the planner and designer with a nonceptual framework within which they can include relevant strut-

tures and processes. Landscape ecology is not unique in this role, of course. For example, ecological economics serves as a similar framework where economic questions are predomi- nant (Costanza, 1989). Human ecology also serves in this role where cultural matters are dominant. Landscape ecology is useful when land is the central focus of attention.

Second, thL ecological background of landscape ecology requires us to focus on interactions between com.po ts a asks that the planner and designer consider the environments that provide energy, materials, and information to the land, and those which receive outputs from the land. Further, it requires that we also consider the context in which the land is placed. I-Iierarchical analysis helps to locate this context.

Third, landscape ecology provides a set of tools, methods, data and experiences to the planner and designer. Fractal geometry applied to boundaries, the interactions between shape and size, and mathematical modeling of landscape processes are examples of these useful techniques. Landscape ecology has not yet developed a theory that has been tested by ob-

servation or experiment. Eventually, this will be achieved, but at present methodology and experience may be more applicable than con- cept. Advanced students can be taught the methods and concepts of landscape ecology and then apply them in practical exercises and research. This type of training will provide the kind of practitioners able to interact with a variety of fields, yet with a deep understanding of the human-land relationship.

Thus, landscape ecology has a relationship with planning and design similar to that between physics and engineering. Students in planning and design should have a grounding in landscape ecology. Planners and designers should look to landscape ecologists for advice on methods and for specific information on landscapes. Landscape ecologists should be able to respond to such requests with an understanding of dynamic performance of the relevant systems, major constraints Q_; a;st;m performance, and the resiliency or resisrance of the landscape. A close interaction between disciplines will develop to the mutual benefit of all the fields concerned.

Alberto, F., Madin, J. and Araques, R., 1986. La problema- tica general de la salinidad en la cuenca de1 Ebro. In: Sis- tema Integrado de1 Ebro: Estudio Interdisciplina. Edito- rial Hermes, Madrid, pp. 22 l-236.

Amezqueta, L.E., 1988. Estudio agroecologico de1 poligono de la Violada (Huesca): Production primaria, mineralo- masa y efficiencia energetica de la cebada en regadio y se- cane. MS Thesis, Institute of Mediterranean Agronomy of Zaragoza, 257 pp.

Aragues, R., Alberto, F., Faci, J., Machin, J., At-rue, J.L., Tanji, K. and Quilez, D., 1986. Calibration de1 modelo conceptual hidrosalino en el poligono pilot0 de1 riego. In: Sis- tema Integrado de1 Ebro: Estudio Interdisciplinan. Edito- rial Hermes, Madrid, pp. 3 1 ! -3 17.

Bellot, J. and Golley, F., 1989. kutrient input and output of an irrigated agroecosystem in an arid Mediterranean landscape. Agric. Ecosyst. Environ., 25. i 75 i 86.

Campillo, R.A., 1987. Estudio agroecologico de1 poligono de riego de la Violada (Huesca): Comparacion de 10s flujos de energia y la productividad de 10s cultivos trigo y maiz. MS Thesis, Institute of Mediterranean Agronomy of Zar- agoza, 168 pp.

Cerezo, R.F., 1987. Estudio agroecologico de1 poligono de

INTERACTIONS OF LANDSCAPE ECOLOGY. PLANNING AND DESIGN 11

reigo de la Violada (Huesca): Production primaria y mi- neralomasa en 10s cultivos de trigo y maiz. MS Thesis, In- stitute of Mediterranean Agronomy of Zaragoza, 259 pp.

Costanza, R.. 1989. What is ecological economics. Ecol. Econ., I: 1-7.

Esquizabel, M.C., 1987. Estudio agroecologico de1 poligono dc la Violada (Huesca): Heterogenidad espacial y din- amica de nutrients en suelos bajo cultivode trigo y maiz. MS Thesis, Institute of Mediterranean Agronomy of Zar- agoza, 193 pp.

Fiuck, R. and Baird, C., 1980. Agricultural Energetics. Avi, Westport, CT, 193 pp.

Golley. F.B., Campillo Ruin, A. and Bellot, J., 1990. Analysis of resource allocatron to irrigated maize and wheat in Northern Spain. Agric. Ecosyst. Environ,, 3 1 ( 1990): 3 13- 323.

Ryden, J.C. and Lund, L.L., 1980. Nitrous oxide evolution from irrigated land. J. Environ. Qual., 9( 3): 387-393.

Spirn. A.W., 1989. Deep Structure: on process form and design in the urban landscape. 4th Annual Landscape Ecol- ogy Symposium, Fort Collins, CO. p. 40.

Tanji. K.K., 1977. A conceptual hydrosalinity model for pre- dicting salt load in irrigation return tlows. In: H.E. Dregue (Editor), Managing Saline Water for Irrigation. Texas Tech University, Lubbock, pp. 49-65.

Trebol, B.M.P., 1988. Estudio agroecologico Gel poligono de riego de la Violada (Huesca): Production, composition mineral y analysis energetic0 de alfalfa en disrinctos tipos de suelo. MS Thesis, Institute of Mediterranean Agron- omy of Zaragoza. 2 16 pp.

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