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  • Agricultural Phosphorusand EutrophicationSecond Edition

    United StatesDepartment ofAgriculture

    AgriculturalResearchService

    ARS149

    September 2003

  • A.N. Sharpley, T. Daniel, T. Sims, J. Lemunyon, R. Stevens, and R. Parry

    United StatesDepartment ofAgriculture

    AgriculturalResearchService

    ARS149

    September 2003

    Agricultural Phosphorusand EutrophicationSecond Edition

    Sharpley is a soil scientist with the USDAARS, Pasture Systems and WatershedManagement Research Unit, University Park, PA; Daniel is a professor with theDepartment of Agronomy, University of Arkansas, Fayetteville, AR; Sims is aprofessor with the Department of Plant Science, University of Delaware, Newark, DE;Lemunyon is an agronomist with the USDANRCS, Resource Assessment Division,Fort Worth, TX; Stevens is an extension soil scientist with Research and Extension,Washington State University, Prosser, WA; and Parry is a national program managerwith the U.S. Environmental Protection Agency, Washington, DC.

  • Abstract

    Sharpley, A.N., T. Daniel, T. Sims, J.Lemunyon, R. Stevens, and R. Parry.2003. Agricultural Phosphorus andEutrophication, 2nd ed. U.S. Departmentof Agriculture, Agricultural ResearchService, ARS149, 44 pp.

    Inputs of phosphorus (P) are essentialfor profitable crop and livestockagriculture. However, P export inwatershed runoff can accelerate theeutrophication of receiving fresh waters.The rapid growth and intensification ofcrop and livestock farming in manyareas has created regional imbalances inP inputs in feed and fertilizer and Poutput in farm produce. In many ofthese areas, soil P has built up to levelsin excess of crop needs and now has thepotential to enrich surface runoff with P.

    The overall goal of our efforts to reduceP losses from agriculture to watershould be to increase P use-efficiency,balance P inputs in feed and fertilizer

    into a watershed with P output in cropand animal produce, and manage thelevel of P in the soil. Reducing P loss inagricultural runoff may be broughtabout by source and transport controlstrategies. This includes refining feedrations, using feed additives to increaseP absorption by animals, movingmanure from surplus to deficit areas,finding alternative uses for manure, andtargeting conservation practices, such asreduced tillage, buffer strips, and covercrops, to critical areas of P export froma watershed. In these critical areas, highP soils coincide with parts of thelandscape where surface runoff anderosion potential are high.

    Keywords: eutrophication, fertilizer,phosphorus, P input, P output, runoff

    While supplies last, copies of thispublication may be obtained at no costfrom USDAARS, Pasture Systems &Watershed Management Research Unit,Curtin Road, University Park, PA168023702.

    ii

  • The U.S. Department of Agriculture(USDA) prohibits discrimination in allits programs and activities on the basisof race, color, national origin, sex,religion, age, disability, politicalbeliefs, sexual orientation, or marital orfamily status. (Not all prohibited basesapply to all programs.) Persons withdisabilities who require alternativemeans for communication of programinformation (Braille, large print,audiotape, etc.) should contact USDAsTARGET Center at 2027202600(voice and TDD).

    To file a complaint of discrimination,write USDA, Office of Civil Rights,Room 326W, Whitten Building, 1400Independence Avenue, SW, Washing-ton, DC 202509410 or call 2027205964 (voice and TDD). USDA is anequal opportunity provider and em-ployer.

    An Adobe Acrobat pdf of this publica-tion is available at www.ars.usda.gov/np/index.html.

    Photocopies or microfiche copies of thispublication may also be purchased fromthe National Technical InformationService, 5285 Port Royal Road,Springfield, VA 22161; phone (703)605-6000 or 1-800-533-6847 and on theWeb at www.ntis.gov. NTIS is requiredby law to maintain archival copies of allFederal technical publications and makethem available for sale on a cost-recovery basis.

    iii

    Issued July 1999,Revised September 2003

  • Introduction ......................................................................................... 1

    Eutrophication .................................................................................. 1

    Agricultural Production .................................................................... 2

    Soil Phosphorus ................................................................................... 5

    The Loss of Phosphorus in Agricultural Runoff ............................... 10

    Forms and Processes ....................................................................... 10

    The Dependence of Agricultural Runoff P on Soil P ..................... 12

    Remediation ....................................................................................... 14

    Source Management ....................................................................... 15

    Transport Management ................................................................... 21

    Targeting Remediation ................................................................... 22

    Making Management Decisions.......................................................28

    Summary ............................................................................................ 31

    References ......................................................................................... 34

    v

    Contents

  • 1

    AgriculturalPhosphorus andEutrophicationIntroduction

    Eutrophication

    Phosphorus (P) is an essentialelement for plant and animal growthand its input has long been recog-nized as necessary to maintainprofitable crop and animal produc-tion. Phosphorus inputs can alsoincrease the biological productivityof surface waters by acceleratingeutrophication. Eutrophication is thenatural aging of lakes or streamsbrought on by nutrient enrichment.This process can be greatly acceler-ated by human activities thatincrease nutrient loading rates towater.

    Eutrophication has been identifiedas the main cause of impaired

    surface water quality (U.S. Environ-mental Protection Agency 1996).Eutrophication restricts water usefor fisheries, recreation, industry,and drinking because of increasedgrowth of undesirable algae andaquatic weeds and the oxygenshortages caused by their death anddecomposition. Associated periodicsurface blooms of cyanobacteria(blue-green algae) occur in drinkingwater supplies and may pose aserious health hazard to animals andhumans. Recent outbreaks of thedinoflagellate Pfiesteria piscicida inthe eastern United States, andChesapeake Bay tributaries inparticular, have been linked toexcess nutrients in affected waters.Neurological damage in peopleexposed to the highly toxic, volatilechemical produced by these algaehas dramatically increased publicawareness of eutrophication and theneed for solutions (Burkholder andGlasgow 1997).

    Eutrophication of most fresh wateraround the world is accelerated by Pinputs (Schindler 1977, Sharpley etal. 1994). Although nitrogen (N)and carbon (C) are also essential tothe growth of aquatic biota, mostattention has focused on P inputsbecause of the difficulty in control-ling the exchange of N and Cbetween the atmosphere and waterand the fixation of atmospheric Nby some blue-green algae. There-fore, P is often the limiting element,and its control is of prime impor-tance in reducing the acceleratedeutrophication of fresh waters.When salinity increases, as inestuaries, N generally becomes theelement controlling aquatic produc-tivity. However, in Delawaresinland bays (coastal estuaries),nitrate-N leaching has elevated Nconcentrations to the point where Pis now the limiting factor ineutrophication.

  • 2

    Lake water concentrations of Pabove 0.02 ppm generally accelerateeutrophication. These values are anorder of magnitude lower than Pconcentrations in soil solutioncritical for plant growth (0.2 to 0.3

    ppm), emphasizing the disparitybetween critical lake and soil Pconcentrations and the importanceof controlling P losses to limiteutrophication.

    Agricultural Production

    Confined animal operations are nowa major source of agriculturalincome in several states. Animalmanure can be a valuable resourcefor improving soil structure andincreasing vegetative cover, therebyreducing surface runoff and erosionpotential. However, the rapidgrowth and intensification of cropand animal farming in many areashas created regional and localimbalances in P inputs and outputs.On average, only 30 percent of thefertilizer and feed P input to farmingsystems is output in crops andanimal produce. Therefore, whenaveraged over the total usableagricultural land area in the UnitedStates, an annual P surplus of 30 lb/acre exists (National ResearchCouncil 1993). This has led to Papplications in excess of cropremoval, soil P accumulations, andan increased risk of P loss in runoff(Kellogg and Lander 1999) (fig. 1).

    Figure 1. Watersheds with a high potential for soil and water degradation frommanure P (Adapted from Kellogg and Lander 1999).

  • 3

    Before World War II, farmingcommunities tended to be self-sufficient in that enough feed wasproduced locally and recycled tomeet animal requirements. AfterWorld War II, increased fertilizeruse in crop production fragmentedfarming systems, creating special-ized crop and animal operations thatefficiently coexist in differentregions within and among countries.Since farmers did not need to relyon manures as nutrient sources (theprimary source until fertilizerproduction and distribution becameless expensive), they could spatiallyseparate grain and animal produc-tion. Today, less than a third of thegrain produced is fed on farmswhere it is grown (Lanyon 2000)resu

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