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Agricultural Phosphorus and Eutrophication - USDA

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					Agricultural Phosphorus and
      Eutrophication

                      by
                   Don Pitts
Agricultural Engineer & Water Quality Specialist
                 USDA, NRCS
                Champaign, IL
            Phosphorus (P)
• Is an essential element for plant growth
• Additions of fertilizer P inputs have
  been long recognized as necessary for
  profitable crop production
• Phosphorus inputs can also increase
  biological productivity of surface
  waters and cause eutrophication
        What is Eutrophication?
 • It is the loading of dissolved and
   particulate matter to a water body at
   rates sufficient to produce high
   biological production
 • It has been identified as the main
   cause of impaired surface water in the
   U.S. (USEPA)

(36 Percent of Illinois Lakes are classified as hyper-eutrophic, IEPA, 1999)
              Eutrophication
• Eutrophication is the natural aging
  process of lakes brought on by nutrient
  enrichment
• Eutrophication is generally accelerated
  by Phosphorus (P) inputs


  Source: USDA (Sharpley et al., 1999)
     Primary Nutrient Inputs for
        Aquatic Biota Growth

                      Aquatic Biota


     Carbon              Nitrogen           Phosphorus


  Since C and N can be obtained from the atmosphere, P is
generally considered the limiting input in fresh water systems.
               Relationship Between P and Chlorophyll-a
                        in Fresh Water Systems
                                                      (assuming sunlight and temperature not limiting)
Lake Productivity (Chlorophyll a, ppm)




                                         100




                                         10


                                                                                                Hyper-eutrophic
                                           1                                  Eutrophic
                                                                Mesotrophic

                                               Oligotrophic

                                         0.1
                                           0.001              0.01                        0.1                        1.0
                                                               P concentration (mg/l)             (source: Sharpley, 1997)
  Phosphorus (P) Water Quality
     Standards and Criteria
• Total P in streams entering a lake should be less
  than 0.05 mg/l (Illinois Water Quality Standard)
• Ambient Water Quality Criteria Recommendations
  for Central Illinois Ecoregion, Total P = 0.02 mg/l
  (USEPA, 2000)
• IEPA criteria for streams and rivers is in
  development
               Phosphorus (P)
• Sediment-bound or Particle P
  – it is generally thought that most of the P losses
    from cropland is in this form (however, in many
    cases, this may not be true)
• Dissolved or Soluble P
  – is defined as P that will pass through a 0.45 micro
    filter (sometimes equated to orthophosphate)
  – is very bio-reactive and available for algae
    production
• Total P = Particle P + Dissolved P
 Several Common Myths about
    Phosphorus Transport

• Soils are infinite sinks for P
• P does not move through the soil
• Erosion control will stop P losses
  in runoff
Soils are not Infinite Sinks for P
• Research has shown that soils cannot
  indefinitely fix applied P
• Continued application of P beyond
  crop requirements will eventually
  result in soil P saturation
  Long-Term Build-up of Soil P
from Continual Over-application
                                   80
                                   70
 Silo Test P (ppm)




                                   60
                                   50
                                   40                                       P levels
                                   30
                                   20
                                   10
                                    0
                     -20     -10         0     10        20       30   40
                                   Annual P Surplus (lbs/ac/yr)


                     From Barber, 1979
       Dissolved P in Runoff verses
               Soil P Level
                                1
                                              New Zealand
                               0.9
                                              Arkansas
                               0.8            Oklahoma
                                              Illinois
          Dissolved P (mg/l)




                               0.7

                               0.6

                               0.5

                               0.4

                               0.3

                               0.2

                               0.1

                                0
                                     0   50   100     150    200     250     300   350   400   450

                                                            Soil P (lb/ac)


Source: Sharpley et al. (1999) and Hoeft (2000)
   Phosphorus Does Move
     Through the Soil
• P may move through the soil given:
  – low soil P-fixing capacity
  – high percolation potential (macro
    pores)
  – high soil test P
Dissolved Phosphorus in Tile
 Water verses Soil P Levels
                      1

                     0.8
Dissolved P (mg/l)




                     0.6

                     0.4

                     0.2

                      0
                           0   100        200           300          400
                                     Soil P (lb/ac)
Source: Heckrath et al. (1995)                        Olsen convert to Bray
                                                      for tile flow P
  Erosion Control May Not
   Stop P Losses in Runoff
• Erosion control measures may not
  reduce dissolved P level in runoff:
   – high soil test P levels may cause
     significant dissolved P losses
   – stratified P (concentrated near the
     surface) may cause high dissolved
     P runoff levels
 Dissolved P in Runoff verses
         Soil P Level
                      0.7
                      0.6        No-Till
 Dissolved P (mg/l)




                      0.5        Chisel

                      0.4
                      0.3
                      0.2
                      0.1
                       0
                            30              60            150     300
                                           Soil Test P (lbs/ac)

Source: Hoeft (2000)
  Illinois Soil Test Laboratory
             Reports


• A survey of agricultural soil test
  laboratories in Illinois indicated 64% of
  the soil samples analyzed had high to
  very high Soil P levels (Fixen, 1998)
   Once elevated, it may take
  many years of no P fertilizer
      application to bring
  soil tests P to normal levels
• It was estimated to take 16 - 18 years of
  corn/soybean production to drop a
  Portsmouth fine sandy loam from 100
  ppm to the agronomic threshold of 20
  ppm (McCollum, 1991).
  Phosphorus
      (TP)
Concentrations
   in Surface
    Water in
     Illinois
(Source: IEPA)
   USDA ARS Bulletin 149




http://www.ars.usda.gov/is/np/Phos%26Eutro/phos%26eutrointro.htm

                     Available online

				
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