Phosphorus and Surface Water

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            2004 IFCA        Phosphorus and Surface Water
             Sponsors
                             Online Version



                                                       PHOSPHORUS AND
            Illinois CCA
                                                        SURFACE WATER
            Convention
           Dec. 18, 2003                       By REGIS VOSS AND BILL GRIFFITH
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                                                         A PROJECT FOR ILLINOIS AGRICULTURE
             Illinois CCA

            IFCA 2004
            Convention
            Jan. 26-28

           MAGIE 2003
           August 19-20
                                                                     FUNDED BY THE




                                      ILLINOIS FERTILIZER & CHEMICAL association
                                                              P.O. BOX 186, ST. ANNE, IL 60964




                             Introduction
                             PHOSPHORUS and SURFACE WATER
                             The concern of the fate of phosphorus in the environment has been at the forefront in discussions
                             among the general public, the scientific community and those who are responsible for developing
                             public policy. A great deal of research relative to phosphorus has been accumulated over the years,
                             however we have lacked a compendium of completed research and additional research needs.


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                          This report, commissioned by the Fertilizer and Agronomy Committee of the Illinois Fertilizer and
                          Chemical Association, is the first step to identifying where we are and what needs to be done. The
                          report should serve as a benchmark for future activities for research and education for those who will
                          play a role in addressing issues associated with the nutrient Phosphorus.

                          The enclosed document, PHOSPHORUS and SURFACE WATER, acknowledges the important role
                          that Phosphorus plays as a nutrient in crop production. The report reflects conditions in which the
                          nutrient may have an environmental influence that may contribute both beneficial and/or detrimental
                          effects.

                          We wish to thank the Authors: Regis Voss, Professor of Agronomy, Iowa State University, and Bill
                          Griffith, Agronomic Management Systems, for their work in researching and producing this important
                          document. We also wish to thank Robert Hoeft, University of Illinois and Kim Polizotto of PCS Sales,
                          Chairman of the Illinois Fertilizer and Chemical Association Fertilizer and Agronomy Committee, for
                          their assistance on this project.

                          Copyright IFCA, October 1998



                          Phosphorus and Surface Water
                          Regis Voss and Bill Griffith
                                Regis Voss, Professor of Agronomy, Agronomy Dept., Iowa State Univ., Ames, IA
                                50011-1010.

                                Bill Griffith, Agronomic Management Systems, 865 Seneca Rd., Great Falls, VA 22066.

                          Agriculture has been designated as the primary source of phosphorus (P) entering inland streams,
                          lakes and water impoundments. Phosphorus, an essential element for all living plant life, is usually the
                          growth limiting factor in inland surface waters for algae and other aquatic vegetation. When
                          phosphorus enters surface waters in substantial amounts, it becomes a pollutant by contributing to
                          excessive growth of algae and other aquatic plants and, thus, to accelerated eutrophication of surface
                          waters.

                          The critical concentration of phosphorus above which accelerates growth of algae and other aquatic
                          plants is very low, 0.01 ppm P for dissolved phosphorus and 0.02 ppm P for total phosphorus. The
                          required concentration of phosphorus in the soil solution for normal plant growth is usually 0.20 to 0.30
                          ppm P. The P concentration in the runoff leaving agricultural fields frequently exceeds the critical value
                          for aquatic plant growth, but the concentration and amount of P in the runoff including sediment
                          depends to a great extent on crop production cultural practices.

                          Phosphorus leaves agricultural fields as dissolved phosphorus and particulate phosphorus, which is
                          that attached to soil sediment. Most of the dissolved phosphorus is available for aquatic plant growth.
                          The availability of particulate phosphorus is variable, depending to a great extent on the phosphorus
                          concentration or saturation of the sediment. In general, the phosphorus concentration in eroded
                          sediment is greater than in the soil from which it came. The combined availability of dissolved and
                          particulate phosphorus is termed bioavailable phosphorus.

                          When agricultural runoff enters streams the bioavailable phosphorus may increase or decrease
                          depending on whether phosphorus is adsorbed or desorbed by stream sediments. Sediments with a
                          high phosphorus concentration that enter a lake can contribute bioavailable phosphorus by desorption
                          for a prolonged period of time. The effect of bioavailable phosphorus entering lakes or surface
                          impoundments on eutrophic growth depends greatly on the characteristics of the lakes. Turbidity,
                          depth of water, flushing rate, whether stratification occurs under normal conditions, and background
                          phosphorus level of the lakes affect growth of algae and other aquatic vegetation. In general,
                          phosphorus control strategies have greatest benefit on deeper, stratified lakes with a low flushing rate
                          (less than six times per year) and the background phosphorus level is low.

                          There is a direct (linear) relationship between the concentration of dissolved phosphorus in surface
                          runoff and soil test phosphorus levels. Because of the percentage of soil samples testing higher than


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                          necessary for optimum crop yields in many states, there is a concern that high to excessively high P
                          testing fields are the primary contributors to pollution problems. Routine soil tests for phosphorus were
                          developed for agronomic purposes and not for an environmental perspective, and therefore,
                          interpretation for environmental purposes does not have a broad scientific base. Some states provide
                          guidelines for soil test phosphorus values at which either no additional phosphorus or no more than
                          crop removal are to be applied. Research has provided some rationale for these guidelines.

                          Tests have been developed to measure bioavailable phosphorus. These include water extraction,
                          chemical extraction, adsorption on ironoxide strips, and phosphorus sorption saturation. These tests
                          provide a more direct measure for bioavailable phosphorus that is related to algae growth than routine
                          agronomic soil phosphorus tests. No test, however, currently is accepted as a standardized
                          environmental test and no interpretation exists for them.

                          Crop cultural practices affect the concentration and amount of bioavailable phosphorus in runoff
                          leaving agricultural fields. Erosion control practices reduce the amount of particulate phosphorus but
                          generally increase the concentration of dissolved phosphorus in the runoff. Surface applied
                          phosphorus without incorporation increases loss of dissolved phosphorus, but knifed-in phosphorus
                          does not. The concentration of dissolved phosphorus in runoff from no-till row cropland and forages is
                          higher than from tilled land, but loss of particulate phosphorus is less. Vegetative buffer or filter strips
                          at field edges where runoff occurs or along streams where runoff enters the watercourse decrease the
                          potential amount of phosphorus entering surface waters. The amount and frequency of rainfall in
                          relation to the timing of surface applications of phosphorus has a great effect on loss. The greater the
                          time between application and rainfall runoff, the less phosphorus in the runoff. Timing of phosphorus
                          application can be a strategic cultural practice in reducing phosphorus loss.

                          Amendments applied to the soil or with manure can reduce phosphorus availability. Manure
                          amendments will not necessarily decrease the phosphorus loading of the soil. The long-term effect of
                          amendments, as a continued practice on crop productivity, has not been investigated.

                          It is generally accepted that phosphorus does not move in the soil when normal agronomic practices
                          are achieved. Movement of bioavailable phosphorus to subsurface drainage through tile does occur in
                          sandy and organic soils. Some downward movement of phosphorus can occur through macropores of
                          fine textured soils. But the major concern is that as the phosphorus sorption saturation of the soil
                          increases to the level that phosphorus movement occurs through successive horizons of the soil
                          profile, a prolonged source of bioavailable phosphorus will enter tile and move to surface waters. If
                          normal agronomic practices are followed for phosphorus management, excessive phosphorus sorption
                          saturation of soils should not occur.

                          Although there are inevitable losses of bioavailable phosphorus from agricultural soils, losses can be
                          ameliorated by proven management practices. Do not build or maintain excessive soil test phosphorus
                          levels. Do not apply more phosphorus than the amount needed to maintain a high phosphorus soil
                          test. Knife in or incorporate phosphorus additions. Use soil conservation practices required to keep soil
                          erosion within acceptable limits. Do not apply phosphorus to frozen ground or on snow cover where
                          runoff is likely to occur. Cover crops and growing high yielding crops may also help reduce any
                          potential problem.

                          Because not all watersheds or fields within a watershed contribute phosphorus to surface waters, a
                          procedure to assess potential contributors of excessive phosphorus to surface waters is needed. A
                          Phosphorus Index that incorporates phosphorus management, erosion and runoff potential could
                          provide a field assessment. Simulation models can provide a watershed assessment. Both procedures
                          can aid in pinpointing potential problem areas.

                          Because of the diversity in agricultural landscapes, soils, and crops, it does not seem reasonable to
                          develop and impose uniform guidelines or standards across all agricultural regions in order to reduce
                          phosphorus loadings to surface waters. Standards should be developed on a regional basis and based
                          on scientific evidence and procedures. Needed information to develop these standards should be the
                          basis for near-term research.

                                                              Phosphorus and Surface Water

                                                                        Introduction
                          There is increasing concern and attention being given to phosphorus (P) losses from agricultural soils.



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                          While the complex chemistry of soil P has not changed, there has been a change to more intensive
                          agricultural production systems. With this intensification has come a build-up of soil P levels in
                          site-specific areas rarely encountered in past decades. As a result, there is an increased potential for
                          P losses from these site-specific areas that present an environmental risk to affected surface waters.
                          Many of these high P soil test areas are located in lake-rich states and near sensitive water bodies
                          such as the Great Lakes, Chesapeake Bay, Delaware Bay, Lake Okeechobee, and the Everglades
                          (Sharpley et al., 1994). The problem arises when adsorption sites for P in a soil become saturated
                          rendering P potentially more available for runoff and leaching losses. Traditional soil test extractants
                          were developed and correlated in research to provide indexes of P availability to plants. Daniel et al.,
                          1998, indicate that 0.01 to 0.02 ppm dissolved P is a critical range above which eutrophication is
                          accelerated in surface waters. These values are roughly one-tenth the concentration critical for plant
                          growth. There is no standardized P testing procedure to specify a critical soil P level that suggests an
                          environmental problem. The main challenges to achieve satisfactory economical and environmental
                          solutions are to develop field/soil measurements that help identify P problem areas, and then to target
                          source management and transport management controls for the various watershed characteristics.

                                                          Phosphorus and the Environment
                          Phosphorus is an essential plant nutrient for terrestrial and aquatic plants. The beneficial effect of P on
                          crop growth and yields has been well documented (Khasawneh et al., 1980). Phosphorus has been
                          associated with environmental pollution when critical levels are exceeded in surface waters causing
                          excessive growth of algae and other aquatic vegetation that lead to eutrophication (National Research
                          Council, 1993; Sharpley et al., 1994; Sharpley et al., 1996; Van der Molen et al, 1998).

                          Eutrophication is a process by which a body becomes rich in dissolved nutrients and, often,
                          seasonably deficient in oxygen.

                          There is a general conclusion that of all the nutrients necessary for algae and aquatic plant growth, it is
                          the P level in water bodies that controls whether excessive growth leading to eutrophication occurs. As
                          P concentration in the surface water increases, aquatic growth increases. Eutrophication due to
                          excessive algal and plant growth and their ultimate decomposition limits the use of surface waters for
                          aesthetics, fisheries, recreation, industry, and drinking. The critical concentration of P in surface water
                          that is frequently cited is 0.01 parts per million (ppm), but a range of 0.01 to 0.03 ppm seems to be
                          accepted (National Research Council, 1993). The same measure of 0.01 ppm can be found in the
                          literature expressed as 10 ug per liter, 0.01 mg per liter, or 10 parts per billion. This paper will use ppm
                          to express all measurements.

                          The identification of P as a major cause of eutrophication in surface waters led to early emphasis on
                          point sources delivering P to surface waters, e.g., sewage systems delivering waste water containing P
                          from detergents. According to the National Research Council, 1993, the overall trends show about
                          equal numbers of U.S. rivers with increasing and decreasing P loads. In general, the decreases are
                          linked to point source reductions and the increases are linked to nonpoint source increases that are
                          associated with increased suspended sediment loads and agricultural land use.

                          The U.S. Environmental Protection Agency (US EPA) has not yet developed P water quality criteria for
                          fresh water bodies as a guide for states. The US EPA criteria for marine and estuarine water is 0.0001
                          ppm elemental P (Parry, 1998). Daniel et al., 1998, stated, however, that water quality criteria have
                          been established to control eutrophication (US EPA, 1986). For example, total P should not exceed
                          0.05 ppm in streams entering lakes/reservoirs, nor 0.025 ppm within lakes/reservoirs. For the
                          prevention of plant nuisances in streams or other flowing waters not discharging to
                          lakes/impoundments the concentration of total P (TP) should not exceed 0.10 ppm. A dissolved P (DP)
                          concentration of 1 ppm is the limit required of sewage treatment output and one advocated by some as
                          a critical flow-weighted-mean-annual concentration for agriculture literature expressed as 1 0 ug per
                          liter, 0.01 mg per liter, or 1 0 parts per billion. This paper will use ppm to express all measurements.

                          The identification of P as a major cause of eutrophication in surface waters led to early emphasis on
                          point sources delivering P to surface waters, e.g., sewage systems delivering waste water containing P
                          from detergents. According to the National Research Council, 1993, the overall trends show about
                          equal numbers of U.S. rivers with increasing and decreasing P loads. In general, the decreases are
                          linked to point source reductions and the increases are linked to nonpoint source increases that are
                          associated with increased suspended sediment loads and agricultural land use.

                          The U.S. Environmental Protection Agency (US EPA) has not yet developed P water quality criteria for



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                          fresh water bodies as a guide for states. The US EPA criteria for marine and estuarine water is 0.0001
                          ppm elemental P (Parry, 1998). Daniel et al., 1998, stated, however, that water quality criteria have
                          been established to control eutrophication (US EPA, 1986). For example, total P should not exceed
                          0.05 ppm in streams entering lakes/reservoirs, nor 0.025 ppm within lakes/reservoirs. For the
                          prevention of plant nuisances in streams or other flowing waters not discharging to
                          lakes/impoundments the concentration of total P (TP) should not exceed 0.10 ppm. A dissolved P (DP)
                          concentration of 1 ppm is the limit required of sewage treatment output and one advocated by some as
                          a critical flow-weighted-mean-annual concentration for agriculture runoff. Studies are needed to
                          correctly define the numerical criteria for water quality. Such criteria are likely not constant but depend
                          on the characteristics of the specific water body as well as the intended use of the water. Fisheries
                          agencies on Lake Erie, for example, don't want P target levels changed without more scientific
                          evidence for a need. They are concerned that further reductions in P levels in the lake could have a
                          serious negative impact on fish stocks (Bruulsema, 1998).

                                                               Transport of Phosphorus
                          The main mechanisms by which P is lost from agricultural soils are by runoff and erosion (Sharpley et
                          al., 1994). The losses occur either as DP or as particulate P (PP). The loss of DP may occur in surface
                          water runoff or leaching and is comprised mostly of orthophosphate which is immediately bioavailable
                          phosphorus (BAP) for algal uptake. Particulate P is associated with eroded soil and organic matter
                          particles. Particulate P contributes a variable, but long-term source of BAP (Sonzogni, 1982; Sharpley
                          and Smith, 1991; Sharpley, 1993).

                          Dissolved Phosphorus. Dissolved P is the P in soil solution that will pass through a 0.45 um filter and
                          is often called soluble P. The accepted analytical procedure for determining DP is the acid molydate
                          blue method devised by Dick and Tabatabai, 1977. Much of the research on phosphorus losses as DP
                          and PP in runoff has been done with rainfall simulators on small plot areas and catching the runoff
                          water and eroded sediment for subsequent analysis.

                          The concentration of DP in runoff has been found to be higher from no-tillage with surface crop residue
                          than from conventional tillage, but the total loss of DP is less (Romkens et al., 1973; Gaynor and
                          Findlay, 1995). Runoff from fields containing frozen crop residue such as frozen alfalfa has been found
                          to be higher in the concentration of DP than from tilled fields (Wendt and Corey, 1980; Andraski et al.,
                          1985; Timmons et al., 1970).

                          Surface applied and non-incorporated fertilizer, animal manure, or sewage sludge causes an increase
                          in DP concentration in runoff (Young and Mutcher, 1976; Truman et al., 1993; Gaynor and Findlay,
                          1995).

                          There is an interaction between rainfall and the 0 to 2 inch layer of surface soil (Oloya and Logan,
                          1980; Sharpley and Smith, 1989; Sharpley, 1995). As a consequence there is a very good positive
                          relationship between soil test P and the concentration of DP in runoff (Abrams and Jarrell, 1995;
                          Romkens and Nelson, 1974; Sharpley et al., 1977; Sharpley, 1995; Pote et al., 1996). This loss is
                          exacerbated by the stratification of surface applied P in no-till and conservation tillage systems
                          resulting in soil test P highest in the 0 to 2 inch layer (Tripleft and Van Doren , 1969; Robbins and
                          Voss, 1991; Holanda et al., 1998). It does not appear that time or frequency of assessment of soil test
                          P affects the ability to predict P runoff losses because rainfall and management have a greater
                          influence (Sharpley et al., 1985). In general, as described by Pierzynski and Logan, 1993, when P
                          additions to the soil continually exceed crop removal, soil test P increases.

                          There has been a general increase in soil test P levels in the U.S. since World War 11 as a result of P
                          applications. A 1989 summary of soil test values showed that in several states more than 50 percent
                          and in some states 75 percent of soil test P samples tested high (Sims, 1993; Sims, 1998; National
                          Research Council, 1993; all cite PPI, 1994). A recent soil test summary from 1997 (PPI/PPIC/FAR,
                          1998) indicates that many agricultural soils remain in the high and above categories. The percent of
                          soils testing high are similar to the 1989 percentages for many states, but there are signs of a
                          decreasing high soil test P trend in some important agriculture states in the Midwest such as Indiana,
                          Illinois, Iowa, Minnesota, and Ohio. In other states such as Arkansas, Wisconsin, North Carolina and
                          Delaware soil test P trends are continuing to increase.

                          A nutrient budget analysis for the states of Iowa and Wisconsin, for example, indicates that these up or
                          down trends might be predicted based on P use and removal. Assuming that all collectable manure in
                          Iowa was applied to cropland, P removal by crops exceeded the inputs in 1996 by 10 percent. In



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                          Wisconsin P crop removal is only 84 percent of P inputs (Bundy, 1998). Soil test P levels may increase
                          when inputs of P equal crop removal because the applied P will be concentrated in the upper 6 to
                          8-inches of soil, but the crop will extract some P at depth of rooting. In many cases, however, the
                          problem of elevated soil test P levels are associated with regions where intensive animal production
                          facilities exist and animal manure supplies exceed crop needs on economically available agricultural
                          land. County-based estimates for the P available in animal manure to meet or exceed crop removal
                          are available to help identify more local soil test P potential problem areas (Lander et al., 1998). The
                          potential for P loss both from surface runoff and, in some situations, subsurface leaching increases as
                          soil test levels exceed the critical soil test values established for crop needs (Sharpley et al., 1996).

                          Because commonly used soil test procedures, e.g., Bray and Kurtz, P-1, Melich I and 111, Olsen, and
                          Morgan, were developed to provide indexes of P availability to plants and not for environmental
                          interpretation, a more rigorous test is desirable to indicate the potential for loss of DP. Soils will adsorb
                          or desorb P depending upon the P sorption saturation of the soil. A standardized procedure was
                          developed by Nair et al., 1984, for determining phosphorus sorption saturation that is defined as:

                                                                             Extractable soil P
                                              P sorption saturation =                                 x 100
                                                                            P sorption capacity

                          where units of extractable soil P and P sorption capacity are unit mass of DP for a given mass of soil. It
                          is a fact that more P is desorbed or released from soil to runoff or leaching as P sorption saturation
                          increases (Sharpley et al., 1996). From this measure it is possible to determine the DP concentration
                          expected in runoff from a soil with a given P saturation. A better relationship was found for DP with P
                          saturation than with soil test P indexes (Sharpley, 1995, 1997). This method is more tedious than soil
                          test P methods, but it provides an integration of soil characteristics that affect desorption of P.

                          Using the P sorption saturation approach the Dutch have designated a critical P saturation value of 25
                          percent (Van der Molen et al., 1998). Sharpley et al., 1996, found that 25 percent P saturation
                          supported a DP concentration of 1 ppm in runoff. This concentration as a flow-weighted-annual DP
                          runoff concentration limit, similar to that of sewage treatment plants, has been proposed for areas of
                          this country (US EPA 1986). Although this test has a better scientific basis than routine soil test P
                          procedures for predicting desorbed and DP concentrations, it is time consuming and costly.

                          This method, like routine soil tests, does not predict total loss of DP for which runoff volume is needed.
                          Routine P soil tests should be used for screening purposes and the P saturation method used only
                          where potential critical areas exist.

                          Particulate Phosphorus. Phosphorus that has formed compounds that have precipitated onto the
                          surface of soil particles, attached to clay minerals, or adsorbed onto the surface of clays is termed
                          particulate phosphorus (PP). Eroded sediments tend to have higher phosphorus concentrations than
                          the field or soil it has been eroded from. This is known as the enrichment ratio (ER) and ranges from
                          slightly less than 2 to 3 or 4 (Alberts et al., 1981; Sharpley, 1980). If excessive soil erosion occurs and
                          low P soil is eroded, the P concentration in the total eroded sediment may be less than the original
                          source (Sharpley and Smith, 1991). Particulate phosphorus can be 75 to 90 percent of the P
                          transported in runoff (Schuman et al., 1973; Sharpley et al., 1993).

                          Although PP loss may be greater than DP loss, only a portion of PP is bioavailable phosphorus (BAP)
                          because some of the adsorbed P will not desorb and be available to plants. Oloya and Logan (1 980)
                          found a good relationship between soil test P and desorbed P. Others, however, have found a much
                          better relationship of P availability to algae with PP extracted from sediment with a sodium hydroxide
                          (0.1 M NAOH) solution (Sonzogni et al., 1982; Dorich et al., 1985; Sharpley and Smith, 1992; Wolf et
                          al., 1985). This extraction procedure is lengthy. Sharpley, 1993, adapted a simpler procedure using
                          iron oxide-impregnated paper strips to determine BAP that is directly related to algae growth. The
                          iron-oxide strips act as a P-sink and simulate P removal from sediment-water samples by algae. Pote
                          et al., 1996, also found the iron-oxide strip method to be effective in determining the concentration of
                          BAP. An advantage of the iron-oxide strip over a chemical extractant is that it can be used in the field
                          to extract BAP from water-sediment samples, dried, and sent to a laboratory for analysis later.

                          Although there are known analytical procedures that provide indexes of P that are related well to
                          concentrations of DP, PP, and BAP loss in runoff water and eroded sediment, they are not reliable
                          indicators of the amount or load of P lost from a field or site in a field. Also, these measures do not



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                          indicate if the lost P arrives to surface waters, but they do indicate a potential for loss if combined with
                          an estimate of runoff or erosion potential.

                          Tile Effluent. Because P is considered to be immobile in the soil, there is generally little concern that it
                          will be a problem for that lost in tile drainage. There are, however, locations with sandy or organic soils
                          where tile effluent has high concentrations of P (Duxbury and Peverly, 1978). In the Netherlands where
                          sandy and organic soils with high water tables are prevalent, restrictions on P use are imposed (Van
                          der Molen et al., 1998). Studies in the United States have in general found very low concentrations of
                          DP in tile effluents, but frequently exceed a projected critical value of 0.01 ppm P (Johnston et al.,
                          1965; Hanway and Laflen, 1974; Baker et al., 1975; Calvert, 1975; Sharpley et al., 1977; Hergert et al.,
                          1981). Similar results were obtained in Canada on a level tile-drained field, but P losses in
                          conservation tillage were greater than from conventional tillage due to greater infiltration (Gaynor and
                          Findley, 1995). In all cases total loss of P was negligible, e.g., less than one lb P per acre. An
                          exception to the low loss of P was that from an organic soil that had a P loss of 1 0 to 33 ppm in the
                          effluent with a total loss of less than one lb up to 27 lb P per acre (Calvert, 1975). In another study
                          where rates of dairy manure were applied in New York, the P concentration in the tile effluent
                          increased as rates of manure increased indicating that excessive manure loading of soil can potentially
                          contribute to DP loss even though the economic loss is negligible (Hergert et al., 1981). In a study on
                          deep calcareous soils in Utah high rates of manure did cause P movement to 7 ft but it was concluded
                          to not be a problem on deep calcareous soils (James et al., 1996).

                          Sims et al., 1998, in a comprehensive review of P loss in agricultural drainage, stated that the most
                          immediate concerns are for those areas where soil P concentrations are already very high, soil P
                          sorption capacities are low, and subsurface transport is enhanced by tiles and surface ditches. In
                          many situations P leaching and transport to surface waters in tile or ditch drainage will be of little
                          consequence, relative to surface erosion and runoff. This includes fine-textured soils with low degrees
                          of P saturation that are fertilized in accordance with soil testing recommendations.

                                                                  Watershed Assessment
                          Because of the diversity in the agricultural landscape, there is a wide range in the potential for loss of
                          P from the landscape. Contributing to the diversity are: physical and chemical characteristics of the
                          soils, topography, crop and plant vegetation, crop production cultural practices, P level of the soil, and
                          method of P application. Most watersheds include field sites that are different in one or more
                          characteristics. If P loss from a watershed is an environmental concern, it would be beneficial to
                          identify the site(s) within the watershed that has the greatest potential for P loss. Current research
                          suggests that strategies to control P loss from non-point sources should focus on specific locations
                          within a watershed where high P soil levels have developed. Control measures should focus on both
                          source and transport management strategies. This conclusion is supported by several studies showing
                          that up to 90 percent of annual P loss comes from less than 1 0 percent of the land in hill-land
                          watersheds (Heathwaite et al., 1998). Knowing where these fields, or areas within a field, are located
                          in impaired watersheds could be an important part of implementing practical solutions to animal waste
                          disposal.

                          A Phosphorus Index has been proposed by Lemunyon and Gilbert, 1993, to assess the various
                          landforms and management practices for potential risk of P movement to surface waters. The
                          Phosphorus Index provides a ranking of sites where the risk of P movement may be higher or lower
                          than other sites. It will help identify problem parameters that can be the basis for planning corrective
                          conservation practices and management techniques. The proposed Phosphonis Index included these
                          site characteristics with weighting factors:

                                soil erosion (1.5)

                                irrigation erosion (1.5)

                                runoff loss (0.5)

                                soil P test (1.0)

                                P fertilizer application rate (0.75)

                                P fertilizer application method (0.5)




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                                organic P source application rate (1.0)

                                organic P source application method (1 .0)

                          A rating value for the potential of P loss due to each specific site characteristic was assigned (Low = 1,
                          Medium = 2, High = 4, Very High 8). The rating value was multiplied times the weighting factor for each
                          site characteristic and summed over the eight site characteristics. The summation of the eight
                          weighted values provides the relative vulnerability of the site for P loss. A total of greater than 32 was
                          suggested as very high vulnerability.

                          The Phosphorus Index was evaluated in Oregon and Washington (Stevens et al., 1993) and in the
                          Southern Plains on 30 watersheds on which vulnerability to P loss in runoff was closely related to
                          actual losses (Sharpley, 1995). In both cases the Phosphorus Index provided a relative ranking and
                          identified P sources within a watershed that will require more intensive management to minimize P
                          loss in runoff and maintain crop productivity. The Phosphorus Index is a tool to evaluate potential loss
                          of P from a site but does not indicate the actual arrival into surface waters.

                          A more recent approach is the use of mass balance and dynamic simulation approaches through
                          computer modeling (Cassell et al., 1998). This approach permits evaluation on a watershed ecosystem
                          basis and the effect of various P management and crop production practices on potential P losses.
                          Although this approach has appeal, criteria for outcome must be established.

                                               Management Practices Affecting Phosphorus Loss
                          Management practices to control P losses have been divided into those that reduce the source of P
                          potentially available for loss (source management) and those targeted at reducing the transfer of P
                          directly to a water body (transport management) (Withers, 1998).

                          Examples of source management strategies are:

                          • Rate of P applications

                          • Method of P applications

                          • Timing of P applications

                          • Use of best management practices (BMPS)

                          • Precision Agriculture and remote sensing technology

                          • Animal manure management

                          • Manure and soil amendments

                          • Feed and feed additives

                          Examples of transport management strategies are:

                          • Conservation tillage practices

                          • Appropriate land use for the site

                          • Buffer zone practices

                          Rate, Method and Timing of P Applications. Routine soil testing is an accepted and proven
                          management practice. Phosphorus applications based on these soil analyses help assure that soil P
                          levels are adequate for profitable crop production and avoid excesses that could be detrimental to the
                          environment. The timing of P applications to avoid, when possible, historic periods of intense storm
                          events has been shown to reduce the probability of DP and TP runoff (Sharpley, 1997). Numerous
                          studies have shown that P placement below the soil surface compared to surface applications reduces
                          loss of P by erosion. The positive effects of P placement at seeding have been recorded for many
                          crops (Murphy & Dibb, 1986). The positive starter effect of P placement is the result of better
                          root/nutrient contact for this relatively immobile nutrient and to a slower rate of P fixation.

                          Best Management Practices (BMPs). In addition to P, there are many controllable agronomic growth


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                          factors that must be considered in crop production. Crop rotation, plant population, variety or hybrid
                          selection, balanced fertilization, soil pH, planting date, pest control, and tillage practices are just a few
                          growth factors to consider. Using recommended BMPs for all controllable growth factors enhances the
                          opportunity for optimum yields and greater P utilization efficiency.

                          Precision Agriculture and Remote Sensing. Managing P and other nutrient inputs to land that has
                          received large and often non-uniform applications of manure can be difficult in terms of soil sampling
                          and nutrient application. Intensive soil sampling often shows areas of medium or lower soil test P
                          levels within fields with excessive P levels and field means that are very high. Using yield monitors,
                          remote sensing and variable rate technology offers promise for use in these situations, but more
                          research is needed to learn how to best use these technologies (Schepers et a[., 1998).

                          Manure Management. Although there may be field research studies underway on potential losses of
                          manure nutrients into surface waters from field applications of manure, few have been reported in the
                          scientific literature, but as previously cited in this paper there have been many reports on the potential
                          loss of soil P into the environment.

                          Young and Mutcher, 1976, determined that more P was lost from manure applied on frozen alfalfa
                          ground than from application on fall plowed corn ground, and loss from manure applied in the spring to
                          snow covered land was similar to loss from frozen ground. Application of swine lagoon effluent to
                          Bermuda grass on 5 and 10 percent slopes of a loamy sand reduced the amount lost from that P
                          applied by 99 percent, but the P concentration lost in the runoff exceeded US EPA values (Liu et a[.,
                          1997).

                          The effect of rainfall on loss of P from surface applied poultry manure was determined in laboratory
                          studies. The first rainfall leached the greatest amount of P from the manure and the amount decreased
                          with each subsequent rainfall (Robinson and Sharpley, 1995). In another study using ten soils a similar
                          effect was obtained, but as the time increased between manure application and rainfall the amount of
                          runoff P decreased (Sharpley, 1997).

                          In determining the amount of manure P to apply to soil there is concern about the availability of the
                          organic P to crops where additional P is needed. Using P leached from poultry lifter and a highly
                          soluble inorganic P source incubated in 193 soils obtained from around the world, P availability was
                          determined by the iron-oxide strip method to be greater for the inorganic P source. Phosphorus
                          recommendations for P deficient soils should preferably be based on field research using manure P
                          rather than inorganic P (Sharpley and Sisak, 1997).

                          Fields that have excessively high soil test P levels due to a history of high manure applications can be
                          a concern. Using the iron-oxide strip method Sharpley, 1996, examined the availability of residual P in
                          17 manured soils that ranged in Mehlich 3 soil test P values from 19 to 418 ppm P. The rate and
                          amount of P released was a function of the P sorbed saturation. The rate of release and the decline
                          with successive extractions were greatest for the highest P testing soil. These results were similar to
                          field studies in the rate of decline of soil test P in that several years are required to reduce soil test P
                          from moderately high soil test values to a responsive level. Webb et al., 1992, reported it took more
                          than 10 years for a corn-soybean sequence to reduce soil test P from 75 ppm to 20 ppm P. McCollum,
                          1991, reported it took 20 years to lower soil test P from 1 00 ppm to a threshold value of 20 ppm. In
                          another similar study soil test P decreased 1 ppm per year (Mallarino et al., 1991).

                          If manures are not to be incorporated or injected into the soil, they should be applied at a time when
                          the probability is low for intense and frequent rains. Where runoff from frozen and snow-covered soils
                          is possible, manure should not be applied to these soils.

                          Manure and Soil Amendments. Reduction of soluble P in soils should reduce the concentration and
                          amount of BAP in runoff. Additions of aluminum sulfate (alum) or ferrous sulfate to poultry lifter
                          decreased the concentration and amount of DP in runoff. Aluminum sulfate also reduced ammonia
                          loss and increased forage yields as a consequence (Shreve et al., 1995). Phosphorus concentrations
                          in runoff water from watersheds fertilized with alum-treated poultry lifter were approximately 70 percent
                          lower than that observed from normal lifter (Moore et al., 1998). Use of aluminum sulfate will acidify
                          soils but the rate and to the degree that this will occur depends on the buffering capacity of the soil. It
                          has also been shown that this practice will reduce the concentrations of heavy metals in runoff such as
                          copper (Moore et al., 1998). Coal combustion by-products added to a high P testing Pennsylvania soil
                          reduced soil test and water extractable P (Stout et al., 1998).




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                          Although amendments may have a favorable effect on a potential P problem, potential deleterious side
                          effects should be investigated. This practice should not justify continued additions of P to high P soils.

                          A new developing technology is the application of a polyacrylamide to furrow irrigated soil. This
                          compound reduces phosphorus and sediment loads in runoff from surface-irrigated fields (Lentz et al.,
                          1998).

                          Advantages claimed for the technology are costs are low, no change in cultural practices is required,
                          and it could reduce tillage operations.

                          Feed and Feed Additives. Much of the P in corn grain is present in the form of phytic acid. Phytic acid
                          P is unavailable to monogastric animals (e.g., swine and chickens) with most being excreted in the
                          waste. As a result most of the P in grain is wasted and may contribute to water quality problems.
                          Because of the low digestibility of grain P by monogastric animals, P sources are added to feed
                          rations. This adds to the P in excreted waste.

                          Phytase enzymes can be added to feed rations and increase the availability of P in corn and decrease
                          the excretion of P (Ertl et al., 1998). This approach adds to the cost of production.

                          A sustainable approach is to identify corn genetic material that has a low phytic acid P content in the
                          grain but normal levels of P. This has been achieved with some success, and preliminary feeding trials
                          resulted in greater P availability and reduced P content in the waste (Ertl et al., 1998). Altering the
                          phytic acid content genetically in corn is possible and may have the potential to improve feeding
                          efficiencies and reduce P in monogastric animal waste. This could reduce the P loadings in fields
                          where manure application is based on the nitrogen needs of the crop to be grown.

                          Tillage Management. Tillage on soils where runoff and erosion

                          will occur will increase total P loss with variable BAP concentrations and amounts as previously cited.
                          No-tillage or very reduced tillage that leaves crop residue on the surface of similar soils will reduce
                          total P and BAP loss but may increase DP concentrations in the runoff water. Periodic inversion of P
                          stratified surface soils may be advantageous to reduce the concentration of P at the soil surface and
                          the potential for P loss.

                          Buffer Zone Management. Vegetative filter strips between agricultural lands and surface waters can
                          be effective in reducing sediment and nutrient loads in runoff waters (Edwards et al., 1996). Buffer
                          zones and wetlands have been found to reduce the losses of PP and TP. The retention of DP is not
                          very effective and sometimes may actually increase (Uusi-Kamppa et al., 1998). This practice,
                          although supported by NRCS, is in its infancy and its efficacy for reducing P loading in runoff water
                          needs further research.

                                                           Crop and Soil Management Options
                          There is ample evidence that the P concentration in water runoff and eroded sediment increases as
                          the soil test level of the surface two inches of soil increases. If this lost P reaches surface waters,
                          increased aquatic growth and eutrophication are highly probable to occur. Not all agricultural
                          watersheds or fields within a watershed contribute to a potential environmental problem caused by P.

                          Crop and soil management options exist to minimize P losses into surface waters where the potential
                          exists. Current and future research will contribute to this list:

                               1. Identify fields that have the greatest potential for P loss.

                               2. Do not build and maintain excessively high P soil test levels.

                               3. Minimize soil erosion with appropriate cultural practices. This will reduce loss of particulate P
                                  and total P, but may increase loss of dissolved P where runoff occurs.

                               4. Apply fertilizer P or manure P according to soil test for the crop to be grown.

                               5. Establish and maintain vegetative buffer strips at the point where runoff leaves a field and along
                                  streams and drainage ditches where agricultural runoff enters these surface waters.




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                               6. Incorporate or knife in fertilizer or manure where possible without destroying crop residue
                                  required for soil conservation purposes.

                               7. Grow high P removing crops, but these should provide a competitive economic return to the
                                  producer.

                               8. Periodic inversion of P stratified surface soils by primary tillage.

                                                                  Suggested Research Needs

                          Past and current research shows that fields with excessively high soil P levels (levels well beyond the
                          point where there are crop responses to additional P) can contribute bioavailable P to surface waters
                          through surface water runoff, sediment loss, and possible subsurface drainage. Not all fields, however,
                          contribute to this potential problem. It is imperative that guidelines and any restrictions on P usage and
                          crop production practices have a scientific basis.

                          Suggested research needs could include:

                                     1. Identify level of acceptable background loss of bioavailable P from agricultural
                                        lands that will occur regardless of implementation of best management practices.

                                     2. Refine Phosphorus Index and simulation models to identify watersheds and fields
                                        within watersheds that potentially contribute excessive bioavailable P to surface
                                        waters.

                                     3. Identify and standardize an environmental soil test for P. Conduct basic research to
                                        better understand the mechanisms controlling P solubility, especially in excessively
                                        high P testing soils.

                                     4. Identify P sorption saturation percentage for surface soil and for subsurface soil
                                        horizons for fields that are tile drained that could lead to prolonged loss of
                                        bioavailable P.

                                     5. Evaluate various designs of vegetative filter strips for efficacy in filtering out
                                        bioavailable P over a period of years.

                                     6. Evaluate various designs of wetlands for efficacy in removing bioavailable P.

                                     7. Evaluate composting processes to reduce volume of manure and produce a
                                        product that is easily transported and commercially acceptable.

                                     8. Evaluate feed components for monogastric animals that will lower P content of
                                        manure, e.g., corn with low phytic acid P content or addition of phytase enzyme to
                                        feed.

                                     9. Evaluate and/or design manure application equipment to accurately control rate
                                        and placement of application.

                                    10. Evaluate efficacy of a knifed-in application of fluid manure to a growing crop, e.g.,
                                        corn.

                                    11. Examine economic and social acceptability of manure cooperatives or banks that
                                        would help disseminate the manure P source to fields needing P.

                                    12. Determine by field research the effect of various soil amendments on P
                                        bioavailability and on the chemical and biological characteristics of the soil that
                                        affect crop productivity when amendments are applied to excessively high soil test
                                        P soils.

                                    13. Evaluate the use of remote sensing in combination with intensive grid sampling and
                                        variable rate application of P.

                                    14. Encourage the "team approach" in P/water quality studies. Team members might
                                        include soil scientists, hydrologists, crop scientists, limnologists, animal scientists,
                                        economists, and others.


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                               15. Determine the numerical criteria for water quality as it relates to the type of water
                                   body and its use.


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Phosphorus and Surface Water                                                                               http://www.ifca.com/programs/phosphorus.htm


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                                         Wendt, R. C. and R. B. Corey. 1980. Phosphorus variations in surface runoff
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DOCUMENT INFO
Description: Phosphorus pollution in stream /BMP to curb pollution/ GIS modeling