Nonpoint sources of P leaving the agricultural landscape can cause eutrophication of surface water and the associated growth of undesirable aquatic plants. USDA is developing an indexing procedure for identifying soils, landforms, and management practices that could have unfavorable impacts on water bodies because of P movement. This indexing procedure uses the characteristic of the field site, including soil erosion rates, runoff, available P soil test levels, and fertilizer and organic P application rates and methods to assess the degree of vulnerability of P movement from the site. A weighting procedure has been developed to include the various contributions each site characteristic may have: A summation of the products of the weighted site characteristic yields a site vulnerability rating. An assessment tool using the Phosphorus Index will assist field staff working with landusers to identify sensitive areas and recommend management alternatives to reduce risk of P losses. Problem The movement of P from the agricultural landscape is a concern because of the potential problem of surface water eutrophication and subsequent growth of undesirable aquatic plants. Landowners, producers, and field staffs striving for natural resource management must assess the soil, hydrology, and management of individual fields in order to identify those areas that have a greater‐than‐desired impact on the movement of P. By targeting these areas, landusers and resource planners can develop the necessary management practices that could reduce the potential for P movement. A field‐level P index is needed to make this assessment and assist in the development of management practices to lessen the potential for P movement. Background Models and equations have been used to assess a number of natural resource concerns, such as soil erosion by water and wind, nitrate leaching, and pesticide movement. A few simulation programs have attempted to calculate the potential delivery of P to the edge of the field. No assessment model, however, provides the user with a simple tool to measure the relative potential of P movement from the site based on readily available field parameter values. Project Description A two dimensional matrix has been developed that relates field site characteristics to values of categories based on the severity of the P movement problem (Table ). The site characteristics have been assigned a weighting factor based on the potential for that characteristic to affect P movement. There are eight site characteristics in version 1.0 of the Phosphorus Index. The eight characteristics with their weighting factor are: soil erosion (1.5) irrigation erosion (13) runoff (0.5) soil P test (1.0) P fertilizer application rate (0.75) P fertilizer application method (0.5) organic P source application rate (1.0) organic P source application method (1.0) Value categories are defined as measured levels of each site characteristic. The higher the value the greater is the potential for phosphorus to leave the site. The five value categories...

Phosphorus in runoff from agricultural land is an important component of nonpoint-source pollution and can accelerate eutrophication of lakes and streams. Long-term land application of P as fertilizer and animal wastes has resulted in elevated levels of soil P in many locations in the USA. Problems with soils high in P are often aggravated by the proximity of many of these areas to P-sensitive water bodies, such as the Great Lakes, Chesapeake and Delaware Bays, Lake Okeechobee, and the Everglades. This paper provides a brief overview of the issues and options related to management of agricultufa! P that were discussed at a special symposium titled, "Agricultural Phosphorus and Eutrophication," held at the November 1996 American Society of Agronomy annual meetings. Topics discussed at the symposium and reviewed here included the role of P in eutrophicationi identification of P-sensitive water bodies; P transport mechanisms; chemical forms and fate of P; identification of P source areas; modeling of P transport; water quality criteria; and management of soil and manure P, off-farm P inputs, and P transport processes.

A study was initiated to investigate the relationship between soil test P and depth of soil sampling with runoff losses of dissolved molybdate reactive phosphorus (DMRP). Rainfall simulations were conducted on two noncalcareous soils, a Windthorst sandy loam (fine, mixed, thermic Udic Paleustalf) and a Blanket clay loam (fine, mixed, thermic Pachic Argiustoll), and two calcareous soils, a Purves clay (clayey, smectitic, thermic Lithic Calciustoll) and a Houston Black clay (fine, smectitic, thermic Udic Haplustert). Soil (0- to 2.5-, 0- to 5-, and 0- to 15-cm depths) and runoff samples were collected from each of the four soils in permanent pasture exhibiting a wide range in soil test P levels (as determined by Mehlich III and distilled water extraction) due to prior manure applications. Simulated rain was used to produce runoff, which was collected for 30 min. Good regression equations were derived relating soil test P level to runoff DMRP for all four soil types, as indicated by relatively high r2 values (0.715 to 0.961, 0- to 5-cm depth). Differences were observed for the depth of sampling, with the most consistent results observed with the 0- to 5-cm sampling depth. Runoff DMRP losses as a function of the concentration of P in soil were lower in calcareous soils (maximum of 0.74 mg L(-1)) compared with noncalcareous soils (maximum of 1.73 mg L(-1)). The results indicate that a soil test for environmental P could be developed, but it would require establishing different soil test P level criteria for different soils or classes of soils.

Research has shown that aluminum sulfate (alum) and phosphoric acid greatly reduce ammonia (NH3) volatilization from poultry litter; however, no studies have yet reported the effects of these amendments on field-scale composting of poultry litter. The objectives of this study were to (i) evaluate NH3 volatilization from composting litter by measuring both NH3 volatilization and changes in total nitrogen (N) in the litter and (ii) evaluate potential methods of reducing NH3 losses from composting poultry litter. Poultry litter was composted for 68 d the first year and 92 d the second year. Eleven treatments were screened in Year 1, which included an unamended control, a microbial mixture, a microbial mixture with 5% alum incorporated into the litter, 5 and 10% alum rates either surface-applied or incorporated, and 1 and 2% phosphoric acid rates either surface-applied or incorporated. Treatments in Year 2 included an unamended control, a microbial mixture, alum (7% by fresh wt.), and phosphoric acid (1.5% by fresh wt.). Alum and phosphoric acid reduced NH3 volatilization from composting poultry litter by as much as 76 and 54%, respectively. The highest NH3 emission rates were from microbial treatments each year. Compost treated with chemical amendments retained more initial N than all other treatments. Due to the cost and N loss associated with composting poultry litter, composting is not economical from an agronomic perspective compared with the use of fresh poultry litter.

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Denitrification was measured in two grass and two forest vegetated filter strips (VFS) in Rhode Island. The grass plots were established on a well‐drained soil and were planted to either tall fescue (Festuca arundinacea) or reed canarygrass (Phalaris arundinacea). One forest site was on an excessively well‐drained soil and was dominated by oak (Quercus sp.), and the other was on a poorly drained soil and was dominated by red maple (Acer rubrum). Denitrification was measured using soil cores under aerobic and anaerobic conditions with a range of treatments: no amendment, acetylene, water, nitrate (NO−3), NO−3 plus C. Unamended rates of denitrification were low in all plots. Nitrate and NO−3‐plus‐C amended rates were consistently higher in the grass plots than in the forest plots. Nitrate‐plus carbon‐amended rates were higher than NO−3‐amended rates in all plots, but the differences were significant (P < 0.05) in the forest plots only. Denitrification enzyme activity (DEA) was measured in 14 additional forest sites of varying natural drainage classes and was related to soil moisture (r2 = 0.56, P < 0.01) and pH (r2 = 0.43, P < 0.01) at these sites. The results suggest that the ability of VFS to support denitrification varies strongly with vegetation, soil type and pH, and that denitrification in VFS may be amenable to management.

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