The accelerated eutrophication of most freshwaters is limited by P inputs. Nonpoint sources of P in agricultural runoff now contribute a greater portion of freshwater inputs, due to easier identification and recent control of point sources. Although P management is an integral part of profitable agrisystems, continued inputs of fertilizer and manure P in excess of crop requirements have led to a build‐up of soil P levels, which are of environmental rather than agronomic concern, particularly in areas of intensive crop and livestock production. Thus, the main issues facing the establishment of economically and environmentally sound P management systems are the identification of soil P levels that are of environmental concern; targeting specific controls for different water quality objectives within watersheds; and balancing economic with environmental values. In developing effective options, we have brought together agricultural and limnological expertise to prioritize watershed management practices and remedial strategies to mitigate nonpoint‐source impacts of agricultural P. Options include runoff and erosion control and P‐source management, based on eutrophic rather than agronomic considerations. Current soil test P methods may screen soils on which the aquatic bioavailability of P should be estimated. Landowner options to more efficiently utilize manure P include basing application rates on soil vulnerability to P loss in runoff, manure analysis, and programs encouraging manure movement to a greater hectareage. Targeting source areas may be achieved by use of indices to rank soil vulnerability to P loss in runoff and lake sensitivity to P inputs.

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Soils that contain high P levels can become a primary source of dissolved reactive P (DRP) in runoff, and thus contribute to accelerated eutrophication of surface waters. In a previous study on Captina soil, several soil test P (STP) methods gave results that were significantly correlated to DRP levels in runoff, but distilled H20 and NH4-o x a l a t e m e t h o d s gave the best correlations. Because results might differ on other soils, runoff studies were conducted on three additional Ultisols to identify the most consistent STP method for predicting runoff DRP levels, and determine effects of site hydrology on correlations between STP and runoff DRP concentrations. Surface soil (0-2 cm depth) of pasture plots was analyzed by Mehlich HI, Olsen, Morgan, Bray-Kurtz P1, NH4-oxalate, and distilled H 20 methods. Also, P saturation of each soil was determined by three different methods. Simulated rain (75 mm h) produced 30 min of runoff from each plot. All correlations of STP to runoff DRP were significant (P < 0.01) regardless of soil series or STP method, with most STP methods giving high correlations (r > 0.90) on all three soils. For a given level of H 20-extractable STP, low runoff volumes coincided with low DRP concentrations. Therefore, when each DRP Concentration was divided by volume of plot runoff, correlations to H 20-extractable STP had the same (P < 0.05) regression line for every soil. This suggests the importance of site hydrology in determining P loss in runoff, and may provide a means of developing a single relationship for a range of soil series. E UTROPHICATION of streams and lakes can be greatly accelerated by the influx of nutrients in surface runoff from agricultural land. Since P has been identified as the nutrient in runoff that is usually the most limiting to algal growth, control of P levels in runoff is often recommended as the best way to minimize the eutrophication of surface waters (Rohlich and O'Connor, 1980; Little, 1988; Breeuwsma and Silva, 1992; Sharpley et al., 1994). Phosphorus is often perceived to be so immobile in soil that losses from agricultural land are not usually considered to be agronomically important, but even small agronomic losses can have serious environmental consequences. In fact, soils that contain high levels of P from excessive fertilization can become a primary source of dissolved reactive P (DRP) in runoff (Edwards et al., 1993). Other investigators have found direct correlations between soil P levels and P concentrations in runoff.

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.

Applications of aluminum sulfate (AIz(SO4)3 ¯ 14H20), commonly referred to as alum, to poultry litter have been shown to decrease P runoff from lands fertilized with litter and to inhibit NH3 volatilization. The objectives of this study were to evaluate the effects of alum applications in commercial broiler houses on: (i) NH3 volatilization (inhouse), (ii) poultry production, (iii) litter chemistry, (iv)runof f following litter application. Two farms were used for this study: one had six poultry houses and the other had four. The litter in half of the houses at each farm was treated with alum; the other houses were controls. Alum was applied at a rate of 1816 kg/house, which corresponded to 0.091 kg/bird. Each year the houses were cleaned in the spring and the litter was broadcast onto paired watersheds in tall fescue at each farm. Results from this study showed that alum applications lowered the litter pH, particularly during the first 3 to 4 wk of each growout. Reductions in litter pH resulted in less NHṽ olatilization, which led to reductions in atmospheric NH~ in the alumtreated houses. Broilers grown on alum-treated litter were significantly heavier than controls (1.73 kg vs. 1.66 kg). Soluble reactive phosphorus (SRP) concentrations in runoff from pastures fertilized with alumtreated litter averaged 73% lower than that from normal litter throughout a 3-yr period. These results indicate that alum-treatment of poultry litter is a very effective best management practice that reduces nonpoint source pollution while it increases agricultural productivity. p IOULTRY LITTER APPLICATIONS to pastures have been shown to result in relatively high P runoff, even when litter is applied at recommended rates (Edwards and Daniel, 1993). Most of the P in the runoff is in the soluble form (Edwards and Daniel, 1993), which is the form most available for algal uptake (Sonzogni et al., 1982). Concerns have arisen over this, since P is normally the limiting nutrient for eutrophication (Schindlet, 1977). Recent research has shown that alum additions to poultry litter can decrease P solubility in the litter by orders of magnitude (Moore and Miller, 1994). Shreve et al. (1995) found that P runoff from tall rescue (Festuca arundinacea Schreb.) plots fertilized with alum-treated litter was 87% lower than plots fertilized with normal litter. The rescue plots receiving alum-treated litter had significantly higher yields and higher N contents than normal litter, indicating that alum had increased N availability in the litter. We hypothesized that the increase in N availability was due to a decrease in NH3 volatilization. This was confirmed in laboratory studies conducted by Moore et al. (1995, 1996), which showed alum amendments to poultry litter could reduce NH3 volatilization losses by as much as 99%, compared with normal litter.

Aluminum sulfate [Al2(SO4)3·14H2O] applications to poultry litter can greatly reduce P concentrations in runoff from fields fertilized with poultry litter, as well as decrease NH3 volatilization. The objective of this study was to evaluate metal runoff from plots fertilized with varying rates of alum‐treated and untreated (normal) poultry litter. Alum‐treated (10% alum by weight) and untreated litter was broadcast applied to small plots in tall fescue (Festuca arundinacea Schreb.). Litter application rates were 0, 2.24, 4.49, 6.73, and 8.98 Mg ha−1 (0, 1, 2, 3, and 4 tons acre−1). Rainfall simulators were used to produce two runoff events, immediately after litter application and 7 d later. Both concentrations and loads of water‐soluble metals increased linearly with litter application rates, regardless of litter type. Alum treatment reduced concentrations of As, Cu, Fe, and Zn, relative to untreated litter, whereas it increased Ca and Mg. Copper concentrations in runoff water from untreated litter were extremely high (up to 1 mg Cu L−1), indicating a potential water quality problem. Soluble Al, K, and Na concentrations were not significantly affected by the type of litter. Reductions in trace metal runoff due to alum appeared to be related to the concentration of soluble organic C (SOC), as well as the affinity of SOC for trace metals. Metal runoff from alum‐treated litter is less likely to cause environmental problems than untreated litter, since threats to the aquatic environment by Ca and Mg are far less than those posed by As, Cu, and Zn.

Field applications of poultry litter at rates to meet forage N requirements normally result in an over‐application of P. Chemical amendments have the potential to reduce the solubility of manure P through precipitation and/or adsorption reactions. This study was conducted to determine the effects of two chemical amendments, alum (Al2 (SO4)3 · 14H2O) and ferrous sulfate (FeSO4 · 7H2O), on P concentrations and load in runoff and to evaluate the effects of amended litter on forage production. Litter was broadcast applied to fescue (Festuca arundinacea Schreb.) plots at 11.2 Mg ha−1 alone and in combination with alum or ferrous sulfate (1:5 amendment/litter). Rainfall simulators were used to produce three runoff events at 2, 9, and 16 d after litter application. Alum reduced the P concentrations in runoff by 87 and 63% of that from litter alone for the first and second runoff events, respectively, whereas ferrous sulfate decreased runoff P concentration by 77 and 48%, respectively. Both chemical amendments resulted in significant reductions (P < 0.05) in total P load for the first runoff event. Litter application significantly increased fescue yields, with total forage yield having the greatest response to alum‐amended litter. Mean forage yield with alum amended litter was 2358 kg ha−1, compared with a mean yield of 1847 kg ha−1 with litter alone. This was probably due to decreased NH3 volatilization with the alum treatment. The combination of decreased P loss and increased forage yields suggest that alum‐amended litter has substantial promise for use as an environmental and economic management tool in the poultry industry.

A 4 × 2 factorial experiment with three replications was conducted to determine how quality of runoff from grassed areas treated with poultry (Gallus gallus domesticus) litter is impacted by litter application rate and rainfall intensity for storms occurring 1 d after application. Poultry litter was applied at 0, 218, 435, and 870 kg N ha−1 to plots established with fescuegrass (Festuca arundinacea Schreb.) on a Captina silt loam soil (fine‐silty, mixed, mesic Typic Fragiudult). Simulated rainfall was applied 24 h after litter application at 5 and 10 cm h−1 until runoff had occurred for a duration of 0.5 h. Flow‐weighed composite samples were collected and analyzed for total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH3‐N), nitrate nitrogen (NO3‐N), total phosphorus (TP), dissolved reactive phosphorus (DP), chemical oxygen demand (COD), total suspended solids, and electrical conductivity. Increasing the litter application rate significantly increased runoff concentrations of all litter constituents investigated. Concentrations of TKN, TP, DP, and COD significantly decreased with increasing rainfall intensity because of more runoff and the associated dilution. Masses of litter constituents transported off the plots via runoff significantly increased with both litter application rate and rainfall intensity. For a given rainfall intensity, the proportions of applied litter constituents lost in runoff were generally indendent of application rate with the exception of total N at the high rainfall intensity.