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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.

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.

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