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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.

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In the Ozark Highlands of the USA (36–38° N, 91–95° W), annual application of poultry litter to pasture land is a routine waste management practice. The objective of this study was to measure the effect of site characteristics and poultry litter application on runoff and nutrient transport from grazed pasture and forest sites at different landscape positions. Sixteen pairs of 1 × 2 m plots were established on Nixa (loamy‐skeletal, siliceous, active, mesic Glossic Fragiudults) and Clarksville (loamy‐skeletal, siliceous, semiactive, mesic Typic Paleudults) cherty silt loams. One plot of each pair received 4.5 Mg ha−1 of poultry litter. Rainfall was simulated at 75 mm h−1 for 1 h (25‐yr return period storm) one month after litter application. A composite runoff sample was analyzed for dissolved reactive phosphorus (DRP), total phosphorus (TP), ammonia N (NH3‐N), nitrate N (NO3‐N), total Kjeldahl nitrogen (TKN), and total suspended solids (TSS). Poultry litter‐treated plots had consistently higher concentrations of all water quality parameters tested compared to untreated plots. Concentration of DRP in runoff from untreated plots was linearly correlated with three soil P tests (0.35 < r2 < 0.85). Soil P on litter‐treated plots had little effect on runoff DRP, which averaged 2.20 mg L−1. High variation in runoff resulted in only NO3‐N showing significantly greater losses due to poultry litter treatment at two pasture sites. Results indicate that variation in runoff has a significant effect on nutrient transport from grazed pastures receiving poultry litter.

In complex landscapes with multiple land uses, it is often difficult to identify the source of contaminant loadings. The objective of this study was to compare nutrient runoff as affected by grazing animal depositions vs. poultry litter application. Simulated rainfall was applied twice to 1.5 by 6.0 m runoff plots of tall fescue (Festuca arundinacea Schreb.) with treatments of no waste (CT), dairy calf feces and urine (DFU), poultry litter (PL), and dairy calf feces and urine with poultry litter (DFU + PL). Chemical properties of the runoff samples including pH, electrical conductivity (EC), C, soluble reactive phosphorus (SRP), total nitrogen (TN), NH4‐N, NO3‐N, K, Mg, S, B, Cu, Fe, Mn, Mo, Na, and Zn were determined. Plots receiving poultry litter had significantly greater losses of most nutrient parameters for both rainfall simulations. For the nutrient parameters of primary interest with regard to water quality, 5.0, 29.5, and 21.9% of the TN, NH4‐N, and SRP applied in the PL treatment were transported in runoff during the first rainfall simulation as compared to 3.9, 5.0, and 15.3%, respectively, for the DFU treatment. Comparable percentages of the applied nutrients were lost from the PL and DFU treatments even though the PL treatment, with the exception of NH4‐N, provided at least six times the amount of each nutrient. A severe rainfall event shortly after poultry litter application produces significantly greater nutrient losses as compared to similar application of grazing animal depositions at the rates used in the experiment.

Controlling phosphorus levels in runoff is often recommended as the best way to minimize eutrophication of streams and lakes. Previous research has shown that increased concentrations of dissolved reactive P (DRP) in runoff from grassland are highly correlated to increased soil test P (STP) levels. We conducted an experiment to investigate the hypothesis that seasonal changes in field conditions (especially soil moisture) along with the practice of air‐drying soil samples prior to analysis may affect such correlations. Grass plots with a wide range of STP were randomly divided into two groups. In May (wet season), soil samples were taken from each plot in the first group, simulated rain was applied (75 mm h−1) to produce 30 min of runoff, and filtered runoff samples were analyzed for DRP. Each soil sample was analyzed for H2O content, sieved (2 mm), and split into two subsamples. One subsample from each plot was kept field‐moist at 4°C, and the other was air dried. Phosphorus saturation was determined only on air‐dry soil, but all soil subsamples were analyzed by Mehlich III and distilled H2O methods. In August (dry season), the second group of plots received the same treatment. All correlations of STP to runoff DRP were significant (P < 0.01), regardless of season or STP method. Water‐extractable STP from air‐dry soil and Mehlich III STP were not affected by season, but DRP concentration in August runoff was almost double that in May , so the resulting correlations were affected. Water‐extractable STP from field‐moist soil was higher in August than in May , and P saturation levels showed a similar trend. Runoff volumes were smaller in August, so season had little effect on mean DRP–mass loss.

Vegetative filter strips (VFS) have been shown to have high potential for reducing nonpoint source pollution from cultivated agricultural source areas, but information from uncultivated source areas amended with poultry litter is limited. Simulated rainfall was used in analyzing