DEVELOPMENT OF A PHOSPHORUS INDEX FOR PASTURES

摘要

Non-point phosphorus (P) runoff from pastures fertilized with animal manures plays an important role in eutrophication of nearby water bodies. Edwards and Daniel (1993) have shown that poultry litter applications to pastures result in relatively high P runoff at recommended rates with as much as 90% of the P runoffbeing in the soluble form. Because P is normally the limiting nutrient for eutrophication, concerns have arisen over animal waste applications. Several researchers have studied the relationship between soil test P and soluble reactive P (SRP) concentrations in runoff. These studies have shown that SRP concentrations in runoff water increase as soil test P increases (Pote et al, 1996; Sharpley et al., 1994; Sharpley, 1995). Currently several states are attempting to determine threshold soil test P levels above which animal manures may not be applied due to increased risk of P runoff. An alternative approach to managing P applications to lands is using the Phosphorus Index (PI). The PI is a risk assessment tool that combines the effects of both P sources and P transport mechanisms in determining the risk of P runoff. However, weighting factors used in the original PI were based on professional opinion rather than actual data. The objectives of this study were to determine the effects of soil test P, poultry litter application rates, P reductions in diets, soluble P in litter, fertilizer type, and weather on P runoff. Results from this research were then used to develop weighting factors for a PI for pastures.