title: Development of a phosphorus index for pastures fertilized with poultry litter--factors affecting phosphorus runoff.
abstract: Currently, several state and federal agencies are proposing upper limits on soil test phosphorus (P), above which animal manures cannot be applied, based on the assumption that high P concentrations in runoff are due to high soil test P. Recent studies show that other factors are more indicative of P concentrations in runoff from areas where manure is being applied. The original P index was developed as an alternative P management tool incorporating factors affecting both the source and transport of P. The objective of this research was to evaluate the effects of multiple variables on P concentrations in runoff water and to construct a P source component of a P index for pastures that incorporates these effects. The evaluated variables were: (i) soil test P, (ii) soluble P in poultry litter, (iii) P in poultry diets, (iv) fertilizer type, and (v) poultry litter application rate. Field studies with simulated rainfall showed that P runoff was affected by the amount of soluble P applied in the fertilizer source. Before manure applications, soil test P was directly related to soluble P concentrations in runoff water. However, soil test P had little effect on P runoff after animal manure was applied. Unlike most other P indices, weighting factors of the P source components in the P index for pastures are based on results from runoff studies conducted under various management scenarios. As a result, weighting factors for the P source potential variables are well justified. A modification of the P index using scientific data should strengthen the ability of the P index concept to evaluate locations and management alternatives for P losses.
authors.affiliation: Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AR 72701, USA. pdelaun@uark.edu
authors.forename: Paul B
authors.initials: PB
authors.lastname: DeLaune
authors.forename: Philip A
authors.initials: PA
authors.lastname: Moore
authors.forename: Dennis K
authors.initials: DK
authors.lastname: Carman
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Sharpley
authors.forename: Brian E
authors.initials: BE
authors.lastname: Haggard
authors.forename: Tommy C
authors.initials: TC
authors.lastname: Daniel
mesh_terms: D000818:Animals; D005308:Fertilizers; D008372:Manure; D010758:Phosphorus / Q000032:analysis*; D011200:Poultry; D011891:Rain; D012016:Reference Values; D012989:Soil Pollutants / Q000032:analysis*; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D005308:Fertilizers; D008372:Manure; D012989:Soil Pollutants; D014873:Water Pollutants; D010758:Phosphorus