title: Evaluation of phosphorus source coefficients as predictors of runoff phosphorus concentrations.
abstract: Many states have adopted a P site index (PSI) as a risk assessment tool to determine when P-based nutrient management is required for a given agricultural field. Some PSIs use a weighting factor, the phosphorus source coefficient (PSC), to account for differences in P solubility between organic P sources. Information relating to appropriate values of PSC for various organic P sources is limited. The objectives of this study were to determine PSCs for organic P sources and to examine the relationship between PSCs and P concentrations measured in simulated rainfall runoff. An incubation study was used to calculate PSCs based on the extractability of P from organic P sources (separated and unseparated liquid dairy manure, digested dairy manure, dairy manure solids, poultry litter, and compost) relative to P from triple superphosphate fertilizer. The PSCs from the 14-d incubations were the best predictors of runoff P after 14 d soil equilibration in the runoff boxes. The values for iron-oxide strip phosphorus (FeO-P) PSC ranged from 78% for compost to 28% for poultry litter and were significantly related to runoff DR-P (r(2) = 0.80***) and FeO-P (r(2) = 0.76***) during the 14-d runoff event. Mehlich 3 PSCs ranged from 59% for compost to 30% for unseparated dairy manure and were better predictors of DR-P and FeO-P during the 56-d event (r(2) = 0.73*** and 0.65***, respectively). The results of this study indicate that PSCs based on soil incubations may improve the ability of PSCs to predict the risk of runoff transport, particularly after manure incorporation.
authors.affiliation: USDA-ARS, Environ. Management and Byproducts Utilization Lab., Beltsville, MD 20705-2325, USA. Matt.Smith@ars.usda.gov
authors.forename: Matt C
authors.initials: MC
authors.lastname: Smith
authors.forename: John W
authors.initials: JW
authors.lastname: White
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Coale
mesh_terms: D000818:Animals; D002417:Cattle; D008372:Manure / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D011200:Poultry; D011891:Rain; D012016:Reference Values; D012987:Soil / Q000032:analysis*; D018505:Waste Management / Q000592:standards; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008372:Manure; D012987:Soil; D014874:Water Pollutants, Chemical; D010758:Phosphorus