Evaluation of phosphorus source coefficients as predictors of runoff phosphorus concentrations.
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.
Smith
Matt C
MC
USDA-ARS, Environ. Management and Byproducts Utilization Lab., Beltsville, MD 20705-2325, USA. Matt.Smith@ars.usda.gov
White
John W
JW
Coale
Frank J
FJ
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*
D008372:Manure; D012987:Soil; D014874:Water Pollutants, Chemical; D010758:Phosphorus