Estimating source coefficients for phosphorus site indices.
Phosphorus release to runoff varies widely for different land-applied organic P sources even when spread at equivalent total P rates. To address this variability, some P site indices include tabulated P source coefficients (PSCs) for differential weighting of applied P materials based on their runoff enrichment potential. Because runoff P can vary widely even within source categories depending on composition, storage, and treatment differences, this study explored a method for estimating PSCs based on the water-extractable P (WEP) content of the applied amendment. Using seven published rainfall-runoff studies that followed National Phosphorus Research Project protocols, runoff dissolved P (RDP) was correlated (r(2) = 0.80) with WEP for multiple surface-applied manures and biosolids. Assuming amendments with WEP >/= 10 g kg(-1) behave as highly soluble P sources and have a maximum PSC of 1.0, an empirical equation was developed for computing source-specific PSCs from laboratory-determined WEP values [PSC = 0.102 x WEP(0.99)]. For two independent runoff experiments, correlations between RDP loss and P source loading rate were improved when loading rates were multiplied by the computed (r(2) = 0.73-0.86) versus generic (r(2) = 0.45-0.48) PSCs. Source-specific PSCs should enhance the ability of assessment tools to identify vulnerable sites and P loss management alternatives, although the exact inclusion process depends on index scaling and conceptual framework.
Elliott
H A
HA
Dep. Agricultural and Biological Engineering, The Pennsylvania State University, University Park, PA 16802, USA. hae1@psu.edu
Brandt
R C
RC
Kleinman
P J A
PJ
Sharpley
A N
AN
Beegle
D B
DB
D000043:Abstracting and Indexing; D000383:Agriculture; D000818:Animals; D002417:Cattle; D004784:Environmental Monitoring; D008372:Manure / Q000032:analysis*; D009930:Organic Chemicals / Q000032:analysis; D010758:Phosphorus / Q000032:analysis*; D011200:Poultry; D012989:Soil Pollutants / Q000032:analysis*; D012995:Solubility; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*
D008372:Manure; D009930:Organic Chemicals; D012989:Soil Pollutants; D014873:Water Pollutants; D010758:Phosphorus