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Journal of Environmental Quality Abstract - Waste Management

Evaluation of Phosphorus Source Coefficients as Predictors of Runoff Phosphorus Concentrations


This article in JEQ

  1. Vol. 38 No. 2, p. 587-597
    Received: Dec 27, 2007

    * Corresponding author(s): Matt.Smith@ars.usda.gov
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  1. Matt C. Smith *a,
  2. John W. Whitea and
  3. Frank J. Coaleb
  1. a USDA-ARS, Environ. Management and Byproducts Utilization Lab., Beltsville, MD 20705-2325
    b Dep. Environ. Sci. and Technol., Univ. of Maryland, College Park, MD 20742-5821


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 (r2 = 0.80***) and FeO-P (r2 = 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 (r2 = 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.

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