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NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Integrating Phosphorus Source and Soil Properties into Risk Assessments for Phosphorus Loss

^a Dep. of Soil and Water Science, Univ. of Florida, Gulf Coast Research and Education Center, Wimauma, FL 33598
^b Dep. of Plant and Soil Sciences Univ. of Delaware Newark, DE 19716

^* Corresponding author (alshober{at}ufl.edu).

Differences in P solubility of biosolids and manures, as a result of chemical treatment or other factors, have prompted states to incorporate weighting factors, sometimes called phosphorus source coefficients (PSCs), into P risk assessment tools. The value of PSCs in risk assessment has been demonstrated when organic P sources are surface-applied, but not when P sources are incorporated into soils. Ten organic P sources were incorporated into eight Mid-Atlantic soils (0–5 cm) at 135 kg total P ha^–1 and incubated for 2, 30, and 180 d. Samples were analyzed for Mehlich 3 phosphorus (M3-P), M3-P saturation ratio (M3-PSR), and water-soluble phosphorus (WSP). Average increases in M3-P (26 mg kg^–1) and M3-PSR (0.03) for all soils were similar for untreated manures and inorganic P compared to alum-treated poultry litter (APL) and biosolids (24 mg kg^–1, 0.03). In contrast, average concentrations of soil WSP (2 d) were highest following incorporation of untreated manures and inorganic P (5.2–8.0 mg kg^–1), followed by biosolids or APL (2.9–3.4 mg kg^–1) and unamended soils (2.7 mg kg^–1) with similar trends at 30 and 180 d. Source effects were most pronounced for soils with higher M3-PSR. Regression equations using soil M3-PSR and default PSCs could predict soil WSP at 2, 30, and 180 d (r² = 0.67, 0.69, 0.60, all significant at P = 0.001). Based on our results, we developed a new weighting factor (using M3-PSR and default PSCs) for risk assessment tools that will better predict the potential for P loss when biosolids or manures are incorporated into Mid-Atlantic soils.

Abbreviations: BPR, biological phosphorus removal • DPS, degree of phosphorus saturation • DRP, dissolved reactive phosphorus • ICP-AES, inductively coupled plasma atomic emission spectroscopy • M3-P, Mehlich-3 phosphorus • M3-PSR, Mehlich-3 phosphorus saturation ratio • PSI, phosphorus site index • PSC, phosphorus source coefficient • TP, total phosphorus • WSP, water-soluble phosphorus