Approximating Phosphorus Release from Soils to Surface Runoff and Subsurface Drainage

Abstract

Phosphorus application in excess of crop needs has increased the concentration of P in surface soil and runoff and led many states to develop P‐based nutrient management strategies. However, insufficient data are available relating P in surface soil, surface runoff, and subsurface drainage to develop sound guidelines. Thus, we investigated P release from the surface (0–5 cm depth) of a Denbigh silt loam from Devon, U.K. (30–160 mg kg⁻¹ Olsen P) and Alvin, Berks, Calvin, and Watson soils from Pennsylvania (10–763 mg kg⁻¹ Mehlich‐3 P) in relation to the concentration of P in surface runoff and subsurface drainage. A change point, where the slopes of two linear relationships between water‐ or CaCl₂–extractable soil P and soil test phosphorus (STP) (Olsen or Mehlich‐3) meet, was evident for the Denbigh at 33 to 36 mg kg⁻¹ Olsen P, and the Alvin and Berks soils at 185 to 190 mg Mehlich‐3 P kg⁻¹ Similar change points were also observed when STP was related to the P concentration of surface runoff (185 mg kg⁻¹) and subsurface drainage (193 mg kg⁻¹). The use of water and CaCl₂ extraction of surface soil is suggested to estimate surface runoff P (r² of 0.92 for UK and 0.86 for PA soils) and subsurface drainage P (r² of 0.82 for UK and 0.88 for PA soils), and to determine a change point in STP, which may be used in support of agricultural and environmental P management.