Estimating phosphorus loss from New Zealand grassland soils

Abstract

The potential for phosphorus (P) loss from New Zealand grassland soils was assessed using a combination of measured soil chemical properties and concentrations of dissolved reactive P (DRP) determined in drainage and overland flow from simulated rainfall experiments. Soil analyses included Olsen P, calcium chloride (0.01M CaCl2) and water extractable DRP, P sorption index (PSI), and % P retention. Results confirmed that DRP concentrations in drainage and overland flow were closely related to CaCl2‐ and water‐extractable DRP in soil, respectively. The preliminary data indicated that the potential concentration of DRP in subsurface and overland flow from pasture soils that have not been recently grazed and at a small scale (e.g., overland flow from 1‐m lengths) could be estimated from Olsen P and PSI (or P retention) data according to the following equations: DRP (subsurface flow) = 1.480 (Olsen P/PSI) = 0.069 (Olsen P/P retention) + 0.007 DRP (overland flow) = 0.495 (Olsen P/PSI) = 0.024 (Olsen P/P retention) + 0.024.