Potential phosphorus losses from organic and podzol soils: prediction and the influence of soil physico-chemical properties and management

Abstract

© 2015 © 2015 The Royal Society of New Zealand. Organic and podzol soils may have properties that exacerbate phosphorus (P) loss to surface water following development for pastoral agriculture, including high porosity and hydraulic conductivity, and poor P retention. Soil samples (from depths of 0-7.5cm and 30-37.5cm) were taken (80 sites) within a catchment to quantify the impacts of land use development on the potential for P loss. Water-extractable P (WEP) and dilute CaCl2-extractable P (CaCl2-P), representing surrogates for surface and subsurface runoff potential, were two and 66 times greater for organic soils compared with podzols, respectively. Variables such as Olsen P and P retention could predict WEP (R2 = 0.52-0.75), but not CaCl2-P. A mass balance estimated that mean P losses with time since development for organic soils (c. 38 kg P ha-1 yr-1) were nearly double those of podzol soils. With such high losses, we recommend using these tests to help identify organic and podzol soils that pose a risk to surface water quality.