Land use and soil factors affecting accumulation of phosphorus species in temperate soils

Abstract

Data on the distribution of phosphorus (P) species in soils with differing land uses and properties are essential to understanding environmental P availability and how fertiliser inputs, cropping and grazing affect accumulation of soil inorganic P (Pᵢ) and organic P (Pₒ) forms. We examined thirty-two temperate soils (with soil organic C concentrations 12-449 g C kg⁻¹ and total P 295-3435 mg P kg⁻¹) for biogeochemical properties of soil C, reactive surfaces and P by common indices and ³¹P-NMR spectroscopy on NaOH-EDTA extracts for P species. Arable soil P was dominated by inorganic orthophosphate (276-2520 mg P kg⁻¹), >monoester P (105-446 mg P kg⁻¹). The limited diesters, polyphosphates and microbial P in arable soils suggest that cropping and fertiliser inputs limit ecosystem microbial functions and P diversity. Intensive grassland had inorganic orthophosphate concentrations (233-842 mg P kg⁻¹) similar to monoesters (200-658 mg P kg⁻¹)> diesters (0-50 mg P kg⁻¹) and polyphosphates (1-78 mg P kg⁻¹). As grazing became more extensive P in semi-natural systems was dominated by organic P, including monoesters (37-621 mg P kg⁻¹) and other diverse forms; principally diester (0-102 mg P kg⁻¹) and polyphosphates (0-108 mg P kg⁻¹). These were related to SOC, water extractable organic carbon (WEOC) and microbial P, suggesting strong microbially-mediated processes. A number of abiotic and biotic related processes appeared to control accumulation of different soil P species and gave considerable variability in forms and concentrations within land use groups. The implications are that to increase agricultural P efficiencies mechanisms to utilise both soil Pi and Po are needed and that specific management strategies may be required for site-specific circumstances of soil C and reactive properties such as Fe and Al complexes.