Phosphate stable oxygen isotope variability within a temperate agricultural soil

In this study, we conduct a spatial analysis of soil total phosphorus (TP), acid extractable phosphate (PO4) and the stable oxygen (O) isotope ratio within the PO4 molecule (delta O-18(PO4)) from an intensively managed agricultural grassland site. Total P in the soil was found to range from 736 to 1952 mg P kg(-1), of which between 12 and 48% was extractable using a 1 M HCl (HClPO4) solution with the two variables exhibiting a strong positive correlation. The delta O-18(PO4) of the extracted PO4 ranged from 17.0 to 21.6 parts per thousand with a mean of 18.8 parts per thousand (+/- 0.8). While the spatial variability of Total P has been researched at various scales, this is the first study to assess the variability of soil delta O-18(PO4) at a field-scale resolution. We investigate whether or not delta O-18(PO4), variability has any significant relationship with: (i) itself with respect to spatial autocorrelation effects; and (ii) HCIPO4, elevation and slope - both globally and locally. Results indicate that delta O-18(PO4) was not spatially autocorrelated; and that delta O-18(PO4) was only weakly related to HClPO4, elevation and slope, when considering the study field as a whole. Interestingly, the latter relationships appear to vary in strength locally. In particular, the delta O-18(PO4) to HClPO4 relationship may depend on the underlying soil class and/or on different field managements that had operated across an historical north-south field division of the study field, a division that had been removed four years prior to this study. (C) 2016 The Authors. Published by Elsevier B.V.