Geospatial modelling of soil phosphorus fractions and sorption indicators from heterogeneous landscapes in Ireland

Abstract

Soil mapping of phosphorus (P) pools at regional scale can be used to inform policy and land management strategies in agri-environmental systems. However, linking an element that is predominantly managed by fertiliser and organic inputs to regional scale geochemistry can be problematic. This study used a geological survey of the northern half of Ireland at ≤4 km2 resolution to map total P (ICP aqua regia), plant available P (Morgan’ P) and Labile P pools (ICP aqua regia and Mehlich-3 P). Spatial modelling was used to map P interactions with total and available aluminium (Al) (ICP aqua regia and Mehlich-3 Al), as predefined sorption indicators. With the aim to develop agri-environmental mapping approaches to link soil P sorption dynamics to geological controls that can assist with regional, catchment and national-scale modelling for policy development.Plant available P concentration showed no spatial continuity in Kriged variogram output and was regulated by fertiliser inputs which mask any underlying geological processes. Subsequently, making this exploration method redundant in highly managed landscapes. Available Al concentrations determined by Mehlich-3 Al (M3-Al) are however regulated by underlying geology. Moreover, they have a significant negative correlation with bioavailable P indices. Areas of high M3 Al concentrations (≥ 702.5 mg kg−1) are dominant in the study area and show mainly low plant available P values (<5 mg l−1), however, potential labile P pools were indicated. Whereas areas of low Al concentrations (≤ 697 mg kg−1) show moderate to high plant available P concentrations. Which could identify areas where P is likely to be more soluble and at greater risk to loss to water. Therefore, using available Al as a sorption indicator can identify regional areas of high P fixation and low soil P retention in soils. Furthermore, using sorption dynamics in geospatial modelling could benefit targeted management approaches.