Biochar increases availability and uptake of phosphorus to wheat under leaching conditions

Phosphorus (P) fertilisers have long been applied to sandy soils in south-western Australia to enhance agricultural production. However, significant P leaching is experienced which decreases P availability to crops. The aim of this study was to determine if biochar could be used as a soil amendment to decrease P leaching and increase P uptake by wheat plants. A lysimeter study was designed where two types of biochar, derived either from chicken manure (CM) or wheat chaff (WC) at 0, 1 and 2 % (w/w) and three P fertiliser rates at 0, 25 and 50 kg/ha, were applied to a loamy sand soil where wheat (Triticum aestivum L. var. Wyalkatchem) was grown under glasshouse conditions. Leaching events were conducted over a period of 8 weeks at two weekly intervals. Leachate volume was less in the biochar-amended soil compared to non-amended soil. Biochar increased plant shoot P uptake but also P leaching, which was attributed to P derived from both the applied fertiliser and the biochar. Biochar also increased available P and microbial biomass P in soil, although the extent of increase with WC biochar was less pronounced than for that with CM biochar. Biochar application increased mycorrhizal colonisation in wheat roots which was higher (up to 70 %) at the P application rate of 25 kg/ha but declined with P application rate of 50 kg/ha (to 35 %). Increase in soil pH and mycorrhizal colonisation from biochar application might be contributing to the increase in plant P uptake and shoot growth. However, biochar was not a mitigation strategy to decrease P leaching on these sandy soils.