Wheat Response to Foliar-Applied Phosphorus Is Determined by Soil Phosphorus Buffering

Abstract

In no-till cropping systems, banding of phosphorus (P) fertiliser at seeding results in low use efficiency due to chemical reactions in soil. Foliar P has the potential to allow grain producers to respond tactically with P application after sowing when P supply from soil and fertiliser is not meeting crop demand. The objective of this study was to evaluate the effectiveness of foliar P on wheat grain yield, grain quality, biomass yield, P uptake and P use efficiency indices. Nine field experiments were conducted to investigate the response of wheat to foliar P. Three rates of P, 0, 2.5 and 5.0 kg/ha, as phosphoric acid (H3PO4 85%) were applied to wheat at three different growth stages: first tiller emergence (Z21), first node detection (Z31) and flag leaf emergence (Z39). Grain yield responses ranging from 176 kg/ha to 505 kg/ha to foliar-applied P were observed in six out of nine experiments. The percent grain yield response to foliar P was negatively related to the P buffering index (PBI, 0–10 cm soil depth), which is attributed to greater sorption by soil of the foliar P at the higher PBI levels. Mean agronomic efficiency (AE) across the experiments was 111 kg/kg P but reached up to 232 kg/kg P. It was also evident that foliar P has the potential to improve P concentration in shoots and grains and increase P uptake but with no or minimal effect on grain quality. Our results suggest that a combination of tissue testing at the seedling stage and soil P buffering can be used to guide when foliar P application is likely to increase grain yield in wheat.