The ability to utilise foliar-applied phosphorus (P) as a strategy to increase the P status and yield of grain crops grown in dryland regions with variable climates is attractive. Several P formulations with varying pH, accompanying cations and adjuvants were tested for their effectiveness as foliar fertilisers for wheat (Triticum aestivum L.) plants, first under controlled and then under field conditions. Experiments under controlled conditions suggested that several formulations with specific chemistries offered promise with respect to wheat fertiliser-P recovery and biomass responses. These formulations were then evaluated in two field experiments, and although wheat grown at the sites showed substantive responses to soil-applied P, there was no significant grain-yield response to foliar-applied P. Following the limited responses to foliar-applied fertiliser in the field, we used an isotopic dilution technique to test the hypothesis that the variation in responses of wheat to foliar addition of P could be explained by a mechanism of substitution, whereby root P uptake is downregulated when P is taken up through the leaves, but this was proven not to be the case. We conclude that foliar P application cannot be used as a tactical fertiliser application to boost grain yield of wheat in dryland regions.

Urease inhibitors are used to delay the conversion of N supplied to soil as urea to better match the mineral N supply to crop demand. Using soil in petri dishes, we compared the spatial and temporal mineral N dynamics close to the site of urea addition for two soils of contrasting texture – a sandy soil (2% clay) and a clay soil (51% clay) – treated with N fertilizer products that had the potential to inhibit urease. The treatments included trace metal oxide coatings (ZnO; NiO; CuO) of granular urea fertilizer, N‐(n‐butyl) thiophosphoric triamide (NBPT; a commercial urease inhibitor) coated urea and uncoated urea. In the sandy soil, NBPT inhibited urea hydrolysis, whereas the metal oxide coated urea had little effect. Unlike in the sandy soil, the most striking result for the clay soil was the ‘disappearance’ of mineral N in the latter part of the incubation. However, a delay in the disappearance of mineral N, hence a higher recovery, for the NBPT‐Urea and CuO‐Urea was observed at day 14 in the clay soil presumably due to the slower hydrolysis of urea compared to other treatments. Overall, the study of both spatial and temporal mineral N dynamics in soils supplied with urea fertilizers suggests that CuO‐coated urea could have properties that delay the hydrolysis of urea in certain soils. Given the strongly contrasting outcomes for the two soils, further experiments with soils that span the range of texture between these two extremes are warranted.This article is protected by copyright. All rights reserved