Wheat grain yield response to and translocation of foliar-applied phosphorus

It is important to apply phosphorus (P) to the soil at the beginning of the crop growth cycle to provide essential P for early growth and to replace P exported in previous crops. With low rates of P added at sowing there may be sufficient P supply to grow crops to tillering, but in seasons of increased yield potential a top-up application of P may be required. Foliar P can be applied directly to the plant when required and in some cases have been shown to provide benefits for increasing P-use efficiency and the P concentration in grain. Wheat (Triticuum aestivum cv. Frame) was grown in two soils of marginal P status with soil moisture maintained at 80% of field capacity. Seven foliar P treatments labelled with P-33 as a tracer were applied at Zadoks growth stage 39, at 1.65 kg P/ha with 120 L water/ha equivalent. Grain, chaff and shoots were harvested to measure yield and then digested to measure P concentrations and P-33 activities. There was no crop response to top-up soil or foliar P on one soil, but on the other soil, foliar phosphoric acid plus adjuvant gave a 25% wheat grain yield response. The use of the tracing technique enabled measurement of the portioning of foliar P fertiliser between stem, chaff and grain. The most responsive treatment had the greatest amount of grain P uptake and the greatest partitioning of the foliar P fertiliser to grain.