Influence of co-application of nitrogen with phosphorus, potassium and sulphur on the apparent efficiency of nitrogen fertiliser use, grain yield and protein content of wheat: Review

The efficient capture and utilisation of fertiliser nitrogen (N) by cereals has implications for crop growth, grain yield, farm profits, the environment and human nutrition. Extensive research has evaluated many innovative ways to improve the efficiency of fertiliser N recovery (N use efficiency; NUE) by wheat (Triticum aestivum). This review paper, prepared as an outcome of a workshop by the Nutrient Use Efficiency in Wheat Expert Working Group of the Wheat Initiative held in Harpenden, UK in May 2017, is specifically focused on the effects of the co-application of fertiliser N with fertiliser phosphorus (P), potassium (K) and/or sulphur (S) on the efficiencies of capture and utilisation of fertiliser N and its accumulation in wheat grain, as this specific aspect of wheat nutrition was identified by the meeting as a major gap in knowledge. The contribution of P, K and S individually to grain yield has been reasonably well studied, and it is generally assumed that interactions between N and P, K and S will improve crop performance. However, a total of 32 field studies only have been published since 1963 that examine the effects of multiple nutrients on wheat yield and NUE, or changes in the apparent recovery of fertiliser N (% applied) in grain and its impact on grain protein content. The published data showed that NxP, NxK and NxS interactions led to improvements in NUE and the apparent grain recovery of fertiliser N, with the strongest effects generally coming from co-applications of N + P, followed by N + K then N + S treatments. Only five studies explored the combined or interactive effects of NxPxK, and just one considered either NxPxS or NxPxKxS. Grain yields were usually improved by applications of three (N + P + K) or four (N + P + K + S) nutrients in combination, but it was difficult to draw conclusions about effects on fertiliser N recovery and NUE because of the small number of studies, the variability in responses, and the lack of a N fertiliser alone comparative treatment. Grain protein content did not appear to be strongly increased by nutrient interactions, but it did not decrease with higher yields under N, P, K, S fertilisation suggesting that balanced nutrition may provide some protection against protein dilution as yields increase. The available literature suggested that ensuring balanced availability of P, K and S has the potential to reduce the rates of fertiliser N required by wheat because N appears to be accumulated in grain with greater efficiency. This would have both positive agronomic and environmental benefits.