The art of splitting nitrogen applications to optimise wheat yield and protein content

The cereals trade association has set up a harvest payment system based on the protein content of ‘TOP’ class wheats. Agroscope has implemented tests to study the impact of splitting the application of nitrogen fertiliser on wheat yield and quality. In Swiss soil and weather conditions, a 20-40-80 kg N/ha split – the third input being made at the CD-37 stage (flag-leaf sprouting) – yielded excellent results, both in terms of grain yield and protein content. Producers keen to produce grains with a high protein content may be tempted to choose the varieties highest in protein, and to manage them very intensively, with a significant third input at flowering; however, this strategy carries a very high risk of non-assimilation of the nitrogen by the plant, and of loss of grain yield. From an economic perspective, the most productive varieties are also the most profitable, even if they belong to lower quality categories. The study also highlighted the fact that in situations of low nitrogen availability, a high-straw variety developing a large number of spikes per m² has the edge. By contrast, the size of the plant militates against grain formation in the more intensive systems.