Combining breeding traits and agronomic indicators to characterize the impact of cultivar on the nitrogen use efficiency of bread wheat

Abstract Nitrogen (N) is an essential compound for the production and grain quality of bread wheat, which must respect market requirements. Improving nitrogen use efficiency (NUE) is a priority to better manage nitrogen for the benefit of farm economy and the environment. Among all the available levers to do this, the choice of the right cultivar is crucial. To this end, an accurate NUE cultivar characterization is needed both for breeding programmes and for agronomic extension services dedicated to advise farmers. These two fields of expertise (genetic and agronomy) do not share exactly the same protocols and indicators to assess the impact of cultivar on wheat NUE. Moreover, although some recent NUE genetic studies have been conducted on cultivars currently available in France, no recent NUE agronomic studies have been made on current French wheat cultivars. Moreover, the latest agronomic studies to date on cultivar effect on wheat N requirement (coefficient “b” used in France) were conducted without considering the need to reach a grain protein concentration of 11.5% (French bread wheat market requirement) in addition to the objective of achieving the yield potential. By using a classical agronomic protocol (network of 12 field trials over 3 years testing bread-wheat cultivars along a complete nitrogen response curve), the presented study aimed to address three specific NUE related topics by characterizing recent French cultivars with a large range of NUE indicators used by geneticists and/or agronomists. Firstly, we demonstrated that N rate and recent French cultivars had a significant effect on NUE and its components (nitrogen uptake efficiency – NupE and nitrogen utilization efficiency – NutE), as well as on apparent fertilizer recovery (AFR). Secondly, we showed that NupE and AFR were strongly correlated, allowing us to compare genetic studies (mainly using NupE) and agronomic studies (mainly using AFR) without any difficulty. Thirdly, we designed a set of new N requirement indicators (coefficients “bc” and “bq”) helping the farmer to grow each bread wheat cultivar with a dual objective of optimum yield and grain protein content in line with the market requirements. This could be achieved without significant impact on nitrogen post-harvest losses. The presented study provides a large set of results, usable for breeding and agronomic research programs.