Delayed and reduced nitrogen fertilization strategies decrease nitrogen losses while still achieving high yields and high grain quality in malting barley

International audience

English. Nitrogen fertilizer applications are essential to achieve high yield and malting specifications in barley, but may also have a deleterious effect on the environment. Most strategies currently being implemented aim to optimize quantitative and qualitative production without taking environmental concerns into account. We used a barley crop model to pinpoint new nitrogen management plans maximizing the calibrated yields (yield of grains larger than 2.5 mm) and the grain quality whilst reducing N gaseous emission and N leaching. We compared the currently recommended N fertilization strategy in France and 44 new ones defined based on expertise knowledge, and differing in the amount of N applied, splitting patterns and time of application. The strategies providing the best compromise between the three criteria were identified by considering Pareto optimal solutions over 25 years in 35 French departements (equivalent to a county). We also identified Pareto optimal strategies for the seven years with the lowest yields and for years in which climatic conditions were unfavorable for efficient use of the early N supplies. The current recommended N fertilization strategy resulted in a high proportion of situations satisfying malting grain protein content requirements, but also to high N losses. We pinpointed new N strategies resulting in better compromise between the three outputs studied. Some Pareto optimal strategies were particularly efficient to reduce N losses in all tested environments regardless of the climatic conditions. They, however, also slightly reduced calibrated yield compared to the reference strategy. Others interesting strategies performed better than the reference simultaneously for all three studied outputs, but depended on the region considered. A common feature of these strategies was later application of smaller doses of N. Our results, thus demonstrated that low-N strategies are possible for malting barley.