Splitting Nitrogen Fertilization Is More Important than Nitrogen Level When Mixed Wheat Varieties Are Cultivated in a Conservation Agriculture System

Nitrogen (N) is one of the most limiting nutrients for cereal production, especially in wheat, which is one of the main crops cultivated globally. To achieve high yields, wheat requires a certain amount of nitrogen (N), as N deficiency can lead to a decrease in yield and thus reduce income for farmers. In contrast, excessive applications of N fertilizer can be detrimental to both terrestrial and aquatic environments. To optimize N fertilizer applications in wheat, a three-year field experiment was conducted to evaluate the impact of different N fertilization strategies on various N-related physiological and agronomic traits. Moreover, to optimize N utilization efficiency while maintaining crop productivity, a mixture of five winter wheat varieties was used to mitigate the possible impact of environmental constraints. These strategies were based on a simultaneous increase in N fertilization and N fertilizer fractionation at key stages of plant development in a soil conservation agriculture (SCA) system in which legumes were grown prior to the cultivation of the main crop. In this SCA system, we observed that 200 kgN·ha−1 was optimal for both N use efficiency (NUE) and aerial and grain biomass production. Moreover, we found that at this level of N fertilization, of the application strategies, a 40%/40%/20% split application at full tillering, at the first node, and at booting, respectively, appeared to be the best option for the highest plant productivity.