Traditional, Modern, and Molecular Strategies for Improving the Efficiency of Nitrogen Use in Crops for Sustainable Agriculture: a Fresh Look at an Old Issue

Reactive nitrogen (N) plays a pivotal role in supplying N to plants and soil microbes, but it has negative environmental impacts through influencing the quality of water and air, which in turn influences human health. Thus, there is an urgent necessity to maximize N benefits while reducing the negative impacts on the environment. Improving crop N use efficiency (NUE) is required for environmental conservation and agricultural sustainability. Thus, the pivotal objective of this article is to introduce the modern developments and imminent prospects of improving crops NUE using various complementary methods. Here, the approaches of site-specific N management, use of synthetic and biological nitrification inhibitors, microbial nitrate (NO3-) immobilization stimulation, and stimulation of the dissimilatory nitrate reduction to ammonium (DNRA), adopting agroforestry system, breeding techniques, quantitative trait loci (QTL) mapping, omics approaches, and potential new targets and overexpression of N-related genes were presented as effective approaches to improving NUE. Optimal rate, time, application methods, using specially formulated forms of fertilizer, and using nitrification inhibitors are the most agricultural practices linked with improving NUE. The fertilizer recommendations could be often justified across the field rather than a uniform application using spatial variability of nutrient content. Restoring soil NO3- retention capacity and adopting agroforestry system can also be promising ways to improve NUE. Furthermore, the use of genetic modification or the development of new cultivars that use N more efficiently is critical. In addition, omics data, including transcriptomics and metabolomics, not only advance our current understanding of N reactions but also help us move towards strategies, which are more effective in improving NUE and enhancing crop production. In conclusion, this article strongly advocates the use of integrated approaches with a private insight of genetics and agricultural management when managing N.