Enhanced Plant Rooting and Crop System Management for Improved N Use Efficiency

Despite the significant inroads into increasing agricultural productivity in recent decades, nitrogen remains a key limiting factor for crop growth and yield. Though highly variable globally, the amount of reactive N added yearly onto cropland that is subsequently lost to the environment remains high. As such the interest in agronomic approaches to address this and improve nitrogen use efficiency (NUE) is currently very high. Here, we have shown the combined approaches of management interventions such as no-till, intercropping with leguminous and grass species, use of nitrogen inhibitors, and combined crop–livestock systems offer considerable potential for enhancing NUE and are already being readily deployed in the tropics. Grass species such as Brachiaria in particular have demonstrated enormous potential via their deep root architectures to reduce losses by leaching. However, the potential for increases in NUE through interaction and association of the root systems with the soil microbial community via rhizodeposits remains a major area for future research. Increasingly it is recognized that truly enhancing NUE requires consideration of the whole system. Improving NUE is not simply a matter of how much fertilizer is used but also the need for a deeper understanding of the interactions between nutrients, plants, microbes, and soils under specific agronomic situations such as the integrated maize/grass–livestock systems that are now regularly employed in the tropics. This more holistic approach to the management of nitrogen offers considerable benefits that can hopefully be realized not only from an agricultural perspective but also from an environmental and socioeconomic view point.