Nitrogen and Legumes: A Meta-analysis

Abstract

The current progress in agricultural production does not really cater to the demand of the burgeoning human population. Consequently, this puts global food and nutritional security at a great risk. This challenge calls for concerted efforts of all stakeholders to produce required quantity and quality of assured foods for ensuring food security. In the past, the principal driving force was to increase the yield potential of food crops and to maximize productivity. Today, the drive for productivity is increasingly combined with a desire for sustainability. For farming systems to remain productive and to be sustainable in the long term, it will be necessary to replenish the reserves of nutrients which are removed or lost from the soil. The nitrogen (N) inputs derived from atmospheric N via biological N fixation (BNF). Therefore, current farming systems need sustainable intensification through the inclusion of legume crops. This facilitates the precise use of nitrogen (N) by reducing their losses into the environment and ensures self-sufficiency in protein. The relevance of legumes in this context is enhanced as these crops offer numerous amenities that remain in line with prevalent sustainability principles. Legume crops provide protein-rich food, oil and fibre while supplying the 195 Tg N year−1 (also includes actinorhizal species) to the agroecosystem through the process of biological nitrogen fixation (BNF). Besides serving as the fundamental global source of good-quality food and feed, legume crops contribute to 15% of the N in an intercropped cereal and mitigate the emission of greenhouse gases (GHGs) by reducing the application demand of synthetic nitrogenous fertilizers. Legume cultivation releases up to seven times less GHGs per unit area than non-legume crops. Legumes allow the sequestration of carbon (1.42 Mg C ha−1 year−1) in soils and induce the conservation of fossil energy inputs in the system. The other benefits of legume crops include their significant positive impacts on biodiversity and soil health. Rotating legume crops with non-legume crops has the dual advantage of cultivating the legumes with slight or no extra N fertilizer. Care should be taken to ensure the availability of adequate N for the succeeding non-legume crops. The legume crops respond very well to conservation of agricultural practices. Overall, these characteristics are crucial to agriculture both in developing and developed countries apart from the conventional farming systems. Legumes in rotation promote exploration of nutrients by crops from different soil layers. They also help in reducing pressure on soil created by monocropping. Thus, crop rotation acts like a biological pump to recycle the nutrients. Hence, inclusion of legumes in the cropping system is inevitable to advance soil sustainability and food and nutritional security without compromising on the long-term soil fertility potential.