Legume Green Manuring: An Option for Soil Sustainability

Abstract

Overuse of nitrogen (N) fertilizer to enhance agricultural production is threatening the environment. The concentrations of reactive forms (e.g., NOx, N2O, NO3−, NH3) of N have increased to around 120% in the atmosphere as a result of different industrial units and use of chemical fertilizers in agriculture. The scenario compels to rethink about the role of biological nitrogen fixation (BNF). Green manuring with inclusion of legumes appears to be the most feasible option. Intensive agriculture with repeated tillage, use of high-analysis fertilizers, burning of agricultural residue, and non-incorporation of biodegradable solid waste from domestic and industrial sectors into soil mass have resulted in the decline of soil organic carbon (SOC). This in turn impaired soil health, decreased soil biodiversity, and aggravated the demand for essential plant nutrients, leading to the agricultural land becoming less productive and sometimes unfit for economic cultivation. The uncontrolled use and improper management of synthetic fertilizers, especially, the nitrogenous fertilizers, emit nitrate (NO3−) causing water pollution and nitrous oxide (N2O), speeding up climate change process and oxides of N (NOx) causing air pollution. The OC and soil nitrogen have a positive correlation. It suggests that soil nitrogen level can be improved with improving levels of soil organic matter (SOM). It will also help in reducing environmental damage due to overuse of nitrogen fertilizers. Green manuring with legumes has added advantage as legumes fix atmospheric nitrogen and are easily decomposable. Legume green manuring (LGM) improves SOC, nutrient availability, physicochemical and biological properties of soil, and crop productivity. Several legumes which were used for green manuring showed high N accumulation rate, i.e., 80–100 kg ha−l in duration of 45–60 days of crop growth. Legume crop cultivation, say seed legumes in symbiotic association with Rhizobium, contributes around 10 Tg N year−1, while forage legumes (cover crops) contribute 12 Tg N year−1. Application of LGM is an important option to optimize the BNF and to ensure soil sustainability. The LGM may have a realistic and applicable potential in the area where soil properties are marginal for crop production.