Inclusion of Legumes in Rice–Wheat Cropping System for Enhancing Carbon Sequestration

Abstract

Sustainability of the rice (Oryza sativa)–wheat (Triticum aestivum) cropping system (RWCS) is fundamental for the food security of Asian countries. Continuous practice of RWCS has emerged soil and environmental issues, which are now increasingly being evident. Lack of crop diversification, intensive tillage practices, residue burning, overexploitation of groundwater and imbalanced use of fertilizers have been found as major reasons for deteriorating soil health and sustainability of RWCS. Results of long-term experiments demonstrated that depletion of soil organic carbon (SOC) in RWCS primarily threatens the sustainability of the system. In parallel, increase in the SOC of tropical soils is equally important for conserving the natural resources and up-scaling resource-use efficiency. Grain legumes add a significant amount of C to soil through root biomass, leaf fall and release of root exudates. Moreover, the potential of legume cover crop on soil health is also known. Therefore, inclusion of grain legumes in RWCS is a promising approach for crop diversification and maintaining positive C balance. Further, stabilization of non-labile C (recalcitrant C-pool) from legume residue is important for SOC persistence in the long term. Particular to the Indo-Gangetic Plain region, growing of mung bean (Vigna radiata) in summer fallow of RWCS and inclusion of chickpea (Cicer arietinum) in RWCS have been found to be effective to improve the SOC, particularly when legume residue is returned to soil. Rice–wheat–mung bean/urdbean (Vigna mungo), rice–wheat–cowpea (Vigna unguiculata), rice–chickpea/lentil (Lens culinaris)/field pea (Pisum sativum) and pigeon pea (Cajanus cajan)–wheat are alternative rotations, which could be popularized in RW-growing areas for improving soil health and to enhance C-sequestration. In-depth understanding of C-sequestration processes is essential to design alternative pulse-inclusive rotation/s and mitigating the known consequences of continuous RWCS.