Legumes in conservation agriculture: A sustainable approach in rice-based ecology of the Eastern Indo-Gangetic Plain of South Asia − an overview

Legumes in Conservation Agriculture (CA) have the potential to increase crop productivity and sustainability of the rice-based system. However, there is limited information available on the importance of legume crops in CA in the rice-based system of the Eastern Indo-Gangetic Plain (EIGP). Rice-based cropping is the mainstay of the people in Bangladesh, on the EIGP. These systems are the major food supplier to the region. In addition, they provide income and employment opportunities to the majority of people in the region. However, the system is facing unprecedented challenges and increased risk due to water, energy, labour and capital scarcity, which are exaggerated due to the effects of climate change. This could be further aggravated by deteriorating soil health, depleting underground water, and reduced land and water productivity which ultimately threaten sustainable food production and food security of the EIGP. Hence, sustainable crop intensification is essential, but increasing cropping intensity has reduced the yield of single crops by degrading soil properties. To address these constraints, Conservation Agriculture (CA), with a minimum tillage system, residue retention and crop diversification with legumes, could be an effective approach for improving crop productivity while sustaining the natural resources in intensive rice-based systems of EIGP. The addition of legumes in crop rotation is a suitable technique for crop diversification due to its multiple benefits related to soil health and natural resources. Diverse legume crops involving rice-based cropping exist at different agro-ecological zones in Bangladesh, and their rotation definitely could act a major role in promoting the CA in rice-based systems. Legume-based rotation offers multiple benefits, such as biological nitrogen fixation, improves soil pores through the deep root system, P-availability, soil fertility and enhanced nutrient cycling, and reducing the use of external input and thereby minimizing greenhouse gas emission and groundwater pollution, improving water productivity, and minimizes diseases and pest incidence. As a result, crop rotation with legumes has a high potential for CA and sustainable rice-based cropping systems in Bangladesh. The gaps between legume and non-legume crops in CA for each parameter suggest a noteworthy possibility for the improvement of rice-based systems in EIGP. This review suggests further sustainability improvements can be achieved through future field research focused on the inclusion of legume crops in the diverse rice-based systems under CA.