Conservation agriculture enhances the rice-wheat system of the Eastern Gangetic Plains in some environments, but not in others

Abstract

• Intensification of the rice-wheat system increased system productivity. • CA further enhanced the baseline system though CA benefits are environment-specific. • In fine-textured soil (silt-loam), CA enhanced system productivity and resource use efficiency. • In course-textured soil (sandy-loam), the system benefit (productivity and resource use efficiency) of full CA seems limited. Increasing productivity of the rice-wheat system (RW) in the Eastern Gangetic Plains (EGP) is a major challenge in the context of the various economic (increasing cost of labour, irrigation water, and energy) and bio-physical (water scarcity, depletion of soil fertility, and climatic variability) constraints. We evaluated the performance of three RW system intensification options with different management interventions over two years, comparing a conventional RW rotation (CS 1 ), with two stages of conservation agriculture (CA) interventions, (i) the simple inclusion of mungbean (CS 2 ), and (ii) the inclusion of mungbean together with full CA implementation (CS 3 ) at two sites in the EGP that differed with respect to soil type, water table dynamics, and agro-climatic conditions. Our evaluation focussed on improving system productivity and resource use efficiency. The addition of mungbean into the conventional RW rotation produced significantly higher system productivity (rice equivalent yield, REY) compared with the existing double-crop rotation across sites. The baseline system was enhanced further when CA-based management practices were adopted, however, the magnitude of system benefit from CA was site and situation-specific. At the fine-textured soil site, gains were observed in system production (by 5.4 %), irrigation water productivity (WP I , by 40 %), and N use efficiency (NUE, by 5%) for the CA-based intensified system (CS 3 ) in comparison with the CT-based intensified system (CS 2 ). The average wheat yield and WP I in the zero-till (ZT) system (CS 3 ) was always higher than in the conventional (CT) systems (CS 1 and CS 2 ), mainly due to enhanced wheat rooting after unpuddled rice across the sites. At the fine-textured soil site, the cessation of puddling in rice cropping maintained rice grain yield, while increasing WP I . However, in the coarse-textured soil site, the cessation of puddling resulted in lower rice grain production (by 14 %), coupled with much higher (1.3 times) irrigation water requirement than the conventional puddled rice systems (CS 1 and CS 2 ) in the second year due to increased percolation rate, which negatively impacted the overall performance of the CA-based system (CS 3 ). Therefore, the modification of the traditional CT-based system to an intensified CA-based approach can improve the productivity of the RW system in terms of yield of the component crops as well as better NUE and WP I in fine-textured soil, while the feasibility of the full CA system in coarse-textured soil seems limited due to poor performance of rice, and requires further research focusing on the best rice establishment option.