Combining soil carbon storage and crop productivity in partial conservation agriculture of rice-based cropping systems in the Indo-Gangetic Plains

Conservation agriculture (CA) is an approach to achieve the 'Sustainable Intensification' of the rice -wheat cropping system of South Asia. However, difficulties in adoption of the full CA principles (zero tillage, soil cover, crop diversification) have been a concern in South Asia and the Indo-Gangetic Plains region. Eventually, partial CA which comprises at least one crop with zero tillage (ZT) with or without crop residues, is being adopted in the rice -wheat system in South Asia. However, long-term impact of partial CA in diversified crop rotations on soil organic carbon (SOC) storage and crop productivity is not elaborately studied in comparison to the conventional tillage (CT) without residues in rice -wheat (conventional practice in the region). The present study concerned a 9 -year experiment with a split -split -plot design testing three factors, soil tillage (main plot), crop residue management (sub -plot), and crop rotations (sub -sub -plot), respectively with permanent tillage or tillage only on rice, without or with all crop residues and rice -wheat, rice -chickpea and rice-chickpea-mungbean (six years) and rice-wheat-mungbean (three years). Soil was sampled from 0-15 cm depth for SOC storage estimation in present study. Partial CA (post -rice ZT with residues in rice-chickpea-mungbean and rice-wheatmungbean rotations) increased the SOC concentration and carbon management index by 39% and 42% at 0-15 cm soil depth over conventional practice within nine years, respectively. Specifically, post -rice ZT resulted in 23% higher (P < 0.05) SOC content over CT in all crops. The crop residue increased SOC storage and carbon management index by 12% and 13% over residue removal (P < 0.05), respectively. In a system mode, partial CA resulted in 39.9% higher SOC storage at 0-15 cm soil depth over conventional practice. It increased the grain yield of rice by 17% and wheat by 13% (nine years mean) over the CT without residue in rice -wheat. Partial CA also enhanced the sustainable yield index of rice, wheat, and system by 22%, 23%, and 69% over CT, respectively. Mean rice grain yield and sustainable yield index of system of nine years were positively correlated with SOC storage (P < 0.05) at 0-15 cm soil depth. Thus, partial CA comprising ZT in post -rice crops with crop residue retention and intensive crop rotations (rice-chickpea-mungbean and rice-wheat-mungbean) can be adopted in the Indo-Gangetic Plains for higher SOC storage and sustainable yield of crops in rice -based cropping systems.