Soil carbon and nitrogen dynamics under conservation agriculture components for direct seeded rice-green gram system

Aims and methods Conservation agriculture practices have been developed for rice-based cropping systems in eastern India to mitigate the negative effects of continuous monocropping. However, the effects of individual and combined conservation agriculture components on carbon (C) and nitrogen (N) mineralization, soil enzyme activities, and C and N fractions are unknown. This study aimed to evaluate the effects of key components of conservation agriculture such as, reduced tillage, crop residue retention and crop diversification both individually and in combinations with the control making 8 treatments, on soil carbon and nitrogen dynamics under direct seeded rice-green gram system. Results Reduced tillage alone and in combination with diversification resulted in 10% and 6% lower CO2-C release than the plots with residue retained. Carbon mineralization in terms of mean cumulative CO2-C (mg CO2-C kg(-1)) fits well with first-order kinetics (R-2 = 0.97-0.99), suggesting that degradation is concentration-dependent. Potentially mineralizable N content ranged from 192.2-222.4 kg ha(-1) day(-1) with mineralization half-time of 28.1-32.3 days. Diversification alone showed the highest dehydrogenase (43-127% higher than control at all stages), fluorescein di-acetate (22-62% higher than control at maximum tillering and panicle initiation stages) and beta-glucosidase (27-40% higher than control in all stages) activities, while residue retention in the rice-green gram system showed the highest nitrate reductase activity (53-83% higher than control at maximum tillering and panicle initiation stages). At all growth stages, diversification had the highest values for microbial biomass C, ammonium N and nitrate N which were 59-95%, 22-53% and 2.2-10 times higher than the control, respectively. Conclusion The effect of conservation agriculture component, such as crop diversification and residue retention in direct seeded rice-green gram system, is more effective for better C and N cycling. While reduced tillage may take longer to show effects, enzymatic activities have significantly increased under diversification and residue retention. By diversifying crops and retaining crop residues, the soil is able to maintain higher levels of C and N. Additionally, the increase in soil enzyme activities improves microbial activity, which can further enhance nutrient availability for plants. The synergistic effect of residue retention and crop diversification is beneficial for improving soil health in this system.