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

Abstract

Abstract Continuous monocropping of puddled rice in Eastern India has decreased crop productivity and contributed to the deterioration of soil structure. To address this issue, conservation agriculture (CA) is being developed as a method to promote sustainability of the rice-based cropping system in eastern India. The study was conducted with the objectives to evaluate the influence of CA components on C and N mineralization and to study the impact of CA on the soil enzymes, C and N fractions. At the research farm of ICAR National Bureau of Plant Genetic Resources, Cuttack, a study was conducted using components of conservation agriculture in different combinations. The study included the effects of different components of CA, such as reduced tillage (T), addition of crop residues (R), and crop diversification (D) both alone and in combinations. Standard methods were used to determine carbon (C) and nitrogen (N) fractions, mineralization, and soil enzyme activities. Results showed that the addition of residue and crop diversification components (crop residues, crop residues with reduced tillage, crop residues with diversification and crop residues with reduced tillage and diversification) had higher CO2-C levels. Carbon mineralization in terms of mean cumulative CO2-C (mg CO2-C kg-1) fit well with first-order kinetics (R2=0.97-0.99), suggesting that degradation is concentration-dependent. Potentially mineralizable N (N0) content ranged from 191.27 to 219.53 kg ha-1, with the highest value in diversification (D). It showed the highest dehydrogenase activity and nitrate reductase activity, while residue addition in rice-green gram system (RD) showed the highest fluorescein di-acetate and β-glucosidase activities. At all growth stages, diversification (D) had the highest values for microbial biomass C, ammonium N and nitrate N. Correlation study shows a positive interaction between carbon and nitrogen fractions with soil enzymatic activities. It can be concluded that the influence of crop diversification (component D) and residue addition (component R) were more effective in C and N mineralization, fractions and soil enzyme activities than the other component of CA. The beneficial effect of incorporating residues is even more effective when it is combined with crop diversification. The combination of some of the components of CA are as good as complete CA in C and N mineralization, fractions and soil enzyme activities for rice-green gram cropping system.