Effect of conservation tillage and rice-based cropping systems on soil aggregation characteristics and carbon dynamics in Eastern Indo-Gangetic Plain

Traditional rice-wheat cropping system, which follows wet puddling in rice and conventional tillage in wheat, is deteriorating soil health resulting yield stagnation in the Indo-Gangetic Plains of South Asia. Conservation agriculture which endorses minimum soil disturbance, residue retention and crop diversification not only improves soil health but also reduces the CO2 concentration in atmosphere. We hypothesized that adoption of conservation agriculture could improve the soil health and soil organic carbon in comparison with conventional practices. A field experiment was conducted during 2012-2015 to observe the effects of different tillage practices and cropping systems on soil aggregation and carbon dynamics. The experiment comprised of three cropping systems, viz. rice-wheat, RW; rice-maize, RM; rice-lentil, RL, practiced in three tillage practices, viz. conventional tillage, CT; reduced tillage, RT; reduced tillage with 30% residue, RT30 in factorial randomized block design. Adoption of RT and RT30 resulted in higher macroaggregate content of 51.7 and 61.2%, respectively, in comparison with CT. Total water stable aggregates and mean weight diameter (MWD) of aggregates were considerably higher in RT and RT30 treatments, and the effect was most pronounced in the upper 0-15 cm soil layer. The rice-maize cropping system registered the highest macroaggregate content, water stable aggregates (WSA) and MWD of 55.6%, 80.0% and 2.28 mm, respectively, in the upper surface soil. The rice-maize cropping systems under RT30 recorded the highest total soil organic carbon (SOC) stock (51.0 Mg ha(-1)) in comparison with other systems after 3 years of experimentation. Reduced tillage and residue management resulted in positive changes in soil infiltration rate. The effect of tillage operations and cropping systems on different soil properties (aggregate distribution, WSA, MWD and geometric mean diameter of aggregates, SOC stock, Bulk density) was mostly limited to surface layer of soil.