Long-term Influence of Crop Residue Management and Tillage Practices on Distribution of C and N within Aggregate Size Fractions in Alluvial Soils

Aims: The goal of this experiment is to observe the variations in soil aggregate fractions and the change in percentage of carbon and nitrogen stored in the fractions due to the effect of crop residue management and tillage practices in Rice-Wheat cropping system. Study Design: An experiment was set up in Randomized Block Design with five treatments, i.e, T0-control, T1- zero-tillage+ no residue application, T2- zero-tillage+ residue application, T3- conventional tillage + no residue application, T4- conventional tillage+ residue application. Place and Duration of Study: It was conducted in a long-term experimental plot situated in University Research Farm at Pundibari in Coochbehar district of West Bengal. The data was taken in the 9th and 10th year of the experiment, i.e, 2018 and 2019. Methodology: Samples were collected from three different depths, i.e., 0-5 cm, 5-15 cm and 15-30 cm from four cropping seasons, i.e., wheat 2018, rice 2018, wheat 2019 and rice 2019 and were prepared and analyzed for physico-chemical factors. Dry stable aggregates were obtained by the method of sieving and change of carbon, nitrogen and C/N ratios in various fractions were observed. Results: Mostly for all the soil depths the total organic carbon content was highest for the treatment with zero-tillage and application of residues (T2). Total nitrogen content also followed the similar trend. Whereas in most of the crop seasons, the C/N ratio was observed to be higher in the treatment where conventional tillage was followed along with residue incorporation (T4). Within the short span of two years positive changes in total organic carbon and total nitrogen content was observed for almost all the treatments, across the depths. Conclusion: The optimum percentage of decrease in C/N ratio of the control as well as the treatment with zero-tillage and residue application (T2) in the large aggregate fractions (<2mm) indicates the suitability of the soil for higher productivity.