Temperature Sensitivity of Soil Organic Carbon as Affected by Crop Residue and Nutrient Management Options Under Conservation Agriculture

Conservation agriculture (CA) helps in soil organic carbon (SOC) restoration and build-up. The aim of the current study was to evaluate the soil aggregation and concentration, mineralization, and thermal stability of aggregate-associated C under CA with different rates of crop residue (CR) retention and nutrient management practices in a 6-year-old experiment situated in the north-western part of Indo-Gangetic Plains (NW-IGP). The treatments were composed of 3 levels of crop residue (CR) retention, i.e., 0 (CR0), 2 (CR2), and 4 (CR4) t ha(-1), and six combinations of nitrogen (N) and potassium (K) fertilizer rates in the sub-plots, i.e., 100 and 150 kg N ha(-1) and 0, 30, and 60 kg K2O ha(-1). Results indicated significant improvement in total SOC, its pools of varying lability, and aggregate-associated C consequent to increment in CR load. Treatment CR4 had similar to 155% and 23.2% higher values of carbon management index (CMI) compared with CR0 and CR2 in 0-5-cm soil depth. Incremental CR load registered accumulation of C-rich macro-aggregates with a subsequent decline in C-poor micro-aggregates. Treatment CR4 recorded the highest values of cumulative C mineralization, but the lowest percentage and decay rate (K-c) of SOC mineralization. The macro-aggregates reported a lower percentage of total SOC mineralized, Kc, and temperature sensitivity (Q(10)) compared with bulk soil and micro-aggregates. Incremental CR load under ZT promoted physical protection of labile SOC in the form of macro-aggregate-associated C, instead of the recalcitrance of micro-aggregate-associated C. Our results point out towards less temperature sensitivity of physically stabilized SOC under CR4, therefore emphasizing the effectiveness of complete CA practices for sequestration and stabilization of C in the impending global warming scenario.