Long‐term nutrient management effects on organic carbon fractions and carbon sequestration in Typic Haplusterts soils of Central India

Abstract

AbstractProductivity of agricultural soils, particularly in India's rainfed tropics, has rigorously fallen because of increased losses of soil organic carbon (SOC) during the last decades; consequently, sustaining crop productivity through the maintenance of SOC level is difficult for dryland farmers. Moreover, systematic research on carbon (C) sequestration, SOC pools, their sensitivity to management change and critical C input level for zero change in SOC, especially under cotton–greengram intercropping in Vertisols of semi‐arid climates, is limited. Therefore, we studied cotton–greengram intercropping after 35 years (1987–2022) under continuous application of organics (farmyard manure/gliricidia), chemical fertilizers and substitution of 50% or 100% fertilizer nitrogen (N) through farmyard manure/gliricidia (integrated nutrient management) (INM). The INM treatments recorded significantly higher cotton–greengram system productivity and sustainable yield index. Continuous cropping without an external nutrient source decreased the soil C, while cropping with INM resulted in a positive build‐up of C in both labile and stable pools. On average, about 62% of total organic carbon was stabilized in the passive pool (CLL, Less Labile C + CRC, Recalcitrant C) of SOC. The increment in SOC stock was linearly (y = 0.0767x – 0.2248; R2 = 0.87, p < .001) related to the system productivity. The very labile C, potassium permanganate oxidizable C and microbial biomass C fractions were the most sensitive to nutrient management. A threshold C input of 0.71 Mg C ha−1 year−1 is required to maintain antecedent SOC, which is readily supplied to the soil using the region's current cotton–greengram intercropping system. Thus, this cropping system is quite capable to maintain antecedent SOC. We conclude that, in the context of changing climates, promoting cotton–legume intercropping using locally available farmyard manure/gliricidia as a substitute for 50%‐‐Fertilizer N is a viable strategy for enhancing SOC storage while achieving sustainable productivity in semi‐arid Vertisols of Central India.