Monitoring temperature sensitivity of soil organic carbon decomposition under maize-wheat cropping systems in semi-arid India

Long-term storage of soil organic carbon (SOC) is essential for sustainability of agricultural ecosystems and maintaining overall environment quality as soils contain a significant part of global carbon stocks. In this study, we attempted to explain the carbon mineralization and temperature sensitivity of SOC in maize-wheat systems, a common cropping system in the semi-arid regions of India. Soil samples(0-0.15 m) from long-term experimental plots laid in split plot design with two tillage systems (conventional tillage and bed planting) and six nutrient management treatments (T-1= control, T-2 = 120 kg urea-N/ha, T-3= T-2 (25 % N substituted by farmyard manure (FYM)), T-4 = T-2 (25 % N substituted by sewage sludge), T-5 = T-2 + crop residue, T-6 = 100 % recommended doses of N through organic source -50 % FYM + 25 % biofertilizer + 25 % crop residue) were incubated at different temperatures (25, 30, 35, and 40 degrees C) to determine the thermal sensitivity parameters associated with carbon mineralization. Earlier reports suggest a selective preservation of C-3-derived carbon fractions over C-4 in the SOC pool, and this is the first instance where delta C-13 signatures (C-4-derived carbon) were used as a qualitative measure to assess thermal sensitivity of SOC pools in the maize-wheat crop rotation systems of semi-arid India. Among the nutrient management treatments, mineral fertilizers were found to add more C-4-derived carbon to the SOC pool in both the tillage systems but shows less promise in SOC stability as indicated by their lower activation energies (Ea) (14.25 kJ mol (1)). Conventional tillage was found to mineralize 18.80 % (T-1-control at 25 degrees C) to 29.93 % carbon (T-3-mineral fertilizer + FYM at 40 degrees C) during the 150 days of incubation whichwas significantly higher than bed planting system (14.90 % in T-1-control at 25 degrees C and 21.99 % in T-6-100% organic sources at 40 degrees C). Organic manures, especially FYM (19.11 kJ mol(-1)) and 100 % organics (19.33 kJ mol (1)) were more effective in enhancing the Ea of SOC than plots with mineral fertilizers alone (14.25 kJ mol(-1)), but had relatively higher Q(10) values thereby corroborating the thermal sensitivity hypothesis of recalcitrant organic compounds in soil. Michaelis-Menten derivatives along with thermal sensitivity indicators such as Ea and Q(10) were found to be efficient parameters for explaining carbon mineralization and CO2 efflux from soils.