The application of graded doses of NPK from 50% (130 kg N, 35 kg P and 41.5 kg K ha−1) to 150% (390 kg N, 105 kg P and 124 kg K ha−1) in the cropping system significantly enhanced SOC, particulate organic C (POC) and KMnO4 oxidizable C (KMnO4–C) fractions in soil.