Long-term fertilization enhanced carbon mineralization and maize biomass through physical protection of organic carbon in fractions under continuous maize cropping

Abstract

Long-term fertilization has been recognized as a key factor controlling soil organic carbon (SOC) and crop yields at various scales. Therefore, the impact of long-term nutrient management on SOC contents, fractional distribution, C-mineralization, and crop productivity under maize mono-cropping was investigated in the present work. For this, a typical black soil in northeast China was collected and analysed to measure the organic carbon (OC) content in the bulk soil, the distribution and OC contents of the different SOC fractions including, coarse particulate organic carbon (cPOC) and free particulate organic carbon (fPOC), intra-aggregate particulate organic carbon (iPOC), free silt plus clay (s + c_f) and micro-aggregate derived silt plus clay (s + c_m), and the SOC mineralization dynamics under different fertilizer treatments. Treatments included: 1) unfertilized control (CK), 2) balanced mineral fertilization (NPK), 3) NPK combined with manure (MNPK), 4) NPK combined with high dose (1.5 times) of manure (1.5MNPK), and 5) NPK combined with crop straw (NPKS). Manure treatments (1.5MNPK and MNPK) led to the largest increase in the SOC content of bulk soil (97% for 1.5MNPK and 41% for MNPK respect to CK). In addition, the long-term fertilization improved the proportions of the cPOC, fPOC and iPOC, especially in the case of manure treatments. In this same way, in comparison to CK, manure treatments (1.5MNPK and MNPK) significantly increased the SOC contents in cPOC (by 96 and 57%, respectively), fPOC (by 146 and 91%, respectively), iPOC (by 160 and 113%, respectively), s + c_f (by 51 and 39%, respectively) and s + c_m (by 56 and 50%, respectively) fractions. Similarly, higher values of SOC mineralization were associated with the 1.5MNPK and MNPK treatments as compared to CK, NPKS, and NPK alone. Finally, the application of 1.5MNPK and MNPK resulted in the highest increase in maize grain yield and in straw biomass yield. Therefore, the results obtained clearly indicate that long-term fertilization using manure combined with mineral fertilizer is the best choice to improve the SOC sequestration and mineralization, as well as the crop yields. All these facts can be considered relevant from points of view related to environmental management, soil fertility, and cleaner crop production.