Effects of maize stover and its biochar on soil CO2 emissions and labile organic carbon fractions in Northeast China

Soil labile organic carbon pools are sensitive indicators of soil quality, early changes in soil organic carbon (SOC) stocks, and effects of different soil tillage practices. Impacts of atmospheric greenhouse gas (GHG) emissions on the global climate have encouraged the search for effective alternative methods to promote sustainable agriculture and mitigate climate change. We measured soil CO2 emissions and dissolved organic carbon (DOC), easily oxidizable carbon (EOC), light fraction organic carbon (LFOC), particulate organic carbon (POC), and microbial biomass carbon (MBC) in maize (Zea mays L.) fields treated with maize stover and a maize stover-derived biochar amendment during three consecutive maize growing seasons in a brown earth in Shenyang, China. We considered the following three treatments: CK (application of mineral NPK fertilizer; 120 kg N ha−1, 60 kg P2O5 ha−1, and 60 kg K2O ha−1), ST (maize stover application; 7.5 t ha−1), and BC (7.5 t ha−1 of maize stover was charred, with a yield of 35% of the original biomass; 2.63 t ha−1). Both ST and BC treatments received the same fertilization as CK. Mean data of the three-year experiment indicated that the CO2 emissions of ST and BC were significantly higher than CK by 129.7% and 24.4%, respectively. In both ST and BC treatments, SOC and labile organic C fractions were increased. The sensitivities of each labile organic C fraction varied with different treatments. Soil CO2 emissions under biochar addition were significantly lower than that of stover incorporation. Overall, biochar application was a more effective practice based on the comprehensive consideration of improving soil quality and with regard to CO2 mitigation in the experiment.