Enhanced conversion of newly-added maize straw to soil microbial biomass C under plastic film mulching and organic manure management

Management of crop production using plastic film mulching (PFM) has the potential to improve soil health by accelerating nutrient cycling and facilitating stable C pool production; however, a key aspect of this process-microbial immobilization of residue C-is poorly understood, especially under PFM when combined with different fertilization treatments. A 360-day in situ 13C-tracing technique was used to analyze the contribution and dynamics of microbial biomass C (MBC) to soil organic C (SOC). Following 27-year PFM and four fertilization treatments, 13C-labelled maize straw residue was applied to micro-plot topsoil in a cultivated maize (Zea mays L.) field. Over the course of the experiment, MBC content was significantly (P < 0.05) higher in treatments of organic manure (M) and manure plus nitrogen (MN) compared to the no-fertilization (CK) and nitrogen (N) treatments, regardless of PFM. Compared to no PFM controls, PFM enhanced the decomposition of maize straw by day 60 in the M and MN treatments, exhibiting increases of 93.0% and 28.6% in straw-derived MBC and 80.4% and 82.9% in the straw-derived MBC/SOC ratio, respectively. Overall, both PFM and organic manure treatments improved soil fertility through microbe-mediated incorporation of C derived from newly-added maize straw. Our results indicate that microbial growth and activity are affected by the utilization of different C sources and most dramatically during early seasonal transition.