Effects of water management with plastic film in a semi-arid agricultural system on available soil carbon fractions

•Film mulched ridge-furrow increased microbial biomass C (MBC) and MBC/SOC ratio.•The system decreased soil light fraction of organic C (LFOC) and LFOC/SOC ratio.•MBC correlated negatively with LFOC and mineral N in soil.•Film mulched ridge and furrow system threatens the sustainability of agroecosystem.

There is little information regarding the sustainability of the high yield agroecosystem with double ridges and furrows mulched with plastic film in semi-arid areas. In this study, we explored the sustainability of this agroecosystem with different mulching time during two growing seasons over 2006 and 2007. Three treatments were designed: (i) plastic film mulching applied at sowing and film removed at harvest (CK); (ii) mulching applied 30 days before sowing and removed at harvest (M1); and (iii) mulching applied at sowing and film left on field after harvest and used continually for mulching in the second season (M2). Microbial biomass C (MBC) and ratio of MBC to soil organic C (SOC) (MBC/SOC) were higher in M1 and M2 than in CK in 2007 growing season. The reduction rates of the ratios of light fraction of organic C (LFOC) to SOC (LFOC/SOC) with sampling dates were 0.0020, 0.0047 and 0.0045 for CK, M1 and M2, respectively. A larger value means a faster reduction rate of LFOC/SOC with sampling dates, and implying farming system would face a higher unsustainable risk. MBC correlated negative significantly with LFOC (R = −0.939, P = 0.0001) and mineral N (R = −0.835, P = 0.0007) due to low soil C pool. Accordingly, film mulched ridge and furrow system would threaten the sustainability of soil ecosystem via MBC increase a semi-arid agroecosystem. The practices of mulching applied 30 d before sowing (M1) and use of plastic film once every two years (M2) lead to increased environmental risk for the farming system.