Response of labile organic C and N pools to plastic film removal from semiarid farmland soil

To examine the effects of plastic film removal on grain yield and soil organic matter (SOM), a spring maize (Zea may L.) field experiment was conducted for 5 yr at Changwu Agricultural and Ecological Experimental Station of Northwest China. Compared with traditional plastic film mulching during entire growing stages (FM), plastic film removal at the silking stage (RM) resulted in a 6.3% higher average maize yield. Under the RM treatment, soil organic carbon and total nitrogen significantly increased after the 5-yr cultivation in the 0- to 20-cm layer. Significant increases in extractable organic C (EOC), KMnO4-oxidizable C (KMnO4-C) and C management index (CMI) in the 0- to 20-cm layer, and light fraction organic C and EOC in the 20- to 40-cm layer were observed in response to plastic film removal after the 1-yr treatment; the responses were more significant after 5 yr. Under the RM treatment, significant increases in microbial biomass C, light fraction organic N, extractable organic N, KMnO4-C and CMI were also observed after five years in the 20- to 40-cm layer. Moreover, KMnO4-C and EOC were much more sensitive than other labile SOM fractions to the application of RM, even after only 1 yr of cultivation. Therefore, compared with mulching for the whole growing season, plastic film removal at the maize silking stage is an effective option for increasing yields and enhancing SOM concentration and soil sustainability in the regions with semiarid monsoon climates that have sufficient rainfall during maize reproductive stages.