The effects of plastic film mulching on soil organic carbon and nitrogen fractions were investigated in a spring maize field. Three treatments

i.e. plastic film mulching

no mulching

and bareland fallow were included and soil organic carbon (SOC)

total nitrogen (STN)

particulate organic carbon and nitrogen (POC

PON)

potential mineralized carbon and nitrogen (PCM

PNM)

and microbial biomass carbon and nitrogen (MBC

MBN) were measured at 0-40 cm soil depth. No significant differences in SOC and STN were found among treatments for all soil depths. Compared with no mulching

the contents of POC

PON

POC/SOC

and PON/STN at 0-40 cm soil depth was decreased by 29.0%

33.3%

29.9%

and 35.7% by plastic film mulching

respectively. The PCM content and PCM/SOC was decreased by 17.8% and 16.1%

respectively

and the MBN content and MBN/STN at 0-10 cm soil depth was increased by 10.6% and 10.5% (p < 0.05)

respectively. Compared with the bareland fallow

the content of PCM and PNM at 0-40 cm soil depth was increased by 12.8% and 14.7 by no mulching

respectively

and was increased by 7.8% and 6.5% (p < 0.05) by plastic film mulching

respectively. The contents of MBC and MBN and their contributions decreased after maize planting in spite of plastic film mulching or not. In general

plastic film mulching could increase microbial biomass carbon and nitrogen at the top layers but decrease both the contents and conributions of moderate labile fractions

indicating that plastic film mulching may not be beneficial for long-term soil carbon and nitrogen sequestration in dryland maize fields.