There is little information regarding the impact of plastic film and gravel mulching on soil organic carbon
(SOC) stocks and labile fractions in semiarid areas of northwest China. Based on a 4-year spring maize
(Zea mays L.) field experiment at Changwu Agricultural and Ecological Experimental Station, we analyzed
the SOC stock, labile SOC pools and the C management index (CMI) in the 0e20 cm and 20e40 cm layers.
The three treatments included non-mulched (CK), gravel-mulched (GM) and plastic film-mulched (FM).
After the 4-year duration, compared with the initial SOC stock, the SOC stock under GM decreased
0.97 Mg C hm2 whereas under FM increased 1.14 Mg C hm2 in the 20e40 cm layer. Across the 0e40 cm
layer, the SOC stock under GM significantly decreased, whereas under FM demonstrated some tendency
to increase. In contrast to the CK, the FM treatment significantly increased light fraction organic C (LFOC)
content (density