Using the static opaque chamber method and choosing a chili-radish cropping system, a field experiment, located in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University in Chongqing, was conducted in situ for one year. Mulching and non-mulching treatments were set in the field, and the seasonal variation of CH4 flux and CH4 concentrations in the soil profile and the seasonal changes in soil moisture and temperature were observed for different treatments to explore the effect of plastic film mulching on soil moisture and temperature. The results showed that plastic film mulching can significantly improve the surface soil temperature during the pepper growing season in spring and summer (P<0.01), but no significant difference was seen during the radish growing season in autumn and winter (P>0.05). The soil moisture of the plastic film mulching treatment was significantly higher than that of no mulching in the radish growing season (P<0.05), but no significant difference was observed for the pepper growing season (P>0.05). During the whole observation period and under the condition of plastic film mulching and conventional planting, the CH4 flux from soil had no significant seasonal variation under all treatments, and the mean CH4 fluxes were -7.64 μg·(m2·h)-1 and -9.00 μg·(m2·h)-1, respectively. The cumulative CH4 emissions for plastic film mulching and conventional planting were -0.54 kg·hm-2 and -0.64 kg·hm-2, respectively, in the whole observation period, and all the treatments showed a net absorption of CH4 for the whole observation period. The results showed that the plastic film mulching could weaken the ability of CH4 as a sink of the CH4 for the whole observation period. The CH4 concentrations in different soil profiles were in the order 10 cm>20 cm>30 cm, and the concentrations of CH4 change patterns in different soil layers were almost identical during the whole observation period. The CH4 concentrations at the depths of 20 cm and 30 cm under the plastic film mulching soil were significantly lower than those under no mulching soil (P<0.05), but no significant difference was observed for the depth of 10 cm (P>0.05). Correlation analysis showed that, under the plastic film mulching conditions, CH4 flux and the 5 cm geothermal showed significant positive correlation (P<0.05), but CH4 flux and soil moisture showed significant negative correlation (P<0.05). However, under the conventional cultivation conditions, there were no correlations between CH4 flux and the 5 cm geothermal or soil moisture. There was also significant positive correlation between CH4 concentration in the 10 cm and 20 cm depth soil layers with the CH4 concentration in surface soil (P<0.01), and the CH4 concentration in the 30 cm depth soil layer had significant positive correlation with the surface soil temperatures and the 5 cm geothermal. There was no significant correlation between soil CH4 concentration and soil water content.
Keywords: CH4 concentration in soil profile; CH4 flux; plastic film mulching; soil moisture; soil temperature; vegetable field.