[Effect of Plastic Film Mulching on Methane Emission from a Vegetable Field].

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.

[Effects of Plastic Film Mulching on Nitrous Oxide Emissions from a Vegetable Field].

Considering the common cropping system (chili-radish rotation) in Southwest China, the objective of this study is to explore the effect of plastic film mulching on N2O flux, N2O concentrations in the soil profile, soil temperature, and humidity from a vegetable field. The method of the static opaque chamber was used and the experimental period lasted for one year. The results showed that the average flux of N2O was 1000.0 µg·(m2·h)-1 in the conventional treatment and 400.6 µg·(m2·h)-1 in the film mulching treatment during the chili growing period. The N2O flux of the film mulching treatment was significantly lower than that of conventional treatment (P<0.05). However, in the radish growing season, the N2O flux of the film mulching treatment was higher than that of conventional treatment, but the difference between the two treatments was not significant (P>0.05). N2O concentrations in the soil profile of the two treatments both increased with the increase in soil depth. The N2O concentrations showed significant correlations among the different soil profiles of each treatment; meanwhile, there was also a significant correlation between soil N2O concentrations at the same soil depth in different treatments. There was a significant positive correlation between the N2O concentration in different profiles and N2O fluxes in surface soils in the conventional treatment, but the N2O flux under the plastic mulching film treatment was only positively correlated with the N2O concentrations of 30 cm deep soil. The soil moisture and temperature observations showed that the effect of plastic film mulching on soil temperature was more significant in summer and the soil moisture was more prominent in autumn and winter. However, the results of the correlation analysis and principal component analysis showed that N2O emissions were mainly determined by the distribution of nitrogen in the soil and were affected by the change in soil total nitrogen content in the conventional treatment but N2O emissions were more sensitive to the variation in soil inorganic nitrogen in the film mulching treatment.

[Effects of Plastic Film Mulching on Methane and Nitrous Oxide Emissions from a Rice-Rapeseed Crop Rotation].

A field experiment was conducted 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. Static opaque chamber and gas chromatography methods were used to study the effect of plastic film mulching on CH4 and N2O emissions characteristics from a rice-rapeseed crop rotation in situ for one year. The results showed that CH4 and N2O emissions are mainly concentrated in the early stages of the growth of each crop and there is a clear seasonal variation of CH4 emissions during the rice growing period and N2O in the rapeseed growing period. The CH4 flux changed from -0.45 to 1.90 mg·(m2·h)-1 and the N2O flux varied between -46.1 and 2040.7 µg·(m2·h)-1 over the entire year. Plastic film mulching was found to increase the total emissions of CH4 and N2 O, with the total CH4 emission of(27.22±4.48) kg·hm-2 over the entire year, which is 26.22% higher than that of the non-mulching treatment(19.93±0.56) kg·hm-2. The total amount of N2O emissions under film mulching treatment increased 16.6% from (11.27±2.77) kg·hm-2 under no mulching treatment to (13.14±0.82) kg·hm-2. The results analyzed for soil moisture and soil temperature showed that mulching significantly increased the soil moisture during the rapeseed season, while there was no obvious correlation with soil temperature (at depths of 5 cm and for the surface temperature) for each crop season. During the rapeseed growing season, CH4 and N2O emissions negatively correlated with soil moisture and has a significant negative correlation during the seedling period with film mulching treatment. Moreover, under the two treatments, the correlation between CH4 and N2O emissions and soil temperature was negligible. This study indicates that plastic film mulching impacts CH4 and N2O emissions at different growth stages of the crops, which changes the proportion of the emission of the two gases over the whole growth period, and promotes the emission of CH4 and N2O in the rice-rapeseed system. In the time scale of 100 years, the integrated global warming potentials (GWP) of CH4 and N2O emission under plastic film was a CO2 equivalent of 4213.00 kg·hm-2 compared with that under conventional treatment of 3454.17 kg·hm-2. Conventional emits 22.0% less CO2, indicating that plastic film mulching is not an effective measure for carbon sequestration.