Study Of Effect Of Plastic Film Mulching On CO₂ And CH₄ Emissions From A Vegetable Field

In recent decades, the Greenhouse effect has become a global environmental problem as the increasingly high concentration of greenhouse gases. In addition to fossil fuels combustion, agro-ecosystems are also an important source of anthropogenic greenhouse gases emission. Plastic film mulching, as a filed management measure, is widely used in agricultural production especially for vegetable application in Southwestern China. How are the emissions of CO₂, CH₄ and sequestration ability of carbon affected after plastic film mulching as well as soil organic carbon and soil active organic carbon contents? These are the scientific problems that should be solved urgently under the increasingly global climate warming background.In this paper, we selected a pepper-radish rotation land, which is a typical vegetable field in Southwestern China as our research object. Eight treatment were set up, followed by mulching with zero nitrogen fertilizer（MN0）, mulching with low nitrogen fertilizer（MN1）, mulching with normal nitrogen fertilizer（MN2）, mulching with high nitrogen fertilizer（MN3） and no mulching with zero, low, normal and high nitrogen fertilizer（CN0, CN1, CN2, CN3）. We want to study the effect of soil hydrothermal condition, soil nutrients, soil organic carbon and active organic carbon contents with plastic mulching, as well as the effects of CO₂, CH₄ emissions of vegetable field by plastic mulching and different rates of nitrogen fertilizer application. In this way, its internal influence mechanism are revealed and theoretical basis are provided for reducing CO₂, CH₄ emission in farmland and increase soil carbon sequestration potential. This study obtained the conclusions as follows:1. Effect of plastic film mulching on soil hydrothermal condition and soil nutrients.（1）Plastic film mulching can significantly improve the surface soil temperature during the pepper growing season, the soil temperatures in depths of 10 cm, 20 cm, 30 cm are 2.3℃, 2.8℃and 2.0℃, significantly higher than those of no mulching treatments, respectively（p<0.05）, while no obvious change between two treatments during the radish growing season. The soil moisture of plastic film mulching treatment was significantly higher than no mulching in radish growing season, while significantly inrelative to pepper growing season.（2） After the two growing season, the soil organic matter（SOM）, ammonium（NH4+-N）, nitrate（NO3--N）, available N P K（AN, AP, AK） content of plastic film mulching treatment were higher than no mulching.2. Effect of plastic film mulching on soil organic carbon and active organic carbon（1） Plastic film mulching treatment significantly increased the soil organic carbon（SOC） content, with 11.05% higher than no mulching.（2） Plastic film mulching treatment significantly increased the soil readily oxidizable carbon（ROC） content, with 12.10% higher than no mulching.（3） Plastic mulching treatment have significantly impact on soil microbial biomass carbon, with 15.43% higher than no mulching in the whole growing season（p<0.05）.（4） The mean contents of dissolved organic carbon in plastic film mulching and no mulching treatment soil are 86.03 and 104.51mg·kg-1, respectively, with no significant difference（p>0.05）.3. Effect of plastic film mulching on soil CH₄ and CO₂ concentrations.（1） In the whole observation period, the CH₄ concentrations at the soil depth of 10 cm, 20 cm and 30 cm were 2.20, 2.06 and 1.80mg·m-3, respectively. Under plastic film mulching and 2.18, 2.15 and 1.90mg·m-3 in corresponding no mulching treatment, all decreased with the increase of soil depth. The plastic film mulching soil CH₄ concentrations at the depth of 20 cm, 30 cm are significantly higher than no mulching（p<0.05）, but no significant difference at depth of 10 cm.（2） The CO₂ concentrations at soil depth of 10 cm, 20 cm and 30 cm were 3968.84, 5855.31 and 9191.84mg·m-3, respectively. Under plastic film mulching treatment and 3382.83, 4178.57 and 6791.73mg·m-3 in corresponding no mulching treatment, all decreased with the increase of soil depth. The plastic film mulching soil CO₂ on centrations at the depth of 20 cm, 30 cm are significantly higher than no mulching（p<0.05）, but no significant difference at depth of 10 cm.（3） The CH₄ concentrations at soil depth of 10 cm, 20 cm were extremely significant correlation with the surface atmospheric CH₄ concentration（p<0.01）, but at the depth of 10 cm extremely significant correlation with the soil temperature. Each CO₂ concentration in different soil depth with no mulching mainly affected by the soil temperature, but is insensitive to temperature changes with plastic mulching.4. Effect of plastic mulching and N fertilizer supply on soil CH₄ emission in vegetable field.（1） In the whole observation period, the soil CH₄ emission flux has no significant seasonal variation under all treatments. The mean CH₄ fluxs during in whole observation period of MN3, MN2, MN1 and MN0 treatment were-7.75,-8.319,-4.02 and-9.94mg·m-2·h-1, respectively. The corresponding mean CH₄ fluxs of CN3, CN2, CN1 and CN0 treatments were-1.86,-8.55,-7.76,-9.32μg·m-2·h-1, respectively.（2） In the whole observation period, the cumulative emissions of CH₄ showed there were the methane sinks in each treatment, and there was no significantly difference inthe cumulative emissions of CH₄ between plastic mulching and N fertilizer supply.（3） The diffusive condition including temperature and each adjacent interfacial concentration difference are the main factors affecting soil CH₄ flux for the two cultivation methods, soil moisture is also positively correlated with CH₄ flux.5. Effect of plastic film mulching and N fertilizer supply on ecosystem respiration rate in vegetable field.（1） During the whole observation period, the mean ecosystem respiration rate of MN3, MN2 and MN1 treatment were 837.195, 698.96 and 772.34mg·m-2·h-1, respectively. The corresponding treatment of CN3, CN2, CN1 were 853.37, 869.72, 861.10mg·m-2h-1, inspectively. N fertilizer suppling has no significant difference in ecosystem respiration rate. Plastic film mulching significantly increased the amouts of CO₂ emissions under normal and high N fertilizer level（p<0.05）.（2） Temperature was positively exponential correlated with ecosystem respiration rate for the two cultivation methods, while the sensitivity of CO₂ emissions to temperature for plastic film mulching cultivation was lower than that of no mulching.（3） Plastic film mulching can reduce soil respiration rate under each N fertilizer supply level. A certain amount of N fertilizer can promote soil respiration rate, but soil respiration rate will be inhibited if N fertilizer supply was excess.6. Effect of plastic film mulching and N fertilizer supply on CO₂ net ecosystem exchange（NEE） in vegetable field.（1）The 2 hours intervals diurnal variation characteristics of NEE indicate that the maximum absorption appeared at 11:00-13:00 and the maximum emission appeared at 19:00-21:00. The NEE at 9:00-11:00 can represent the mean NEE in a whole day, approximately.（2） During the whole observation period, the cumulative carbon sequestration of MN1, MN2 and MN3 treatments were 9.10, 10.80 and 13.04 t·hm-2, respectively. The corresponding treatment of CN3, CN2 and CN1 were 8.33, 10.93 and 12.72 t·hm-2, respectively. Plastic film mulching and N fertilizer supply can increase the CO₂ sequestration invegetable field ecosystem.