| Cropland ecosystem is an important source of greenhouse gases emission, and the plant is one of the important factors affecting greenhouse gases emission. Rice-rapeseed rotation is one of the major cropping system in Southwest China, and plastic film mulching is widely used in crop planting for conserving soil moisture and increasing soil temperature. Plastic film mulching changed the basical physic-chemical properties of soil, inevitably affects the greenhouse gas emission. Therefore, this study located in Agricultural Purple Soil Ecological Environment Key Field Scientific Observation and Experiment Station of Southwest University in Chongqing, using the static chamber and gas chromatography method, diurnal and seasonal variation of greenhouse gas emissions from a typical rice-rapeseed system for a year in situ were measured, in order to reveal the effect of plastic film mulching on rules and the main control factors of greenhouse gases emission from a typical cropland ecosystem in southwest China, and calculate the total GWP and their emission intensity caused by CO2, CH4 and N2 O emission from cropland, and explore the reduction of greenhouse gas emissions of farm management practices and provide a theoretical basis. After a large number of long-term field observation and indoor analysis, the main results are as follows: 1. The impact of plastic film mulching on GHGs emission flux(1) In the diurnal variation, greenhouse gas emission presented with the change of temperature, showed single peak emissions increased first and then decreased, the CH4 emission flux and CO2 net emission flux in summer are significantly higer than winter(P<0.05), while N2 O emissions flux in winter is significantly higer than summer(P<0.05). Diurnal variation during the rice growing season(summer), the maximum rate of greenhouse gases occurred about 11:00 or 13:00, and the minimum was 7:00 in the morning or afternoon 19:00, there was no significant difference in the average(net) emission flux between mulching and conventional treatment(P>0.05); During the rapeseed growing season(winter),the greenhouse gases(net) emissions diurnal maximum value appeared at 13:00 or 15:00, the minimum at 7:00 in the morning, there were significant difference in the CH4 and CO2 average(net) emission flux between mulching and conventional treatment(P<0.05), but no significant difference in N2O(P>0.05).(2) In the seasonal variation, compared with the conventional treatment, the rice season, plastic film mulching increased the CH4 and N2 O emission flux, in which CH4 reached significant difference(P<0.05), decreased the net CO2 emission flux, but the difference was not significant(P>0.05); fallow period, plastic film mulching significantly increased the CH4 and CO2(net) emission flux(P<0.05), but significantly reduced the N2 O emission flux(P<0.05); rape season, between the two treatments CH4 emission flux differences were not significant, but the plastic film mulching significantly increased the N2 O emission flux(P<0.05), and significantly reduce the net CO2 emission flux(P<0.05). 2. Effect of plastic mulching on GHGs emissions and average emission flux(1) Mulching annual CH4 emissions for 26.85 kg·hm-2, compared to conventional processing 18.58 kg·hm-2 high 44.51%, significantly difference(P<0.01), the total N2 O emission 12.31 kg·hm-2, compared conventional treatment 9.62 kg·hm-2 high 27.96%, reached a significant difference(P<0.05); net CO2 fixed amount on 24634.49 kg·hm-2 was significantly lower than that in the conventional treatment 36645.31 kg·hm-2(P<0.01).(2) Plastic film mulching, compared to conventional processing, significantly increased CH4 emissions of rice cropping and fallow, no significant difference in rape season; increased N2 O emissions in rice season and rape season and reached significant difference in the later, but significantly reduced the N2 O emission from the fallow period, and to sink; plastic film mulching significantly reduced CO2 net emissions of rice season and rape season and in fallow period without significant difference between treatments.(3) From the point of emissions, mulching increased or reduced the crop growth season most fertility period(net) emissions of greenhouse gases, but did not change greenhouse gas distribution in the crop growth period, only changed the growth of greenhouse gas emissions accounted for the proportion of the crop seasons in greenhouse gas emissions.(4) The mulching and conventional treatment mean greenhouse gas emission flux differences consistent with emissions, but significantly differences among the growth period of crop, indicating that plastic film mulching significantly affected the emissions rule of greenhouse gas in the growth period of crop. 3. Effect of plastic mulching on crop yield, GWP and greenhouse gas intensity(1) Film mulching crop total yield was 10232.49 kg·hm-2, higher than conventional treatment 9561.37 kg·hm-2 was 7%, there was no significant difference(P>0.05). Rice yield 9335.36 kg·hm-2, compared with conventional processing 8611.07 kg·hm-2, the yield increased by 8.41%, reaching significant difference(P<0.05); rape yield 897.14 kg·hm-2, compared to conventional treatment of 950.30 kg·hm-2 decreased 5.59%, the difference was not significant(P> 0.05).(2) The annual GWP of film mulching-20214.16 kg CO2·hm-2, equivalent to-33176.47 kg CO2·hm-2 of conventional treatment in 60.93%, reached a very significant difference(P<0.01). The rice and rape season GWP mulching treatment for-6886.37 and-8843.01 kg CO2·hm-2, compared to conventional processing reducced by 28.62%(P<0.05) and 55.15%(P<0.01),respectively; fallow mulching GWP increased by 17.64%, to-4484.78 kg CO2·hm-2, difference with conventional treatment to-3812.12 kg CO2·hm-2 was not significant(P> 0.05).(3) Plastic film mulching annual greenhouse gas emissions intensity to be-1.98 kg CO2·kg grain yield-1,compared to conventional treatment significantly reduced the 42.94%(P<0.05);in rice season and rape season with conventional treatment for the performance of the significant or extremely significant differences, reduce 33.93%(P<0.05) and 52.48%(P<0.01),respectively, showed that plastic film mulching significantly reduces the carbon sequestration function. 4. Effect of plastic mulching on distribution of carbon and nitrogen of crop(1) The content of organic carbon in different plant organs to grain > root> stem> seed shell. Plastic film mulching did not change its distribution, but reduced the content of organic carbon in most organs except root.(2) The total nitrogen content in different plant organs to grain grain > seed shell > root > stem. Plastic film mulching did not change its distribution, but significantly increased the total nitrogen content in grain. 5. Relationship between greenhouse gas emissions of plastic film mulching and environmental factorsUnder film mulching, soil misture and CH4, N2 O emission flux showed a significant negative correlation, the correlation coefficients of-0.622,-0.673, respectively; the temperature and net CO2 flux significant positive correlation(r=0.426). At the same time, the underground temperature of 5cm and N2 O emission flux was significant positive correlation(r=0.554), DON and MBN was positively correlated with CH4 fluxes(r=0.570, r=0.533, respectively). The result showed that misture temperature, underground temperature of 5cm, DON, MBN are the key effect factors of film mulching to greenhouse gas emissions. |
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