Effect Of Plastic Film Mulching And Nitrogen Application On CH₄ And CO₂ Emissions And Soil Organic Carbon Components From A Vegetable Field

Plastic film mulching and nitrogen applicaton have been used to improved crop production.With the greenhouse effect problem attracting people's attention,the effects of film mulching and nitrogen application on greenhouse gases emissions from farmland have also been reported.However,most studies focused on the N₂O emission flux,and few of them studied on CH₄ and CO₂ emission flux and their profile concentration changes and soil organic carbon and active components in vegetable ecosystems under plastic film and nitrogen application conditions.In response to the above problems,this paper takes the pepper-radish rotation field as the research object,from May 2014 to April 2017,a three-year field observation experiment was conducted at the Chongqing Purple Soil Ecological Environment Key Observation and Experiment Station.In the experiment,under the film-covering and conventional planting conditions,no nitrogen,low nitrogen,medium nitrogen,and high nitrogen treatment were applied?film treatment:FM₀,FM₁,FM₂,FM₃,and conventional treatment:BP₀,BP₁,BP₂,and BP₃?.In the research,it aimed at finding the influencing factors of mulching and N fertilizer application on CH₄ and CO₂emissions from vegetable ecosystems,and the organic carbon,active components and hydrothermal conditions in mulch-covered soils,to reveal the impact of mulching on GHG emissions.In addition,to better explore the energy conservation and emission reduction measures for vegetable farmland under three-year field experiment research basis,a potted experiment was also conducted to simulate cropland planted with lettuce under plastic mulch.In each of them,biomass carbon,urease inhibitor?NBPT?,nitrification inhibitor?CP,DCD?and combined application?CP+DCD?were applied to determine the reduction degree of CH₄,then calculated the reduction of CH₄emissions from farmland with different additives covered by plastic film.Finally,we summarized better measures to reduce CH₄ emissions from farmland under plastic film mulching,and providing a theoretical basis for rational cultivation,nitrogen application and reduction of CH₄ in the croplands of China.The results of the study are as follows:1.Effect of Plastic Film Mulching on Soil Hydrothermal ConditionsDuring the three-year experiment period,the average soil moisture content of the covered and conventional soils were 18.20%and 17.53%,respectively,and the plastic film significantly increased the soil moisture content?P>0.05?;the plastic film significantly increased soil temperature at the depth of 10,20,and 30 cm?P>0.05?,with an average increase of 2.6%,2.0%,and 3.0%,respectively.2.Effects of Film Mulching and Nitrogen Fertilizer on CH₄ Emission from Vegetable Field Ecosystem?1?During the three-year observation period,the mean CH₄ emission flux at each nitrogen application level?FM₀?FM₁?FM₂ and FM₃?were-7.22?-0.97?-4.49?-2.36?g·m^-2h^-1,respectively;BP₀?BP₁?BP₂ and BP₃ were-10.08?-8.09?-3.29?-4.40?g·m^-2h^-1,indicating that the uptake of CH₄ in the soil of dry vegetable plots reflects the weak‘sink'of CH₄.And in the second and third vegetable plots,the ability of the soil to absorb CH₄ emissions weakened.?2?There was no correlation between land surface temperature and CH₄ emission flux under film-covered planting conditions,but there was a significant positive correlation between CH₄ flux and ground temperature?P<0.05?,and a significant negative correlation with soil moisture?P<0.05?.Under conventional planting conditions,there was no correlation between CH₄ emission flux and land surface temperature and at the depth of 5 cm soil temperature,and there was a significant negative correlation with soil water content?P<0.05?,while covered and conventional treatment,CH₄ flux and NH₄⁺-N.The contents of all of them showed extremely significant positive correlation?P<0.01?.3.Effects of Film Mulching on Concentrations of CH₄ and CO₂ in Soil Profiles of Vegetable Fields?1?During the whole observation period,the concentrations of CH₄ at surface,at the depth of 10 cm,20 cm and 30 cm soil under plastic film and conventional treatment were 2.46,2.31,2.20 and 2.03 ppm and 2.46,2.37,2.23 and 2.18 ppm,respectively.The concentrations of lower CH₄ decreased with the depth of soil,and the concentrations of CH₄ in different soil layers were significantly different?P<0.05?.The paired T-test was performed on the CH₄ concentrations of the soil layers during the three-year planting period.The soil CH₄ concentration decreased after the film was covered.However,the effect of plastic film coverage on the CH₄ concentration in all soil layers was not significant.The analysis results showed that the concentrations of CH₄ at the depth of 10 cm and 20 cm soil layers of the two treatments were significantly positively correlated with the surface CH₄ concentrations?P<0.01?.There was a significant positive correlation of the CH₄ concentration at the depth of 30cm soil layer and the 5 cm ground temperature and surface temperature.There was no significant correlation of the CH₄ concentrations in the soil layers with soil moisture.It can be seen that the concentration of CH₄ at the depth of 10cm and 20cm soil layer is mainly affected by the concentration of CH₄ on the surface,while the concentration of CH₄ at the depth of 30cm soil layer is mainly affected by the ambient temperature.?2?During the three-year planting period,the average annual CO₂ concentration in conventionally planted at the depth of 10,20,and 30 cm soil layers were 3255.44,3334.48,and 5308.87 ppm,respectively,and the average annual CO₂ concentrations at the depth of 10,20,and 30 cmsoilunder plastic film treatment were 3688.70,4172.84,and 6874.35 ppm respectively,the concentrations of all soil layers in both treatments increased with the increase of soil depth?30cm>20cm>10cm?.No correlation was found between CO₂ concentration and land surface temperature in the film-covered and planted at the depth of 10 cm soil layer and there was a significant positive correlation between CO₂ concentration and soil temperature?P<0.05?or extremely significant positive correlation?P<0.01?;The concentrations of CO₂ in both the film-covered and conventionally planted soil layers were significantly?P<0.05?or significantly positively correlated with land surface temperature?P<0.01?.In this experiment,the soil moisture content of CO₂ was different for each soil layer.No significant correlation was found.4.Effect of Film Mulching and Nitrogen Fertilizer on the net exchange flux of CO₂?NEE?in vegetable ecosystem?1?During the whole monitoring period,the plastic mulching could increase the CO₂ net ecosystem exchange?NEE?in vegetable soils under different nitrogen application levels.Moreover,the results of paired T-test showed that the CO₂ NEE in high nitrogen level was significantly higher in film-covered treatment?FM₃?than that in conventional treatment?BP₃??P<0.05?.Otherwise,the CO₂ NEE as well as the net absorption of CO₂ increased with the increase of nitrogen fertilizer level under film-covered treatment and conventional treatment,with FM₃>FM₂>FM₁>FM₀ and BP₃>BP₂>BP₁>BP₀.In addition,there was no correlation between the surface temperature and the CO₂net flux,but a highly significant negative correlation in film-covered treatment between the CO₂ net flux and 5 cm ground temperature?P<0.01?,and a significant negative correlation in conventional treatment between the CO₂ net flux and 5 cm ground temperature?P<0.05?.While the CO₂ net flux was positively correlated with soil moisture?P<0.05?under the film-covered and conventional treatments.?2?During the three-year observation period,it was found that the soil carbon sequestration of vegetable plots with different nitrogen levels increased year by year,and the film-covering and conventional treatments were also found.Next,the carbon sequestration in vegetable ecosystems increased with the increasing of nitrogen fertilizer application.5.effect of Plastic Film Mulching on Soil Organic Carbon?SOC?and Active Components in Vegetable ecosystemDuring the three-year planting period,the annual average of the SOC in film-covered and conventional treatment were 12.57 and 11.50 g·kg^-1,respectively,and the film-covered treatment could significantly increase the content of SOC in soil?P<0.01?.And the annual average of the SOC were 250.38 and 229.60 mg·kg^-1,respectively,and the results of paired t-test showed that the effect of film-covered treatment on SMBC in vegetable soil was not significant?P>0.05?.Moreover,there was no significantly correlation in the ROC between the film-covered treatment(2.74g·kg^-1)and conventional treatment(2.93 g·kg^-1).6.Effect of mulching and nitrogen application on yield of vegetable cropsWith the increase of nitrogen fertilizer application,the crop yields both increased under film-covered and conventional treatments,which means that the nitrogen fertilizer application increased the crop yields,with high nitrogen>medium nitrogen>low nitrogen>no nitrogen.Only in high nitrogen level,the yield-increasing effect of the film-covered treatment was significant?P<0.05?,while the effect was not significant in other nitrogen-applied at film-covered treatment?P>0.05?.7.Effect of nitrification inhibitors?CP,DCD,CP+DCD?,urease inhibitors?NBPT?,and biochar on the emissions of CH₄ in film-covered vegetable fieldsAddition of CP,DCD,CP+DCD,and NBPT reduced the emission of CH₄ in the vegetable field under film-covered and conventional conditions,which showed that DCD>NBPT>CP+DCD>CP,and found that the emission reduction rate of CH₄ in conventional treatment was greater than that in film-covered treatment,except CP+DCD treatment.This can be seen that the film-covered treatment did not show the promotion effect of different additives on the CH₄ emission.The addition of biochar increased the CH₄ emissions from the soil?covered:10.03%<conventional:79.43%?...