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

In the last decades,with the concentration of greenhouse gases rising,greenhouse effect has become a global environmental problem.Except fossil fuel combustion,the release of CO₂,CH₄ and N₂O from agricultural soil are also an important source of greenhouse gases that produced by human activities.Plastic film mulching is widely used in agricultural production in China,especially in the process of vegetable planting.There were many studies had proven that plastic film mulching had advantage to the water conservation,heat preservation,fertilizer retention,weed control and yield increase etc.However,how does plastic film mulching affect the ecosystem of farmland,the release of CO₂ and CH₄,and also the physical and chemical properties of the soil? It's still lack of correlational studies.In this paper,a 2-year field experiment in Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China was conducted?from May 2014 to March 2016?,and the pepper-radish rotation vegetable field was taken as the research object,eight treatments were set up,there are: plastic film mulching with zero,low,normal,high nitrogen fertilizer?FN₀,FN₁,FN₂,FN₃?;no mulching with zero,low,normal,high nitrogen fertilizer?NN₀,NN₁,NN₂,NN₃?.In the research,it aimed at finding the effects of plastic film mulching and nitrogen application on CO₂ and CH₄ emission and influencing factors of vegetable ecosystem and the effects of plastic film mulching on soil organic carbon and active components,soil hydrothermal conditions,and the mechanism of plastic film mulching on greenhouse gases emission,and providing a theoretical basis for China's farmland CO₂ and CH₄ emission reduction.The results showed as follows:1.Effect of plastic film mulching on soil hydrothermal condition,soil carbon and nitrogen?1?During the two-year planting period,the average soil moisture of the film and the conventional soil were 18.76% and 17.98% respectively,plastic film mulching could significantly improve soil moisture?P<0.05?,and it increased soil temperature of 10,20,30 cm?P<0.05?,the average soil temperature was increased by 0.77,0.69 and 1.03? with plastic film mulching,while the effect of film mulching on soil Eh and pH was not apparently difference.?2?During the two-year planting period,the mean values of soil organic carbon?SOC?were 22.47 and 20.46 g·kg^-1,respectively,and the film was obviously higher than that of the conventional soil?P<0.05?,the mean values of DOC were 68.95 and 80.83 mg·kg^-1,respectively,and the routine was significantly higher than that of the membrane?P<0.05?,while the film had no significant effect on soil microbial biomass?SMBC?and aerobic organic carbon?ROC?.2.Effect of film mulching and nitrogen fertilizer on crop yield and nitrogen uptake?1?The pepper yields of FN₁,FN₂ and FN₃ were 1.87,2.19 and 1.93 kg·m^-2,and the yields of NN₀,NN₁,NN₂ and NN₃ were 0.94,1.80,1.79 and 1.97 kg·m^-2,respectively.The radish yields of FN₀,FN₁,FN₂ and FN₃ were 7.38,13.74,16.46 and 23.80 kg·m^-2,and the yields of NN₀,NN₁,NN₂ and NN₃ were 6.50,12.82,15.52 and 17.80 kg·m^-2,respectively.The results showed that the application of nitrogen fertilizer increased the yield of crops and promoted the growth of underground biomass on the ground.However,in the summer,with the thick temperature,high humidity and abundant rainfall,the impact of the yield of the film was not obvious,that is to say,it's not a determinant factor to yield increase.?2?The total nitrogen of FN₀,FN₁,FN₂ and FN₃ in the radish were 3.75,5.22,7.14 and 7.78 g·kg^-1,NN₀,NN₁,NN₂ and NN₃ were 1.97,3.88,5.17 and 6.50 g·kg^-1,respectively.The total nitrogen of FN₀,FN₁,FN₂ and FN₃ in the leaves were 9.80,11.76,12.21 and 25.53 g·kg^-1,and NN₀,NN₁,NN₂ and NN₃ were 5.42,8.20,9.62 and 10.05 g·kg^-1,respectively.The content of nitrogen in the body increased with the increase of nitrogen application rate,while the film was observably higher than the conventional treatment,indicating that the film and nitrogen fertilizer can enhance crop nitrogen uptake.3.Effects of plastic flm mulching on CO₂ and CH₄ concentration within soil profles?1?During the planting period,the CH₄ concentration in the soils profile under 10,20 and 30 cm depth under film mulching were 2.31,2.18 and 1.92 ppm?1 ppm = 10-6 V/V?,respectively,and the conventional treatments were 2.33,2.20 and 1.97 ppm.CH₄ concentration decreased with depth of soil,and the effect of film mulching on CH₄ concentration in 10,20 and 30 cm soil layer was not obvious.There was a remarkable positive correlation between the surface CH₄ concentration and the CH₄ concentration in the soils profile under 10,20 and 30 cm depth?P<0.05?.The surface temperature,10 and 20 cm depth soil temperature had no obvious effect on the soil CH₄ concentration,but flm mulching and conventional 30 cm CH₄ concentration had a positive correlation between underground and surface temperature?P<0.05?.?2?The average annual CO₂ concentration in the 10,20 and 30 cm soil layers with no film mulching were 3461.16,398.41 and 6050.00 ppm,respectively,and the flm mulching were 3907.56,5335.37 and 8167.39 ppm,respectively.The mean CO₂ concentrations at the soil depth of 20 and 30 cm under plastic flm mulching were higher than no mulching?P<0.01?,and increase with depth.Except that CO₂ concentration at 10 cm soil layer with plastic flm mulching was not correlated with the surface temperature,there was a significant positive correlation between CO₂ concentration and surface temperature and corresponding soil temperature with plastic flm mulching as well as no mulching.4.Effect of plastic flm mulching and nitrogen fertilizer on CH₄ flux in vegetable field?1?The average CH₄ flux of FN₀,FN₁,FN₂ and FN₃ were-6.92,3.12,-3.64 and-2.93 ?g·m^-2h^-1,NN₀,NN₁,NN₂ and NN₃ were-11.71,-10.03,-0.931,-6.23 ?g·m^-2h^-1?P<0.05?,while NN₀ and NN₁ were significantly lower than those of CH₄ emission flux of NN₂?P<0.05?,and the CH₄ flux of FN₁ were significantly higher than those of FN₀ and NN₁?P<0.05?,indicating that the film and nitrogen fertilizer to promote the CH₄ emissions or reduce the absorption of CH₄.?2?The correlation between film and conventional CH₄ flux and soil moisture content,underground temperature of 5cm,Eh and pH were not significant.While the film and nitrogen fertilizer to promote soil NH₄⁺-N accumulation,NH₄⁺ will inhibit the oxidation of CH₄,thereby promoting CH₄ emissions or reducing the absorption of CH₄.5.Effect of film mulching on soil respiration rate in vegetable field?1?From March 2015 to March 2016,the average soil respiration rate of NN₂ and FN₂ were 293.04 and 226.27 mg·m^-2h^-1,respectively.Continuous sampling for three days in different treatments before planting,the average soil respiration rates of FN₀,FN₁,FN₂ and FN₃ were 147.02,259.21,225.92 and 211.79 mg·m^-2h^-1,respectively,and the mean values of NN₀,NN₁,NN₂ and NN₃ were 219.14,378.65,393.29 and 345.20 mg·m^-2h^-1?mean average of three planting periods?.It is indicated that the film significantly reduced soil respiration rate,while nitrogen fertilizer could promote soil respiration rate,but excessive application of nitrogen fertilizer would inhibit soil respiration rate.?2?Underground 5cm temperature,water content,SOC and DOC all affected soil respiration rate,nevertheless,the correlation between pH,SMBC,ROC and soil respiration rate was not significant.The sensitivity of the soil respiration rate to the temperature was decreased by the film.The sensitivity index Q10 was 1.62 and 1.75,respectively.6.Effect of film mulching and nitrogen fertilizer on ecosystem respiration rate and CO₂ net exchange flux in vegetable field?1?FN₁ and FN₂ were significantly lower than NN₁ and NN₂?P<0.05?.FN₀ was significantly lower than that of FN₁,FN₂ and FN₃?P<0.05?,and NN₀ was significantly lower than that of NN₁,NN₂ and NN₃?P<0.05?,that showed plastic film mulching could reduce the rate of ecological respiration,the application of nitrogen fertilizer would promote the ecological respiration rate.After the plastic film mulching significantly reduced the sensitivity of the underground 5cm temperature and surface temperature,and the underground 5cm temperature sensitivity to ecosystem respiration was more sensitive than surface temperature and atmospheric temperature.?2?CO₂ net ecosystem exchange of FN₃ treatment was higher than NN₃ treatment?P<0.05?,and the residual was not,that is,the plastic film mulching could increase the net exchange flux of CO₂.And the sample with plastic film and the conventional both shown CO₂ net ecosystem exchange increased with the increase of N fertilizer,while,CO₂ net ecosystem exchange would be inhibited if N fertilizer supply was excess.