Effect Of Plastic Film Mulching And Nitrogen Application On Nitrous Oxide Emission From A Vegetable Field

Plastic film mulching and nitrogen fertilizer application,as two important agronomic measures in modern agricultural production,have important effects on crop and soil properties and have been extensively studied before.Nitrous oxide?N₂O?is one of the most important greenhouse gases,which has a strong destructive impact on the ozone layer,and mainly comes from agriculture ecosystems.At present,there are few studies on the effect of film mulching and nitrogen application on N₂ O emission from cropland ecosystem,while less rare studies are reported from vegetable ecosystem.Therefore,in this study,a 2-year field experiment from May 2014 to March 2016?The first year: from May 18,2014 to March 22,2015,the second year: from March 23,2015 to March 14,2016?in 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,and the pepper-radish rotation vegetable field was taken as the research object,meanwhile,eight treatments: mulching with non-nitrogen fertilizer?FN₀?,mulching with low nitrogen fertilizer?FN₁?,mulching with normal nitrogen fertilizer?FN₂?,mulching with high nitrogen fertilizer?FN₃?and no mulching with zero,low,normal and high nitrogen fertilizer?NN0,NN1,NN₂,NN3?were set up,to explore the effects of film mulching and different nitrogen application rates on the N₂ O emission characteristics,soil hydrothermal condition and carbon and nitrogen components of the vegetable ecosystem,and the influencing factors,to show the characteristics of N₂ O emission from the soil under the film,and to provide the theoretical basis for exploring the farmland management measures to reduce N₂ O emission from vegetable ecosystem.The main results are as follows:?1?N₂O average emission flux of FN₃,FN₂,FN₁ and FN₀ were 503.76,163.31,137.47 and 46.98 ?g·m-2h-1;and that of NN3,NN₂,NN1 and NN0 were 468.91,264.42,165.28 and 52.04 ?g·m-2h-1,respectively.Film mulching could significantly reduce N₂ O emission under low nitrogen and medium nitrogen conditions?P<0.05?.Further comparison in different periods found that the effect of film mulching on soil N₂ O emission depended largely on the environmental and precipitation conditions ofdifferent seasons.In general,mulching measures could reduce the N₂ O emission in spring and summer,while in autumn and winter film mulching showed promotion to N₂ O emission.?2?Nitrogen fertilizer application was a key factor to promote N₂ O gas emission from vegetable field.During the two years of observation,the average emission flux of N₂ O increased with the increase of nitrogen application rate.And one-way analysis of variance showed that compared with the non fertilized vegetable field,the high nitrogen treatment was more obvious to the N₂ O emission of the film mulching and conventional vegetable field.In this study,the N₂ O emission coefficient of vegetable field was highest in the first winter and autumn season under FN₃ condition,and it was 0.14% ².91% in other planting seasons.?3?Except high nitrogen treatment,mulching measures made the N₂ O accumulation of soil reduce by 61.73%,20.25% and 28.50% under medium,low and no nitrogen treatment,respectively,while the fertilization increased the N₂ O accumulation in soil,and the amount of fertilization the higher,the greater the cumulative N₂ O emissions were(conventional: high nitrogen 74.95 kg·hm-2>medium nitrogen 42.26kg·hm-2>low nitrogen 26.42 kg·hm-2> non-nitrogen 7.89 kg·hm-2;film mulching: high nitrogen 80.52 kg·hm-2>medium nitrogen 26.13 kg·hm-2>low nitrogen 21.97kg·hm-2>non-nitrogen?6.14 kg·hm-2?.In addition,the cumulative N₂ O emissions from each treatment also showed significant inter annual differences,the cumulative annual emissions of the second year were significantly lower than those of the first year,which was mainly due to the cumulative N₂ O emissions were much higher in the first year of pepper planting period than those in the same planting period of second year.?4?During the whole observation period,the concentration of N₂ O at different depths of the soil was similar to that of the surface.The average concentrations of N₂ O at 10 cm,20 cm and 30 cm in soil profile were,film mulching: 1.84,2.77 and 2.95ppmv?1 ppmv=10-6 V/V?,conventional: 1.56,2.71 and 2.70 ppmv,respectively.The N₂ O concentration in the soil profile under the condition of mulching and non-mulching both increased with the depth of the soil.There was no significant difference in soil N₂ O concentration between the two treatments?P>0.05?.?5?The average emission flux of N₂ O of film furrow treatment?56.91 ?g·m-2h-1?was slightly higher than that of ridge?49.30 ?g·m-2h-1?in the first year of the winter radish planting season.During the second year of pepper and radish planting,there was little difference between N₂ O emission flux of conventional furrow and furrow covered with film,lower than that of the ridge,indicating that effects of mulching on N₂ Otransport between mulching and conventional farmland were slight.?6?The soil temperature of 10 cm,20 cm and 30 cm soil layers increased by 3.8%,3.4% and 4.9% under the mulching,respectively,compared with the conventional treatments.The water retention of the plastic film was reflected in autumn and winter radish cultivation?P<0.05?.Film mulching had a positive effect on soil inorganic nitrogen and Alkali hydrolyzable nitrogen,but the effect on soil TN and its soluble components were not significant?P>0.05?,indicating that the mulching played a vital role in the soil mineral nitrogen content.The effect of film mulching on the average content of SMBC and SMBN during the whole observation period of vegetable soil was not significant,but the content of SMBC and SMBN could be increased obviously in autumn and winter in the first year.Moreover,the soil urease activity was higher in the mulching treatment than that in conventional treatment in the two radish planting seasons,however,there was no notably difference between the two treatments in spring and summer.The water content might be the main reason to limit the content of SMBC and SMBN in the vegetable soil under the condition of little temperature difference,meanwhile,urease activity was greatly affected by soil pH.?7?Under the condition of high nitrogen level,the yield of radish of film mulching was increased by 42.39% and 33.70% compared with that of non plastic film during the two years of radish planting,respectively.Under other conditions,there was no significant difference between the yield of film mulching and conventional vegetable crops,but the yield of crops under different nitrogen treatments was 2 to 3 times than that of nitrogen application.That was to say,the effect of film mulching on the yield of vegetables was only realized under the condition of high nitrogen.?8?The N₂ O emission fluxes were closely related with soil temperature,soil ammonium nitrogen content and carbon nitrogen ratio?C/N?,in addition,the N₂ O emissions of conventional treatment were restricted by precipitation,and soil pH was one of the important factor that effect the N₂ O emission fluxes of film mulching vegetable soil.