Effects Of The Application Plastic Film Mulching,Nitrogen Fertilizer And Inhibitors On Nitrous Oxide Emission From A Vegetable Field

Due to the increasing vegetable planting area,high multiple crop index and the large amount of use of fertilizer,the greenhouse gases emissions on the vegetable land ecosystem have increased.Nitrogen fertilizer application is an important factor affecting N₂O emission in soil,and nitrification inhibitors could improve the fertilizer-nitrogen use efficiency?NUE?and increase crop yield effectively.Plastic film mulching and nitrogen application are two important agricultural measures,and there were a large amount of reports on the studies of growing conditions,crop yields and effects on the physical and chemical properties of soil.Furthermore,there were just a few researches on effects of plastic film mulching,nitrogen application and inhibitors on N₂O emissions from the farmland ecosystem,even fewer researches on the vegetable land ecosystem.Taking pepper-radish rotation as the research object and static opaque chamber/GC techniques as analysis methods,the field observation experiment was conducted for three years in common vegetable fields in Southwest China.Four nitrogen concentration gradients?high nitrogen,medium nitrogen,low nitrogen and zero nitrogen?were set under mulching and no mulching.In this study,the effects of plastic film mulching and nitrogen application on N₂O emissions,N₂O concentration in soil profile and soil environmental factors were investigated.In addition,the influence mechanisms of plastic film mulching and nitrogen application on N₂O emissions were discussed.Based on indoor pot tests for three months in a row,the effects of different kinds of nitrification inhibitors on N₂O emissions in vegetable fields were investigated,which will offer the scientific basis for reducing greenhouse gases emission from farmlands.The main results of this study are as follows:?1?During the complete observation period,under high nitrogen conditions,the average N₂O flux of the film-covered treatment was significantly higher than that of the conventional treatment?p<0.05?(film-covered:433.23?g·m^-2h^-1,conventional:411.45?g·m^-2h^-1);Under medium nitrogen conditions,the average flux of N₂O under film-covered treatment was lower than that under conventional treatment?p<0.05?(film coating:148.44?g·m^-2h^-1,conventional:242.47?g·m^-2h^-1);Under normal nitrogen conditions,the average flux of N₂O was significantly lower than that of the conventional treatment?p<0.05?(film-covered:123.07?g·m^-2h^-1,conventional:143.45?g·m^-2h^-1).It shows that the film-covered treatment can significantly reduce the N₂O emissions under normal nitrogen and low nitrogen conditions.During the complete observation period,the average flux of N₂O of film-covered treatment was significantly lower than that of the conventional treatment in the pepper season?p<0.05?,the radish season was just the opposite,it showed that film coating in spring and summer can reduce N₂O emissions,autumn and winter can promote its emissions.?2?During the complete observation period,there was an extremely significant positive correlation between N₂O concentrations in soils depths of 10,20 and 30 cm?P<0.01?,under conventional and film-covered treatment.The correlation analysis of N₂O concentrations in the same soil layer depth between the film-covered and conventionally-treated,it showed that there was also a extremely significant correlation between soil N₂O concentrations at the same soil depth in different treatments?P<0.01?.The correlation analysis of N₂O concentration and emission in soils showed that there was a extremely significant positive correlation between N₂O concentration and N₂O emission in conventional treatments?P<0.01?.The N₂O emission of the film treatment were significantly correlated with the N₂O concentration in the depth of 20cm?p<0.05?and more significantly correlated correlated with the N₂O concentration in the depth of 10cm and 30cm?P<0.01?.?3?In the first year of the radish season,the average emission N₂O flux of film furrow treatment was the highest in three years,which was 65.96?g·m^-2h^-1.There was no significant difference in cumulative N₂O emissions from film furrow and film ridge.In the second year of the radish season,the average emission flux of N₂O of film ridge was significantly higher than that of furrow?p<0.05?;there was no significant difference between the radish seasons in the third year?p>0.05?;In the second and third year of the pepper season,the average emission flux of N₂O of film ridge was significantly higher than that of furrow,and there was no significant difference between film furrowand conventional furrow?p>0.05?.This showed that the film has no significant effect on the main transport mode of soil-to-gas N₂O.?4?Under conventional treatment,when CP and DCD were used in combination,N₂O had the highest reduction rate of 90.12%;Under film-covered treatment,other inhibitors could reduce N₂O emissions,in addition to NBPT.When CP and DCD were used in combination,N₂O had the highest reduction rate of 55.72%;Through comparison,it was found that the inhibitory rate of each inhibitor of conventional treatment was higher than film-covered treatment.?5?During the observation period,the average WFPS of the film-covered treatment was significantly higher than that of conventional treatment?film-covered:18.21%;conventional:17.53%??p<0.05?.Further analysis showed that the average WFPS of the film-covered treatment was significantly lower than that of the conventional treatment?covered:16.06%conventional:16.68%??p<0.05?,and the conventional treatment increased by 3.86%compared with the film-covered treatment during the whole pepper season;during the entire radish season,the average WFPS of the film-covered treatment was significantly higher than that of the conventional treatment?film-covered:20.01%conventional:18.13%??p<0.05?,moreover,the plastic cover treatment increased by 10.37%compared with the conventional treatment,indicating the water-retaining effect of the plastic cover treatment was more noticeable in autumn and winter.Compared with the conventional treatment,the soil temperature at the 10,20 and 30cm under the film-covered treatment had average increases of 3.34%,3.01%,and 3.54%,respectively,in the whole pepper season.While,In the entire radish season,the soil temperature at 10,20,and 30cm under the film-covered treatment had average increases of 2.46%,1.72%,and 3.11%,respectively,compared with the conventional treatment.It indicated that the effect of the plastic cover treatment on the temperature was more prominent in summer.Plastic cover treatment could significantly increase the content of NH₄⁺-N and NO₃^--N in the soil.NH₄⁺-N in the soil was more significantly increased in the treatment of film-covered in pepper season than that in radish season?pepper season:67.09%,10.49%,45.14%;radish season:7.64%,48.04%,5.92%?;Otherwise,the content of the Alkali-hydrolytic nitrogen and TN in soil,can be improved by the film-covered treatment in the second year and the third year,except for the first year.The film covered treatment could significantly increase the content of SMBC in soil?25.49%,30.33%?;while had little effect on the content of SMBN in soil in the first and third year of the radish reason in this study.The soil urease activity in the film-covered treatment was significantly higher than that in the conventional treatments?p<0.05?,in the other crop seasons except for the second year of the pepper season,while the growth rate of soil urease activity under the treatment of film-covered in radish season was significantly higher than that in pepper season?p<0.05?.?6?In this study,increased production had nothing to do with film-covered treatment in pepper season,but applyed nitrogen fertilizer could increase the yield of pepper;The film-covered treatment increased the radish yield by 42.39%,33.70%and17.96%respectively in the three-year radish season,and only under high nitrogen conditions,the effect of film-covered treatment on the yield of radish was obvious.?7?Factor analysis of soil N₂O emissions under plastic film and conventional treatment,under conventional treatment,the variance contribution rates of the four main factors were 29.51%,18.84%,16.13%and 14.12%respectively,cumulative contribution rate was 74.60%;Under the film-covered treatment,the variance contribution rates of the three main factors were 28.14%,24.47%,and 18.06%,respectively,cumulative contribution rate was 70.67%.In order to further illustrate the relationship between the main factors of factor analysis and N₂O emissions,used multivariate stepwise regression analysis method to establish an optimal regression equation,finally,it was found that the distribution of nitrogen in the soil was the most important factor in determining N₂O emissions from the vegetable ecosystem.