CH₄ And N₂O Emissions Of Paddy Fields And Their Influence Factors Of Different Water And Nitrogen Managements Under Straw Returning In Black Soil Region

Rice is one of the main food crops in China.Heilongjiang province as a big rice province in China,its rice yield is of great significance to Chinese food security.However,a large area of rice fields will produce a large amount of CH₄and N₂O,causes a series of environmental problems.In recent years,the land area of rice planting in Heilongjiang province has been expanding year by year,it cause a large amount of rice is produced and the emissions of CH₄and N₂O are also increasing year by year.Straw is rich in nitrogen,traditional straw burning not only wastes straw resources,but also cause environmental pollution.As an economic and feasible treatment method,straw returning is great significance to reduce the emission of CH₄and N₂O.However,straw returning is bound to have an impact on the paddy field surroungding,so the traditional irrigation and fertilization methods should be adjusted.Therefore,it is great significance for rice production in Heilongjiang province to explore a reasonable way of irrigation and fertilization under the condition of straw returning,which can not only ensure the rice yield in Heilongjiang province,but also reduce the emission of CH₄and N₂O.On the basis of straw returning to field,the author set up three irrigation methods:flooding irrigation and intermittent irrigation and controlled irrigation,with four nitrogen gradients.The CH₄and N₂O emission fluxes of each treatment were measured by static box gas chromatography.Greenhouse gas emission intensity and global warming potential were calculated,and paddy soil under the coupling action of water and nitrogen was analyzed.The changes of soil redox potential,soil ammonium nitrogen content,nitrate nitrogen content and straw decomposition rate in different growth stages,as well as the effects of various factors on CH₄and N₂O emissions from paddy fields.The main results are as follows:（1）The daily average CH₄and N₂O emission fluxes of the three irrigation methods were basically consistent with that of CH₄and N₂O emissions between 9:00 and 12:00,and sampling between 9:00 and 12:00 could represent the daily CH₄and N₂O emissions.Under the same irrigation mode,the CH₄and N₂O emissions of each treatment were the same,the CH₄emission peak of the control irrigation was 66.13%～185.78%lower than that of the flooding irrigation,and the CH₄emission peak of the intercropping irrigation was 72.16%～106.75%lower than that of the flooding irrigation;the CH₄cumulative emission of the inter irrigation treatment was 21.09%lower than that of the flooding irrigation,and the CH₄emission of the control irrigation treatment was 63.63%lower than that of the flooding irrigation The emission of CH₄was 26.06%～44.48%lower than that of control irrigation,and the cumulative emission of CH₄was significantly increased by nitrogen fertilizer application under intercropping and controlled irrigation.Under the same nitrogen application rate,the CH₄emission flux under flood irrigation was 1.20～3.65 times that under controlled irrigation,and the CH₄emission flux under flood irrigation was47.29%～58.20%higher than that under intermittent irrigation and controlled irrigation.（2）The daily N₂O emission flux of controlled irrigation was significantly higher than that of inter irrigation and flooding irrigation,but there was no significant difference between them.The N₂O emission peak of each treatment under controlled irrigation was 90.78%～128.35%higher than that of flooding irrigation,and the N₂O emission peak value of each treatment under intercropping irrigation was 4.72%～163.29%higher than that of flooding irrigation,and there were multiple emission peaks in the whole growth period of rice under intercropping irrigation.The average cumulative N₂O emission of each treatment under controlled irrigation was 78.73%higher than that of flooding irrigation,and the average cumulative emission of N₂O under intercropping irrigation was 48.28%higher than that under flooding irrigation;under the control irrigation and inter irrigation mode,the cumulative N₂O emission increased by 14.85%～39.78%.Under the same nitrogen application rate,the average N₂O emission flux of different growth stages under controlled irrigation was 21.45%～30.50%higher than that of flooding irrigation,and the average N₂O emission flux of intercropping irrigation was 13.67%～18.21%higher than that of flooding irrigation.（3）The GWP of intercropping irrigation was 35.80%～85.85%higher than that of controlled irrigation,52.43%higher than that of submergence irrigation,and 160.18%higher than that of submergence irrigation.With the increase of nitrogen application rate,the GWP of controlled irrigation was increased by 19.93%～55.37%,and that of intercropping irrigation was increased by13.38%～23.89%.Under the same nitrogen application rate,the yield of intercropping and controlled irrigation decreased by 16.02%and 18.04%respectively compared with the control irrigation treatment;compared with the conventional nitrogen application,the yield of intercropping and controlled irrigation increased by 3.34%～4.77%.Under the same nitrogen application rate,the GHGI of control irrigation treatment was 67.88%deeper than that of flooding irrigation treatmentt,and the GHGI of flooding irrigation treatment was 55.08%higher than that of intercropping irrigation treatment.（4）The results showed that soil ammonium nitrogen significantly affected CH₄emission,but had no significant negative correlation with N₂O emission.There was no significant negative correlation between soil nitrate nitrogen and CH₄and N₂O emissions;soil eh had a significant negative correlation with CH₄and N₂O emissions;straw decomposition rate had a significant positive correlation with CH₄and N₂O emissions;There was no significant negative correlation between soil temperature and CH₄and N₂O emissions.The effects of nitrogen application rate on CH₄,N₂O emission and ammonium nitrogen content were significant at 0.01 level,while nitrate nitrogen content,soil Eh and straw decomposition rate were significant at 0.05 level.The effects of irrigation mode on CH₄and N₂O emissions were significant at 0.01 level,and significant at 0.05level for ammonium nitrogen,nitrate nitrogen content,soil Eh and straw decomposition rate;the interaction between nitrogen application and irrigation mode was significant at 0.05 level.To sum up,the recommended irrigation mode under straw returning is controlled irrigation with nitrogen application rate of 110kg/hm²,which can achieve the purpose of water saving,emission reduction and yield increase.