Greenhouse Gases Emission Of Wheat-Maize Rotation Farmland Under Deficit Irrigation Based On DNDC Model

Agricultural production is one of the main causes of greenhouse gas emissions,and a lot of water resources are consumed during agricultural production.Studying the characteristics of farmland greenhouse gas emissions under deficit irrigation is of great significance for saving water resources and mitigating climate change caused by greenhouse gases.In this paper,the winter wheat/summer maize rotation system in Guan-zhong Plain of Shaanxi is taken as the research object.The field experiment and DNDC model are used to study the characteristics of N₂O emission under deficit irrigation.The field trials were conducted from October 2017 to October 2018,and three irrigation levels?100%ET,80%ET,60%ET?were set for each of the four growth periods of winter wheat and summer maize?seedling stage,jointing stage,heading/tasseling stage,and filling stage?,a total of 6 treatments?CK?T1?T2?T3,?T4?T5,and CK treatment was full irrigation treatment?;use DNDC model to simulate the output of winter wheat and summer maize under water deficit at different growth stages and N₂O emissions from farmland soil,a total of 9 treatments were set up:CK is a sufficient irrigation control treatment,A11 and A12 are 20%and 40%water deficit at seedling stage,A21,A22 is 20%,40%water loss during jointing period,A31,A32 is 20%,40%water loss during heading/tasseling period,A41,A42 is 20%,40%water loss during filling period.The results indicated as follow:?1?The N₂O gas emissions from winter wheat-summer maize farmland soil have obvious seasonal changes,which are higher in summer,followed by spring and autumn,and the lowest in winter.The characteristics of soil N₂O gas emissions between different irrigation treatments were similar,and peak emissions occurred within 2-5 days after irrigation.The main peaks of N₂O gas emissions from various treatments in the winter wheat season appeared after fertilization and seeding at the seedling stage?October 23,2017?,reaching 281.05?366.06?g·?m²·h?^-1;the secondary peaks occurred during the heading irrigation?April 3,2018?on the 3rd day(20.34?99.02?g·?m²·h?^-1).The main peak of N₂O emission in summer maize season after planting at the seedling stage?July 5,2018?reached 129.73?211.78?g·?m²·h?^-1;the secondary peak appeared in irrigation at the jointing stage of corn?July 26,2018?on the second day,it reached 68.45?206.95?g·?m²·h?^-1.?2?Deficient irrigation can reduce farmland N₂O emissions to a certain extent.The average emission flux of N₂O gas in each growth stage of winter wheat is seedling stage>joint stage>heading stage>grouting stage>overwintering stage;the average emission flux of N₂O gas in different growth stages of summer maize is seedling stage>joint stage>tasseling stage>grouting stage.The total N₂O gas emissions from soils with different deficit irrigation treatments showed the highest CK in the full irrigation season,and T2?T3and T5 were significantly lower than CK by 29.72%,24.90%,and 23.12%?P<0.05?;the maize season showed:T4 treatment was the largest,followed by CK treatment,and the severe water deficit treatment T2 was significantly reduced by 20.05%compared with T4?P<0.05?.The difference between the other treatments was not significant?P>0.05?.?3?The N₂O emission flux of winter wheat-summer maize rotation farmland soil under deficit irrigation was significantly positively correlated with 0?10 cm WFPS?water filled pore space??P<0.05?,and some treatments reached extremely significant levels?P<0.01?.There is a positive correlation between the N₂O gas emission flux of farmland soil and the soil temperature at 0?10 cm,but it has not reached a significant level?P>0.05?.?4?The DNDC model can better simulate the growth of winter wheat-summer maize rotation cropland and soil N₂O emissions under different deficit irrigation treatments.The DNDC model simulation test results show that:considering comprehensive economic and environmental benefits,seedling stage and jointing stage are important periods for water saving and emission reduction of winter wheat/summer maize.A11?20%water deficit at seedling stage?treatment is the optimal treatment for winter wheat season water emission reduction,followed by A21?20%water deficit at jointing stage?treatment;A21?20%water deficit at jointing stage?treatment for summer maize season is the optimal water-saving and emission-reducing treatment,followed by A11?20%water deficit at seedling stage?and A31?20%water deficit at tasseling stage?treatment.In summary,the results of the field positioning test and the DNDC simulation test showed that deficit irrigation can reduce soil N₂O gas emissions,increase WUE,and reduce N₂O emission intensity while ensuring crop yield.If we can combine the emission and absorption of N₂O and soil carbon,we can more comprehensively explore the effect of winter wheat/summer maize farmland emission reduction under deficit irrigation.