Abstract: To seek a better management measure of irrigation and nitrogen application for carbon emission reduction in summer soybean cropland in Yili River valley of northern Xinjiang, a field experiment with two-factor split plot design was conducted in Yining County in 2013. There were four levels of irrigation (3000, 3600, 4200, 4800 m³·hm^-2, designated as W1-W4) and three levels of nitrogen application (0, 150, 300 kg·hm^-2, designated as N0, N1 and N3). We examined the impacts of different irrigation and nitrogen fertilizer managements on carbon fixation, carbon emissions during production, soil respiration, net carbon absorption of cropland ecosystem. The results showed that under the irrigation levels of W2, W3 and W4, the changing curve of the total carbon fixation in soybean field emerged a climbing tendency firstly and then decreased with the increasing nitrogen application rates. The total carbon fixation of W3N1 treatment was 13902.53 kg CO²·hm^-2, being 16.4% and 6.5% higher than W1N0 and W4N2, respectively. Irrigation electricity, as the main source for carbon emission in agricultural inputs, accounted for 58.0%-77.1% of the total carbon emissions of production materials. Following that of irrigation electricity, chemical fertilizer accounted for 6.0%-21.6% of the total emission. The more production materials were inputted, the higher amount of total carbon emission was detected. The value of net carbon absorption of each treatment was positive, indicating carbon fixation in the soybean cropland ecosystem. W3 irrigation had the highest net carbon absorption. Under the condition of irrigation amount of 4200 m³·hm^-2 and nitrogen application amount of 150 kg·hm^-2, high soybean yield and carbon fixation were obtained, with net carbon absorption being enhanced.  

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