Abstract:In order to find out the effect of different water and nitrogen coupling methods on the carbon cycle of paddy fields in the black soil area of Northeast China, the field experiment was conducted in the black soil paddy field in Heilongjiang Province. Field irrigation experiments were conducted in 2018. The conventional irrigation (F) and controlled irrigation (C) were used as two irrigation methods. Four N application rates: N0 (0kg/hm2), N1 (85kg/hm2), N2 (110kg/hm2) and N3 (135kg/hm2) were set in the whole growth period. Average soil respiration, microbial respiration and root respiration rates of rice under eight different waternitrogen coupling modes were measured during the period from regreening stage to milky stage and carbon sequestration of rice organ were measured after harvesting. The results showed that the total carbon sequestration of rice plants was 446.49~716.92g/m2, of which the total carbon sequestration of CN2 treatment was the largest. At the same time, the carbon sequestration of rice organs after harvest from large to small was in the order of panicle, stem, leaf and root. The average carbon sequestration of four organs accounted for 53.69%~59.44%, 27.42%~30.12%, 7.24%~8.96% and 4.71%~8.35% of the total carbon sequestration of rice plants, respectively. Controlled irrigation mode could increase carbon sequestration of rice. Under the same nitrogen application rate, carbon sequestration of stem, leaf and root organs under controlled irrigation mode was higher than that under conventional irrigation mode. Carbon sequestration of panicles under controlled irrigation was higher than that under conventional irrigation except that of CN0 treatment, which was lower than that of FN0 treatment. The average soil respiration rate, microbial respiration rate and root respiration rate of rice were increased first and then decreased under all waternitrogen coupling modes, and reached the peak at tillering stage. Compared with nonfertilization, the average soil respiration, microbial respiration and root respiration were increased after applying fertilization, and increased with the increase of nitrogen application, except the period of seeding. The average soil respiration rate, microbial respiration rate and root respiration rate of rice under controlled irrigation mode were higher than those under conventional irrigation mode at all growth stages, except the period of seeding. The carbon sink intensity of black soil paddy field was stronger under different nitrogen application coupling modes, but the carbon sink intensity was different among different treatments, and the carbon sink intensity of CN2 treatment was the largest. The research results can provide the necessary theoretical basis for improving carbon sequestration and emission reduction potential of black soil paddy field, and provide data support for estimating regional and global carbon balance.
