Abstract:To investigate the impact of water and nitrogen management on the carbon budget of rice field ecosystems, field experiments were conducted, with two irrigation modes: dry-wet-shallow irrigation (D) and flooded irrigation (F), as well as three fertilization levels: 110kg/hm2 (local fertilization standard, N1), 99kg/hm2 (nitrogen reduction of 10%, N2), and 88kg/hm2 (nitrogen reduction of 20%, N3). The dry matter quality and carbon content of different organs of rice harvested in residual rice fields were observed, the CO2 and CH4 emissions fluxes from rice fields were simultaneously monitored, and the net primary productivity (NPP) of rice and the net ecosystem primary productivity (NECB) of rice fields were calculated. The results showed that water and nitrogen management would affect the dry matter and carbon content of various organs in rice plants. Among all treatments, the NPP of DN2 treatment was the highest (8918.02kg/hm2), and the NPP of dry-wet-shallow irrigation mode was greater than that of flooded irrigation mode, increasing by 12.13%, 36.73%, and 8.01%, respectively. The dry-wet-shallow irrigation mode increased the CO2 emission flux of rice field soil respiration, reduced the application of nitrogen fertilizer reduced the CO2 emission flux, and reduced the application of nitrogen fertilizer in dry-wet-shallow irrigation reduced the CH4 emission flux. The total emissions of CO2 and CH4 from each treatment under both irrigation modes dwere ecreased with the decrease of nitrogen fertilizer application. The total emissions of CH4 from each treatment under flooded irrigation mode were significantly higher than those under dry-wet-shallow irrigation mode (P<0.05). The net carbon budget of the rice field ecosystem under each treatment was positive,and the rice field ecosystem with high residual stubble in the black soil area showed a carbon “sink”, with the highest NECB of 1950.96kg/hm2 in the DN2 treatment. Overall, the carbon sink of the rice field ecosystem treated with dry-wet-shallow irrigation mode and 10% nitrogen reduction treatment was the strongest, and the research results can provide theoretical reference and technical support for the protection of black soil in cold regions.
