Experimental Study On Effects Of Different Water And Fertilizer Managements On Water Use And Carbon Balance Of Paddy Fields In Black Soil Region Under Straw Returning

Farmland ecosystem carbon pool is an important part of terrestrial ecosystem carbon pool,accounting for 17%of the global land area,and it is the most active part.Carbon sequestration and emissions of farmland ecosystem are sensitive to different field management measures,and have important impacts on carbon balance of terrestrial ecosystems and global climate change.Irrigation mode and nitrogen application rate are the two farmland management measures which have great influence on carbon sequestration and emissions.Different water and fertilizer management will affect the carbon cycle,but due to the spatial heterogeneity of soil,the effects of the same field management measures on carbon cycle of different soil types of farmland ecosystems may be different.Obviously,integrating the factors of soil types will help to accurately evaluate the effects of different water and fertilizer management on soil carbon poolAs an important rice planting area in China,the average amount of water resources occupied by cultivated land in northeast black soil area is far lower than the national average level.Therefore,it is imperative to implement water-saving irrigation for the sustainable development of agriculture in northeast black soil area.Abundant straw resources have been produced in the process of rice production,but the black soil area in northeast China is still facing the problems of serious straw burning and low utilization rate.Therefore,it is of great significance to explore the effects of different water and fertilizer management measures on the carbon balance of black soil paddy fields under straw returning to promote the sustainable development of agriculture in northeast black soil region and ensure national food security.The experiment was carried out in Qing’an irrigation experimental station of Heilongjiang Province in 2019.The effects of different water and fertilizer management measures on rice yield,water use efficiency,total soil respiration rate,heterotrophic respiration rate and root respiration rate during the whole growth period of rice were analyzed by using the method of field experiment plot.The net primary productivity and carbon emissions from heterotrophic respiration of black soil paddy fields under different water and fertilizer management measures were studied,and the carbon balance of black soil paddy fields ecosystem was calculated.The main results are as follows:（1）Compared with conventional irrigation mode,both controlled irrigation and intermittent irrigation can improve rice yield and water use efficiency.Under the two water-saving irrigation modes,rice yield and water use efficiency increased with the increase of nitrogen application rate.The yield of different nitrogen application rate treatments under controlled irrigation were significantly higher than that under intermittent irrigation and conventional irrigation.The yield of N2 treatment under intermittent irrigation was significantly higher than that of CK treatment（P<0.05）.Water use efficiency of CK treatment was significantly lower than that of controlled irrigation and intermittent irrigation,and water use efficiency of controlled irrigation was significantly higher than that of intermittent irrigation（P<0.05）.（2）Compared with the conventional irrigation mode,the total soil respiration rate,heterotrophic respiration rate and root respiration rate were increased under controlled irrigation and intermittent irrigation.During the whole growth period of rice,the total soil respiration rate,heterotrophic respiration rate and root respiration rate increased with the increase of nitrogen application rate under controlled irrigation and intermittent irrigation.Except for the turning green stage,the total soil respiration rate,heterotrophic respiration rate and root respiration rate of different nitrogen application rates under the controlled irrigation were higher than those under the intermittent irrigation.The total soil respiration rate,heterotrophic respiration rate and root respiration rate of CK treatment were higher than those under the controlled irrigation and intermittent irrigation.The total soil respiration rate,heterotrophic respiration rate and root respiration rate of CK treatment were lower than those of controlled irrigation and intermittent irrigation.（3）Compared with the conventional irrigation mode,both controlled irrigation and intermittent irrigation can improve the net primary productivity of black soil paddy fields,and increase with the increase of nitrogen application rate.The net primary productivity of different nitrogen application rate treatments under controlled irrigation were higher than that under intermittent irrigation,but there was no significant difference（P>0.05）.the net primary productivity of CK treatment was higher than that of N1 treatment under controlled irrigation and intermittent irrigation by 14.57%and 14.99%,respectively,but there was no significant difference（P>0.05）.The net primary productivity of N2treatment was significantly lower than that of controlled irrigation and intermittent irrigation（P<0.05）.（4）The results showed that the carbon emissions of heterotrophic respiration increased with the increase of nitrogen application rate,and the carbon emissions of heterotrophic respiration of different nitrogen application rates under controlled irrigation were higher than those of the same nitrogen application rate under the intermittent irrigation.The carbon emissions of heterotrophic respiration of CK treatment were higher than those of N1 treatment under controlled irrigation and intermittent irrigation by 11.11%and 16.11%,respectively.However,there was no significant difference（P>0.05）.The carbon emissions of heterotrophic respiration of CK treatment was significantly lower than that of controlled irrigation and intermittent irrigation（P<0.05）.（5）Compared with the conventional irrigation mode,controlled irrigation and intermittent irrigation enhanced the carbon sink capacity of black soil paddy fields.Under straw returning,the black soil paddy fields under different water and fertilizer management measures acted as carbon sink.Under intermittent irrigation mode,the net ecosystem productivity of N2 treatment was the highest,which was4242 kg·hm^-2.The net ecosystem productivity under intermittent irrigation was higher than that under controlled irrigation,but there was no significant difference（P>0.05）;the net ecosystem productivity of CK treatment was lower than that under controlled irrigation and intermittent irrigation,but there was no significant difference（P>0.05）.