Effects Of Different Water Managements On Greenhouse Gas Emissions,Nitrogen Use Efficiency And Yields From Rice Fields

Rice is one of the staple foods in China,accounting for 35%of the total crop output,but the annual consumption of freshwater resources accounts for 60%.Paddy fields are grown in submerged soil,consume large amounts of water,and emit more greenhouse gases than most crops.Most rice production requires the application of nitrogen fertilizer to meet the needs of crops.Nitrogen fertilizer applied to rice crops is partially lost through different mechanisms such as ammonia volatilization,denitrification and leaching.These losses not only cause waste but may also cause environmental problems,such as pollution of the atmosphere,aquatic systems and groundwater.Therefore,it is of great significance for developing water-saving,low-carbon and high-yield rice cultivation technology to effectively reduce irrigation water and improve the utilization efficiency of water and nitrogen.This experiment studied the different moisture management on upland rice paddy soil available nitrogen,water soluble carbon,soil oxidation reducing state,functions of microbial abundance,greenhouse gas emissions（methane and nitrous oxide）,the influence of crop yield.Two irrigation methods were used in the experiment,namely flooded irrigation and water-saving irrigation.Three rice varieties were tested,huanghuazhan,7you88 and 7you370.Among them,Huanghuazhan is the local high-yielding conventional rice variety,and 7you88 and 7you370 are two newly bred three-line hybrid varieties with the characteristics of drought tolerance and high yield.Split-plot grouping design was adopted,with water management as the main plot and rice variety as the sub-plot.The experiment included 6 treatments,which were flood irrigation+Huanghuazhan,flood irrigation+7you88,flood irrigation+7you370,water-saving irrigation+Huanghuazhan,water-saving irrigation+7you88,water-saving irrigation+7you370,respectively.The main research results were as follows:（1）Different water management had significant effects on the available nitrogen and dissolved organic carbon（DOC）in paddy field soil.Compared with the flooding treatment,the content of ammonium nitrogen in the paddy field soil in water-saving treatment decreased by52.1%,the content of nitrate nitrogen increased by 50.2%,and the content of DOC decreased by 15.8%.Rice varieties had no significant effect on soil available nitrogen and DOC.（2）Different water treatments and rice varieties have significant effects on greenhouse gases CH₄ and N₂O in rice fields.Compared with the flooded water treatment,the cumulative CH₄ emissions in the whole rice season were reduced by 64.9%,the cumulative N₂O emissions were increased by 47.6%,the greenhouse warming potential（GWP）was reduced by 54.7%,and the greenhouse gas intensity（GHGI）was reduced by 46.5%.Compared with Huanghuazhan variety,the cumulative CH₄ emissions of 7you88 and 7you370 varieties decreased by 7.4%and 11.8%,the cumulative N₂O emissions decreased by 7.9%and 12.5%,the GWP decreased by 29.2%and 38.5%,the GHGI decreased by 18.2%and 25.5%respectively.（3）Different water treatments had significant effects on the abundance of functional genes of methane-metabolizing microorganisms,nitrogen cycling microorganisms and denitrifying bacteria in the paddy soil.Compared with the flooded treatment,the abundance of mcrA,a functional gene of methane-metabolizing microorganism,decreased by 43.3%and the pmoA increased by 46.2%.Compared with the flooding treatment,the functional gene abundance of AOA and AOB increased by 44.6%and 39.1%respectively.The functional genes of denitrifying bacteria nirK decreased by 36.4%,nirS decreased by 41.9%,and nirZ decreased by 42.3%compared with that of flooded water treatment.（4）Different water treatments had significant effects on rice yield and effective panicle number per unit area,and different rice varieties had significant effects on grain weight per thousand grains.Compared with flooded irrigation,rice yield and effective panicle number per unit area of water-saving irrigation decreased by 10.2%and 8.5%respectively.（5）Different water treatments had significant effects on nitrogen absorption and nitrogen absorption efficiency of rice.Compared with the flooded water treatment,the nitrogen absorption and nitrogen absorption utilization efficiency of rice under water-saving treatment decreased by 17.8%and 16%respectively.Rice varieties had no significant effect on nitrogen absorption and nitrogen absorption utilization efficiency.