Effect Of Optimized Water And Nitrogen Management On Greenhouse Gas Reduction,Carbon Footprint And Profit Increase In A Double Rice System

The effect of water-saving irrigation,controlled release urea and reduced nitrogen application on carbon footprint,input-output benefit was evaluated in a double rice cropping system,and the optimized water and nitrogen practice which achieved the goal "low input-low emission-high output" was identified.The study focused on double rice cropping system in the Jianghan Plain,Hubei province,Central China.Designing 6 different water and nitrogen management measures :(1)U+CI: urea + conventional irrigation,as the control(CK);(2)U+SWD: urea +water-saving irrigation;(3)US+SWD: reduce 20% nitrogen application + urea + water-saving irrigation;(4)CRU+CI: polymer-coated controlled release urea + conventional irrigation;(5)CRU+SWD: polymer-coated controlled release urea + water-saving irrigation;(6)CRUS+SWD: reduce 20% nitrogen application + polymer-coated controlled release urea+ water-saving irrigation.Measurements were taken using the automatic static chamber-GC(gas chromatography)method,calculating the total greenhouse gas(CH4 and N2O)emissions of early and late rice growing season under different treatments;Calculating carbon footprint of double-cropping rice by life cycle method;Combining yield and production cost,carbon emission intensity per unit yield,net profit per unit area and net income per unit of double cropping rice under different treatments were calculated.The results are as follows:(1)CH4 and N2_O emission flux in different water and fertilizer treatments had an obvious seasonal variation law in double rice cropping system.CH4 emission was mainly concentrated at pre-tillering stage and earing stage.emission was mainly concentrated in the period of middle season field drying.Under watersaving irrigation,N2_O emission peak also appeared in wet-dry rotation.(2)In 2017 and 2018,CRUS+SWD caused the lowest CH4 emission and CRU+CI caused the lowest N2_O emission during whole double rice season.Water-saving irrigation caused the trade-off in CH4 and N2_O emissions and reduced the greenhouse effect in all rice season.Controlled release urea and reduced nitrogen application reduced CH4 and N2_O emission and the greenhouse effect in all rice season.(3)In 2017 and 2018,CRU+CI caused the highest grain and US+SWD caused the lowest grain during whole double rice season.The CRU treatments reached the higher grain than the U treatments with the rate by 6.8-17.5%(p<0.05).Water-saving irrigation and reduced nitrogen application had an unsettling effect on rice yield(p>0.05).CRUS+SWD still reached the higher grain than CK.(4)In 2017 and 2018,CRUS+SWD caused the lowest carbon footprint(p<0.05),followed by CRU+SWD?US+SWD?CRU+CI?U+SWD?U+CI.CH4 and N2_O emission was the biggest part of double rice carbon footprint(50.7%-69.9%).Carbon emissions from nitrogen fertilizer production was the second biggest part(21.6%-33.4%).(5)In 2017 and 2018,CRU+CI caused the highest cost during whole double rice season,about 32,500 yuan per year.US+SWD caused the lowest cost during whole double rice season,about 29,200 yuan per year.CRUS+SWD reached the highest net income per unit area,39.3%-51.3% higher than CK(p<0.05).CRUS+SWD caused the lowest carbon emissions per unit net income,58.6-63.1% lower than CK(p<0.05).The older of carbon emissions per unit net income from big to small was U+CI>U+SWD>US+SWD>CRU+CI>CRU+SWD>CRUS+SWD.In summary,water-saving irrigation,controlled release urea and reduced nitrogen application are the effective technology that can simultaneously mitigate GHG emissions,achieve high grain yield,reduce input of nitrogen fertilizer,water and manpower and increase net profit per unit area in the double rice cropping system.