双季稻减排增收的水氮优化管理模式筛选

Pattern selection of water and nitrogen practices to reduce greenhouse gas emission and increase profit in a double rice system

为筛选出"低投入-低排放-高收益"的稻田水氮管理模式,该研究以汉江平原双季稻为研究对象,设计4种氮肥管理方式:1)普通尿素;2)树脂包膜控释尿素;3)普通尿素减氮20%;4)控释尿素减氮20%,和2种水分管理方式:1)常规灌溉;2)薄浅湿晒节水灌溉。采用静态箱-气相色谱法测定甲烷(CH4)和氧化亚氮(N2O)的排放量,应用生命周期法(Life Cycle Assessment,LCA)计算水稻生产碳足迹,基于成本收益核算分析单位水稻产量和单位净收益的碳排放强度。结果表明,控释尿素能有效提高双季稻产量,节水灌溉和减氮20%能节约投入成本,对双季稻产量存在一定负效应,但差异不显著。相比普通尿素和常规灌溉,不同水氮优化处理可不同程度降低水稻生产的碳足迹和排放强度,并有助于提高收益。其中节水灌溉搭配控释尿素减氮的综合减排效果最好,早、晚稻总减排量分别为45.8%和42.5%(P<0.05),同时全年净利润最高,达14340元/hm^2。因此,节水灌溉、控释尿素同时减氮20%的组合技术可实现稻田节本减排增收。

Rice paddy field has been an important emission source of greenhouse gas.A combination of water-saving irrigation,controlled release urea,and reduced nitrogen can offer the promising potential to decrease the emissions of greenhouse gas,while,to increase grain yield simultaneously in rice cultivation.Aiming to verify which the water and nitrogen practice can achieve the goal of"low input-low emission-high benefit",a field experiment was conducted in a double rice cropping system in the Jianghan Plain,Hubei province,China.Four nitrogen practices were designed:1)urea(U),2)polymer-coated controlled release urea(CRU),3)20%reduced urea application(US),and 4)20%reduced polymer-coated controlled release urea application.Two water practices were integrated,1)the conventional irrigation with mid-season drainage(CI),and 2)water-saving irrigation with shallow water depth and alternation of wetting and drying(SWD).The automatic static chamber method equipped with gas chromatography was applied to the sample,further to measure the emissions of greenhouse gas(CH4 and N2O)during the rice growing season under various treatments.A life cycle analysis(LCA)was used to calculate the carbon footprint in the rice production system.The intensity of carbon emission per unit grain yield was estimated using cost-benefit analysis,together with the unit net income.The results showed that the controlled release urea and reduced rate of nitrogen application can alleviate both emissions of CH4 and N2O,while,the water-saving irrigation decreased CH4 emissions but increased N2O emissions.The yield of grain increased with the application of controlled release urea,while,decreased with the water-saving irrigation,and 20%reduction in nitrogen application,but these negative effects can be ignored in the practical case.The LCA indicated that CH4 and N2O emissions in the double rice cultivation contributed the highest portion to total carbon footprint(50.7%-69.9%),followed by nitrogen input(21.6%-33.4%).The carbon footprint and net income decreased at varied levels under the treatments of water-saving irrigation,controlled release urea,and reduced rate of nitrogen application.Compared with the treatment of U+CI,the CRUS+SWD treatment achieved the highest reduction in carbon emissions(P<0.05),followed by CRU+SWD,US+SWD,CRU+CI,and U+SWD.It infers that the application of controlled-release urea led to much higher input cost,while,the reduction of nitrogen application amount can decrease this cost.The water-saving irrigation directly saved the water,electricity and manpower consumption,showing a lower cost.Considering both input cost and yield production,the controlled-release urea contributed to the increase of net profit for the double rice,where the CRUS+SWD achieved the highest net profit,followed by CRU+CI.The net income of carbon footprint decreased noticeably under all other treatments,compared with the urea and conventional irrigation.Particularly,the treatment of CRUS+SWD achieved the lowest intensity of carbon emission(0.51 kg/yuan),62.7%lower than that of U+CI.The data confirmed that the combination of water-saving irrigation,controlled release urea with 20%reduction in nitrogen application rate can be used to save the input cost,while to improve net profit,and thereby to effectively reduce carbon emission intensity in a double rice cropping system.These findings can also provide a promising theoretical support for the production of low carbon rice in China.