典型区域稻田温室气体（CH4和N2O）减排对策及机理研究

The paddy fields under perennial flooding are the type of paddy fields highest in potential for reduction of CH4 emissions. The most effective way is undoubtedly to let this type of paddy fields drained up during the non-rice growing season. However, this mitigation option seems impractical due to water shortage in these regions. Plastic film mulching cultivation is a promising alternative technology for the traditional flooded cultivation system of rice. Water-saving management is adopted for plastic film cultivation of rice. Then, with flooded cultivation being replaced by plastic film mulching cultivation, it becomes practical to drain up rice fields perennially flooded during the non-rice growing season. While suppressing CH4 emission from rice fields, water-saving irrigation usually promotes N2O emission. The by-effect can be reduced by application of nitrification inhibitor. Unlike traditional cultivation with both basal fertilization and topdressing, fertilizer is only applied before rice transplanting for plastic film mulching cultivation. The controlled-release fertilizer may be more suitable for plastic film mulching cultivation. This experiment will be conducted in Ziyang, Sichuan province. Double-crop rice field quite high in soil moisture content during the fallow season is another type of rice field with high potential of reduction of CH4 emissions. For this type of rice field, the effect of ditching to reduce soil moisture content during the non-rice growing season on reduction of CH4 emission during the rice growing season would be pronounced. Also due to lack of post-rice-harvest field management, rice stubbles remain standing until they are incorporated with soil by spring ploughing for early rice cultivation next year. The returning of generally fresh rice straw will increase CH4 emission during the early rice growing period significantly. If rice stubbles are ploughed into soil as soon as possible after late rice harvest, its stimulating effect on CH4 emission might be reduced sharply. Apart from CH4 emission, CH4 production and oxidation will also be monitored by stable carbon isotope technique to clarify the microcosmic mechanisms. Both CH4 and N2O emissions will be measured simultaneously in these experiments which will be conducted in Ziyang, Sichuan province and Yingtan, Jiangxi province.

四川、江西等省份存在大量冬季淹水或水分含量较高的稻田，其CH4排放量居于全国前列。加强这些典型区域冬季农田管理或采用以覆膜栽培为核心，结合控释肥和硝化抑制剂施用的栽培管理方式，应能大幅减少稻田温室气体排放。稳定性碳同位素方法是研究与稻田CH4排放密切相关的CH4产生和氧化等土壤微观过程的最佳手段。本项目将选择稻田CH4减排研究方面具有重要地位的两类典型稻田，四川常年淹水稻田和江西冬闲双季稻田，通过田间和培养试验，充分应用国际先进的稳定性碳同位素方法，研究冬季农田管理和水稻栽培方式等对稻田CH4和N2O排放的影响及其机理，提出综合温室效应最小、切实可行且易于大面积推广的减排措施。本项目研究结果将为稻田CH4和N2O减控措施及机理研究提供丰富信息，为我国实现减排承诺作出重要贡献。

针对我国温室气体排放地位重要且减排潜力巨大的两类典型稻田，即常年淹水稻田和双季稻田，分别开展了稻季覆膜栽培和冬季农田管理等切实可行并易于大面积推广的减排技术研究，并结合稳定性碳同位素方法和分子生物学技术，从CH4产生和氧化过程方面深入阐明了稻田CH4减排机理。与此同时，全年观测CH4和N2O排放通量，从综合温室效应（GWP）与净生态系统经济预算（NEEB）的角度科学评价了各减排措施的效果。.连续4年的大田、温室盆栽及室内培养试验结果表明：常年淹水稻田在冬季仍然排放大量CH4，约占全年的18~60%。稻季排水减少CH4排放55~77%，导致GWP减少43~53%。若在冬季进行排水，则不仅能显著减少冬季CH4排放，还能减少后续稻季CH4排放，并进一步减少GWP 37~38%；深入分析发现：排水显著减少了土壤和水稻根的CH4产生，并提高了根际CH4氧化百分率10~20%，从而显著降低了常年淹水稻田的CH4排放；与常规栽培相比，覆膜栽培显著减少常年淹水稻田CH4排放但增加N2O排放，从而显著降低GWP 47%；覆膜栽培条件下施用硝化抑制剂显著减少N2O排放，并增加水稻产量2~8%；施用缓释肥增加CH4排放，但也显著降低N2O排放，从而对GWP无明显影响。综合经济效益和环境效益分析发现，覆膜栽培较常规栽培每年增加NEEB 5000 CNY ha−1以上，农户每年净经济效益（NEB）增加近2000 CNY ha−1；覆膜栽培条件下施用硝化抑制剂进一步提升NEEB，每年增幅约为200~1800 CNY ha−1，NEB每年约增加250~1600 CNY ha−1；与冬季不排水相比，冬季排水减少全年CH4排放20~24%，增加N2O排放38~48%，从而降低全年GWP 20~24%；冬季翻耕较不翻耕减少全年CH4排放10~15%，于是减少全年GWP 10~16%，冬季排水结合翻耕进一步减少稻田CH4排放，因此减少全年GWP 31%。.我国是农业大国，农田温室气体排放受到各方关注。本项目有助于从土壤微生物过程层次上探清常年淹水稻田和双季稻田温室气体排放巨大的原因，可为常年淹水稻田和双季稻田CH4和N2O减排提供数据支撑，并为提出符合我国农业生产实际的温室气体减排措施以及探明其机理提供科学的理论依据。