The effect of crops production on the greenhouse gas emissions and agricultural option for mitigation of greenhouse gas emissions

Abstract

作物生產過程所排放之溫室氣體，以甲院及氧化亞氮為主。依據目前資料所示，每年農業（作物與畜牧）所排放之溫室氣體（包括CO2、CH4及N2O)，所增加之輻射溫暖化作用（radiative forcing）之比例，佔全球人為增加輻射溫暖化作用之20％。甲院與氧化亞氮的生成量依次佔全球人為排放量之50％與70％。本省農業土壤每年約排放35000公噸之cH4及10492公噸之N2O-N。大氣中CO2濃度的增加可直接促進光合作用而增加作物產量。但增溫與CO2之增加對作物其他生理反應，如呼吸作用，水分蒸散，水分利用效率，生育期的改變，作物品質等皆可能有正面或負面的影響。此外，對作物的生長環境，如土壤有效水分與養分的供應及土壤溫度等等，均將因氣候改變而間接影響作物的生產。減緩大氣中CO2濃度之上升，在作物生產上，應自減少石化燃料之消耗，增加碳在土壤中或地表貯存量。例如改用最少耕耘法，灌溉程序之訂定，日光乾燥作物，改善有機肥料管理及利用生物燃料。耕地排放甲院主因水田或大雨後土壤浸水而生成，欲降低CH4自農耕生產中生成，應設計較佳的水田浸水管理制度，動物廄肥之貯存，處理與利用。農業上N2O之釋放，主要係來自施用氮素肥料與土壤有機質之礦化，欲減少N2O自農耕地中排放，最佳方扶為增進肥料利用率，其次為使用硝化及尿素水解之抑制劑，整合作物與畜牧生產等。未來研究是(l)建立CO2,CH4及N2O自各重要土壤排放量，(2)研究其有效減量措施，(3)比較CO2、CH4及N2O田間實測值與IPCC怯之測值，(4)建立合用於台灣之土壤排放CO2,CH4及N2O之模式。 Crops production contributes significantly to anthropogenic emissions of carbon dioxide, methane and nitrous oxide. Current data shown that, Agriculture accounts for 20% of the annual increase in anthropogenic greenhouse warming. Most of this is due to methane and nitrous oxide agriculture produces about 50 and 70%, respectively, of their anthropogenic emission. The annual emissions of CH4 and N2O were about 35,000 CH4 tons and 10,492 tons N2O-N, respectively, in Taiwan area. Crop production may increase with increasing of CO2 level by stimulating photosynthetic rate. However plant respiration, transpiration, water use efficiency, growth development and the quality of the crops may be positively or negatively altered by increasing CO2 level and warming. In addition, CO2 level and warming may also affect soil moisture status, nutrient applying capacity, soil temperature and so on. Significant mitigation in CO2 from agricultural can be achieved through reducing fossil fuel usage, for example, minimum tillage, irrigation scheduling, solar drying of crops, improved fertilizer management and boifuel production, in-crease the carbon pooi in soil or on soil surface. The CH4 emission from soils, the major factor is water immersion field soil, e.q. paddy soil and after heavy rain. Significant decrease in CH4 emission from agriculture can be achieved through better management of paddy rice fields, alternative treatment and management of animal wastes. Agricutural N2O emission are thought to arise from fertilization of soils with mineral N and animal manures, and mineralization of soil organic matter, N2O emission from agriculture could be reduced by improving agriculture management with available techniques, for example, improving fertilizer use efficiency, applications of nitrification and urease inhibitors, integrating crop and animal forming et al. Future studies are: 1) Estimation of CO2, CH4 and N2O emissions from various important soils of Taiwan, 2) Study of their mitigations , 3) Comparison of field measurement data of CO2, CH4 and N2O emissions with those by IPCC method, and 4) Development of suitable models to estimate CO2. CH4 and N2O emissions in Taiwan