耕作措施对陕西耕作土壤碳储量的影响模拟

MODELING THE IMPACTS OF MANAGEMENT ALTERNATIVES ON SOIL CARBON STORAGE OF FARMLAND IN SHAANXI PROVINCE

鉴于农业生态系统土壤有机碳(SOC)平衡对中国农业可持续发展的重要性,文章以陕西农业生态系统为对象,整合农业生物地球化学模型(DNDC)与陕西农业地理信息系统数据库,利用陕西地区气象和作物资料,对陕西省2000年作物生长发育和土壤碳循环进行了模型模拟,实例探讨了耕作管理对土壤碳储量的影响,并由此评价生物地球化学模型在气候变化、土壤性质及农业耕作管理措施对土壤碳含量影响方面的预测能力。敏感性分析表明土壤性状,尤其是初始有机碳含量是影响模型区域尺度模拟的最主要敏感因素。区域模拟使用灵敏系数分析法,分别采用敏感因子的最大、最小值驱动模型在每一模拟单元内的运算,以产生一个土壤有机碳变化的范围值,土壤有机碳变化的真实值应以较大机率包含在这一范围内。分析模拟结果可以得出3点结论:1)2000年陕西耕作土壤总有机碳储量约为103TgC,是一个大气CO2源,向大气释放碳0.5TgC;2)提高作物秸秆还田率是提高陕西农田碳库储量的有效可行措施,将作物秸秆还田率从当前的15%提高到50%或90%会使陕西农田土壤从大气CO2源转变为汇,每年分别增加土壤有机碳库储量0.7TgC或2.1TgC;3)施用有机农肥(500kg/hm2)也会增加土壤碳输入,从而提高土壤碳储量,使陕西农田系统转变为较弱的碳(C)源,每年可多固定0.2TgC。

During the past century China had experienced substantial economic, cultural and social changes that have set significant impacts on the agro-ecosystems. Decreases in soil organic carbon content and soil fertility have been widely observed in many agricultural regions. Maintaining farmland soil organic carbon content is essential for the sustainable development of Chinese agriculture. Shaanxi Province with typical inland agro-ecosystems was selected as a geographic domain for a modeling study reported in this paper. A process-based biogeochemical model DNDC was linked to a Geographic Information System （GIS） database holding spatially differentiated information of climate, soil, vegetation and management for Shaanxi to quantify impacts of farming management alternatives on C sequestration in farmland of this province. DNDC was first validated against a long-term SOC dataset observed in Hequ County in Shaanxi Province, which shared similar climate, soil and management conditions with Shaanxi. Sensitivity tests indicated that soil property especially initial SOC content was the major source of uncertainty generated from upscale modeling. The 300 million hectares of farmland in Shaanxi were modeled with a baseline management scenario as well three alternative management scenarios with increased crop residue incorporation and farmyard manure application. The modeled results can be summarized as follows： （1） Total SOC storage in all farmland of Shaanxi was 103TgC for the year 2000. Shaanxi farmland was an atmospheric carbon source with about 0.5TgC released into the atmosphere annually under the baseline farming management conditions. （2） An increase in the rate of above ground crop residue incorporation from 15% to 50% or 90% converted the entire farmland in Shaanxi from a source to a sink of atmospheric CO2 with 0.7TgC or 2. 1TgC annually sequestered into the SOC pool of the farmland respectively. （3） Application of farmyard manure enhanced SOC storage through increasing carbon input and converted the farmland into a weak C sink with 0.2TgC sequestered per year.