MODELING THE IMPACTS OF MANAGEMENT ALTERNATIVES ON SOIL CARBON STORAGE OF FARMLAND IN SHAANXI PROVINCE
耕作措施对陕西耕作土壤碳储量的影响模拟*

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 CO_(2) 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.