The Research Of Soil Carbon Balance In Different Land Use Systems

In order to research the soil carbon balance in different land use systems, soil respirations were measured under farmland and grassland which transformed from farmland in Beijing suburb. The over ground and underground biomass, soil total nitrogen, soil organic carbon (SOC), soil light fraction organic matter and microbial biomass were also measured.In 2003, the soil respirations of the winter wheat-summer maize optimization system were measured, the grazing system in the same land with the farm system (clover and ryegrass), and the grassland which transformed from farmland for six years by soda lime absorption technique. Peak value of soil CO₂ efflux was in the period of 7/22⁷/30, and the grassland had the highest value, up to 27.0 g m^-2 d^-1.The sum soil CO₂ efflux of grassland were higher than farmland and grazing.The carbon balance were researched through the biomass and soil respirations. The result showed that the farmland system and the grassland system were all carbon pool of the atmosphere CO₂. The average NPP carbon and soil efflux carbon ratio (NPP/Rs) was from 0.93 to 1.33.SOC of 2004 was higher than SOC of 2003 in the plowed layer, the SOC of the grazing which transformed from farmland was increasing. The SOC of the grassland was higher than others. The content of soil inorganic carbon (SIC) decreased when the SOC content increased in the plowed layer, it showed that when the total carbon was immovable, the SIC and SOC were negative relative. The total nitrogen and SOC of soil were researched, the relativity of the grazing soil was well, and the relative quotient was 0.9946. The total carbon of farmland was the highest, 83745 g m^-3.The plowed layer soil light fraction organic matter of 2004 was higher than 2003. And soil light fraction organic matter of plowed layer was all higher than subsoil in different land use systems. The light fraction organic matter of grassland was much higher.The microbial biomass carbon were measured in 2004. The microbial biomass carbon of grazing plowed layer was higher than farmland. The microbial quotient had the same change trend with the farmland. The qCO₂ of grazing was higher than the farmland.