[Objective] This study aimed to investigate the effect of soil organic carbon mineralization at different temperature on the amount of nitrogen application, in order to provide references for the establishment of carbon circulation model for orchard eco-system. [Method] The effects of nitrogen treatments on soil organic carbon mineralization of citrus orchard soil were investigated under 10, 20, 30 ℃ by laboratory simulated experiment. [Result] The mineralization rate decreased quickly at the be- ginning of the experiment but remained stable at the late period under three temper- ature treatments. The amounts of CO2 ranged from 1 328.25-2 219.42 mg/kg under three temperature condition, and the amount of soil organic carbon mineralization of 100 mg/kg （N4） treatment was the greatest, while that of CK was the lowest. High level nitrogen treatment （N4 and N3） were significant higher than the lower level nitro- gen treatment （N2 and N1）. The soil organic carbon mineralization rate increased with the temperature from 10 to 30℃. The dependence of soil carbon mineralization to temperature （Q10） was different under different nitrogen treatments that the Qlo value of N2 treatment was the lowest while that of the N4 treatment was the greatest. The soil organic carbon mineralization in Citrus orange orchard soil was affected significantly by high level nitrogen treatment, but with no significance under lower nitrogen treatment. [Conclusion] The dependence of soil carbon mineralization to temperature （Q10） increased with the increasing nitrogen input. The combination of nitrogen with temperature may increase the CO2 emission from Citrus orchard soil.
Studies related to the quantitation and distribution of soil organic carbon （C） under different land use types can help to fill the knowledge gaps regarding estimation of the amount of C stored in soils at a global scale. Orchards are an important land use type in southern China; the total area （1.15 x 107 ha） of orchards in China comprises approximately 20.5% of the area of all orchards worldwide. We assessed soil organic C stocks （SOCS） in citrus orchards in Yongchun County （consisting of 22 towns）, Fujian Province, China in 1982 and 2010. The southeastern part of the county, an area featuring extensive citrus farming with a gently sloping landscape and low rates of water erosion, had the highest SOCS. In contrast, the lowest SCOS was observed in the northern part of the county, where steep hills with severe erosion problems are common and citrus orchards are sparsely distributed. From 1982 to 2010, the mean SOCS in citrus orchards increased from 22.1 to 41.7 Mg ha-1 which indicated that current management practices such as fertilization, irrigation, and cultivation enhanced soil C stocks. Further in-depth studies on the effects of these practices on C sequestration would be worthwhile and surveys of SOCS throughout Fujian Province are needed, to support efforts to mitigate global C emission.
WANG YixiangWENG BoqiTIAN NaZHONG ZhenmeiWANG Mingkuang
