Effect of Different Cultivation Years on Soil Organic Carbon Pools in Citrus Orchards

Soil organic carbon is an important component of the global carbon cycle,and it has direct effects on the global carbon balance. Orchard is an important part of the landscape land, the area of which accounts for 1.15% of the total land area in China. To study the dynamic of soil organic carbon stock in orchard,would provide an important scientific basis to accurately evaluate carbon sequestration potential of terrestrial ecosystems. Effect of different cultivation years on soil stable organic carbon pools and fractions in Citrus orchard was investigated to elucidate the mechanism responsible for orchard soil carbon sequestration using the temporal-spatial substitution and physical and chemical fractionation methods. The results showed that the particle organic carbon content of 60' citrus orchards in the 0~20 cm and 20~40 cm soil layers increased by 9.6% and 2.57% than those of 30' citrus orchards, respectively, the light fraction organic carbon content increased by 23.6% and 3.63%, respectively. The variation of labile organic carbon in the 0~20 cm soil layer was significantly higher than that of the 20~40 cm soil layer. It indicated that the effect of orchard management on labile soil organic carbon decreased with the increase of soil layer depth. The results also showed that the 60' s citrus orchard compared with 30's citrus orchard citrus orchard, the content of organic carbon in the 0~20 cm soil layer increased by 27.%, dissolved organic carbon content increased by 20.1%, microbial biomass carbon content increased by 5.3%. Soil organic carbon storage of 60's citrus orchard in 0~100 cm soil layer increased 30.30% more than that of 30's citrus orchard. Compared with 30's citrus orchard, soil particulate organic carbon, light fraction organic carbon, dissolved organic carbon and microbial biomass carbon in the ratio of total organic carbon in 60's citrus orchard were all lower. It showed that more than 30 years after planting period, there is degradation risk of soil organic carbon quality with the increasing of growing years.