Abstract: With 5-, 17-, 30-year-old Chinese prickly ash orchards (designated as PO₅, PO₁₇, PO₃₀ respectively) and a forest land (FL, about 60 years) as control in a demonstration area of desertification control in southwestern Guizhou as our research objects, the dynamics of soil organic C mineralization were assessed by fitting equation methods. The effects of planting Chinese prickly ash orchards on soil organic C mineralization and chemically stable organic C were analyzed. The results showed that the double exponential equation fit well for the variation of soil organic C mineralization, with a correlation coefficient of >0.95. The correlation of soil slowacting C with cumulative C mineralization was significant (R=0.792,P<0.01). The concentration of Na₂S₂O₈resistant organic C at all soil layers was highest in the forest compared to the three Chinese prickly ash orchards, whereas its proportion to SOC was the lowest. The concentration and proportion of H₂O₂resistant organic C at 0-15 cm soil layer were the highest in thePO₃₀, and those at 30-50 cm were the highest in the PO₁₇. The concentration and proportion of HF soluble organic C at all soil layers were the highest in the PO₁₇. Soil organic C concentration of the four forest types accounted for only 1.6%-29.3% of the slowacting C, the concentration of which was close to the cumulative mineralization amount of soil organic C after 92 days. The mineralization rate of slowacting C (k_s) fluctuated slightly (0.013-0.025), and the k_s values of PO₃₀ were the highest at 0-15 cm and 15-30 cm layers. With the increases of cultivation duration, soilactive organic C and slowacting C concentrations showed increasing and decreasing trend,respectively. In conclusion, reasonable cultivation duration of Chinese prickly ash orchard can improve soil quality and C sequestration.

Key words: sugarcane, subsoiling, yield, sugarcane field, soil physical property