Abstract: In Horqin Sandy Land, a semiarid region of Northeast China, soil freeze-thaw caused by the temperature change in late autumn, winter, and early spring has significant effects on soil CO₂ emission, and thus, it is of significance to study the effects of the interaction between soil moisture content and freezethaw on soil respiration. Taking the silvopasture system, cropland, and grassland in Horqin Sandy Land as test objects, a simulation experiment was conducted to study the effects of soil moisture condition and freeze-thaw cycle on the soil respiration under different land use patterns. The results showed that soil moisture condition, freeze-thaw cycle, and land use pattern all had significant effects on soil respiration. Before freeze-thaw, the soil respiration rate was significantly higher in grassland than in silvopasture system and cropland. During freezethaw, soil respiration rate was higher in silvopasture system than in cropland. After freeze-thaw, soil respiration rate was significantly higher in grassland than in silvopasture system. When the soil moisture content was 80% of water-holding capacity (WHC), soil respiration rate was significantly higher than that when the soil moisture content was 60% of WHC. During the whole incubation period (20 days), the amount of soil CO₂ emission from silvopasture system, cropland, and grassland under 60% of WHC was 21.535, 19.908, and 25.037 g CO₂·m^-2, and that under 80% of WHC was 26.407, 29.447, and 36.246 g CO₂·m^-2, respectively.

Key words: cotton water requirement, rainfall insurance rate, precipitation deficit.