Abstract: By using geostatistic methods, this paper studied the spatial variation and dist ribution of soil organic matter as well as its ecological processes and related mechanisms in four typical disturbed areas (cropland, man-made forest, secondary forest, and primary forest) of karst peak cluster depressions in nort hwest Guangxi of China. Eighty soil samples (0〖KG-*2〗-〖KG-*7〗20 cm) were coll ected from an aligned grid of 10 m×10 m for the analysis of soil organic matter . The soil organic matter content increased significantly (P<005) with the decrease of disturbance and the vegetation succession from crop to man-made fo rest to secondary forest to primary forest. Soil organic matter content had good spatial autocorrelation in all of the four typical disturbed areas, but its spa tial heterogeneity differed. Gaussian model fitted best to the semivariance fun ctions of soil organic matter content in the study areas except secondary forest area where exponential model fitted well. In cropland area, the spatial autocor relation of soil organic matter was at medium level, with the C0/(C0 +C) being 265%; while in the other three areas, the spatial autocorrelatio n was at high level, with the C0/(C0+C) being 90%〖KG-*2〗-〖K G-*7〗226%. The range and scale of the spatial autocorrelation of soil orga nic matter in cropland and man-made forest areas were larger than those in the other two areas, possibly due to the strong human disturbance and the homogeneit y of low energy. The range of the spatial autocorrelation of soil organic matter in primary forest area was large due to the high vegetation coverage, while tha t in secondary forest area was the lowest due to the diverse vegetation communit ies and their uneven distribution. The low fractal value (D) of semivariance fu nctions of soil organic matter in man-made forest and primary forest areas sugg ested that a strong spatial dependence existed, while the high D in cropland and secondary forest areas suggested a great random variance of spatial distributio n of soil organic matter occurred. The spatial pattern of soil organic matter pr esented a unimodal distribution in cropland and man-made forest areas, a concav e distribution in secondary forest area, and a gibbous distribution in primary fo rest area. To reduce human disturbance would be helpful to the soil quality impr ovement, rapid vegetation restoration, and ecological reconstruction of karst de generative ecosystems.

Key words: conservation tillage, nitrogen use efficiency., wheat, nitrogen fertilizer