Abstract: Based on soil bulk density in 0~5 cm, 5~10 cm, 10~15 cm and 15~20 cm soil layers measured with oven drying method, the changing trend of spatial variability of soil bulk density with increasing soil depth was studied using semi-variance and Kriging interpolation methods. The results showed that, for different soil layers, the average value of soil bulk density ranged from 1.23 g/cm³ to 1.33 g/cm³, its degree of variation was weak, its spatial correlation range was between 20.40 m and 75.64 m, its spatial correlation degree changed from 28.89% to 73.55%, and there were obvious patch structure in its spatial distribution. As soil depth increased, the average value of soil bulk density firstly increased and then decreased, its degree of variation increased after fell first, its fitted model of semi-variance changed from exponential model to linear model, its spatial correlation range increased at first and remained unchanged later, its spatial correlation degree did not present a regular changing trend, and there were differences in number and location of its high and low value area.

Key words: geostatistics, farmland, soil bulk density, spatial variability