Abstract: The spatial variability of soil alkaline phosphatase and urease activity at different cotton growth stages was researched by sampling and testing the activity of alkaline phosphatase and urease in soil samples collected from the 10 m×10 m sample plots in a highyield cotton field. Their semivariogram figures and contour figures were charted using the method of geostatistics, and their horizontal and vertical spatial variability and temporal variability with cotton growth were lucubrated. The results showed that the variability of activity of alkaline phosphatase and urease in soil was moderate at three cotton growth stages. In vertical direction of soil, urease activity(0-20 cm) was higher than CV of urease activity(20-40 cm), the same as alkaline phosphatase activity. The vertical spatial variability of soil alkaline phosphatase and urease activity was different, the variability coefficient of urease activity in soil layer of 0-20 cm was higher than that in soil layer of 20-40 cm, but the vertical spatial variability of soil alkaline phosphatase was opposite. There was also the temporal variability of soil enzyme in cotton field, and the activity of soil alkaline phosphatase and urease was decreased with the increase of soil depth at three cotton growth stages.

Key words: cotton field, growth stage, soil, alkaline phosphatase, urease, spatial variability