Soil moist ure of soil profile(0—210 cm)in a black soil during crop growth(May to September)was monitored.Distribution characteristics of soil moisture of soil profile

seasonal dynamic variation

and variation coefficient were analyzed.Results showed that the variation of soil moisture in the soil profile had an "increasing-decreasing-increasing"trend with soil depth increasing in observation period.Soil moisture in each layer presented a"decreasing—increasing—decreasing"trend with time increasing and it was closely related with rainfall and crop growth.The acute change layer was not found in observation period.The biggest variation coefficient of soil moisture was observed within 10 cm of surface soil and the variation coefficient decreased with soil depth increasing.