The precipitation is known as the main source of water for the planosol (a bleached soil). According to the nature of the soil moisture regime,the annual moisture cycle of the planosol may be divided into two periods,i. e. the frozen period and the crop growth period at summer and autumn. These two periods can be also subdivided into five phases. The former period involves two phases:the freezing and thawing of the sail,while the latter period contains three phases:lower moisture in early-summer;an excess of soil water in mid-siunmer and a humid soil condition in late-autumn.