Soil Moisture Dynamic Characteristics of Dryland Field in Northern China

The soil moisture characteristics of dry-land field in Northern China are affected by precipitation and evaportranspiration. The field evaportranspiration in semiarid and arid zone is the largest, that in semi humidity arid zone the middle, and that in semiarid zone the smallest. The average water deficit amount is about 517 mm in dry-semiarid zone, the maximum value 968 mm，the minimum value 162 mm; And in semiarid zone, the average value, the maximum value and the minimum value are 274, 688 and －34 mm, respectively; in semihumid arid zone, the 3 parameters are 157, 469 and －180 mm, respectively. Due to the temporal and spatial variation of precipitation， the deposited amount of soil water has their spatial, temporal variation too in 3 different zones, and their values in crop growth season are semihumid arid zone is the largest, that in semiarid zone the middle, and that in semiarid dry zone the smallest. The crop water use is from precipitation and soil water before sowing.