Abstract
Precipitation is scarce so much enough, it rains at long intervals and it seldom rains heavily during the growing season at OTOSHIBE region. It has been revealed from soil moisture distribution in situ measured by the soil sampling method that (1) the rateof evapo-transpiration is about 2.8mm/ day over the whole moisture range, (2) the field capacity in the top layer is about 50%, (3) the volume of water moved upward from the sand layer to the top layer is about 1/ 3 of evapo-transpiration, (4) this upward movement begins when the average water content in the top layer soil reaches 40%, and (5) water content in sand never decreases to 10% and less.
It is concluded from these characteristics of precipitationand soil water movement that (1) effective rainfall (699mm) is larger than evapo-transpiration (546mm) during the growing season, but in May and June, evapo-transpiration (156mm) exceeds effective rainfall (130mm), and that (2) in April soil moisture depression caused by the use of water is usually supplied by rainfall, but in May and June water content in the soil keeps decreasing and soil moisture moves upward. This soil moisture depression is usually supplied by rainfall in July and August.
