Abstract
There are some problems peculiar to the rotational upland field, whose soil condition and water use are different from the ordinary upland fields. One is that the depth of the effective soil layer, soil moisture extraction pattern, and the soil moisture condition when irrigation is started in the rotational upland field, are different from ordinary upland field. The other is that the furrow irrigation methods of rotational upland field are devided into two types, permanent or temporary ponding in furrow, whose water use is different. This paper clarified the above two problems by investigating many test fields. The results were summarized as follows.
1. In the rotational upland field that remains plowsole layer, soil moisture is consumed only in the upper soil layer above the plowsole and not consumed in the lower layer than plowsole. The depth of effective soil layer is about 25cm. On the other hand, in the rotational upland field whose plowsole layer is destroyed, soil moisture is consumed in the deeper layer, and its pattern is that the moisture consumption becomes gradually small downward. And its depth of effective soil layer is about 50cm.
2. In the rotational upland field whose plowsole is destroyed, irrigation is started when the soil moisture suction decrease to about pF2.6. But in the rotational upland field that remains plowsole, irrigation is started at the higher soil moisture content, bellow pF2.5-2.6.
3. Furrow temporary ponding irrigation is applied to the crops that require the good drainage and high airpermeability. This irrigation is the way that when the field is dried, the furrow is ponded, infiltrated and saturated, and then the ponding water on the ground surface is released. Amount of each irrigation is about 150mm and irrigition interval is changing according to meteorological conditions.
4. Furrow permanent ponding irrigation is applied to the crops that require the high water content in the effective soil layer. The irrigation is the way that the furrow keeps to be ponded by making the use of low permeability of lowsole layer. At the begining of irrigation period, 80-100mm of water is irrigated for initial ponding in the furrow. Afterward, the amount of each irrigation is 5-20mm and irrigation interval is 2-3days.
