Abstract
For the study of effective utilization of rainfall, experiments were conducted with various levels of irrigation coordinating two kinds of soil at depths of 10, 20 and 30cm.
The results observed were as follow.
1) On the case of a shallow irrigation system of 10cm soil depth, the soil moisture of the deeper layer was heavily utilized, because the capillary moisture moves upward. Therefore, as the deeper soil layer has less moisture, rainfall was effectively stored there.
2) From the relation between the soil moisture and root distribution, it was found that the absorption of the moisture by upland-rice was conducted near the surface layer, within a depth of 10cm.
3) The best irrigation system in which the rainfall was used most effectively, and irrigation water was most available for the plant was with irrigation at a depth of 10cm.
4) Considering soil of quite different composition, the utilization rate of rainfall or irrigation water of Kamigamo Soil with more available soil moisture was smaller than that of Kyodai Soil with less available soil moisture.
5) Comparing the utilization percentage of rainfall on different groups of soil having different available moisture, it was found that soils having higher available moisture are more advantageous with regard to moisture utilization than that of soils with less available moisture. This is particularly evident in the case of the soil layer at a depth of 10cm, compared with the other depths for irrigation.
