Abstract
The effects of difference of the soil structure on the drying characteristics and the bearing capacity of paddy field, both direct drilling on the ponding condition system and the upland condition system were investigated in connection with increase of cracks after drainage of residual water.
The results obtained are as follows:
1) The arable soil in the upland condition system made rapid prpgress in drying as compared with the ponding condition system. It was originated from the speed of drainage of the gravitational water. But in the subsoil, the ponding condition system made progress in drying as compared with the upland codition system.
2) The development of cracks showed apparent difference between the upland condition system and the ponding condition system. The former developed much more cracks in number, but smaller in width and depth of them than the latter.
3) The cracks were developed up to subsoil with drying over pF 2. 0 of soil moisture in the arable soil in the ponding condition system. But in the upland condition system, they did not reach tosubsoil even if the arable soil was fairly dried.
4) The bearing capacity of arable soil in the upland condition system is superior to that in the ponding condition system, the corn index being closely related with the pF value of soil moisture. And especially, it was increased rapidly due to drying over pF 2.0 of soil moisture.
