Abstract
A series of experiments was carried out with various crops. The crops used were barley, wheat, groundnut, soybean and paddy rice. The aim of the experiments was to know of the exact influence of soil moisture deficit upon the photosynthesis of the plants, as well as to compare the characteristics of the crops in their response to soil moisture. 1. Decrease in soil moisture exerted its first effect on the stem or leaf sheath, keeping the water content of the leaf blade as high as possible. However, when the soil moisture decreased near by down to the permanent wilting point, the water content of the leaf blade began at last to decrease, accompanying with a decrease in photosynthetic rate. 2. The decrease in photosynthetic rate began just before the first sign of wilting of the plant appeared and became severe as wilting proceeded. From these results it was concluded that soil moisture exerted its influence on photosynthesis through its effect upon the water content in the leaf blade. As to the characteristics of each crop, it was deduced that the difference in the ability of the plant to keep water in the leaf blade against the soil moisture deficit was the main factor for determining the response of the crop. The ability of the crops examined was in the following order; groundnut>barley>wheat>soybean>paddy rice.
