Studies on Water Economy in Crop Plants : (II) Water economy in upland rice and soybean with special reference to temperature and soil moisture

Abstract

The influences of night temperature and soil moisture on the water economy in upland rice and soybean plants were observed. The results of the experiment were as follows: (1) Norin 22, a rice variety of panicle-number type, developed with a similar tendency in the response to night temperature as Iwate Ryoon I, a variety of panicle-weight type. (2) The accumulating degree of dry substance was the largest at the heading period in upland rice plant. But it was rather larger at the period prior to blooming than at the blooming period in soybean plant. (3) The amount of water transpired through upland rice plant was comparatively copious from the panicle developing stage to the earlier stage of ripening, and that transpired through soybean plant was the most at the blooming period. (4) The water requirements of upland rice and soybean under cool night conditions became less than those under warm night conditions from the stage of heading in the former and before blooming in the latter. As aforesaid, that of oats under cool night condition was less than under warm night condition through almost every stage of growth. These facts seemed to be ascribed to the differences between them in their physiological and ecological characters responding to temperature. (5) The period of the highest efficiency of transpiration for producing crop materials in soybean plant was found before its blooming. The fact appeared to be of special interest from the point of view of both food value of the plant and use of the soil moisture in green forage cropping. (6) The water requirement of soybean decreased progressively up to a certain point in accordance with the decrease of soil moisture. With a further decrease of soil moisture to a point where the plants wilted often transiently, the water was spent less efficiently.