Relationship between Growth and Transpiration in Rice Plants.

Abstract

The seasonal changes in transpiration were measured with the rice of early, ordinary, and late season culture. The t/E values (t: amount of rice transpiration, mm., E: amount of evaporation from free water surface, mm.) were used in order to eliminate climatic effects on transpiration. In spite of the difference of the time of transplantation, the t/E values changed similarly. (See Fig 2) When the plants were not yet so leafy and leaf area was small, the t/E values were parallel with growth. When the plant became highly leafy and the L.A.I. (leaf area per unit field area) was larger than 4∼5, the t/E values were constant and scarcely affected by growth. These facts may presumably be due to mutual shading, considering from the following results: the relation between t/E and leaf area (Fig 3), the change of t/E per unit leaf area (Fig 4), the relation between t/E per unit leaf area and leaf area per hill (Fig 5), and the relation between transpiration amount per unit leaf area and net assimilation rate (NAR). (See Fig 6) It was concluded that rice transpiration amounts in any cultivations could be estimated by measuring two factors, the growth magnitude of the plant and the evaporation from free water surface.