ANALYSIS OF HEAT AND WATER MOVEMENT THROUGH A RICE PLANT CANOPY BY TWO LAYER MODEL

Fundamental studies on evapotranspiration in paddy fields (II)

Abstract

In the present study, determination was made of the basic evapotranspiration mechanism by analysis of flux and water movement in a rice plant canopy and the development of a “two layer model”. First, a comparison between potential evapotranspiration as calculated by the Penman method and actual evapotranspiration measured by the water balance method was carried out. Actual evapotranspiration was found to exceed the potential one by a factor of about 1. 0 with growth of rice plants.
Secondly the reason for this is considered to lie in differences between heat and water transfer mechanisms.
Thus, the “two layer model” was proposed and distribution of heat components was analyzed using observed data, such as evapotranspiration, temperature, vapor pressure and net radiation. In addition, certain parameters such as K_P, K_W and K_T, which represent the transfer coefficients defined in this paper, were calculated and the conductivity of water movement in a plant body itself was evaluated.
According to the results obtained, the occurence of extensive evapotranspiration can be reasonably explained from the fact that heat transfer under a canopy is relatively difficult but movement of water within a plant body is relatively easy.