The Aerodynamic Measurement of Photosynthesis over a Nursery of Rice Plants
1958 Volume 14 Issue 2 Pages 45-53
Details
1958 Volume 14 Issue 2 Pages 45-53
The aerodynamic method of measuring the rate of photosynthesis over the cultivated fields, which makes use of the equation of turbulent transfer such as
P=(U2-U1)(C1-C2)/33.1(logZ2-d/Z1-d)2
and has been applied successfully to the unlimitedly wide fields, is to be applied with much care to the narrow fields of limited dimension such as a nursery of rice plants. The reasonable heights of Z1 and Z2 where the velocities U1 and U2 and the concentrations C1 and C2 are to be obtained are examined taking both the height of plants and the windward length of the field concerned into account simultaneously, and also taking account of the thermal stability of the air layer. Alternative two methods of some possibilities are presented. One is the fluctuation method making use of the mean product of the vertical components of wind velocity fluctuations and the CO2 concentration fluctuations, and the other is the traverse method which makes use of the vertical integration of the horizontally flowing CO2 flux.
The aerodynamic method has been applied practically to a nursery of rice plants 20cm high of limited scales with much caution in order to avoid meeting anticipated difficulties. The profiles of U, C, Θ (air temperature) and E (humidity) over the nursery have been obtained during almost a whole day in June 1957. The net radiation flux has been obtained simultaneously by means of a Beckman-Whitley net-radiometer. The assimilation type of C-profile in daytime characterized by increasing CO2 concentration with height and the respiration type in nighttime characterized by decreasing concentration with height have been obtained.
All of profiles have been compared with the logarithmic laws and the relevant zero-plane displacement d and roughness length Z0 have been obtained as 20cm and 1cm, respectively. The fluxes of turbulent transfer of heat, water vapor and CO2 have been calculated by the aerodynamic method and compared with each other. The amounts of heat energy required for the evapotranspiration and for the photosynthesis of rice plants have been also calculated and the heat budget of the net radiation flux has been considered briefly.
