Abstract
The net photosynthetic and evapotranspiration rates, and sensible and latent heat transfer rates of tomato plug sheets consisting of plugs, soil mix and a tray in a greenhouse were estimated continuously. Absolute humilities (q1 and q2), CO2 concentrations (C1 and C2) and air temperatures (T1 and T2) were measured at two heights (z1 and z2, respectively) above the plug sheets with a dew point analyzer, an infrared CO2 analyzer and thermocouples. The weight of the plug sheet was also measured with an electronic balance. The evapotranspiration rate, E, was determined based on the difference between weights of the plug sheet at time t-Δt/2 and t+Δt/2. The diffusion coefficient, K, was determined based on E and the absolute humidity gradient with the equation E=-K (q2-q1) / (z2-z1) . The net photosynthetic rate was determined from the CO2 gradient, (C2-C1) / (z2-z1), multiplied by K. The sensible heat transfer rate was determined from the air temperature gradient, (T2-T1) / (z2-z1), multiplied by K and the heat capacity of the air. The latent heat transfer rate was determined from the evapotranspiration rate multiplied by the latent heat of vaporization. This technique was useful to estimate the rates of net photosynthesis, evapotranspiration and the sensible and latent heat transfers of plug sheets under the growing conditions in the greenhouse.
