Abstract
Characterizing mass and energy balance at a plug sheet consisting of plug seedlings and soil mix is essential for optimum control of soil-mix moisture in plug seedling production. Time courses of rates of net photosynthesis, evapotranspiration and sensible and latent heat transfers of a tomato plug sheet under artificial light and the volumetric percent water content of soil mix were estimated micrometeorologically using the measured data on CO2 concentrations, dewpoint temperatures at two heights above the plug sheet and weight of the plug sheet measured with an electronic balance. The first watering was done at the start of measurements and the second watering 16 hours after the first watering. After the first watering, the volumetric percent water content of soil mix decreased with time. Sensible heat transfer rate increased, and evapotranspiration and latent heat transfer rates decreased with decreasing volumetric percent water content when it was lower than about 20%. Net photosynthetic rate decreased with decreasing volumetric percent water content when it was lower than about 12%. One to three hours after the second watering, all the rates returned to the levels at the start of measurement. The present method is useful for on-line monitoring of micrometeorological and water-stress status of the plug sheet and for automatic watering based upon the status.
