Numerical Estimation of Evapotranspiration Rate in a Greenhouse

Abstract

A simulation model constructed in this study consisted of three sub models, i.e. the radiation environment model, the crop transpiration model, and the soil water and heat transfer model. The radiation model was used for simulating the distribution of short- and long-wave radiation in a greenhouse. Amounts of short-wave radiation in several processes such as transmission on a plastic film, interception by crop plant, arrival on soil surface were estimated. The distribution of short-wave flux on soil surface was obtained by reproducing the process that short-wave radiation passes through foliages. Crop transpiration rate was calculated via a heat balance on surfaces of a single big-leaf. The processes of water and heat transfer in the soil were calculated for the two-dimensional plane. The accuracy of the sub models was confirmed by comparing estimates with measurements. The short-wave radiations arriving on a canopy and soil surface were estimated well. Then, the reproduction of a short-wave radiation environment around a canopy could be successful. The estimates of temperature of leaf and soil surfaces also agreed with measurements. This simulation model would be useful to estimate evapotranspiration rate by distinguishing into transpiration and soil evaporation.