A LEAF TEMPERATURE MODEL FOR CROPS GROWN IN GREENHOUSE AND ITS APPLICATIONS

A leaf temperature model suitable for conditions where free convection was dominant such as inside greenhouses, was developed and tested aga inst measured leaf temperatures. Results indicated that the developed model produced reliable estimates. Using the model, effects of various environmental and plant factors to leaf temperature were studied. The model indicated that leaf temperatures increased when air temperature s were increased, but air temperature should not be used as a substitu te of leaf temperature. Leaf temperatures were higher than air tempera tures either under strong solar radiation or under high humidity condi tions. When incident solar radiation and humidity inside greenhouses w ere both low, leaf temperature could be significantly lower than air t emperature. The environments inside greenhouses in Taiwan at noontime in summer were usually hot but dry. Therefore, to relieve heat stress occured, we could lower the air temperature inside greenhouses, or to reduce the amount of solar energy received by leaves, but have to main tain the dry condition inside the greenhouses. Effects of three common ly used cooling systems, mist, pad and fan and shading, on leaf temper atures were also compared. Results indicated that though mist and pad system were useful to reduce air temperatures inside greenhouses, they were not effective to lower leaf temperatures due to elevated humidit y inside the greenhouses. Particularly, the effects of mist cooling we re about the same as those of using 50% shading net.