REAL-TIME COMPARISON OF SEVERAL TRANSPIRATION METHODS FOR ESTIMATING GREENHOUSE VENTILATION RATE VIA WATER VAPOUR BALANCE METHOD

Abstract

Transpiration rate is an essential factor in the water vapor balance method for estimating the ventilation rate in a greenhouse continuously. Several methods of transpiration measurement, i.e., electronic weighing device (Control), the sap flow measurement (SF), water level measurement (WL), and water flow rate measurement (WF) tested and evaluated on tomato crops in a naturally ventilated greenhouse. The objective was to compare these methods and establish the most affordable one to be used in a greenhouse condition to determine the ventilation rate using the water vapor balance approach. Results obtained with the SF particularly have a strong correlation and are not statistically different from the Control (r=0.89). The WF method gave good results and reliable for predicting the total of transpiration in the greenhouse. However, in our conditions, this method generally had a lag time of the transpiration rate in a short time interval basis (minute and hourly). But it had an excellent predicted transpiration rate in daily evapotranspiration. The WL suffered weak agreement to the Control due to the scattering data. It was affected by the very high sensitivity of the device, and it is not recommended to use on the farm level, like in a greenhouse. It appears that measurements with the control and the SF could be considered for monitoring the ventilation rate in the greenhouse using a water vapor balance technique.