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The Penman-Monteith Equation As a Predictor of Transpiration in a Greenhouse Tomato Crop

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  034095,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.15035) @2003
Authors:   D. H. Willits
Keywords:   Greenhouse, transpiration modeling, tomato, Penman-Monteith

The Penman-Monteith equation has been used to describe the transpiration of greenhouse crops; however, it generally requires re-parameterization for each dataset, restricting the robustness of the equation for predictive purposes. This paper applies the equation to a transpiration dataset for greenhouse tomatoes collected over a period of three years. The parameters needed were taken from directly from the literature. The resulting model predicted transpiration surprisingly well, but the error dependent upon leaf area index. A significant improvement in performance was obtained by making the vapor pressure deficit term dependent on a declining function of leaf area index and by fixing the internal resistance of the canopy as a constant. The resulting model predicted transpiration within a mean error of 3.64% over the entire dataset and the errors were much more consistent across canopy density, vapor pressure deficit and ventilation flow rate than with the original model.

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