Simulation of Greenhouse Tomato Crop Transpiration by Two Theoretical Models

Mexican greenhouse industry is mainly distributed on semi-arid regions where it is critical water optimization. Knowledge on crop transpiration rate is important not only because it is needed to optimize water supply but also because it is required in order to know effects of greenhouse climate control such as heating and ventilation on crop growth. The aim of the present study was to measure transpiration rates in a tomato crop by means of a weighing lysimeter and also the evaluation of the performance of two transpiration mathematical models. The experiments were carried out at greenhouse facilities of the University of Queretaro, state of Queretaro, Mexico. The greenhouse has 8 m width and 35 m long. The total 2 ventilation area is 257 m(2) with 2 side vents and two roof vents, which can be closed and opened automatically. The cover is plastic of caliber 700 with UV treatment. All the vents had anti-insects screens. The greenhouse has a fertigation system in order to program irrigation for short times. Temperature and relative humidity were measured with a capacitance type sensor. Global solar radiation was measured using a pyranometer. Leaf temperatures were measured by using thermocouples inserted into the leaf veins of tomato plants. Crop transpiration was determined by a weighing lysimeter (maximun load 150 kg, precision +/- 2 g) supporting four plants. The sampling time for transpiration rates was 1 min and averaged each 5 min. The performance of both the Penman-Monteith and the Stanghellini transpiration models was studied by comparing model's predictions against actual crop transpiration measurements. Results showed that due to a more detailed estimation of net radiation, leaf area index of the crop and a better estimation of the stomatal resistance of the tomato crop, the Stanghellini model performed much better than the Penman-Monteith equation.