Determination of evapotranspiration of tomato and squash using lysimeters in central Saudi Arabia

Abstract

Nine non-weighing reinforced concrete lysimeters were used to grow alfalfa (Medicago saliva) as a reference crop, and tomato (Lycopersicon esculentum L. cv. Tristar) and squash (Cucurbita pepol) as experimental crops to measure their evaporranspiration (ET,). Crop coefficients ( K J were estimated for tomato and squash at different stages of growth, based on lysimeter measured ETC and reference alfalfa ET. The estimated values of Kc for tomato at four growth stages (initial, crop development, reproductive and maturity) were 0.28, 0.8, 0.96 and 0.75 and the corresponding values for squash were 0.56, 0.72, 0.96 and 0.63. These values of both tomato and squash were to be lower than that suggested by FAO for arid areas. Five climatological methods (FAO-Penman, Blaney-Criddle, Jensen-Haise. pan evaporation and Thomthwaile) were selected for estimating ETC on a daily basis. An attempt was made to develop relationships between the ETC measured by the lysimeters and that estimated by the climatological methods. Performance of the climatological methods in estimating ETC as compared to measured ETC were evaluated using the deviation between the values, root mean square error (RMSE) and coefficient of determination (R2). Comparisons between various indirect methods to estimate ETC and measured ETC revealed that the pan evaporation method for tomato and the FAOPenman method for squash produced the best daily estimates of ETC