Comparison of Shuttleworth-Wallace model and dual crop coefficient method for estimating evapotranspiration of tomato cultivated in a solar greenhouse

The accurate determination of crop evapotranspiration (ETc)is important for improving irrigation water use efficiency and optimizing fruit quality in solar greenhouses. Taking drip-irrigated tomato in a solar greenhouse as an example, this study simulated the variations of ETc, by the Shuttleworth-Wallace (S-W) and Dual crop coefficient (Dual-K-c) models at initial, development, mid and late stages in 2015 and 2016 respectively. Continuous measurements of crop ETc, with weighing lysimeter, and sap flow system combined with microlysimeter were used to validate the performance of two approaches. Results indicated that the total soil evaporation accounted for 25% of ET, over the whole growth period, and decreased gradually with the increasing of canopy coverage ratio. The locally developed basal crop coefficients values during the initial, mid, and late stages were 0.15, 0.94 and 0.65 in 2015, and 0.15, 1.02 and 0.70 in 2016, respectively. The variations of the estimated ETc, from S-W and Dual-K-c models were similar to the measured ET(c )The S-W model performed well in estimating ETc when LAI was between 0.5 and 2.7, but slightly overestimated and underestimated at initial and mid stages, respectively. Additionally, the performance of the S-W model was also better under different weather conditions as well as after irrigation. However, the Dual-K-c method was superior to the S-W model in estimating daily soil evaporation and daily plant transpiration. The good agreements were found between the predicted ETc using the Dual-K(c )method and the measurements for the greenhouse tomato, with the coefficients of regression of 1.03 (R-2 = 0.93) in 2015, and 0.96 (R-2 = 0.93) in 2016. Therefore, the Dual-K-c method was finally recommended for estimating evapotranspiration of tomato cultivated in the solar greenhouse.