Studies on dual crop coefficient method in a greenhouse require accurate values of reference evapotranspiration (ET o ). A study was conducted in a solar greenhouse at the experimental station of the Chinese Academy of Agricultural Sciences during 2015 and 2016. An automatic weather station was installed in the center of the same greenhouse to record weather parameters at 30-minute intervals.
Five ET o models (Penman-Monteith, Penman, radiation, pan evaporation, and Priestley-Taylor) were employed, and their performance was evaluated using the dual crop coefficient method. The basal crop coefficient Kcb and soil evaporation coefficient Ke were adjusted according to the surrounding climate inside the greenhouse. Crop evapotranspiration (ET c ) was continuously measured using sap flow system combined with microlysimeter in 2015 and weighing lysimeters in 2016. Daily ET o was simulated from the five models and compared with the measurements.
Results show that the adjusted Kcb values were 0.15, 0.94, and 0.65 in 2015 and 0.15, 1.02, and 0.70 in 2016 at initial, midseason, and late-season, respectively. The Ke varies between 0.10 and 0.45 during the whole growth period. The ET c was ≈345 mm for drip-irrigated tomato in solar greenhouse at the whole growth stage. The radiation and pan evaporation models tend to overestimate ET o values. Results of the Penman-Monteith, Penman, and Priestley-Taylor models show comparatively good performance in estimating ET o.
Considering the robustness and simplicity, the Priestley-Taylor was recommended as the first choice to estimate ET o of tomato grown in a solar greenhouse. This work can help farmers to optimize the irrigation scheduling based on an ET o model for solar greenhouse vegetables in northern China.