Because the PM model was insensitive to the aerodynamic resistance, several studies treat it as a constant in different greenhouse types ( Fernández et al., 2010, 2011 Gong et al., 2017b Yan et al., 2018). Zhang and Lemeur (1992) reported that the aerodynamic resistance can be calculated by using the heat transfer coefficient inside greenhouse, but this coefficient needs canopy temperature, which is difficult to obtain. Aerodynamic resistance has usually been considered a function of wind velocity, but it can become infinite when wind velocity is close to zero. The structure of PM model must be redefined if applied in a greenhouse. However, its application was still limited due to less information on two forms of resistance (e.g., aerodynamic resistance and canopy resistance). For example, the FAO56 Penman-Monteith (PM) model is the most commonly used because of its simple structure and relatively high precision ( Allen et al., 1998). Establishing an ET c model is a simple method to get water requirements of crops, thus many greenhouse ET c models have been developed. Therefore, improving water use efficiency is an effective way to maintain long-term greenhouse development.ĮT c is an important parameter for determining a scientific and rational irrigation schedule to improve water use efficiency ( Qiu et al., 2017, 2019 Yan et al., 2017 Yuan et al., 2001). Long-term overexploitation of groundwater resources will lead to a series of environmental degradations (e.g., soil salinization and desertification) ( Xia et al., 2016). Deep groundwater has been extracted for irrigation to maintain tomato production. A large amount of water is needed to supply tomatoes cultivated in a greenhouse, especially in the flowering and fruit setting stages ( Gong et al., 2017a). In recent years, greenhouse tomato cultivation has been becoming an important industry for the local economy. Tomato ( Lycopersicon esculentum) has high nutritional value, rich in vitamins A, B 1, B 2, and C in carotene and calcium ( Lupini et al., 2017). These simple-structured greenhouses have emerged as a favorite technique in northern China because it bridges the season gap in vegetable and fruit production ( Wei and Sun, 2014). Second, the top and south vents are used to regulate temperature and humidity according to the characteristics of crop growth. The heat in the daytime comes from solar radiation and in the evening comes from the rear wall and surface soil. First, there is no heating system in a solar greenhouse. It is different from glass and plastic greenhouse in two ways. Keywords: drip irrigation dual crop coefficient plant transpiration soil evaporation solar greenhouseĪ solar greenhouse is an energy-saving greenhouse that consists of gables on both sides, a maintenance rear wall, a supporting skeleton, and covering materials. This work can help farmers to optimize the irrigation scheduling based on an ET o model for solar greenhouse vegetables in northern China. 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. Results of the Penman-Monteith, Penman, and Priestley-Taylor models show comparatively good performance in estimating ET o. The radiation and pan evaporation models tend to overestimate ET o values. The ET c was ≈345 mm for drip-irrigated tomato in solar greenhouse at the whole growth stage. The K e varies between 0.10 and 0.45 during the whole growth period. Results show that the adjusted K cb 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. Daily ET o was simulated from the five models and compared with the measurements. Crop evapotranspiration (ET c) was continuously measured using sap flow system combined with microlysimeter in 2015 and weighing lysimeters in 2016. The basal crop coefficient K cb and soil evaporation coefficient K e were adjusted according to the surrounding climate inside the greenhouse. 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. An automatic weather station was installed in the center of the same greenhouse to record weather parameters at 30-minute intervals. This study was conducted in a solar greenhouse at the experimental station of the Chinese Academy of Agricultural Sciences during 20. Studies on dual crop coefficient method in a greenhouse require accurate values of reference evapotranspiration (ET o).
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