Modeling evapotranspiration for cucumber plants based on the Shuttleworth-Wallace model in a Venlo-type greenhouse

Abstract

Partitioning of evapotranspiration (ETc) into soil evaporation (Eg) and plants transpiration (Tr) is of great importance to assess biomass production and improve water use efficiency under greenhouse conditions. The Shuttleworth-Wallace (SW) model, which is used to separately predict Eg and Tr has been validated by many studies in open field, however, the model's parameters for the low wind speed and heterogeneous underlying surface in greenhouses are quite different from the open field. Therefore, an experiment was conducted in a Venlo-type greenhouse in south-east China during two planting seasons of cucumber plants in 2018, where the ETc and Tr were directly measured by lysimeters and sap flow sensors. The soil surface and canopy resistances were parameterized based on the soil water content at 5–10 cm depth and solar radiation inside the greenhouse, respectively. The SW model simulated ETc and Tr at hourly interval with root mean square error (RMSE) and index of agreement (d) of 42.10 W m−2 and 0.93; 40.50 W m−2 and 0.91 for the spring season, while for the autumn season the values were 26.60 W m−2 and 0.93; 15.63 W m−2 and 0.93, respectively. The average Eg / ETc were 7.75% and 21.87% for spring and autumn planting seasons, respectively, indicating that the Tr was the dominant component of ETc of cucumber grown in greenhouse over the full crop season. Our research shows the parameterized SW model would be a relatively accurate way to separately simulate the dynamic variations of the Tr and Eg, and for future use to improve irrigation scheduling for cucumber plants under greenhouse conditions.