Energy budget for tomato plants grown in a greenhouse in northern China

Research is ongoing to increase our understanding on the mechanisms responsible for the variation in energy fluxes in greenhouses. In this study, a four-year experiment (2016, 2017, 2019, and 2020) was carried out to investigate the energy budget for drip-irrigated tomato plants in a greenhouse, where the latent heat flux (lambda ET) was measured by two weighing lysimeters. Factors that determine energy budget and lambda ET were also investigated. The results indicated that lambda ET was the principal component of net radiation (Rn), accounting for 66.4-71.7%, followed by sensible heat flux (H) and ground soil heat flux (G). The low values (0.25-0.32) of the seasonal mean midday Bowen ratio (beta=H/lambda ET) also indicated that seasonal lambda ET was greater than H for well-watered tomato plants. Leaf area index (LAI) strongly influenced the energy budget. The ratio lambda ET/Rn increased linearly as LAI increased, whereas H/Rn decreased linearly and G/Rn and beta decreased logarithmically. Seasonal mean lambda ET was 76.8 +/- 4.7 W mxe213; 2, which was less than the reported values for field crops. This difference was attributed to the semi-closed microclimate in the greenhouse. The high values of the Priestley-Taylor coefficient (alpha=1.03 +/- 0.05) and the decoupling factor (0.69 +/- 0.05) showed that lambda ET was principally determined by Rn. These values support the conclusion that lambda ET was energy limited rather than water limited in the greenhouse. Canopy conductance (Gc) also influenced lambda ET as indicated by the high correlation between alpha and Gc, especially during the middle growth stage. These findings are of great importance in creating an energy-driven model and will lead to improved water management in greenhouse agriculture.