Abstract:

The experiment was conducted from January 6 to February 2, 2024 in a Liaoshen type II energy-efficient solar greenhouse at the Shenyang Agricultural University research base. Tomato plants were grown in substrate bags. The ground was covered with black plastic film to minimize soil evaporation. The stem sap flow rates of tomato plants were measured via thermal dissipation probes (TDPs) to calculate transpiration as the measured evapotranspiration (ET) value. Four evapotranspiration models (FAO56 PM, FAO24 Pen, PT and Mak) were evaluated, and the Mak model subsequently was modified with the aim of identifying a suitable ET estimation model for solar greenhouses in northeast China. The results revealed that: (1) the model overall performance, ranked by the mean absolute percentage error (MAPE), mean prediction error (MPE) and root mean square error (RMSE), was FAO24 Pen>PT>FAO56 PM>Mak. Although the FAO24 Pen model achieved the highest performance indices (MAPE=20.263%, MPE=0.122mm·d⁻¹ and RMSE=0.149mm·d⁻¹), its predictive accuracy remained insufficient for the estimation of actual evapotranspiration (ET). (2) Principal component analysis (PCA) revealed that temperature, relative humidity and solar radiation were the dominant factors influencing evapotranspiration within the greenhouse. In order to enhance the model performance compared to the measured values, the Mak model was modified by incorporating a relative humidity parameter. Compared to the measured values, the modified Mak model demonstrated a significant improvement in accuracy, with evaluation metrics of MAPE=9.391%, MPE=0.051mm·d⁻¹ and RMSE=0.068mm·d⁻¹. Significantly, the RMSE was reduced by approximately 80% compared to the original Mak model and by 54% lower than that of the FAO24 Pen model. These findings suggest that the modified Mak model achieves validated accuracy in estimating the evapotranspiration of tomato in solar greenhouses in northeast China during winter. The results of this study provide valuable references for intelligent irrigation systems for crops in solar greenhouses in northeast China during the cold winter seasons.

Key words: Solar greenhouse, Substrate bag cultivation of tomato, Evapotranspiration model, Thermal dissipation probes, Applicability