Modeling crop evapotranspiration in a drip-irrigated sweet potato [Ipomoea batatas (L.) Lam.] field with plastic film mulching

As evapotranspiration (ET) is the main parameter determining crop water demand, accurate estimation of evapotranspiration rates is critical for optimizing water management strategies in agriculture. Using Bowen ratio energy balance (BREB) data measured in Shandong Province, China, during 2021–2022, along with corresponding meteorological and soil data, the adjusted Shuttleworth-Wallace (SW) model, along with adjusted single and dual crop coefficient models, were evaluated for their ability to accurately estimate crop ET (ET_c) for a drip-irrigated sweet potato [Ipomoea batatas (L.) Lam.] field crop with plastic film mulching. The BREB method effectively measured ET_c under these crop production conditions and can thus be regarded as a reference benchmark to verify the reliability of other ET_c calculation models. Under these production conditions, ET_c was low during the initial growth stage, gradually increased and remained at a high level during the middle growth stage, then began to decrease gradually during the later growth stage. The average proportions of ET_c during the sweet potato crop's early, middle, and late growth stages were 7.28 %, 61.67 %, and 31.05 % of the total growing season evapotranspiration, respectively. Soil evaporation (E) and crop transpiration (T) accounted for 9 % and 91%, respectively, of ET_c in this study. The adjusted SW model and the adjusted single and double crop coefficient models estimated ET_c accurately, with the adjusted dual crop coefficient model providing more accurate ET_c estimates than the single crop coefficient model. The SW model best reflected variations in ET_c under the present study conditions. The R², MAE, RMSE, and IA between the adjusted-SW-model-estimated ET (ET_c-SW) and the ET measured using the BREB system (ET_c-BREB) were 0.79, 0.29 mm d^‑1, 0.69 mm d^‑1, and 0.92, respectively in 2021, and 0.77, 0.26 mm d^‑1, 0.67 mm d^‑1, and 0.93 in 2022, respectively. The adjusted SW model can be applied to the estimation of soil E and crop T in drip-irrigated sweet potato field with plastic film mulching.