Enhancing irrigation scheduling by application efficiency estimations and soil moisture simulations

Abstract

Additional water supply by irrigation is increasingly applied to high-value crops as potatoes in humid and temperate biomes to maximize yield and quality. In the light of increasing drought risks, innovative adjustments are required in irrigation scheduling to increase the efficiency and sustainability of supplemental irrigation. Hence, this study aims to (i) propose an easy-to-adopt, soil-property based approach to estimate the application efficiency under open-field conditions, and (ii) compare the accuracy of simulated soil moisture dynamics provided by two different physically based water balance models (AMBAV, HYDRUS-1D). Variable rate gross irrigation depths were applied during the growing seasons 2021 and 2022 on two loamy-sand potato fields (27 ha and 35 ha) in Mecklenburg-Western Pomerania, Germany. The average application efficiency of the utilized gun sprinkler irrigation system was 77.2 %, ranging between 71.6 % and 81.4 % (71.3 %–80.9 %) in 2021 (2022). It was higher than expected in agricultural practice, which allowed for potential seasonal water savings of 6.3 L m⁻² on loamy sands, in comparison with the customary potato irrigation. HYDRUS-1D provided a significantly increased accuracy of simulated soil moisture dynamics, when compared to AMBAV. The overall average model performance metrics in comparison with in-situ measurements were: Root Mean Square Error (RMSE): 0.044 (AMBAV), 0.021 (HYDRUS-1D); Mean Absolute Error (MAE): 0.041 (AMBAV), 0.018 (HYDRUS-1D); coefficient of determination (R²): 0.567 (AMBAV), 0.649 (HYDRUS-1D). Simulated soil moisture dynamics of both models showed greater variations in topsoil (0 cm–30 cm) than in subsoil (40 cm–60 cm) and diverged in their accuracy in different months of the growing season of the potato crop. These novel insights on unproductive water losses during irrigation and on the simulation accuracy of different physically based soil water balance models significantly improve the irrigation scheduling under open-field conditions. The results of this study may hence serve as important cornerstones for establishing water-saving irrigation strategies in the humid and temperate biomes of Central Europe.