Evaluation of simulated transpiration from maize plants on lysimeters.

In central Europe expected climate change will lead to strongly changing regional water availability and will affect future crop production systems and yields. To adapt these production systems and estimate the irrigation necessity for yield optimization—today and in the future—crop water demand as a function of its environment and development stage must be understood. Crop models are often applied to simulate water demands, but the accuracy of the simulations and the underlying mechanisms remain unclear. We therefore grew maize (Zea mays L.) in field lysimeters in 2013 and tested the ability of six model configurations (two crop models CERES (Crop Environment Resource Synthesis) and SPASS (Soil–Plant–Atmosphere System Simulation) combined with three evapotranspiration models) to simulate measured sap flow and components of the water balance. Sap flow measurements (i.e., heat ratio method [HRM]) determined transpiration. All models simulated the measured diurnal cycles of sap flow rates. Higher simulated leaf area indices by the CERES model runs caused an overestimation of transpiration in the beginning of the measurement period. The models overestimated daily actual evapotranspiration when water input was high due to an overestimation of actual evaporation and transpiration resulting from high water contents at the top soil layers. All models simulated the occurrence of measured percolation peaks, but only partly captured their intensities. Soil water contents in the 50- and 80-cm depths and the daily water content change of the whole lysimeter were well simulated by the models. Deviations between models and measurements might have been caused by the so-called pot effect and by drought stress influencing the root distribution in the lysimeter