COMPARISON BETWEEN MEASURED AND SIMULATED PLANT WATER POTENTIAL DURING SOIL WATER EXTRACTION BY POTTED RYEGRASS

We conducted a combined simulation-experimentation study to monitor the simultaneously changing states of plant water and of soil water during a period of continuous transpiration by uniformly rooted ryegrass, grown in pots filled with a sandy soil, under two levels of evaporative demand. The pattern of soil moisture extraction was measured by weighing and tensiometry, and that of plant water potential, by leaf psychrometry. A macroscopic-scale extraction model, previously published by the authors, was modified to account for the water-storage characteristics of the crop. Both the original and the modified versions of the model were found able to provide a realistic description of the diurnal fluctuations of plant water potential during the period prior to the onset of plant water stress, but they were less realistic in describing the decline of plant water potential during the dehydration and wilting phases. The rehydration of the crop from a stressed condition could be simulated realistically only by assigning a higher value of root resistance than during the initial extraction phase.