Abstract
We investigated the transient soil water movement of a potato field in Scotland during the whole 1987 growing season. The numerical simulation of water movement, considering climatic change, water uptake by roots and evapotranspiration, were based on the soil-plant-atmosphere continuum (SPAC) model. We compared the results of two simulation cases and the ob-served soil water distribution to evaluate the hysteretic effect in θ(h) relations for the soil water movement, where h is the pressure head and θ is the water content. Case I is the drying simulation using the main drying functions of the θ(h), and case II is the hysteretic simulation based on the simplified hysteresis model of θ(h). We used the mixed form of continuous eguation as the governing equation of the soil water flow to avoid the water balance error in the numerical solution. Consequently, the results of the hysteretic simulation were found to have high accuracy in representing the observed soil water distribution. Hysteresis does not affect the prediction of actual transpiration rates from the plants, since the soil water in the root zone was used by the plants as the effective water for the plant growth. The water balance error for the two cases of simulation, that based on the mixed form of continuous equation, was less than 2% during the 142 days of growing season.
