MODELING SOIL-WATER CONTENT AND PRESSURE-HEAD WITH SWACROP IN POTATO FIELDS

Distribution of water in the soil profile is the result of interaction s between many variables related to crop, soil, climate, and agricultu ral practices. Crop growth models are effective tools in integrating t hese interactions. In this study, soil water contents and pressure hea ds simulated by the SWACROP model were compared with those measured in sandy soil fields cropped with potatoes in Quebec. A sensitivity anal ysis was performed to identify the input parameters of SWACROP that mo st influence output results. Hydraulic conductivity, soil water retent ion parameters (saturated and residual soil water contents), crop para meters (leaf area index, soil cover, rooting depth), and the number of discretization nodes substantially affected model output. Simulated s oil water content values were close to those measured with a mean bias error ranging from 1.1 to 3.5% and a mean absolute error between 3.3 and 4.1%. The parameter values obtained by this model compare well wit h those reported in other studies. SWACROP overestimated soil water pr essure heads near the soil surface in the middle of the growing season , most likely due to soil disturbances occurring near the porous cup o f the tensiometers caused by farming operations and tuber growth.