TESTING AND COMPARISON OF 3 UNSATURATED SOIL-WATER FLOW MODELS

The performance of three soil water flow models is compared using fiel d data collected from a structureless sandy loam soil cropped to soybe ans (located near Simcoe, Ontario, Canada), and a structured clay soil cropped to grass hay (near Ottawa, Ontario, Canada). Two of the model s, Soil Water and Actual Transpiration Rate, Extended (SWATRE) and Lea ching Estimation and Chemistry Model (LEACHW), are based on the one-di mensional pressure head form of Richards' equation, and the third, SWA SIM, is based on the one-dimensional diffusivity-water content form of Richard's equation. The models are tested and compared on the basis o f their ability to predict in situ measured soil water content profile s during the growing season at the two field sites. All three models p roduce acceptable predictions, as evidenced by an average error within +/- 0.0404 cm3 . cm-3 and a relative error within +/- 0.2915. None of the models is consistently more accurate than the others. Discrepanci es between the models are attributed primarily to differences in how t he models account for soil evaporation and plant transpiration.