10.2190/49JM-R4GV-BV0B-24PK 49JMR4GVBV0B24PK 4 Evaluation of Soil Water Characteristics Models Under Zero Tillage and Conventional Tillage Treatments 289 303 20020509 20020509 20020509 20020509 49JMR4GVBV0B24PK.pdf http://baywood.metapress.com/link.asp?target=contribution&id=49JMR4GVBV0B24PK 3 J. Y. Diiwu R. P. Rudra W. T. Dickinson G. J. Wall University of Guelph, Ontario, Canada The effect of tillage and soil horizon on the performance of three soil water characteristics models, the Hutson and Cass, van Genuchten, and Verma and Brusaert models, was investigated. the impact of field scale heterogeneity on the estimated parameters of the models was also analyzed. Variabilities in model parameters were found to be significant at 5 percent significance level. the model predictions were more reliable for conventional tillage treatment than for zero tillage treatment. For both tillage treatments all the models performed equally well for the A horizon, while the van Genuchten model was the best choice for the B horizon. All the models accounted for over 97 percent of variability of soil water characteristics, yet no one model pave a best theoretical representation of soil water characteristics in both the A and B horizons over the entire field. Sensitivity analyses on the van Genuchten parameters indicated that ζ is a more sensitive parameter than a in both the A and B horizons for zero tillage and conventional tillage treatments. D. Hillel, <i>Fundamentals of Soil Physics</i>, Academic Press, Inc., San Diego, California, 1980. J. L. Hutson and A. Cass, A Retentivity Function for Use in Soil Water Simulation Models, <i>Journal of Soil Science, 38</i>, pp. 105-113, 1987. G. K. Felton and J. L. Nieber, Four Soil Moisture Characteristic Curve Functions for Numerical Modelling of Sand, <i>Transactions of American Society of Agricultural Engineers, 34</i>:2, pp. 417-422, 1991. M. T. van Genuchten, A Closed-Form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils, <i>Soil Science Society of America Journal, 44</i>, pp. 892-898, 1980. R. D. Verma and W. Brutsaert, Unconfined Aquifer Seepage by Capillary Flow Theory, <i>Journal of Hydraulics Division, American Society of Civil Engineers, 96</i>:6, pp. 1331-1344, 1970. R. H. Brooks and A. T. Corey, Hydraulic Properties of Porous Media, <i>Hydrology Paper No. 3</i>, Colorado State University, Fort Collins, 1964. G. S. Campbell, A Simple Method for Determining Unsaturated Conductivity from Moisture Retention Data, <i>Journal of Soil Science, 117</i>:6, pp. 311-314, 1974. J. Y. Diiwu, <i>Transfer Function Modelling of Drainage and Solute Transport through Layered Macroporous Soil</i>, Ph.D. thesis, School of Engineering, University of Guelph, Guelph, Ontario, 1997. J. Y. Diiwu, R. P. Rudra, W. T. Dickinson, and G. J. Wall, Dependence of Variability in Hydraulic Properties on Physical Properties of Field Soil, <i>Journal of Environmental Systems, 26</i>:2, pp. 171-189, 1998. L. Wilkinson, M. A. Hill, J. P. Welna, and G. K. Birkenbeuel, <i>SYSTAT for Windows: Statistics</i>, Version 5.2 Edition, SYSTAT, Inc., Evanston, Illinois, 1992. A. J. Peck, Field Variability of Soil Physical Properties, in <i>Advances in Irrigation, Vol. 2</i>, D. Hillel (ed.), Academic Press International, pp. 189-221, 1983.