USE OF SOIL PHYSICAL CHARACTERISTICS FROM LABORATORY MEASUREMENTS OR STANDARD SERIES FOR MODELING UNSATURATED WATER-FLOW

Soil physical characteristics are important input parameters for simul ation modelling of unsaturated flow in soils and associated solute flo w. The determination of soil water retention and hydraulic conductivit y curves in the laboratory is laborious and expensive. For modelling s tudies that require characteristics for many soil horizons, such as re gional studies or scenario studies, it may be impossible to measure al l the necessary characteristics. An alternative would be to use charac teristics inferred from readily available soil data by class-pedotrans fer functions, In this study such a comparison was made for six sites on sandy soils in the Netherlands using the soil-water model SWACROP w ith soil physical characteristics from either laboratory measurements or from a standard series as input. For this the simulated pressure he ad values and moisture content values were compared with measured valu es at eight different depths using statistical criteria. Furthermore t wo functional criteria, i.e. the number of workable days and number of days with possible drought, were inferred from simulated pressure hea d values and again the different results were compared, It was found t hat simulation results were not significantly different, implying that standard series or class-pedotransfer functions could be used in stud ies like these for simulating the unsaturated water flow regime in san dy soils on field/farm level or regional level, Differences for specif ic criteria for individual sites were sometimes substantial and in suc h cases (at field level) it will make a difference which soil physical characteristics are used.