USE OF SOIL SURVEY DATA FOR MODELING SOLUTE TRANSPORT IN THE VADOSE ZONE

Soil surveys have now been completed in many countries and qualitative interpretations in terms of soil suitability for different forms of l and use, which are part of most soil survey reports, are being used wi dely. These interpretations are, however, essentially based on expert judgement and they are inadequate to answer many modern questions abou t ecological and environmental aspects of alternative forms of land us e. Simulation modeling of solute transport and plant growth has become an operational tool in land use studies and soil survey databases can be an important source of basic soil and landscape information to be used in modeling. Still, many data are not in a form that can be used directly and an effort has to be made to transform soil survey data in to a usable format, by developing pedotransfer functions. In discussin g soil survey data, a distinction can be made between point- and area data. Case studies for leaching of nitrates (NO3-) and growth of potat o (Solanum tuberosum L.) in a loamy and clayey soil, illustrate use of different types of class-pedotransfer functions for functional soil h orizons. Monte Carlo techniques are used to illustrate the effect of v ariability of hydraulic basic data on results obtained. Soil surveys d efine soil data and interpretations for areas of land by considering ' 'representative'' soil profiles for delineated areas on the map. Inter nal variation is expressed only in qualitative terms. Geostatistical t echniques can be used to interpolate point data to areas of land, allo wing quantitative expressions including error statements. The effects of upscaling of point data to cells of different sizes on leaching of NO3- and growth of potato are illustrated for data derived from a Dutc h field. All illustrations demonstrate the crucial role of Geographic Information Systems (GIS) in storing and manipulating basic soil and l andscape data.