Pedotransferfunctions and the Functional Characterization of Soils.

Soil survey interpretations are based on `representative` profiles for each mapping unit and are qualitative  as they define limitations for a wide range of land uses in terms of slight, moderate and severe. Modern interpretations require more quantitative approaches using simulation modelling techniques. Lack of measured data are (or should be) a serious drawback on using such models. Here pedotransferfunctions (pdf), relating easily available soil survey data to parameters needed for simulation, have a crucial function. The parameters of the classis :”Van Genuchten” equation for hydraulic conductivity and moisture retention have successfully been related to soil texture, bulk density and organic matter content as obtained from soil survey. Such a pdf was applied to simulate four functional soil characteristics related to precision agriculture: water stress in a dry year, N-stress in a wet year; N-leaching from the rootzone and residual N content in a wet year. Simulations for each of 612 observations in a 100ha farm were interpolated to form areas of land to be used as management units. Effects of uncertainty associated with using pdf’s, were found to be important in another study considering two functional characteristics: days with good workability and  days with sufficient aeration. When, however, simulating the characteristics of chloride breakthrough and adsorption of cadmium and isoproturon, the variation in basic soil properties and in groundwater depth was much more important than the variation of the soil hydraulic characteristics. Adequate descriptions of soil hydraulic pdf’s, including their variation,  is particularly needed when functional aspects of soil behaviour  of a physical nature are studied