Quantitative prediction of the leaching of organic and inorganic solutes in soil

The quantitative description of chemical leaching in soil, long a focal point for soil science research efforts, is being pursued with increased intensity. Although much is known of the physics and chemistry of well-defined, homogeneous soils studied under controlled situations, only recently have there been attempts to apply these concepts to the description of field conditions. The interpretation of results is a challenging task, as field-scale variability and non-equilibrium processes are proving to be substantial issues in natural systems. New models of leaching are required to describe the macropore flow of water and chemicals, kinetic-equilibrium sorption processes and the inherent spatial variation in soil hydraulic properties and biological and chemical processes. Development of these models depends upon increased understanding of leaching processes in the field, that can only come from increased numbers of experimental studies in which appropriate parameters are recorded. Until improved models are available, those currently available will be used by a variety of individuals to estimate the environmental fate of chemicals. Defining the proper use of such models is the responsibility of soil scientists. This is a new responsibility that they must assume if quantitative estimation of chemical leaching is to be accomplished in an accurate and meaningful manner.