Concepts of solute leaching in soils: a review of modelling approaches

A number of conceptual models for solute leaching in soil are reviewed, quantitatively compared and classified as far as possible within a framework that makes distinction between deterministic and stochastic, mechanistic and functional and rate and capacity models. They are also discussed with reference to their purpose (viz research or management), complexity, flexibility, transferability and usefulness for field soils. The basic assumptions and structures of the models impose definite limits on the ways in which they can be used. The spatial variability of soil properties caused problems for deterministic models using rate parameters, but stochastic elements can be incorporated in these models. Simpler capacity-type models and non-mechanistic stochastic models offer other answers to this problem. Few data sets are available for testing a range of models and few models have been tested on a range of soil types, and very few models have much demonstrable ability to simulate transient field leaching conditions. Examples of a model being tested by someone other than the developer seem very rare.