MATHEMATICAL EXPRESSION OF ELUVIATION‐ILLUVIATION PROCESSES AND THE COMPUTATION OF THE EFFECTS OF CLAY MIGRATION IN HOMOGENEOUS SOIL PARENT MATERIALS

Abstract

SummaryClay movement and its effect on the differences in texture between the A and B horizons are expressed by mathematical equations. The factors which are considered are the actual amount of clay which has moved (l), the ratio of the thick nesses of the horizons (N), and the original clay content (C). Parent materials are assumed to be homogeneous.Knowing the clay contents of the A and B horizons, it is possible to calculate for given N ratios the theoretical amount of clay which has moved in order to achieve the observed textural difference. The theoretical clay content C'of the parent material can also be computed. All computations assume homogeneous parent materials and closed profiles, i.e. materials that do not collapse, shrink, or swell, and consider all other clay transformations non‐operative.An eluviations index k, which indicates the proportion of the original clay that has been translocated, is proposed for evaluating the intensity of clay migration.Examples of practical applications are given: i.e. the required difference in clay content between A and B in the definition of the argillic horizon should not be kept constant in soils which have variable initial clay contents; graphs illustrate the effects of clay migration for constant C and k values (isoparentic and isoluvic lines).All computations can be made by desk calculators provided with an extended memory for storage of data and programmes.