Soil mineralogy effects on seal formation, runoff and soil loss

Interaction between clay particles is one of the main factors responsible for soil aggregation. Therefore, soil mineralogy, which has substantial effects on clay dispersion, may also influence aggregate stability, seal formation, runoff and soil loss. In spite of this, the effects of soil mineralogy on these phenomena have received much less attention in the literature than those of other soil properties. This paper reviews the effects of soil mineralogy on aggregate stability, seal formation and micromorphology, and on the associated infiltration rate (IR), runoff and soil loss. The paper is focused mainly on the authors' previous studies. In order to determine these effects, various soils with different mineralogy were collected from Israel, South Africa and Kenya. In these soils, the aggregate stability was determined under fast wetting conditions, and the IR and the interrill soil loss were determined using rainfall simulator of a rotating disk type. The micromorphology of the crust, which was developed at the soil surface by the rainstorm, was determined by scanning electron microscope. Clay mineralogy was found to be a dominant factor in controlling aggregate stability, seal formation, soil IR and interrill soil loss. The phyllosilicate soils, which were review in this paper, were divided into two main groups: (i) stable soils with final IR>8.0 mm h^-1 and (ii) unstable soils with final IR<4.5 mm h^-1. These two soil groups differ in their mineralogy. Kaolinitic and illitic soils that do not contain smectite were stable soils and less susceptible to seal formation. In contrast, kaolinitic and illitic soils that contain some smectite and smectitic soils were unstable. Examination of the susceptibility of 21 phyllosilicate soils to interrill erosion indicated that these soils could be divided into three groups. Soil loss was higher for unstable soils than for stable soils, but the soil loss of the smectitic soils was significantly higher than that of the unstable soils, which contained kaolinite or illite as the dominant clay.