The Red Latosols of Sri Lanka: I. Macromorphological, Physical and Chemical Properties, Genesis, and Classification
1976
de Alwis, K. A. | Pluth, D. J.
The Red Latosols of Sri Lanka have developed on the Quaternary Red Earth Formation into very deep, excessively drained soils with weak horizon differentiation. The three major soil series of this subgroup, the Gambura, Mullaitivu and Wilpattu series, were studied from the point of view of their morphological properties, particle size distribution, bulk density, 1/3 and 15 bar moisture, pH, organic carbon, total nitrogen, CEC, exchangeable cations and free Fe and Al oxides by means of representative pedons for purposes of characterization and determination of the genetic processes. The Red Latosols all show some clay illuviation with the vertical distribution of the illuviated clay inversely related to the clay content. Free iron oxides are present largely as discrete particles and have themselves migrated downward, though to a lesser extent than the clay. The CEC values are low and consistent with clay fractions dominated by the kaolinite group. The CEC's also indicate a high proportion of pH-dependent exchange sites. The exchange acidity appears to result largely from the presence of Al-hydroxy compounds in the exchange complex. The dominant basic cation is Ca. The free iron oxides are almost entirely crystalline and seem to have moved principally by physical translocation of the particles, although another mechanism has also been postulated. Differences in the properties of the three series of the Red Latosols mainly reflect differences in clay and iron oxide contents. According to the USDA Soil Taxonomy the Gambura series is a fineclayey kaolinitic isohyperthermic Rhodic Oxic Paleustalf, whereas the other two series are fine-loamy siliceous isohyperthermic Rhodic Oxic Paleustalfs.
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