New Approach to Soil Formation in the Transitional Landscape Zone: Weathering and Alteration of Parent Rocks

Background and Objectives: Many studies have addressed the relation of soil formation and weathering. However, in the transitional landscape zone the soil formation is resulting not only from weathering process but also from alteration of parent rocks. The comparison of soil formation rates due to both processes is not studied yet. In Java, a transitional landscape zone is widely formed, and causes different types of soil formation in particular areas. The objective of this study was to compare the common concept of parent rock weathering with the concept of parent rock alteration in the soil formation. Materials and Methods: Purposive soil sampling was applied to collect the soils derived from weathering process and alteration. Laboratory analyses were applied to assess physical and chemical properties of soils. XRPD and XRF analyses were also conducted for mineralogical analysis. Results: The results showed that soil on weathered materials had brownish to grayish color, less than 30% of clay, 20-70 meq/100gr of CEC, 1.8-4.3% of organic matter, medium to high cation bases and base saturation. While soils on altered materials showed reddish to orange color, contained more than 60% of clay, <10meq/100 gr of CEC,1.4-2% of organic matter, and very low cation bases and base saturation. Difference of mineral properties of soil developed on weathered- and altered materialswas shown by the presence of hematite. XRF results showed that weathered materials contained by SiO2> Fe2O3> Al2O3, however, altered materials contained by SiO2> Al2O3> Fe2O3. Conclusion: It was concluded that in the transitional landscape zone, the soil formation was not always started by parent rock weathering. Weathering process resulted in top down process of soil formation. Alteration resulted in two processes of soil formation (bottom-up and top-down).