Soil characteristics, revised soil classification, and soil geochemistry related to soil suitability of West Lampung tropical volcanic residual soil, Sumatra, Indonesia

In the area of West Lampung, Sumatra, Indonesia, soil quality problems have occurred. They include landslides, erosion, and soil cracks due to the increased dry land agriculture (coffee-based farming), rice fields, and residential areas. Here we provide information about optimizing land use based on geological, geotechnical, and geochemical approaches. For optimization of land use we determined salinity, plasticity, and mineral content in the soil. The aims of this study are: 1) identifying soil characteristics and classification based on geological, geotechnical, RSCS, and soil activity approach. 2) identifying the minerals contained in the soil based on XRD analysis. 3) determine soil suitability based on soil characteristics. 4) to quantify the area that has certain soil suitability. The methods used are geological and geotechnical soil characterization (USCS and soil activity analyses), XRD analysis, and Revised Soil Classification Systems (RSCS) analysis. The results showed that the study area is composed of tropical volcanic residual soil: Andosol soil type. The soil has low to high plasticity and it is included in the inactive to active soil category. Based on their characteristics, the soils of the studied area are divided into two categories. The first category are soils with low plasticity characteristic, have LL brine value <50% (low to intermediate salt content), electrical sensitivity of 0.18 to 1.48; soils with the inactive soil category, and contain minerals: despujolsite, hematite, chlorite, montmorillonite (0.3% - 0.6%), and quartz (2.8% - 30.2%). This category will be suitable for agriculture purposes, building foundations, and earth construction. The first category occupies 65% of the study area. While the second category are soils with intermediate to high plasticity characteristics, have LL brine value >50% (intermediate to high salt content), electrical sensitivity of 0.38 to 1.10, soils with the normal to active soil category, and contain minerals: despujolsite, hematite, magnetite, illite, montmorillonite (0.4% - 0.9%), dickite, and quartz (2.50% - 17.90%). The second category occupies 35% of the study area was more ideal for the primary forest growth.