Morphology and Some Physical Properties of Soil in Areas Presented of Stem and Root Rot Disease of Cassava in Thailand

Soil morphological features were investigated, and soil samples were collected in cassava stem and root rot disease areas in Thailand for elucidating soil physical properties that are specific characteristics of cassava stem and root rot disease areas. Soil samples were collected in diseased areas with reference to the geographic coordinates and soil series data from the provincial soil map of Thailand of the Land Development Department. Soil morphological features were studied by excavating the soil with a soil auger. Soil samples at depths of 0-20, 20-40, and 40-60 centimeters were collected at the study locations for analyzing the soil texture, soil bulk density, and hydraulic conductivity. The results of the study showed that soil morphological characteristics of the study sites, with spreading disease, were of hard layers, shallow soils, mottle, and an accumulation of clay in the subsoil. The soil physical properties showed that soil texture from spreading areas of disease ranged from coarse texture to fine texture (sand texture to clay texture). It was clearly shown that the soil bulk density was very high in the subsoil while the saturated hydraulic conductivity of these soils was low in the subsoil. The morphological characteristics found in disease incidence areas were based on basic soil datasets in soil series such as shallow soils, mottle, and accumulation of clay in the subsoil. However, disease incidence was also due to soil management that resulted in soil properties including the presence of a shallow tillage layer, a dense layer, and a high bulk density, which are limitations of soil drainage and further enhance disease incidence.