Properties and Genesis of Associated Red and Black Soils in North Karnataka

Three pairs of red and associated black soils on basalt, granite-gneiss and chlorite - schist formation from Bidar, B'Gudi and Mantagani in North Karnataka were compared to study their genesis. Red soils were characterised by redder hue, high chroma and abundance of coarse fragments. Black soils on the other hand were characterised by yellower hue, low chroma and fewer coarse fragments. Clay content in black soils was more than their associated red soils. All red soils showed accumulation of clay in B horizons but was more evident in B'Gudi. The surface area of soil and clay content were highly correlated and the study also revealed the predominance of smectite in the black soils compared well with that of red soils. Dithionite-extractable iron content was also more in red than in associated black soils. Based on these properties it is hypothesized that the difference in genesis and occurrence in close proximity of these two contrasting soils is mainly related to drainage as conditioned by relief. The low chroma and dithionite-Fe along with smectitic minerals of black soils are the clear cut indications of the impeded drainage in black soils compared to their red counterparts.