Morphological, Physicochemicaland Mineralogical Properties of Soils Developed from Basalt Atikom, Cross River State, Nigeria

Soils developed from basalt were studied along with a top sequence of a deeply excavated basaltic quarry site at Ikom, Cross River State, Nigeria. The soils were very deep and occupy gently sloping plains of 0 – 8% gradients. Each pedon examined, had four distinct layers, the Ap, BA, Bt and Crtg horizons. The Ap horizons have dark reddish grey (5YR 4/2) to dark reddish-brown (5YR 3/4) colours while the Bt horizons have mostly red (2.5 YR 4/6) colour with friable consistence. The Crtg horizons have dominantly grey (2.5Y 5/0) to greyish brown (2.5Y 5/2) matrix colours and contain many, medium, distinct dark grey (2.5YR 4/0) to weak red (2.5YR 4/2) mottles and many rotten basaltic fragments. Soil texture was uniformly clay with Bt horizon values of 61 to 67% clay. The soils were well aerated with macroporosity, which ranged from 4.8 to 18.8% in all the horizons studied. The soils were extremely strongly acid in reaction with pH (H2O) ranging from 4.4 to 5.2 in all horizons of the three pedons examined. Organic carbon content was low with values that varied from 6.22 to 8.78 gkg-1in the Ap horizons. Total N, available P, and exchangeable cations were all low to very low indicating that the soils are impoverished of plant nutrient elements. Cation exchange capacity (pH 7.0) values were low to very low with values ranging from 4.0 to 7.10 cmolkg-1 with a mean of 4.8 cmolkg-1in all the three pedons studied. X-ray diffraction studies of the whole soils indicated that kaolinite constitutes 71 to 78% of the mineralogy of the soils while only very resistant minerals such as quartz, anatase (TiO2), hematite (Fe2O3) and goethite (αFeOOH) were detected in the soils. The properties of the soils indicate that they are highly leached, highly weathered, nutrient-poor, sesquioxide and kaolinitic tropical soils.