Chemistry and Mineralogy of Soils Derived from Different Parent Materials in Southeastern Nigeria

Knowledge of the soil minerals is an important index in understanding the soil fertility properties since mineral surfaces serve as both the source and sink of plant nutrients. Soils developed from contrasting parent materials viz: Coastal Plain Sand, Sandstone, Basalt and Shale at different soil horizons (0-20 cm, 20-40 cm and 40-60 cm) in South Eastern Nigeria were studied for mineralogical properties. Soil samples were collected from the different parent material in three replicates and a total of thirty six composite samples were collected. These samples were subjected to X-ray diffraction analysis with Siemens D5000 diffractometer using Cuką radiation with Iron(fe) filter (λ = 1.5409A) at 40kv and 30 mA, at a scan rate of 2° per minute. The experimental design was a 4 x 3 factorial in Randomized Complete Block Design (RCBD). Statistical analysis revealed significant (P<0.05) variation in soil physical and chemical properties with parent material and soil depth except organic matter “OM”, total nitrogen “TN”, magnesium “Mg+2” total exchangeable acidity “TEA” and base saturation “BS” where variations were not significant. However, interaction between parent material and soil depth was only significant in influencing the pH. Top soil layers had a significant greater amount of OM, TN, AP, cations, Sand and Silt. Generally, soil of shale formation was superior, followed by basaltic soil in these soil fertility indicators, while soil of Coastal Plain Sand formation had the least amounts. Parent material and depth played dominant roles in the type and distribution of clay minerals in the study area. The concentration of these minerals varied with parent material and soil depth. Significant variations with parent material were observed in the minerals identified except in Halloysite and Chlorite where non-significant variations were observed. While variations with depth were statistically significant (P<0.05) in Chlorite, Geothite, Hermatite, Montmorillonite and Quartz, the influence of the interaction between parent material and soil depth were only significant in Gibbsite, Kaolinite and Montmorillonite. Soil derived from Coastal Plain Sand had, Kaolinite (9.94 to 28.83%) and Quartz (56.4 to 87.3%) as the dominant clay minerals and these decreased with depth. Soil formed in shale had mixed clay mineralogy of montmorillonite (14.37 to 21.88%), goethite (23.58 to 25.09 %), hermatite (20.39 to 24.19%), gibbsite (8.48 to 12.10%), kaolinite (6.89 to 3.56%) and others with depth. Soil formed in sandstone has Kaolinite accounted for 26.42 to 31.26%, goethite, 7.77 to14.87%, and quartz accounted for 35.4 to 51.8%. Other minerals identified were: hermatite (4.58 to 14.62%), gibbsite (1.70 to 5.23%), while soils derived from basalt had kaolinite (14.64 to 27.44 %), quartz (23.7 to 42.5%), hematite (11.0 to 23.14%), goethite (13.94 to 26.48%) as the dominant crystalline minerals present in the soil. The study concludes that the mineralogy of Southeastern Nigeria consists of quartz, kaolinite, hermatite, goethite and gibbsite with traces of smectite in soil derived from shale as the dominant minerals and their percent mass occurrences varied with soil parent material and depth. Since the mineralogy of the soils studied is mainly kaolinitic, the soils can said to be low in terms of fertility and therefore require adequate soil fertility management strategies to enhance their fertility and productivity.