Characterization of two benchmark soils of contrasting parent materials in Abia State, Southeastern Nigeria

Detailed characterization of two important agricultural soils of contrasting parent materials, found in southeastern Nigeria was carried out. The Amakama soil formed over Coastal Plain Sands has a deep, well drained profile greater than 240cm deep. The soil texture varies from loamy sand in the surface layer to sandy clay loam down the profile. The Ibeku soil formed over Bende-Ameki (clay shale) formation has a deep profile that is gravelly in the upper 60cm and clayey in the lower horizons. Bulk density on oven dry basis ranged from 1.3 to 1.66 g cm-3 in the Ibeku soil and from 1.43 to1.52 g cm-3 in the Amakama soil. Water content at 33 kPa ranged from 13.7 to 14.9 in the Amakama soil and from 27.8 to 48.4 in the Ibeku soil. Chemically, the Amakama soil is deficient in basic cations with aluminum saturation being greater than 83%. The soils are very acidic (pH 4.5 – 4.9) and low in organic carbon, total nitrogen and available phosphorus. In contrast, the Ibeku soil has high levels of calcium, sum of basic cations that range from 9.2 to 23.5 cmol(+) kg-1 and aluminum saturation of 25 - 40%. Total nitrogen and organic carbon are medium and available phosphorus is low in this soil. The mineralogy of clay sized particles showed a dominance of kaolinite in both soils with some quantities of montmorillonite that increased down the profile. In the Ibeku soil, the mineralogy of coarse silt fractions showed that goethite and quartz were the dominant minerals in upper horizons (< 1 m) while potassium feldspar and goethite dominated the lower horizons. Amakama soil was classified as Fine loamy, siliceous, isohyperthermic, Rhodic Haplustox while Ajata –Ibeku soil was classified as very fine, kaolinitic, isohyperthermic, Aquertic Paleustalf.KEY WORDS: Benchmark soil, Mineralogy, Morphology, Soil properties.