Classification and fertility status of soils developed on granite - gneiss in southern Cross River State, Nigeria

Abstract

Morphological, physical, chemical and mineralogical properties were determined with a view of classifying the soils using the United States Department of Agriculture (USDA) Soil Taxonomy System and correlated with the Food and Agriculture Organization- World Reference Base (FAO-WRB) for Soil Resources and assess the soil fertility status. Three representative soil profile pits were dug in Mkpot, Ikpai and Ojok in Akamkpa Local Government Area of Cross River State. The soils studied had deep profiles (> 100cm) with mainly sandy loam in the surface and sandy clay loam to sandy clay at the subsurface horizons. Bulk density (1.2 – 1.5 Mgm^-3) increased with increase in soil depth. The soil pH (H2O) ranged from 4.8 – 6.8, organic carbon from 1.2 – 24.34 gkg^-1, total nitrogen from 0.42 – 1.69 gkg^-1, effective cation exchange capacity ranged from 1.77 – 5.61 cmolkg^-1 and base saturation from 36 – 99%. Extractable micro nutrients 
such as copper (Cu), manganese(Mn), zinc (Zn) and iron (Fe) were medium to high except boron (B) which was low due to high soil acidity. Minerals such as quartz (59.13%), Kaolinite (21.72%), Microcline (7.18%), Muscovite (2.91%), Hornblende (2.1%), Diopside and plagioclase (1.71%) were identified. Based on the USDA soil taxonomy criteria, the soils were classified as loamy, skeletal, mixed, Isohyperthemic typickandiudults, its equivalent by Food and Agriculture Organization – World Reference Base for soil Resource of the soils were Dystric Acrisols. The soils can be managed through mulching, crop rotation and adoption of zero tillage to reduce the leaching of basic nutrients, liming as well as cultivating acid tolerant crops.