CHARACTERIZATION AND IDENTIFICATION OF CONTEMPORARY DIAGNOSTIC (B) HORIZONS OF SOILS IN IDEATO NORTH LOCAL GOVERNMENT AREA OF IMO STATE, SOUTHEASTERN NIGERIA
There is a dearth of scientific information on the soils of Ideato North Local Government Area of Imo State in Southeastern Nigeria. This study was carried out to characterize and classify these soils with special emphasis on the identification of diagnostic B- horizons present in them. Free survey method was employed to locate the representative profiles. Ten profile pits were dug, properly studied macromorphologically, georeferenced using handheld Global Positioning System (GPS) Receiver and sampled based on the identified horizons. Another set of samples at 10 cm intervals from top to bottom were collected. A total of 491 samples were collected. 56 soil samples and 54 core samples were collected from the identified horizons, while 195 soil samples and 186 core samples were collected from the 10 cm interval sampling and these were analyzed for chemical and physical properties. Results were presented using descriptive statistics. Two major parent materials in the area were identified as Shales and Sandstones. Results show that the soil texture classes consist of sand, loamy sand, sandy loam and sandy clay loam. However the dominant soil textures in most of the profiles were loamy sand which mostly occurred in the subsurface layer. Profiles 1-7 of soils investigated were well- drained, while profiles 8, 9 and 10 were poorly drained. Most of the soil colours consist of Hues of 2.5YR, 5YR and 7.5YR except for profiles- SE/IM/IDN/ ARO 1 – 008 and SE/IM/IDN/ ARO 2 – 009 that have varying Hues of 5Y, 10YR, 5GY and 2.5Y. Soil bulk density was low to high ranging from 1.23g/cm3 to 1.94g/cm3. Soil pH values ranged from extremely acidic (pH 4.4) to slightly acidic (pH 6.1). The values of exchangeable calcium and magnesium are low to high, ranging from 0.20 cmol/kg to 6.20 cmol/kg for calcium and from trace to 30.20 cmol/kg for magnesium while the values of sodium and potassium are very low ranging from 0.005 to 0.052 cmol/kg for sodium and from 0.003 cmol/kg to 0.016 cmol kg-1. The cation exchange capacity (CEC) is low to high ranging from 5.20 cmol kg-1 to 51.20 cmol kg-1. The exchangeable acidity is trace to low, the soil organic matter is low to high ranging from 0.07 g/kg to 5.00 g/kg with the high values occurring on the epipedons. The values of percentage base saturation (PBS) of rthe representative profiles are low to very high ranging from 2.32% to 82.20%. The values of effective cation exchange capacity (ECEC) are low (1.457 cmol kg-1) to high (35.56 cmol kg-1). The available phosphorus is low ranging from 0.004 cmol/kg to 0.013 cmol/kg. The values of water dispersible clay (WDC) range from 4.32% – 20.32%. The diagnostic criteria such as clay coatings/cutans, subsurface to surface clay ratio of 1.2, lithologic discontinuity, abrupt textural changes, artifacts, CEC. ECEC, etc. were identified. The two diagnostic B- horizons identified in the study area are Kandic horizon and Argillic horizon (USDA) which are similar to Argic horizon (FAO/UNESCO (WRB). The soil profiles were classified according to the nomenclature of Soil Taxonomy (ST) and correlated with FAO/UNESCO(WRB) as follows: USDA are: Kandic, Arenic Rhodic Kandiudults, [Urualla]; Kandic, Arenic Rhodic Kandiudults [Isiokpo]; Kandic, Rhodic Kandiudults [Akpulu]; Kandic, Arenic Rhodic Kandiudults [Akokwa]; Kandic, Arenic Kandiudults [Osina]; Kandic, Arenic Kandiudults [Uzii]; Argillic, Rhodic Paleudults [Obodoukwu]; Argillic, Arenic Oxyaquic Hapludalfs [Arondizuogu I (wetland)]; Argillic, Typic Hapludalfs [Arondizuogu II] and Argillic, Typic Paleudults [Umualaoma]. The corresponding nomenclatures arising from classification of the soils by FAOUNESCO (WRB) are: Rhodic Acrisols (Arenic) [Urualla]; Rhodic Acrisols (Arenic) [Isiokpo]; Rhodic Acrisol [Akpulu]; Rhodic Acrisols (Arenic) [Akokwa]; Haplic Acrisols (Arenic) [Osina]; Haplic Acrisols (Arenic) [Uzii]; Rhodic Acrisols (Cutanic/Differentic) [Obodoukwu]; Gleyic Lixisols (Cutanic/Arenic) [Arondizuogu I (wetland)]; Abruptic Lixisols (Cutanic) [Arondizuogu II] and Leptic (Abruptic) Lixisols (Cutanic) [Umualaoma].