Study of Basaltic Soils Along the Toposequence of Aya River in Ogoja, Cross River State, Nigeria

An investigation was carried out on selected properties of basaltic soils along the toposequence of Aya river in Ogoja Cross river state. The soils are deep and occur on a gentle and undulating landscape with a gradient of <4%. Three profile pits were dug in each of the mapping units identified as crest, mid-slope and valley bottom. Each Pedon had four distinct genetic horizons (Ap, AB, Bt1 and Bt2). The dominant matrix for the Ap horizon was dark brown (7.5YR3/4), brown (7.5YR6/4) and yellowish brown (10YR6/8) for pedons I, II and III respectively. The particle size distribution data indicates the preponderance of sand fraction while the percentage sand mean values are 82.45 %, 81.45 % , 85.78 % and 81.0 % for pedons III, II and I respectively. The soils reaction pH H2O is assessed as strongly acidic ranging from 5.25-5.75. The exchangeable Ca2+, Mg2+ and K+ are in low concentrations but are within the threshold of critical limits. Organic carbon and total nitrogen and available P were generally low (N: 1.7-1.1 g/kg; OC:7.3-5.1 g/kg and P:18.25- 12.60 g/kg). The Organic C/N ranged from 3 – 7 and Ca/Mg had mean of 1.40, 1.36 and1.31 in pedons I, II, and III respectively. The base saturation (%BS) was high to very high (64.70-79.26 %) while effective cation exchange capacity was generally low (2.03 cmol/kg, 2.29 cmol/kg, and 1.93 cmol/kg for pedons I, II, and III respectively). The soil on the toposequence of Aya river showed evidence of oxic properties with absence of weatherable minerals in the sub stratum. The soil suitability class were moderately suitable with limitations in pH and low soil organic matter content. The soils were classified as Isohyperthermic ustalfs which corresponded to Arenic Luvisols (pedons 1 and 2) with fluvic characteristics in pedon 3 (WRB, 2006). Soil quality of the studied soils is low due to the established unfavourable fertility indicators; hence soil conservation and use of integrated soil fertility management- organic sources (compost manure), inorganic sources (NPK fertilizers) and crop rotation as well as conservational tillage is recommended.