Soils on coastal plain sands of southeastern Nigeria have hitherto been referred to as fragile sandy and acidic soils of low base saturation, cation exchange capacity (CEC) and fertility, as evidenced by the extensive land degradation evident in the region. This underscores the need for the characterization of the soils for sustainable use. Three profile pits were therefore dug on the upper, middle and bottom slopes of three towns in the rainforest belt underlain by the coastal plain sands. The results showed that the topsoil of the soils was generally sandy, with relatively more clayey subsoil. The pH ranged from extremely acidic (< 4.4) to slightly acidic (6.1- 6.5). They had low organic matter, low total nitrogen, low effective CEC, low Al saturation and moderate base saturation. The soils of the upper and the middle slopes were classified as Arenic Kandiudult by the United States Department of Agriculture’s (USDA) Soil Taxonomy or as Chromic Acrisols by the World Reference Base (WRB) for Soil Resources classification system, while that of the bottom slope was classified as a TypicDystrudept (USDA Soil Taxonomy) / Dystric Cambisol (WRB classification system). The upper slope had a USDA land capability class of IIes and a United States Bureau for Reclamation (USBR) land capability class of 2v/C. The middle slope and the bottom slope both had USDA and USBR capability class of IVs and 3v/C, respectively. Though moderately to marginally irrigable, the soils can still produce increased and sustainable agricultural yield if the appropriate land use and husbandry practices are adopted.
Key words: Coastal plain sands, land use planning, soil characterization, toposequence, tropical rainforest
The impact of four spacing of cooking banana (CB) within the immature rubber avenues on some soil fertility attributes, maturity rate of rubber trees and dry rubber content (DRC) during the initial six years after planting (YAP) were evaluated in a humid forest area of South Eastern Nigeria relative to sole rubber. The CB spacings within immature rubber avenues were 6.7 × 3.4 m; 4.0 × 2.0 m, 3.0 × 3.0 m and 2.0 × 2.0 m, while the sole rubber was at 6.7 × 3.4 m, all laid out in randomized complete block design with five replications. Quantities of soil organic C, extractable P, Ca, Mg and earthworm activities were significantly higher in the intercrops, with the highest value coming from the 4 × 2 m CB spaced plots. However a significantly higher value of K stock was observed in the sole rubber plot and declined as the CB spacing narrowed. While the highest proportion (>90%) of matured hevea tree at six YAP was observed in the 2 × 2 m CB spaced plots; the highest DRC of 1.7 t?ha<sup>–1</sup>?yr<sup>–1</sup> was obtained from CB 4 × 2 m treatment. Consequently, with some of the observed soil fertility attributes and DRC recorded, 4 × 2 m CB spacing seems to be a more suitable CB spacings within immature rubber avenues, especially in view of the levels of K in the 2 × 2 CB plots
Data on the nature, properties and potentials of soils is grossly inadequate in the rainforest belt of southeastern Nigeria. As such, policymakers and other land users have tended to subscribe to unduly generalized ideas about the soils of the region. This has led to improper land use planning and aggravated land degradation. This necessitated the need for the comparative evaluation of the nature and potentials of the soils of the region to determine their degree of variability. Profile pits were dug in four towns underlain by different geologic formations: Umungwa (Benin Formation), Umuawa Ogii (Nsukka Formation), Ikpem (Igbaku Sandstones) and Amuro (Imo Clay Shales). The soils were characterized and classified using the World Reference Base for Soil Resources (WRB), United States Department of Agriculture (USDA) Soil Taxonomy and land capability classification. The variability of soils across the different sites was subsequently analysed using the coefficient of variation (CV). The results show that the variability of sand across the study sites was moderate (20 – 21 %), silt was high (63 %), clay ranged from moderate (34 %) to high (52 %), while hydraulic conductivity was very high (128 – 144 %). Similarly, with regards to the chemical properties, soil pH and base saturation ranged from moderate (20 – 49 %) to high (52 %), while effective cation exchange capacity (ECEC) and aluminium saturation were high (70 – 77 %). It was concluded that the soils of southeastern Nigeria are very heterogeneous. Undue generalization should consequently be discouraged.
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