Fertility status and management of a tropudult toposequence sustaining gmelina arborea roxb plantation in humid forest zone of southeastern Nigeria.
This Gmelina arborea plantation was established on Tropudults since 1976 to supply raw material to a Newsprint Manufacturing company in Nigeria. The main objective of this study was to investigate the native fertility status and recommend management strategies of this Tropudults sustaining the plantation. Profile pits were dung at the crest, middle slope and valley bottom. Core samples were collected for physicochemical analysis. All the profiles had coarse texture. Bulk density ranged between 0.75 - 1.25g cm-3 that do not hinder root penetration. Porosity ranged from 53 – 73 % hence best for agricultural soils, while pH was acidic ranging from 4.51 – 4.80. Organic matter value of 2.84 % and 2.24 % for surface horizon of middle slope and valley bottom respectively were considered medium whereas that of the crest was considered low (1.12 %). The major nutrients; nitrogen, phosphorus and potassium (NPK) were rated below critical levels (N < 0.1 %, P < 10 mg kg –1 and K < 0.15 cmol kg-1). The sulphur content was rated medium (between 5.0 – 7.0 mg kg-1). The contents of exchangeable Ca, Mg and Na were below critical levels (Ca < 2.5 cmol kg-1., Mg < 0.3 cmol kg-1 and Na < 0.35 cmol kg-1). The base saturation calculated was appreciable (49%). the effective cation exchange capacity (ECEC), the electrical conductivity (EC) and exchangeable acidity (EA) were all low. These chemical properties results indicate that the soil sustaining this plantation is poor in native fertility. Application of lime, inorganic fertilizer and/or avoidance of annual bush fire are a necessity, if soil fertility and land use sustainability must be maximized.
Keywords: Gmelina arborea, Tropudults, fertility status, humid tropics, Nigeria.