Abstract

This study assessed the changes in soil properties in sites subjected to continuous logging in exotics plantation sites of Gmelina arborea and Tectona grandis with the aim to evaluate the deterioration level of the soil productivity in respect to human disturbance. Thirty five sampling plots, each measuring 40 m x 25 m were used for soil sampling. Standard field and laboratory methods were employed in the collection of data for 18 soil characteristics (sand, silt, clay, water holding capacity, electrical conductivity, bulk density, total porosity, pH, organic matter , total nitrogen, available phosphorus, exchangeable calcium, magnesium, potassium, sodium, exchangeable acidity, cation exchange capacity and base saturation) at depths of 0 - 15 cm and 15 - 30 cm. The results indicated that values of soil and plant parameters decreased with length of continuous logging (1, 5 and 10 years respectively). The soil deterioration indices of the logged plots showed high deterioration of all the soil properties except electrical conductivity, bulk density exchangeable acidity and in exchangeable sodium, percent silt and sand at both levels of soil depths. The two exotic species were impacted differently on the soil properties on the study area as a result of adverse logging. If these plots area are left to fallow for a considerable period of time, the lost soil nutrients may be replaced. 

Key words: Deterioration level, soil productivity, textural properties, electrical conductivity, Gmelina species, Tectona species, continuous logging and sustainable productivity.