The Dynamics of Soil Physical Properties and Exchangeable Cations in Secondary Forests Regenerating from Degraded Abandoned Rubber Plantation (Hevea brasiliensis) in Orogun Area of Southern Nigeria

Abstract

The regeneration of soil physicochemical properties in three secondary forest fields aged 1, 5 and 10 years of age following the abandonment of degraded rubber (Hevea brasiliensis) plantation in Orogun were investigated. In addition a mature forest was selected and investigated as the control. Values of important indices of soil physicochemical parameters were ascertained for the three secondary forests categories and the mature forest. The results obtained revealed that there was no significant improvement or changes in soil particle size composition during the course of secondary forest regeneration. The concentrations of the exchangeable cations were higher in the mature forest than the different secondary forest categories. Soil bulk density decreased while water holding capacity and total porosity of soil increased with increasing age of secondary forest. Exchangeable cations improved in the first five year of secondary forest regeneration, after which their values declined by the tenth year in the topsoil (0-10cm layer). Similarly, exchangeable potassium and sodium improved significantly in the subsoil (10-30cm layer) by the fifth year of secondary forest regeneration from degraded abandoned rubber plantation, after which their values declined by the tenth year. However, exchangeable magnesium and calcium declined in the subsoil throughout the course of forest recovery. Effective cation exchange capacity in the topsoil and the subsoil increased linearly with increasing age of secondary forest, while soil pH decreased with increasing age of secondary forest. These results demonstrate that fallowing exerts beneficial effects on soil fertility (i.e. soil fertility improved as fallow age increased).

Keywords: Dynamics, Secondary forests, Degraded, Abandoned rubber plantations, Exchangeable cations, total porosity.