Total Nitrogen and Available Phosphorus Dynamics in Soils Regenerating from Degraded Abandoned Rubber Plantation in Orogun Area of the Rainforest Zone of Southern Nigeria

Total nitrogen and available phosphorus concentration of soils in three secondary forest fields aged 1, 5 and 10 years of age regenerating from degraded abandoned rubber plantation (Hevea brasiliensis) and a mature forest in the west African Rainforest belt in southern Nigeria were investigated in order to determine the trend of change in the properties of soil in secondary forest during the course of forest restoration from degraded deserted rubber plantation (Hevea brasiliensis). There was a continuous increase in the concentration of total nitrogen in the soil (both topsoil and subsoil). The concentrations of total nitrogen and available phosphorus in the topsoil are higher than the subsoil. The concentration of available phosphorus during the first five years of secondary forest regeneration increased, after which their values declined by the tenth year in both the topsoil and the subsoil. Should this trend of decline in the concentration of phosphorus continue phosphorus may become a limiting factor to plant growth the older the secondary forests become.