Organic Matter Dynamics in Soils Regenerating from Degraded Abandoned Rubber Plantation in Orogun Area of the Rainforest Zone of Southern Nigeria
The area of secondary forest (SF) regenerating from degraded abandoned rubber (Hevea brasiliensis) plantation is increasing in the rainforest zone of south southern Nigeria; however, the build-up of soil organic matter following abandonment is not well understood. This study examined the build-up of soil organic matter in a mature forest and three secondary forest fields aged 1, 5 and 10 years of age following the abandonment of degraded rubber (Hevea brasiliensis) plantation in Orogun in a part of the rainforest zone of south southern Nigeria. This is in order to ascertain the rate of build-up of organic matter in the soil during the course of forest regeneration from degraded abandoned rubber plantation (Hevea brasiliensis). There was a progressive increase in organic matter content of the soil with increasing age of the secondary forest. Organic matter increase was more rapid in the topsoil (0-10cm) than the subsoil (10-30cm): the level of organic matter in the topsoil reached 92.94% of the level of organic matter in the mature forest topsoil by the tenth year and 84.62% of the level of organic matter in the mature forest subsoil by the tenth year. The concentration of organic matter in the topsoil is higher than the subsoil. Reviews of the reported trends in soil organic matter build up during forest establishment after agricultural use show no common trend. This study showed a great variation in soil organic matter build up even within the same locality.
Keywords: Organic matter, Rubber plantation, Degraded, Orogun, South Southern Nigeria, Secondary forest.