Physico-chemical properties of topsoil under indigenous and exotic monoculture plantations in Omo Biosphere Reserve, Nigeria.
Sustainable management of soil in plantations to a large extent depends on a thorough understanding of the trend and dynamics of soil properties under them. This study evaluated selected physico-chemical properties of topsoil under monoculture plantation of an indigenous tree species - Nauclea diderrichii, and those of four exotic tree species - Theobroma cacao, Gmelina arborea, Pinus caribaea and Tectona grandis, located in Omo Biosphere Reserve, Ogun State, Nigeria. Percentage sand, silt and clay did not vary significantly (p>0.05) among monoculture plantations at the 0-5 cm depth while significant variations were observed at lower soil depths in some of the plantations. Iron, Zinc, Copper and Manganese varied significantly (p<0.05) among monoculture plantations. Zinc and Copper were highest in Gmelina arborea Plantation at the 0-5 cm depth, while Iron and Manganese were highest in Theobroma cacao and Nauclea diderrichii Plantations respectively at the same depth. Organic matter and total nitrogen varied significantly (p<0.05) among plantations and were highest in Theobroma cacao, Tectona grandis and Nauclea diderrichii at the 0-5, 5-10 and 10-15 cm depths respectively. Available phosphorus varied significantly (p<0.05) among plantations and was highest in Nauclea diderrichii, Theobroma cacao and Gmelina arborea at the 0-5, 5-10 and 10-15 cm depths respectively. Indices of change (%) based on average values of soil properties for the three sampled depths revealed a degradation of organic matter, total nitrogen, available phosphorus, potassium, sodium, iron, and pH in most of the exotic plantations, while calcium, zinc, copper and manganese improved except in Pinus caribaea plantation. The use of Nauclea diderrichii for plantation establishment and taungya farming in the reserve is recommended for soil conservation.