Open Science Journal of Bioscience and Bioengineering 2014; 1(2): 19-22 Published online September 30, 2014 (http://www.openscienceonline.com/journal/bio) Evaluation of phosphorus and exchangeable bases status of soil under rubber plantation of different ages in south-eastern Nigeria Ekaette Usenetim Ekukinam 1 , Anthony Inah Iwara 1 , Bayero Sule Gani 2 1 Department of Geography, University of Ibadan, Oyo State, Nigeria 2 Dept. of Agricultural Economics, University of Ibadan, Oyo State, Nigeria Email address iwaradream2008@gmail.com (A. I. Iwara) To cite this article Ekaette Usenetim Ekukinam, Anthony Inah Iwara, Bayero Sule Gani. Evaluation of Phosphorus and Exchangeable Bases Status of Soil under Rubber Plantation of Different Ages in South-Eastern Nigeria. Open Science Journal of Bioscience and Bioengineering. Vol. 1, No. 2, 2014, pp. 19-22. Abstract In this paper, the levels of available phosphorus (Av. P), exchangeable Ca, Mg, Na and K were evaluated under rubber plantation of different ages in Calabar, Cross River State. Soils were sampled under rubber plantations of 7, 16, 39 and 41 years. In each of the rubber plantation, five plots of 10m x 10m were established and surface soil samples (0-10cm) were randomly collected. Result showed that the contents of Av. P, Ca, Mg and K varied significantly among the rubber plantations. Av. P level in the rubber plantation soils declined substantially by 62.6 per cent with increasing age of rubber tree. The Av. P content under the 7-year rubber plantation (36.16 mg/kg) was rated very high, while the content under 41- year rubber plantation (13.52 mg/kg) was rated moderate. The levels of exchangeable Ca, Mg and K in the rubber soils declined with the age of rubber tree and were inadequate in comparison with some critical limits. The study called for proper management of soils under rubber plantation to reduce soil deterioration and maintain soil conditions for improved rubber production. Keywords Rubber Plantation, Rubber Age, Available Phosphorus, Exchangeable Bases 1. Introduction Available phosphorus and exchangeable bases are among the 17 nutrients essential for plant growth. Phosphorus is one of the major soil nutrients that are required by plants in relatively large amount because it plays a vital role in nearly every plant process that involves energy transfer. However, among the nutritive elements essential for plant growth, only calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na) are found in exchangeable form in the soil (I). These soil nutrients become depleted in the soil following the cultivation of forest tree. The depletion in soil nutrients among other factors is attributed to the dominance of a single tree species (2). In the rainforest belt of southern Nigeria, rubber tree (Hevea brasiliensis Muel. Argo.) is one of the major forest trees grown to meet the increased demands for latex production. Like other forest trees such as teak, oil palm, cashew and kola nut, rubber plantation has a lot of ecological and edaphic effects on the soil and the atmosphere. In Calabar, Cross River State, rubber is grown in large commercial scale and it contributes a significant proportion of export earnings. Plantations are generally known to bring about modifications in the edaphic, micro-climatic, flora, fauna and other components of the ecosystem through bio- recycling of mineral elements and changes in flora and fauna composition (3 - 4). According to Aweto (2) monoculture plantation such as rubber plantation may affect soil chemical properties through nutrient depletion from the soil into the tree components (leaves, twigs, branches and stem log) as well as modifies the chemical status of the soil since the litter