ORGANIC CARBON AND TOTAL NITROGEN STATUS OF SOILS UNDER RUBBER PLANTATION OF VARIOUS AGES, SOUTH-SOUTHERN NIGERIA

¹Njar, G.N.; ²Iwara, A. I.; ²Ekukinam U. E.; ³Deekor, T. N. and ²Amiolemen, S. O.

¹Department Geography and Environmental Studies, University of Calabar, Nigeria

²Deparment of Geography, University of Ibadan, Nigeria

³Department of Geography and Environmental Science, University of Port Harcourt, Nigeria

E-mail: iwaradream2008@yahoo.com

ABSTRACT

In the tropics, the continuous destruction of the forest mostly for food crop cultivation accompanied with high rainfall in the region has resulted in the rapid loss of soil nutrient, thereby making most soil infertile. The need to restore and conserve soil fertility for agricultural productivity has led to the planting of forest trees/plantation with the sole aim of improving the nutrient bal­ance of soil by reducing unproductive nutrient losses from erosion and leaching. The study examined the trend of organic matter and total nitrogen in rubber plantation plots of 7, 16, 39 and 41 years. The grid system of sampling was employed to collect soil samples from five quadrats of 10m x 10m in each of the plantation plots.  Result showed that pH of the soils decreased with the age of plantation, while the content of organic matter (OM) and total nitrogen (TN) increased with the age of trees probably as a result of the increase in vegetation cover and tree size. This is so, as mature rubber trees have a large biomass which not only affords the ground adequate cover, but also acts as a huge reservoir of nutrients, thereby preventing them from being leached away from the plantation. The study revealed that rubber trees had no adverse effect on the depletion of OM and TN status in the soil. However, for sustainable rubber production, mature rubber trees in plantation plots should be properly managed through routine treatment, as well as selectively replaced with new ones.

Keywords: Rubber Plantation, Organic Matter, Total Nitrogen, Age of Plantation, Tree Size, Vegetation Cover, Biomass