Effects of Tectona grandis (teak) plantation on soil microorganisms in a ferruginous soil of north central Nigeria

Abstract

Effects of Tectona grandis age series plantation on soil microorganisms were investigated. Using completely randomised block design (CRBD) soil samples were collected from the rhizosphere, non-rhizosphere and the natural forest for December, 2003, February, 2004, April, 2004, and June, 2004. The collected samples were treated and later plated using different media. Nutrient agar (N/A, oxoid) was used for bacteria isolation while potato dextrose agar (PDA, oxoid) was used for fungi isolation. Colonies of the microorganisms were examined, counted and identified with microscopes and biochemical tests. Results showed significant differences of micro-organisms counts (bacteria, P=0.01) between Tectona grandis plantation and natural forest while no significant difference was observed between the months of sampling for non-rhizosphere soil. There existed no significant difference in the bacteria count between blocks (P=0.006) in the rhizoshere soil while significant count in bacteria was observed (P=0.04) between the treatments. Fungi population did not show any significant difference in the rhizospre for both the blocks and the
treatments (P=0.0001; (P=0.0002) respectively while significant differences exited between the treatments (P=0.66; P=0.42) respectively. The distribution of both the gram positive and gram  negative microorganisms was not significantly different between the plantation and the natural forest. It was concluded that T. grandis plantation has
significant effects on the microbial populations only during early years of establishment. It was found that T. grandis should be used as an agroforestry species to boost micro-organisms populations.