Journal of Advances in Microbiology

Soil heavy metal contamination is a serious environmental problem that needed to be addressed due to the toxicities of metals to both humans and living organisms. soil degradation is linked to off-site issues including sedimentation, climate change, the operation of watersheds, and changes in natural ecosystems that result in a loss of genetic diversity and biodiversity. A pot experiment was conducted at the College of Plant Science- Screenhouse, Federal University of Agriculture, Abeokuta (FUNAAB), Ogun state, Nigeria, to evaluate influence of Trichoderma inoculants and organic manure on growth, nodulation and nitrogen fixation by soybean (Glycine max, L. Merrill) in zinc contaminated soil. The experiment was a 2 x 3 x 3 factorial combination arranged in completely randomized design (CRD) with three (3) replicates. Treatments were two levels of cattle dung (0 and 4.46 g kg^-1), three levels of Trichoderma at NI (No inoculation), Trichoderma asperellum, and Trichoderma harzianum (5 ml per pot) and three levels of heavy metal (zinc) at 0, 300 and 600 mg kg-¹. Five (5) kilograms of the 2 mm sieved soil was weighed into each plastic buckets and amendments was applied thereafter Trichoderma was applied at 5 ml per pot while cattle dung was applied at 4.46 gkg^-1. It was moistened to 100% field capacity and left for one week after contamination. Two seeds of soybean were planted per hole and wetting was done at 75 % field capacity when due. Number of leaves, leaf area, plant height, shoot dry weight and number of nodules were determined fortnightly. Inoculation with Trichoderma recorded higher number of nodules and percentage of N₂ fixed while zinc contamination did not significantly affect the percentage of N₂ fixed. It is concluded that Trichoderma asperellum in combination with cattle dung had great potential in enhancing nodulation and nitrogen fixation by soybean in zinc contaminated soil.