ABSTRACT

 A study involving pot and Held trials was carried out to detennine the ability of vetiver grass to grow and improve some degraded sites. Five sites; a nursery top soil (control), kaolin mine site, laterite excavation site, Riversand and refuse dump site were selected lor the study. The Randomized Complete Block Design using the fixed effects model was adopted fbr the design and statistical analysis of results. Single tillers of vetiver grass were prepared and planted on the sites in four replications for 18 weeks. Physicochemical properties and the amounts of heavy metals in both the soil and grass samples were evaluated. Growth parameters measured were survival rate, tiller number, clump size, leaf breadth, clump height, shoot biomass, root biomass and total biomass. In the topsoil, percentage silt increased from 8.0 —10.0%, and clay from 18.2-18.8%. There was a decrease of 3.2% in the sand content ofthe soil. Organic matter increased by 0.3% while soil acidity and exchangeable bases such as Ca, K and Na decreased in amounts. The kaolin mine site remained clayey with a decrease in organic matter and exchangeable Mg from 0.79-0.2% and 1.2, 0.4cmolkg_, respectively. Sand and silt increased by 2% in the laterite excavation site with no change in clay content. An increase in organic matter, Total N as well as exchangeable K was observed. The amount of Riversand decreased by 3.4%, silt and clay increased by 2.5% and 0.6%. Organic matter improved by 0.3% with a decrease in soil acidity. Percentage sand and silt increased by 2.6% with a decrease in clay (5.4%) on the Refuse dump site. An increase in Total N, available P, exchangeable Mg and Ca by 0.02%, 5ppm, 2.4 cmolkg'1 and 0.8 cmolkg-1 respectively. There was high survival of the grass, between 98-99.8% in both trials. Significant growth (P<0.01) in number of tillers was observed on the trials. The refuse dump site had the highest number of tillers while the kaolin mine site and the excavation site had the least (3.9 tillers) in pot and field trials respectively. Clump size of the grass was also significant (P<0.01) in the trials. In the pot trials. Reliise dump site had the highest value in size (24.1cm) and the least (kaolin mine site) with 10.4cm. Clump size of the grass in the field was highest in the top soil (27.3cm) and least in the excavation site. There was no signiilcant difference in the leaf breadth of the grass in both trials. Clump height was significant (P<0.01) in the trials with the tallest plants on the reftise dump site (139.4cm), followed by the top soil (80.1cm) in the pots and kaolin mine site (85.6cm) in the field. Total biomass in the trials was significant (P<0.01). Plants on the refuse dump site were heaviest (67.2g) in the pots and the kaolin mine site heaviest (42.9g) in the field. The grass absorbed two heavy elements: Zn (35ppm) and Cd (5.8ppm) on the reftise dump site and kaolin mine sites respectively. These results considerably confirmed the ability of vetiver grass in modifying the degraded sites.