20 J. Agric. Res. & Dev. 16(1)20-30. Copy@2017. Faculty of Agriculture, University of Ilorin. Nigeria SOIL WEED SEEDBANK DYNAMIC AND ALLELOPATHIC POTENTIAL OF Tithonia diversifolia (HEMSL) * TAKIM, F.O., OYEKUNLE,G.O. AND ODEYEMI, J.O. Department of Agronomy, Faculty of Agriculture, University of Ilorin, Ilorin PMB 1515, Ilorin, Nigeria.*Corresponding author’s email address: felixtakim@yahoo.co.uk. https://dx.doi.org/10.4314/jard.v16i1.3 ABSTRACT The phenomenon of allelopathy is receiving increased attention as a possible alternative weed control method that is environment-friendly when compared with the use of herbicides with a wide range of toxic side effects which pose potential hazards to the environment. This study was designed to estimate the distribution of weed seeds in Tithonia diversifolia dominated fields and to evaluate the effect of leaf, stem and root extracts of T. diversifolia on the emergence of weed seeds in a southern Guinea savanna agro-ecology of Nigeria. To achieve the stated objectives, soil samples were taken from T. diversifolia dominated field and enumerated using direct seedling germination method. The phyto- sociological survey and growth parameters of T. diversifolia were assessed with the aid of permanently fixed quadrats measuring 0.5 m x 0.5 m placed at 1 m interval between quadrats during the rainy seasons (May– November, 2014 and 2015). The aqueous extracts of the leaf, stem, root and whole plant of T. diversifolia were prepared and applied to soil samples taken from different arable fields. The results of the study shows that 23 weed species belonging to 19 genera and 12 families were enumerated in the seedbank and 65 % of emerged weed seedlings were found between 0-10 cm soil depth. Digitaria gayana contributed (21.90 - 24.45 %), Brachiaria lata (17.07 – 19.24 %) while T. diversifolia (8.53 – 11.58 %). The similarity between the composition of the seedbank and that of the established vegetation was 24.42. The aqueous extract of the whole plant of T. diversifolia was found to have suppressed the emergence of 80.29 % weed seedlings, stems extract 79.57 %, leaves extract 74.35 % while the root extract suppresses 55.95 %. This study indicates that T. diversifolia has the potential to interrupt emergence of most weed species. It can further be used as a tool to formulate new eco-friendly bio-herbicides to control weeds in agro-ecosystems. Keywords: Allelopathy, Aqueous extracts, Seedbank, Tithonia diversifolia, Weed emergence INTRODUCTION Introduction of plant species, especially the invasive ones, into a new environment, deliberately or otherwise, may result to a cascade of unexpected ecological effects. It has been reported that naturalized or invasive species may influence other species through competition, altered eco- system processes or through other pathway such as allelopathy or phytotoxicity (Samuel et al., 2005). The two species of the genus Tithonia, Tithonia diversifolia and Tithonia rotundifolia are native to North and Central America from where they were introduced to Africa. They belong to the tribe Heliatheae and the family Asteraceae. Tithonia diversifolia naturalized in West Africa (Moughalu and Chuba, 2005). In these areas, the species have established themselves as serious weeds of arable crops, plantations, abandoned lawns and roadsides. They are aggressive colonizers of new sites, colonizing every available sunny space with high water table.