Soil weed seedbank dynamic and allelopathic potential of Tithonia diversifolia (Hemsl)
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 phytosociological 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