Allelopathic Potential of Tithonia Diversifolia and Lantana Camara Leafy Materials on Germination and Growth of Sb 19 and Sb 97 Soybean Varieties

Abstract

Soybean is a legume which is widely grown in western Kenya for its edible seed but their yields are reduced by the effect of low soil fertility. In Western Kenya, farmers are being encouraged to use shrubs as green manure such as Tithonia diversifolia and Lantana camara which have shown to improve soil fertility by 24% to 54%. Information available on their allelopathic potential on germination and growth of soybean is not exhaustive. The objectives of this study was to investigate the allelopathic effects of fresh leaf aqueous extracts and fresh leaf material of T. diversifolia and L. camara on germination of seeds, growth and yield of SB97 and SB19 soybean varieties. The experiments were carried out in the laboratory and greenhouse at Maseno University. In the lab, different concentrations of aqueous extracts, (25%, 50%, 75%, and 100%) and the control- tap water was used. Germination experiment was set in petri dishes and growth, yield and physiological parameters was carried out in the green house. Fresh leaf material of T. diversifolia and L. camara of 4g, 8g, 12g and 16g was added to soil in pots. The control only composed soil. This was replicated four times and laid out in Completely Randomized Design. Data on germination count were recorded daily, while growth parameters were recorded weekly. Data were subjected to analysis of variance using SAS 9.1 to establish significant differences among treatments, varieties and plant materials. The treatment means were separated and compared using the Least Significance Differences at P = 0.05. The results revealed that leaf extracts from Lantana camara and Tithonia diversifolia reduced the germination of both soybean varieties. These extracts contained bioactive compounds that inhibited germination, root and shoot growth and yield of Soybean varieties SB 19 and SB 97. Lantana camara exhibited stronger allelopathic activity than Tithonia diversifolia. On growth parameters, including shoot height, leaf number, leaf area, fresh and dry weights, and yield, the presence of allelochemicals in the biomass was suggested to have hindered growth by disrupting enzyme activities and nutrient uptake. Farmers are therefore advised not to incorporate Lantana camara and Tithonia diversifolia leafy biomass in farms where soy bean varieties SB 19 and SB 97 are growing.