Influence of Invasive <i>Tithonia rotundifolia</i> Leachate and Litter on the Germination and Growth of <i>Corchorus olitorius</i> and <i>Amaranthus hybridus</i>

ABSTRACT Tithonia rotundifolia (Miller) S. F. Blake is an invasive weed in southwestern Nigeria that displaces native flora and creates a monoculture stand. Its impact on plant species richness has led to investigations into its invasive strategies, including its allelopathic potential. The study investigated the effects of T. rotundifolia leachates and litters on the germination and growth of Corchorus olitorius L. and Amaranthus hybridus L. and the influence on the soil physicochemical properties. The germination of the vegetables in aqueous leachates of T. rotundifolia tissues, at concentrations (%) of 20, 40, 60, 80 and 100, was compared with the control (in distilled water). Different dosages (0, 10, 20, 30, 40 and 50 g) of T. rotundifolia litter were incorporated into a 3 kg of soil and used to monitor the growth of the test plants in a completely randomised design. Differences in treatment were subjected to Analysis of Variance (ANOVA) followed by Duncan's Multiple Range Test to determine significant effects. The dried leaf leachates completely inhibited germination at 60%–100%. They inhibited seedling growth more than stem, root and flower leachates (leaves &gt; flower &gt; root &gt; stem). Leaf litter, at low concentrations, enhanced the growth of the vegetables; highest growth parameters obtained for A. hybridus and C. olitorius were height (65.25 ± 11.29 and 40.77 ± 2.72 cm), girth (8.64 ± 0.47 and 3.09 ± 0.13 cm) and number of leaves (24.10 ± 6.24 and 21.90 ± 5.93) at 30 g and control, respectively. The organic carbon and nitrogen composition of A. hybridus biomass were also highest at 30 g (99.54 ± 0.64 and 3.95 ± 0.02) mg kg −1 . T. rotundifolia litter has no significant effect on the K + and Na + content of the soil. The OC and TN content in A. hybridus grown soil were significantly higher ( p &lt; 0.05) above the 20 g litter dosage than the control, while OC in the control soil (3.36 ± 0.05 g kg −1 ) was significantly higher ( p &lt; 0.05) than C. olitorius soil treated with 40 (2.60 ± 0.04 g kg −1 ) and 50 g (2.52 ± 0.03 g kg −1 ) litter. These results suggest that T. rotundifolia has allelopathic effects at high concentrations but may improve soil fertility and plant growth at low dosages. Although at low magnitude of the biomass it serves as soil amendment, but regular removal from the field is essential to prevent biomass accumulation that will hinder seed germination and crop growth.