Evaluation of the Formulation of Praxelis clematidea and Soap Nut (Sapindus rarak) Extracts on the Germination of Rottboellia exaltata

Abstract

Rottboellia exaltata is an invasive weed species that rapidly spreads through seeds and exhibits vigorous growth, leading to severe yield losses in agricultural lands. Weed management through the exploitation of plant allelopathy offers a sustainable approach to controlling such species. Praxelis clematidea and the pulp of soap nut (Sapindus rarak) are known to possess allelopathic properties that can inhibit weed germination. This study aimed to evaluate the effect and identify the most effective formulation of P. clematidea and S. rarak extracts in suppressing the germination of R. exaltata.The research was conducted from July to October 2025 in the Weed Science Laboratory and greenhouse of the Faculty of Agriculture, University of Lampung. A Completely Randomized Design (CRD) with a single factor and six replications was employed. The treatments consisted of different extract formulations of P. clematidea and S. rarak: P0 = control (distilled water), P1 = 50% P. clematidea extract, P2 = 50% S. rarak extract, P3 = 25% + 75%, P4 = 50% + 50%, and P5 = 75% + 25%. Data were analyzed using analysis of variance (ANOVA) after testing homogeneity (Bartlett test) and additivity (Tukey test), followed by the Least Significant Difference (LSD) test at a 5% level.The results demonstrated that both single and mixed extract formulations of P. clematidea and S. rarak inhibited germination percentage and germination rate of R. exaltata. The strongest inhibitory effect was observed with the 75% P. clematidea + 25% S. rarak formulation, which significantly reduced germination percentage, germination speed, root and shoot length, and dry biomass. The inhibitory effect was more pronounced on root growth than shoot growth, indicating that root length serves as a more sensitive indicator of allelopathic effects during germination.