Humic Acid Dose–Response in Cocopeat Medium on the Growth of Bird’s Eye Chili (Capsicum frutescens L.) cv. Ori 202

Abstract

Cocopeat is widely used as an organic growing medium in horticultural cultivation due to its high water-holding capacity and favorable aeration; however, its relatively low nutrient availability often limits optimal plant growth. Humic acid has been recognized as a plant biostimulant that improves nutrient availability and stimulates plant physiological processes. This study aimed to evaluate the dose–response effect of humic acid on the vegetative growth of bird’s eye chili (Capsicum frutescens L.) cv. Ori 202 grown in cocopeat medium. The experiment was conducted using four concentrations of humic acid (0, 2.5, 5.0, and 7.5 mL L⁻¹). Growth parameters, including plant height, number of leaves, stem diameter, root length, fresh biomass, and dry biomass, were measured during the early vegetative stage. The results showed that observation time significantly affected plant height and stem diameter, indicating active vegetative growth dynamics during the early growth phase. Humic acid application significantly influenced several growth parameters, particularly biomass accumulation. The highest vegetative performance was observed at 7.5 mL L⁻¹, which produced the greatest plant height as well as the highest fresh and dry biomass. In contrast, the 5.0 mL L⁻¹ treatment showed comparatively lower growth performance, suggesting a non-linear dose–response pattern. The growth-promoting effects of humic acid are likely associated with stimulation of root development, enhanced nutrient uptake efficiency, and improved biomass production. These findings demonstrate that humic acid can serve as an effective biostimulant to improve the growth of C. frutescens cultivated in cocopeat-based substrates and provide a potential strategy to enhance productivity in soilless horticultural systems.