Synergistic potential of yeast, seaweed, and green tea extracts for reducing the application of NPK fertilizers in Duranta repens L. fertilization

Introduction Fertilization is essential for the cultivation of ornamental and medicinal shrubs, but excessive application of chemical fertilizers contributes to environmental pollution and may adversely affect human health and beneficial soil microorganisms. Natural biostimulants such as active dry yeast (ADY), seaweed (SW), and green tea (GT) contain nutrients, bioactive compounds, and growth-promoting substances that can enhance plant growth. However, their combined use with reduced NPK fertilization has not previously been investigated in Duranta repens L. This study evaluated the potential of these natural biostimulants to reduce mineral fertilizer requirements while maintaining plant growth and quality. Methods A randomized complete split-plot design was employed with three NPK fertilizer levels (50%, 75%, and 100% of the recommended dose) as main plots. The recommended dose consisted of 18, 12, and 6 g plant −1 of ammonium sulfate, calcium superphosphate, and potassium sulfate, respectively. Subplot treatments included an untreated control, ADY + GT, ADY + SW, SW + GT, and ADY + SW + GT. Results The 75% NPK treatment significantly increased plant height, branch number, leaf area, chlorophyll index, shoot and root fresh and dry weights, total carbohydrates, and leaf nitrogen and phosphorus contents during both seasons. It also enhanced peroxidase and polyphenol oxidase activities, total phenolic compounds, and antioxidant activity, while catalase activity showed a non-significant increase. In contrast, the 100% NPK treatment produced the highest stem diameter, relative water content, and leaf potassium content. All biostimulant treatments significantly improved plant growth and biochemical characteristics compared with the untreated control. The interaction between fertilizer levels and biostimulants demonstrated that 75% NPK combined with ADY + SW + GT produced the highest shoot biomass, chlorophyll index, leaf nutrient contents, carbohydrates, total phenolics, antioxidant activity, and catalase activity. Meanwhile, 75% NPK with ADY + SW maximized plant height, branch number, and root biomass, whereas 75% NPK with SW + GT was the most effective in improving relative water content and oxidative enzyme activities. Discussion These results demonstrate that integrating ADY, SW, and GT with 75% of the recommended NPK dose can reduce chemical fertilizer use while sustaining or enhancing the growth and physiological performance of D. repens .