Optimisation of seaweed-based biostimulant application to improve bell pepper yield and quality using Topsis-Shannon entropy

The effectiveness of seaweed-based biostimulants is strongly influenced by application concentration and phenology-based timing. This study aimed to optimise these factors to improve the yield and fruit quality of bell pepper ( Capsicum annuum L.) using the Technique for Order Preference by Similarity to Ideal Solution combined with Shannon entropy (TOPSIS–Entropy). An Ecklonia maxima -based biostimulant was applied at five concentrations (0–0.8%) and at different phenological stages: one day before transplanting (ODBT), fourteen days after transplanting (14DAT), fruit set, and fourteen days before harvest (14DBH), applied individually or in combination, with no use of fertilisers before and during the experiment. Analysis of variance indicated significant effects of concentration and application timing on yield and fruit quality parameters. The application of 0.4% extract at 14DAT + fruit set + 14DBH achieved the highest overall performance, with the greatest TOPSIS–Entropy closeness coefficient (0.77) compared with the control (0.46). This treatment increased yield from 2.01 to 4.43 kg m −2 and improved fruit quality, resulting in higher TSS/TA ratio (1.85 vs. 1.26), and increased total phenolic content (238.9 vs. 173 mg 100 g −1 fresh weight). The optimised application strategy consistently enhanced both productivity and internal fruit quality, indicating its potential as an efficient management practice in bell pepper production. Future research should focus on elucidating physiological mechanisms and validating performance under diverse environmental and field-scale conditions.