Comparative Analyses of the Effects of Chemical Fertilizer, Black Solder Fly Frass, and Their Combination on the Morphology and Metabolite Profile of <i>Brassica juncea</i>

ABSTRACT Leafy vegetables require sufficient nutrients to maintain good health and development. The extensive use of chemical fertilizer in agriculture has raised concerns regarding its negative environmental impact. Nowadays, frass from Black Soldier Fly (BSF) has been utilized as one of the organic fertilizers that potentially improve plant growth and yield, due to its high organic matter and nutrient contents. This study aimed to assess the effects of nitrogen, phosphorus, potassium (NPK) chemical fertilizer, BSF frass and the combination of both on the morphological growth and metabolite compositions of Brassica juncea . In this study, B. juncea plants were treated with four different treatments (T1: control‐No chemical fertilizer or frass), T2: NPK fertilizer only, T3: BSF frass only, T4: NPK + BSF frass). Morphological parameters such as plant height, number of leaves, stem length, root length, fresh, and dry weight of the shoots were measured and chlorophyll contents were also recorded. Additionally, B. juncea shoots were analyzed for carbohydrate and Total Phenolic Content (TPC). The correlations of morphological parameters and the tested metabolite contents were compared using Pearson correlation coefficient. In our study, the T4 treatment produced plants with the highest plant height (21.94 ± 0.71 cm), fresh weight (11.18 ± 0.71 g), dry weight (1.07 ± 0.06 g), and carbohydrate content (229.16 ± 11.04 mg/g dry weight). Meanwhile, T2 produced plants with the highest TPC (1.05 ± 0.21 mg/GAE g). All morphological parameters were positively correlated to the metabolite compositions. Overall, T4 provided the best nutrient conditions to support plant growth. It is suggested that the T4 fertilizer formulation could be a cost‐effective alternative to chemical fertilizer, promoting sustainable farming practices.