Vermicompost Enhances Proximate Composition, Mineral Accumulation, and Storage Quality of Cowpea (Vigna unguiculata L.) Seeds
Abstract
The present study evaluated the effect of vermicompost on the proximate composition of selected cowpea (Vigna unguiculata L.) varieties. Four cowpea varieties (Waruni, Dawala, MICP 1, and MI 35) were cultivated under four fertilizer treatments: T1 (100% topsoil, control), T2 (50% vermicompost + 50% topsoil), T3 (75% vermicompost + 25% topsoil), and T4 (the recommended chemical fertilizer dose of the Department of Agriculture, Sri Lanka). The experiment was conducted using a completely randomized design (CRD) with 10 replicates per treatment. Mature harvested seeds were analyzed for proximate composition, including crude protein, moisture, ash, crude fat, crude fiber, and carbohydrate contents, following the standard methods of the Association of Official Analytical Chemists (AOAC, 2019). Data were subjected to one-way analysis of variance (ANOVA), and treatment means were separated using Tukey's honestly significant difference (HSD) test at p ≤ 0.05. Vermicompost significantly improved the protein content of selected cowpea varieties. The highest crude protein contents were consistently recorded under the 75% vermicompost treatment (T3), reaching 27.72%, 25.81%, 27.12%, and 25.82% in Waruni, Dawala, MICP 1, and MI 35, respectively, with values statistically comparable to those obtained under the 50% vermicompost treatment (T2). Vermicompost also significantly increased ash content, indicating enhanced mineral accumulation, while maintaining seed moisture within the safe storage range (6.90–10.50%). Crude fiber content showed an increasing trend under vermicompost treatments, although significant differences were observed only in Dawala. In contrast, crude fat content was not significantly influenced by fertilizer treatments across the tested genotypes. A corresponding reduction in carbohydrate content was observed under vermicompost treatments, reflecting increased protein synthesis and mineral accumulation in the seeds. Among the evaluated genotypes, Waruni exhibited the greatest improvement in seed protein content in response to vermicompost application.