Varietal Response of Cowpea (Vigna unguiculata L.) to Vermicompost Application: Enhancing Growth and Yield Components in Tropical Agroecosystems of Sri Lanka

Abstract

The excessive dependence on synthetic fertilizers in crop production has raised concerns regarding soil degradation, environmental sustainability, and long-term agricultural productivity. Vermicompost represents a promising organic nutrient source; however, its effectiveness in improving crop performance may vary depending on application rate and crop genotype. This study evaluated vermicompost as a sustainable biofertilizer for improving growth and yield of cowpea (Vigna unguiculata L.). A factorial experiment was conducted to evaluate the effects of vermicompost application levels and cowpea genotype on growth and yield performance. Four cowpea varieties were tested under four vermicompost-to-soil ratios of 25:75, 50:50, 75:25, and 100:0 together with chemical fertilizer and untreated control treatments. Growth and yield parameters were analyzed using analysis of variance in Minitab 15. Vermicompost significantly enhanced vegetative growth and reproductive performance compared with the control and chemical fertilizer treatments (p < 0.05). Improvements were evident across all vermicompost levels, with 25–75% applications already producing substantial gains in growth and yield attributes. Maximum values were generally observed at the 100% level, including plant height (50.94 ± 3.00 cm; Bombay), leaf number (39.00 ± 1.22; MI 35), branch number (14.20 ± 1.48; MI 35), nodes per main stem (20.00 ± 2.45; MI 35), and leaf area index (79.26 ± 14.97 cm²; Bombay). Yield-related traits also responded positively to vermicompost, as indicated by earlier flowering (35 ± 0.83 days; Waruni and Dawala), earlier maturity (47.40 ± 1.14 days; Waruni), longer pods (16.24 ± 0.68 cm; ANKCP 2), higher seed number per pod (11.00 ± 1.58; ANKCP 2), greater pod number per plant (4.40 ± 1.14; Waruni), and increased seed size (0.72 ± 0.08 mm; Bombay). Vermicompost showed beneficial effects under the tested pot conditions; however, further field validation is necessary to assess its effectiveness and suitability as a partial or complete alternative to conventional fertilizers.