Effect of Maturity Stages on the Nutritional Composition and Crude Protein Levels in Kenaf (HC-95)

Kenaf (Hibiscus cannabinus L.), a rapidly growing multipurpose crop, holds significant potential as a protein-rich forage due to its high biomass yield and mineral content. This study evaluated the stage-wise nutritional composition and crude protein accumulation in the leaves of the BJRI-developed kenaf variety HC-95 across six maturity stages: 45, 60, 75, 90, 105, and 120 days after sowing (DAS). The experiment was conducted at the Department of Agricultural Chemistry, Bangladesh Agricultural University, following a randomized design. Leaf samples were collected at each stage and analyzed for crude protein using the modified micro-Kjeldahl method, while mineral content (P, K, Ca, S, Na) was determined through spectrophotometric and flame photometric techniques. Crude protein content progressively increased from 27.87% at 45 DAS to a peak of 33.75% at 105 DAS, followed by a marginal decline to 33.49% at 120 DAS. Concurrently, phosphorus (P) and potassium (K) concentrations peaked during mid-growth stages (75–90 DAS), whereas calcium (Ca) and sodium (Na) increased steadily with plant maturity. Principal Component Analysis (PCA) revealed strong positive associations between crude protein, P, and K, while sulfur (S), Ca, and Na showed weaker or independent correlations. The results identify 105 DAS as the optimal harvest window for maximizing protein yield and nutrient density, making kenaf a viable and nutritious fodder resource. Strategic nutrient management and timely harvesting based on these findings can improve feed quality, reduce reliance on commercial supplements, and enhance the sustainability of forage production systems.