Optimizing Watermelon (Citrullus Lanatus) Production and Profitability on Sandy Ferralsol in Kenge through Integrated Organic and Mineral Fertilization

This study evaluated the agronomic performance and economic viability of watermelon (Citrullus lanatus) in Kenge, Kwango Province (DRC), using a 2 × 5 factorial split-plot design with NPK as the main factor and five organic amendments as subplots. Growth and yield traits were measured across 12-plant subplots. Integrated nutrient management significantly improved plant performance, with Neptune’s Harvest™ Fish Fertilizer + NPK producing the highest yield (24.4 t ha⁻¹). Organic amendments enhanced soil physico-chemical properties, increasing NPK retention and nutrient-use efficiency. Marketable yields ranged from 20.3 to 11.6 t ha⁻¹ depending on NPK supplementation. Economic analysis showed strong profitability for combined treatments, with Marginal Rate of Return values of 1.83 for Neptune’s Harvest™ Fish Fertilizer + NPK, 1.76 for biochar + NPK, and 1.70 for Tithonia + NPK, whereas treatments with MRR < 0.5 were not economically viable. Results demonstrate that watermelon production in Kenge is feasible and profitable under integrated nutrient management.