Integrated application of sugarcane by-product-derived organic fertilizer (SOFA) and mineral nitrogen enhances yield, fruit quality, and soil properties of eggplant (Solanum melongena L.) in sandy soil conditions
Low soil fertility and restricted nutrient bioavailability are critical limiting factors for sustainable vegetable production, particularly in marginal sandy soils. This study addressed these challenges by investigating the efficacy of a novel sugarcane-derived molasses treated (SOFA) as a soil conditioner and nutrient source for eggplant (Solanum melongena L.), a crop for which comprehensive studies on such integrated approaches in these soil types are limited. Field experiments were conducted over two consecutive growing seasons to evaluate the impact of SOFA, applied either independently or in combination with mineral nitrogen (N), on soil physicochemical properties and crop performance.The study results demonstrated that integrated fertilization significantly improved soil physicochemical properties and crop performance. The treatment T3 (50% mineral N + 50% SOFA) achieved the highest total fruit yield (8.84 kg plant−1), representing a 111% increase compared to the control (4.18 kg plant−1). Similarly, T2 (75% N + 25% SOFA) significantly enhanced vegetative growth, chlorophyll content, and fruit nutritional quality. Soil organic matter increased by up to 56%, while available nitrogen, phosphorus, and potassium increased by up to 240%, 209%, and 67%, respectively, compared to the control. Moreover, SOFA application contributed to moderating soil alkalinity and improving nutrient availability, despite slight increases in electrical conductivity at higher application rates. Eggplant fruit quality traits were also significantly improved, with total soluble solids (TSS) increasing by 42% and anthocyanin content by 49% under optimized treatments. Economic analysis revealed that T2 and T3 achieved the highest profitability, with investment factors approaching 5.0, indicating superior economic efficiency. These findings highlight the potential of treated molasses-based amendments (SOFA) as a sustainable strategy for restoring marginal sandy soils and optimizing the productivity and nutritional quality of S. melongena.