NUTRITIONAL VALUES OF WATERMELON (Citrullus lanatus) FRUITS IN RESPONSE TO DIFFERENT NUTRIENT SOURCES IN OGBOMOSO, NIGERIA

Abstract

Watermelon (Citrullus lanatus) is an economically and nutritionally valuable fruit crop widely cultivated in tropical and subtropical regions. However, its productivity and fruit quality are often constrained by declining soil fertility and the overreliance on inorganic fertilizers. This study investigated the effects of different nutrient sources on nutritional composition of watermelon under field conditions at the Ladoke Akintola University of Technology (LAUTECH) Teaching and Research Farm, Ogbomoso, Nigeria in years 2022 and 2023. Eight fertilizer treatments (no fertilizer, 100% NPK, 100% compost, Supergrow, poultry manure, 75% NPK + 25% compost, 50% NPK + 50% compost, and 25% NPK + 75% compost) were arranged in a randomized complete block design with three replications. The fruit elemental composition, bioactive compounds, vitamin Content and proximate composition were all determined. Results showed that nutrient sources significantly affected fruit elemental, proximate, and bioactive composition (p ≤ 0.05). The fruit Nitrogen (N) content ranged from 6.43 g kg⁻¹ in the unfertilized control to 16.60 g kg⁻¹ in the 50% NPK + 50% treatment. Phosphorus (P) peaked at 8.30 g kg⁻¹ under 100% compost, while potassium (K) reached 6.40 g kg⁻¹ in 75% NPK + 25% compost. Calcium (Ca) and magnesium (Mg) were highest in 75% NPK + 25% compost (0.50 g kg⁻¹ and 33.00 g kg⁻¹, respectively). Poultry manure improved crude fibre (0.34%) and protein (0.60%), whereas integrated fertilizers increased total sugar (16.47%) and total solids (6.13%). Lycopene and carotenoid contents were enhanced by Supergrow (10.88 mg 100 g⁻¹ and 8.57 mg 100 g⁻¹, respectively), while vitamin B₆ was highest (19.73 mg 100 g⁻¹) under 50% NPK + 50% compost. The study concludes that integrating organic and inorganic fertilizers, particularly 75% NPK + 25% compost and 50% NPK + 50% compost, optimizes watermelon fruit nutritional quality and supports sustainable soil fertility management.