Optimizing nitrogen fertilizer levels for improved growth, yield, and fruit quality in horned melon (Cucumis metuliferus E. Mey. ex Naudin)

Nitrogen (N), a fundamental macronutrient essential for all plants, critically impacts cucurbit productivity. A deficiency in this element compromises photosynthetic efficiency, impedes vegetative development, depresses overall yields, and leads to stunted, commercially undesirable fruit, thereby posing a substantial economic challenge. Therefore, improved nitrogen fertilization strategies are needed to enhance production, especially for crops like horned melon. A study at Midlands State University conducted in 2023 and 2024 evaluated five levels of ammonium nitrate (34.5% N) (AN0 = 0 kg AN ha-1, AN30 = 30 kg AN ha-1, AN60 = 60 kg AN ha-1, AN90 = 90 kg AN ha-1, and AN120 = 120 kg AN ha-1) on horned melon landrace to determine the optimum N rate. Results indicated that N enhanced fruit size and weight, with the best outcomes at AN60 and AN90. Nitrogen fertilization consistently enhanced shoot biomass, fruit biomass, juice content, and juice percentage across both years peaking at AN120. Fruit yield increased with N application up to specific thresholds (AN60 in 2023 and AN30 in 2024), beyond which yield either plateaued or declined, particularly at higher N levels. Additionally, N significantly affected the total soluble solids (TSS) content of horned melon, with higher N levels (AN90) associated with the highest TSS values. Nitrogen use efficiency (NUE) improved up to the AN30 level but sharply declined at higher levels, especially at AN120. Across both years, the data indicated a decrease in both shoot and fruit agronomic efficiency as N application increased from AN30 to AN120. The study concluded that between AN30 and AN60 fertilization application is optimal for maximizing agronomic efficiency and fruit quality for commercial production.