Variety, plant spacing, and NPK fertilizer rate influence postharvest quality and nutritional composition of cucumber fruits in Southwest Nigeria

Sustainable intensification of smallholder vegetable production in sub-Saharan Africa requires management strategies that advance crop yield, nutritional quality and fertilizer efficiency simultaneously, yet most tropical agronomic trials optimise only one dimension at a time. This four-trial, two-year field study evaluated two cucumber ( Cucumis sativus L.) varieties (CU 999, Monalisa), three plant spacings (75 × 25, 75 × 50, 75 × 75 cm) and four NPK 15-15-15 fertilizer rates (0, 100, 200, 300 kg ha −1 ) in a split-split plot RCBD with three replications at FUNAAB, southwestern Nigeria (2019–2020). The core finding was a consistent and mechanistically coherent trade-off: CU 999 at 75 × 75 cm × 300 kg ha −1 NPK ranked highest under multi-criteria analysis (TOPSIS closeness coefficient CC = 0.768), while treatments maximising per-hectare yield (CU 999, 75 × 25 cm) produced fruits with lower vitamin C concentrations driven by nutrient dilution at high plant density. CU 999 produced consistently firmer fruits, while Monalisa exhibited greener skin colour (more negative CIELAB a*) across all four trials. NPK at 300 kg ha −1 significantly increased vitamin A (up to 35.93 µg/100 g), vitamin C, vitamin K, dry matter and carbohydrate across trials. The principal recommendation is that CU 999 at 75 × 25 cm × 300 kg ha −1 NPK maximises per-hectare yield, while both varieties at 75 × 75 cm × 300 kg ha −1 are recommended for nutritional quality-premium markets. Economic and environmental feasibility of the 300 kg ha −1 rate warrants dedicated investigation under smallholder conditions. This study provides one of the first integrated multi-criteria decision frameworks for cucumber management in West Africa, advancing the methodological standard for sustainable intensification analysis in tropical vegetable systems.