Optimization of N-P-K Nutrient Ratios for Three Leafy Vegetables Using Response Surface Methodology and Principal Component Analysis

This study determined the optimal nitrogen–phosphorus–potassium (N-P-K) ratios for maximizing growth performance in spinach (Spinacia oleracea), bok choy (Brassica rapa subsp. chinensis), and Chinese cabbage (Brassica rapa pekinensis). A response surface methodology experiment with 15 N-P-K treatments (0–1.5 g/L per nutrient) was conducted under controlled conditions. Growth parameters including plant height, biomass, leaf area, and root development were measured after four weeks and analyzed using principal component analysis and Pearson correlation analysis. Optimal ratios were species-specific: spinach achieved maximum performance with N-P-K = 2-0-2 (13.15 g fresh weight, 13.88 g total biomass), bok choy with N-P-K = 0-2-2 (2631.31 mm2 leaf area, 4.42 mm stem diameter), and Chinese cabbage with N-P-K = 2-0-2 (14.14 cm height, 9883.44 mm2 leaf area). High nitrogen levels were negatively correlated with root development across all species (r = −0.531 to −0.690, p < 0.05). These findings demonstrate that species-specific nutrient management strategies are essential for optimal leafy vegetable production. Balanced N-P-K ratios prevent nutrient toxicity while maximizing growth, providing evidence-based guidelines for precision fertilization in controlled environment agriculture.