Growth and yield response of Chinese kale to nitrogen fertilization across contrasting tropical soil textures

Efficient nitrogen (N) management is critical for optimizing leafy vegetable production under contrasting soil conditions. A greenhouse experiment was conducted at Mahasarakham University, Thailand, to evaluate the growth, yield, and N use efficiency of Chinese kale (Brassica oleracea var. alboglabra) grown in loamy sand and clay soils under four N rates applied as urea (46% N): 0, 0.32, 0.64, and 0.96 g pot-1. Growth and yield responses differed between soil textures; clay supported greater overall biomass accumulation, whereas loamy sand produced higher shoot fresh weight, reflecting differences in soil fertility and nutrient availability. Increasing urea rates enhanced chlorophyll (SPAD) content and biomass, with the highest values recorded at 0.96 g pot-1. Pearson’s correlation analysis showed strong positive associations among biomass traits (r > 0.90***), moderate correlations with chlorophyll content, and weak or nonsignificant correlations for leaf number. Principal component analysis indicated that biomass-related traits dominated PC1 (61.9%), while leaf number contributed mainly to PC2 (14.1%), effectively separating samples by soil texture. Nitrogen use efficiency was optimized at 0.32 g pot-1 in loamy sand and at 0.96 g pot-1 in clay, underscoring the need for soil-specific nutrient management. Overall, the results identify biomass traits as reliable indicators of yield potential and highlight the value of targeted N management for improving Chinese kale production in tropical soils.