Cultivar-Specific Responses of Jerusalem Artichoke to Potassium and Zinc Fertilizationin a Low-Fertility Sandy Loam Soil

Cultivar-dependent responses of Jerusalem artichoke (Helianthus tuberosus L.) to combined potassium (K) and zinc (Zn) fertilization remain poorly understood, particularly under low-fertility sandy loam conditions in tropical environments. This study evaluated growth, yield, and tuber-quality responses to K and Zn fertilization in a greenhouse. A 2 × 4 × 3 factorial experiment included two cultivars [CN 52867 × JA6-23 (V1) and JA37 × HEL65 (V2)], four supplemental K application rates (0, 0.61, 1.22, and 1.83 g K pot−1) and three supplemental Zn application rates (0, 0.05, and 0.10 g Zn pot−1). Potassium exerted a more consistent influence on growth and tuber production than Zn, whereas Zn responses varied with cultivar, trait, and nutrient combination. Significant cultivar × K × Zn interactions were detected for tuber number (p < 0.001) and tuber dry weight (p = 0.016). At the highest K rate (1.83 g K pot−1), increasing Zn reduced tuber number in V1 from 38.00 to 19.00 tubers plant−1, whereas in V2 it increased from 17.33 to 26.67 tubers plant−1. Across cultivars and Zn treatments, tuber dry weight increased from 38.53 g plant−1 without supplemental K to 45.91 g plant−1 at 1.83 g K pot−1 and was positively correlated with aboveground biomass (r = 0.77) and stem diameter (r = 0.76). Multivariate analysis further illustrated associations among growth, yield, physiological, and quality traits. From a practical perspective, these results indicate that K and Zn management in Jerusalem artichoke should consider cultivar-dependent nutrient responses rather than assuming a uniform fertilizer response. However, these findings are specific to the tested fertilizer rates and controlled pot conditions and require field validation before cultivar-specific fertilizer recommendations can be established.