Leaching Fraction Regulates Root-Zone Salinity, Gas Exchange, and Ornamental Quality in Off-Season Potted Curcuma cv. ‘Jasmine Pink’ Under Crop Coefficient-Based Irrigation

Containerized ornamental plant production requires efficient irrigation strategies to balance plant quality with water and nutrient conservation. This study evaluated four leaching fraction (LF) levels (0%, 20%, 40%, and 60%) in a completely randomized design with three replications, each consisting of three pots, to determine their effects on plant growth, ornamental quality, gas exchange, water use efficiency (WUE), and macronutrient leaching in off-season potted Curcuma cv. ‘Jasmine Pink’. Irrigation volumes were determined using crop coefficient (Kc)-based estimates derived from evaporation pan measurements. The results showed that the highest LF level (60%) significantly improved several ornamental quality traits, including flower number per cluster, leaf greenness, specific leaf area, and compactness index, while also increasing aerial dry weight and improving gas exchange parameters during the flowering stage. These improvements were associated with reduced substrate electrical conductivity, indicating lower soluble salt accumulation in the root zone under higher LF treatments and more favorable conditions for plant growth. Leaching fraction is commonly used in containerized crop production to prevent excessive salt accumulation in the root zone by allowing excess irrigation water to drain from the substrate. However, increasing LF also resulted in greater irrigation water consumption and higher macronutrient losses through leachate, particularly potassium. In contrast, lower LF treatments (0–20%) improved water use efficiency and reduced nutrient losses but were associated with higher substrate electrical conductivity, suggesting greater soluble salt accumulation in the root zone. Overall, the results indicate that a higher LF (60%) provided the greatest improvement in plant growth and ornamental quality under the conditions of the present study for off-season potted Curcuma alismatifolia production, although integrated strategies may be required to reduce water and nutrient losses. These findings provide practical insights for optimizing irrigation management in container-grown ornamental crops.