Optimizing Brackish Water Irrigation Scheduling for Honeysuckle (Lonicera japonica Thunb.): Reconciling the Trade-Off Between Yield and Chlorogenic Acid Accumulation

While brackish-water irrigation alleviates freshwater scarcity in coastal saline agriculture, its optimization for medicinal crops demands balancing yield and bioactive compounds. This study established a quality–yield decision framework for honeysuckle in the Yellow River Delta via a two-year field experiment with four per-event irrigation amounts: 0 (W1), 40 (W2), 80 (W3), and 120 mm (W4). Soil properties, yield, and medicinal quality were measured. The incremental honeysuckle quality-yield brackish water productivity (ΔHQYP) was calculated, while Entropy-weighted Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) was used to generate comprehensive scores integrating yield, quality, and soil. Results showed that irrigation reduced root-zone salinity but increased pH and decreased nitrate nitrogen and available potassium, with interannual variation. Chlorogenic acid content peaked at 80 per-event mm (W3) and declined at 120 per-event mm (W4), mirroring the honeysuckle quality index (HQI) pattern, while yield peaked at 120 mm, revealing a mismatch between yield and quality optima. Regression analysis indicated that ΔHQYP was co-regulated by soil water content and salinity, not by single factor. By combining TOPSIS scores with coefficients of variation and stability, 80 mm was identified as the preliminary optimal among the tested levels based on data collected over two years spanning three flowering periods. This level optimally balanced desalination, nutrient maintenance, yield, and bioactive accumulation, and is thus recommended. This framework shifts management from yield maximization toward quality-integrated, multi-objective decision-making for medicinal agriculture.