Pre-Harvest Seaweed Biostimulant Applications: Optimizing Concentration, Timing, and Frequency for Cultivar-Specific Improvements in Potato Yield and Quality

The aim of this study was to optimize the pre-harvest application of seaweed-based biostimulants (BIOs) to improve potato yield, quality, and post-storage attributes. To achieve this, six potato cultivars differing in maturity periods were subjected to three BIO concentrations (2.4, 7.2, and 9.6 g/L), application timings (from planting to post-bloom), and frequencies (1–4 applications). The results indicated that BIO efficacy was strongly cultivar-specific. Responsive cultivars (such as ‘Minshu No. 1’, ‘Leshu No. 1’, ‘Xiazhai 65’, and ‘Qingshu No. 2’) showed significant yield increases when treated with 7.2 or 9.6 g/L BIO applied 3 to 4 times during key developmental stages (from seedling to 3 weeks after full bloom). In contrast, ‘Qingshu No. 10’ and ‘Qingshu No. 9’ exhibited no significant response. Post-storage analysis revealed that optimal BIO treatments in responsive cultivars (‘Minshu No. 1’ and ‘Xiazhai 65’) delayed the losses in dry matter content and starch content after 3 months of storage at 7.5 °C. Furthermore, BIO application significantly enhanced the uptake of potassium (K) in ‘Minshu No. 1’, ‘Xiazhai 65’, and ‘Qingshu No. 2’ potatoes. In conclusion, applying 7.2 g/L BIO three times during the seedling to post-bloom period is a potential strategy to enhance yield and quality for responsive early- and mid-maturing potato cultivars, offering a targeted solution for sustainable potato production.