Fulvic Acid and Potassium Application to Mitigate Drought Effects on Sweet Potato

Abstract This study uniquely explores the synergistic effects of a combined fulvic acid and potassium application on sweet potato under water stress, shedding new light beyond individual applications. Two field experiments were conducted during the summer seasons of 2023 and 2024, using the sweet potato cultivar Aibs. Six treatments were applied in a randomized complete block design with three replicates. These included the following: (1) 14-day irrigation interval with 120 kg ha −1 K, (2) 21-day irrigation interval with 120 kg ha −1 K, (3) 21-day irrigation interval with 120 kg ha −1 K and 12.4 kg ha −1 of fulvic acid, (4) 21-day irrigation interval with 120 kg ha −1 K and 24.7 kg ha −1 of fulvic acid, (5) 21-day irrigation interval with 90 kg ha −1 K and 12.4 kg ha −1 of fulvic acid, and (6) 21-day irrigation interval with 90 kg ha −1 K and 24.7 kg ha −1 of fulvic acid. The findings reveal that water deficit conditions significantly reduce growth parameters, yield (19.6 and 19%), leaf chlorophyll (12.6 and 13.9%), and total applied irrigation water per hectare (24.3 and 21%). However, they increase the contents of leaf proline (65.5 and 63.2%), tuber root dry matter (46.2 and 48.5%), and total soluble solids (22.8 and 24.4%), as well as water use efficiency (6 and 2.5%), in both seasons, respectively. The fulvic acid application significantly mitigated these effects, particularly at a higher rate alongside adequate potassium (120 kg ha −1 K). This mitigation is likely attributable to improved nutrient water uptake and osmotic adjustment. These findings highlight the potential of fulvic acid combined with an adequate potassium level for improving crop performance under drought conditions.