Effect of foliar-applied humic acid-based fertilizers on potato (Solanum tuberosum L.) yield, tuber quality, and nutrient uptake efficiency, with implications for sustainable fertilization

This study investigated the effects of foliar-applied humic acid-based fertilizers on potato (Solanum tuberosum L.) yield, tuber quality, and nutrient uptake efficiency under irrigated conditions in Western Kazakhstan. A three-year field experiment (2021–2023) was conducted using the Silvana potato variety, a medium-early cultivar with high yield potential. The randomized complete block design included five treatments: (1) Control (no fertilizers), (2) Reasil Micro Hydro Mix, (3) Reasil Micro Hydro Mix + Reasil Forte Carb-Nitrogen-Humic, (4) Potassium Humate, and (5) Potassium Humate + Reasil Forte Carb-Nitrogen-Humic. All fertilizers were applied as foliar sprays at three critical growth stages: stem formation, bud appearance, and tuber formation. The humic acid-based fertilizers used in the study were produced by LLC "Life Force Group". Potassium Humate is an 80% alkaline extract of humic and fulvic acids from leonardite. Reasil Micro Hydro Mix contains various essential micronutrients, including N, Mg, B, Fe, Zn, and amino acids. Reasil Forte Carb-Nitrogen-Humic is rich in N (20%, including 18% amide-N) and also contains humic acids (6.2%), hydroxycarboxylic acids (6.2%), and amino acids (6%). Results showed that foliar humic acid application significantly increased potato yield and improved tuber quality. The highest average marketable yield (28.79 t/ha) was obtained with Potassium Humate + Reasil Forte Carb-Nitrogen-Humic, reflecting a 20% increase over the control. Starch content was also highest in this treatment (16.9%), while vitamin C content was better maintained in treated plots under stress conditions. Additionally, nitrate accumulation in tubers was reduced, improving food safety. Nutrient uptake efficiency was significantly enhanced by humic acid-based foliar treatments. The Potassium Humate + Reasil Forte Carb-Nitrogen-Humic treatment recorded the highest N, P, and K absorption levels, confirming the role of foliar humic applications in optimizing nutrient translocation. These findings demonstrate that humic acid-based foliar fertilization is an effective strategy for increasing potato productivity while reducing reliance on conventional fertilizers. These findings highlight the potential of foliar-applied humic substances as a sustainable alternative to conventional fertilization, particularly in semi-arid agricultural systems.