Humic acid and potassium synergy drives metabolic activation, antioxidant enhancement, and improved nutrient absorption in garlic plants (Allium sativum L.)

Garlic is a widely cultivated vegetable valued for its health-promoting compounds. This study investigated the effects of humic acid (HA) and potassium (K) on garlic productivity, bioactive compounds, and nutrient uptake. A field trial was conducted to evaluate treatments combining potassium sulfate (120 and 150 kg K₂O ha⁻¹) and humic acid (10 and 20 kg ha⁻¹). Potassium and humic acid significantly enhanced garlic performance, with combined treatments producing the most potent effects. Applying humic and K significantly increased productivity. Photosynthetic pigments increased up to 22% for chlorophylls and 45.7% for carotenoids, improving photosynthesis and photoprotection. HA raised TSS by 20% and vitamin C by 32%. Potassium enhanced TSS by 24%, carbohydrates by 3%, and vitamin C by 28%. Combined treatments maximized TSS (+32%) and vitamin C (+38%), with polyphenols restored to 40%. Bioactive compounds, metabolites, and antioxidants were enhanced, with proline up to 45%, H₂O₂ up to 55.7%, APX up to 25%, SOD up to 42%, and CAT up to 25–79%, indicating improved osmotic and oxidative management. Nutrient uptake (N, P, Ca, Mg, S, and K) improved markedly, highlighting balanced nutrient allocation from leaves to cloves. Moderate combinations (K120+HA10) maximized yield, improved photosynthetic pigments, increased vitamin C and total soluble solids, and balanced nutrient allocation between cloves and leaves. These results demonstrate that integrating HA and K provides a practical strategy to support sustainable production under nutrient-efficient management.