Humic Acid-Salinity Interaction on Morphophysiological and Post-Harvest Characteristics of Red Beet

Salinity is one of the most severe abiotic stresses in agriculture. Red beet is moderately salt-resistant, with its growth, yield, and quality being strongly impaired by high salinity. Humic acid (HA) helps counter salt stress in various plants, showing promise for boosting crop yield. This study assesses the impact of humic acid on red beet growth, physiology, and quality under salt stress. Red beet plants were grown in a completely randomized design, arranged in a 3 × 2 factorial scheme (three HA concentrations × two salt stress levels). HA treatments corresponded to 0, 38, or 76 mg of humic acid pot^− 1, and salinity corresponded to either saline (80 mM NaCl) or non-saline irrigation water. HA boosted water use efficiency but did not counteract salt stress effects on red beet gas exchange and chlorophyll fluorescence. Despite salt stress increased electrolyte leakage and impacted photosynthesis, root growth was not hindered, and shoot growth even increased, showing its considerable salt tolerance of red beet. Salt stress resulted in a more saturated peel color of root and increased total sugars, soluble solids, and betacyanins, while decreasing root firmness. HA, however, reduced total sugars, betacyanins, phenolics, and betaxanthins in beet roots. In sum, the soil application of humic acids had no positive effects on the growth, physiological and quality attributes of red beet evaluated under moderate salinity stress. Therefore, the HA doses studied here are not recommended for red beet production.