This study aimed to investigate the effects of different humic acid application methods (control, soil, foliar and soil foliar) on chlorophyll content, dry matter weight of shoots and roots, concentrations of potassium (K), calcium (Ca) and sodium (Na), and K/Na and Ca/Na ratios of bean plants exposed to increasing salinity levels (0, 50, 100 and 150 mM). The effects of salt damage on shoots and roots of bean plants were significantly differed in humic acid application methods. Chlorophyll content decreased with the increase in salt doses at control and soil application of humic acid, while the decrease in chlorophyll content was lower in foliar application of humic acid. Shoot dry weight was not affected by humic acid applications, while root dry weight increased in soil foliar application method. Soil foliar humic acid application caused the highest shoot and root Na concentrations. Shoot Ca (2.61%) concentration in soil foliar application was significantly higher compared to the other treatments, while the highest Ca concentration in roots (1.55%) was recorded in soil humic acid application method. The highest K concentration in roots was obtained in the control treatment (2.50%) followed by soil foliar humic acid application (2.48%). The ratios of K/Na and Ca/Na in shoots decreased with the increase in salt application rates. The highest shoot K/Na (1456.1%) and Ca/Na (1274.1%) ratio in humic acid x salt interactions was found in soil application of humic acid without salt treatment. The root and shoot dry matter yield and K and Ca concentrations of the plants indicated that soil foliar application method has a preventive effect for the plants against the 50 mM salt damage. The results showed that soil foliar humic acid application in addition to the mineral fertilization required for beans can contribute to the growth and mineral nutrition of the plants under moderate salt stress (50 mM NaCl).
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