Effect of Humic Acid on Germination, Growth, and Photosynthetic Pigments of Medicago sativa L. under Salt Stress

Aims Salt stress is one of the most important environmental stresses that cause to reduce biological function in plants. In this context, appropriate biotech is needed that would not only improve the productivity of the product but also improve the soil. Regarding the problem, the use of humic acid in addition to the positive effects on soil properties, it is useful in terms of economic, environmental, and social aspects and can be an appropriate alternative to chemical fertilizers. Materials & Methods The present research was conducted as a factorial experiment in a completely randomized design. The first factor was humic acid (0, 0.009 mg Li−1). The second factor was salt stress, which was applied at three levels of 2, 6, and 12 dS m−1. In each treatment, seed germination, seed vigor index, growth traits (allometric coefficient, radicle and pedicle length, total dry, and fresh weight), and photosynthetic contents of Medicago sativa L. were measured. Findings The findings showed that under salt stress, humic acid increased the seed germination of M. sativa L. Humic acid was effective in increasing the plant growth. In connection with the photosynthetic contents, the humic acid showed positive effects, especially in terms of 2 and 12 dS m−1 salinity levels, respectively. Conclusion In general, humic acid had high impact on reducing the negative impacts of salt stress. Due to the fact that majority of the world’s rangelands are in arid and semi-arid areas, and salt stress is one of the most important factors in reduced plant growth, more comprehensive and accurate survey in the field is recommended.