Investigation of the Effects of Different Humic Acid Applications on Seedling Development of Rapeseed (Brassica napus L.) Under Salt Stress

Salt stress negatively impacts plant development in various ways. Some of these adverse effects manifest as impaired root and seedling growth and a decrease in chlorophyll content. However, fertilization can mitigate this damage. In recent years, many organic fertilizers, such as humic acid, have become preferred over chemical fertilizers. This study was designed to investigate the effects of applying humic acid at different doses on the seedling development of rapeseed (Brassica napus L.) under salt stress conditions in laboratory conditions. In the study, rapeseed (Süzer) was subjected to four different salt doses (0 (control), 75 mM, 150 mM, 225 mM) along with six different humic acid doses (0 (control), 2 kg da-1, 4 kg da-1, 6 kg da-1, 8 kg da-1, 10 kg da-1) applied from the soil. The research was conducted in a factorial experimental design with three replications. As a result of the study, it was observed that increasing salt doses led to decreases in chlorophyll content, plant height, stem thickness, root length, root thickness, as well as fresh and dry weights of the plants. Furthermore, increased doses of applied humic acid were noted to have a positive effect. It was determined that the highest salt dose (225 mM) had the most significant adverse effect on the seedling development of the plants. However, it was found that the 4th and 5th applications of humic acid (6 kg da-1 and 8 kg da-1) were more effective in reducing the effects of salt stress. The protective effects of humic acids on plants under salt stress are noteworthy. Research indicates that humic acids support plant growth and development under salty conditions and alleviate the negative effects of salt.