Compound Microbial Strains and Humic Acid Improve Physicochemical Properties of Salinized Soil and Physiological Characteristics of Oil Sunflower: An Experimental Investigation

Soil salinization commonly prevails in global arid and semi-arid areas, shrinking farmland and endangering ecological, agricultural and social sustainability. Therefore, it is essential to develop effective strategies for salinized soil remediation. In this study, soil samples were collected from Nanliang Farm in Yinchuan, China. Compound microbial strains (CMS) and humic acid (HA) were selected as soil amendments. A total of eight treatments with different application rates of CMS and HA were set up in pot cultivation experiments, where oil sunflower was planted. The results showed that both amendments effectively elevated soil water content and chlorophyll content, as well as multiple physiological indices of sunflower. Meanwhile, they decreased soil total salinity, proline content and malondialdehyde (MDA) content. For single humic acid treatments, Treatment F1 achieved the optimal amelioration effect: it reduced soil total salinity by an average of 24.34%, and increased sunflower plant height, leaf area and aboveground fresh weight by 5.84%, 95.01% and 77.40%, respectively. Among the single CMS treatments, Treatment S3 performed best, with an average reduction of 31.04% in soil total salinity, and increases of 5.66%, 2.85% and 8.16% in plant height, leaf area and aboveground fresh weight correspondingly. Notably, among all eight groups, the control group CK1 exhibited the most prominent improvement effect, which was significantly superior to F1 and S3. This finding suggests that long-term application (one year or more) of CMS can produce an especially strong ameliorative effect on salinized soil.