Sargassum horneri drift as a soil amendment for soybean (Glycine max (L.) Merr.) and its effects on microbiome composition

Sargassum horneri which seasonally enters East Asian waters frequently leads to negative economic consequences despite its ecological importance. It damages vessel engines and fishing gear and releases hydrogen sulfide and ammonia as it rots. Traditionally, seaweed drifts have been used as fertilizers in certain coastal areas in Korea, but there have been no scientific reports regarding this kind of application of seaweeds. Hence, this study attempted to use Sargassum biomass as a soil amendment by monitoring soil properties and microbiome changes and soybean growth in Sargassum-added soil. Our results suggested that the addition of S. horneri biomass to soil improved soil physicochemical properties such as cation exchange capacity (CEC) levels that represents soil’s capacity to retain cations leading to more soil fertility. As (max. value 24.97 mg kg⁻¹) and Cd (max. value 0.58 mg kg⁻¹) concentration increases were notable in the soil, but all the metal levels were well below the Korean soil quality standards for agricultural uses except for As (25 mg kg⁻¹ limit) which is just a little lower than the limit. Diversity index results indicated that fungal and bacterial diversities were affected by the amount of Sargassum added. Our study demonstrated that seasonal drifts of S. horneri could be used as an excellent soil amendment. Moreover, Glycine max (L.) Merr. cultivation experiments suggested that 4% of S. horneri was the optimal amount to enhance soybean growth in agricultural practice.