Controlled-release potassium sulfate combined with the deep banding method on soybean productivity and soil microbial characteristics

Controlled-release potassium sulfate (CPS) and deep banding fertilization are promising strategies for improving crop productivity, but their combined effects on soybean growth remain unclear. In this study, field experiments were performed over two growing seasons (2023–2024) to evaluate how potassium (K) fertilizer types (potassium sulfate and CPS) and fertilization methods (broadcast incorporation and deep banding) influence soil microbial composition, soil enzyme activity, and soybean growth characteristics. The results indicate that deep banding and CPS application consistently increased soybean yield, K use efficiency, and nitrogen use efficiency. Relative to broadcast incorporation, the application methods of deep banding increased soybean yield by 1.1%–2.7% in 2023 and 3.7%–3.8% in 2024, while the application of CPS increased soybean yield by 6.0%–7.7% and 9.6%–9.7% compared with potassium sulfate (PS) application. Additionally, deep banding of CPS increased soil protease, urease, acid phosphatase, and phosphodiesterase activities and improved plant enzyme activities and hormone contents. Microbial analyses showed that CPS combined with the deep banding method (DCPS) enriched several microbial taxa ( Bradyrhizobium , Lysobacter , Rhizophagus , and Funneliformis ) potentially associated with nutrient cycling and was associated with more connected genus-level microbial co-occurrence networks. Structural equation modeling further indicated that microbial diversity, soil fertility, enzyme activity, and plant growth characteristics were jointly linked to soybean productivity. These results suggest that DCPS is a promising K management strategy for improving soybean productivity and nutrient use efficiency in the North China Plain.