Analysis of Chemical Properties of Paddy Soils According to the Severity of Rice Brown Spot (Bipolaris oryzae)

This study investigated the relationship between soil chemical properties and rice brown spot severity, caused by Bipolaris oryzae, by comparing soils with different disease levels within the same paddy fields. Soil samples were collected from five regions in Korea (Muju, Buan, Sunchang, Iksan, and Boeun), where disease severity was categorized as mild, moderate, or severe. Most parameters—including pH, electrical conductivity, organic matter, NH<sub>4</sub>-N, total nitrogen, available P<sub>2</sub>O<sub>5</sub>, exchangeable cations, cation exchange capacity, and micronutrients—did not differ significantly among severity levels. In contrast, available silicon (Avail. SiO₂) was significantly lower in soils from severe disease plots compared with mild and moderate plots (P<0.05), indicating a potential role of Si availability in disease development. However, in the Boeun region, higher available silicon content was observed in plots with more severe disease, indicating that disease severity cannot be explained by silicon status alone and that other factors may have acted as overriding conditions. These findings suggest that the development of rice brown spot is influenced not only by silicon availability but also by the interaction of multiple factors, including regional cultivation environments, nutrient management, and agronomic practices. Therefore, future studies should evaluate the effect of silicon application together with integrated considerations of soil properties, cultivation practices and environmental factors. The results of this study provide fundamental information for establishing soil-based and integrated management strategies for rice brown spot.