Evaluation of Soil Chemical Characteristics by Agricultural Land Use Type in South Korea over the Recent Four Years

The Rural Development Administration (RDA) of South Korea periodically conducts the "Survey on the Status of Agricultural Resources and Environment" to conserve agricultural resources and improve the agro-environment. This program monitors changes in soil fertility, heavy metals, pesticide residues, and microbial communities, as well as agricultural water quality, input usage, and the public functions of agriculture. The results serve as fundamental data for establishing national agricultural policies. Among these factors, soil chemical properties are critical indicators linked to both crop productivity and environmental pollution. This study analyzes the results of soil chemical property surveys conducted over the past four years (2021–2024) and evaluates trends since 1999. From 2021 to 2024, annual topsoil (0–15 cm) samples were collected from uplands (1,760), orchards (1,470), paddy fields (2,110), and greenhouse cultivation sites (1,374). The samples were analyzed for pH (1:5), EC, organic matter (OM), available phosphate (Avail. P), exchangeable cations (K, Ca, Mg), and available silicate (for paddies). Analytical accuracy was strictly managed using reference materials provided by the National Institute of Agricultural Sciences (NAS). The results showed that the mean soil pH was 6.1 for paddies and 6.5 for uplands, while the mean OM content was 27 g kg⁻¹ for both land use types, maintaining levels within the optimal range. These values indicate an increasing trend compared to 1999, reflecting the positive effects of long-term government support programs for soil amendments (since 1957) and organic fertilizers (since 1999). Nutrient contents, including Avail. P, K, and Ca, showed a gradual increasing trend over time. Notably, greenhouse cultivation sites exhibited more severe nutrient accumulation compared to other land use types, largely due to the closed environment of rain-sheltered facilities preventing leaching. These findings suggest that national policies should encourage the use of appropriate fertilizer amounts on agricultural land. Furthermore, integrating these soil monitoring results with fertilizer input data would enable the identification of nutrient sources, facilitating more efficient and sustainable nutrient management strategies.