Comparison of Soil Taxonomy (2022) and WRB (2022) Systems for Classifying Paddy Soils with Different Drainage Grades in South Korea

Soil classification is the systematic classification of soils based on distinguishing the characteristics of soil, aiding in understanding the properties of soils through soil survey and establishing appropriate strategies for effective soil utilization and management. Globally, the Soil Taxonomy (ST) and the World Reference Base for soil resources (WRB) are widely used for soil classification. However, the two classification systems have differences in criteria, thus exhibiting difficulties in exchanging classification results. In South Korea, soil classification has been steadily implemented to provide useful soil information to farmers for efficient soil management, contributing to the sustainability of paddy lands, but it has not been easy to establish an accurate classification system due to intensive soil management and variation in soil redox conditions. In this study, two paddy soils with different drainage grades, pedon 1 and pedon 2, were classified using the ST and WRB, and based on the comparative results, a classification criterion for paddy soil in Korea was recommended. According to ST, pedon 1 was classified as a coarse loamy, mesic family (the mean annual soil temperature, 11–14 °C) of Anthroaquic Eutrudepts (artificially irrigated, base saturation > 60%), whereas pedon 2 was a coarse loamy, mesic family of Fluvaquentic Endoaquepts (organic carbon content > 0.2%, water-saturated across the soil profile). Based on the WRB, the two soils were categorized as follows: Stagnic Hydragric Anthrosols (Eutric, Loamic, Oxyaquic) (saturated with surface water, subsurface horizon that is wet-field and human-affected) for pedon 1 and Stagnic Gleyic Hydragric Anthrosols (Eutric, Loamic, Oxyaquic) (saturated with surface and ground water, subsurface horizon that is wet-field and human-affected) for pedon 2. Overall, the two classification systems categorized these pedons consistently by judging the soil properties according to depth, but there was a difference in layer classification upon saturation by water across the soil horizons. Poor soil drainage hinders rice growth in paddies due to lowering soil and water temperature and the occurrence of harmful reduction products. In this regard, we proposed a draft of the classification criteria specialized for paddy soils in Korea based on drainage grades. This will contribute to sustainable paddy soil management by accurately classifying paddy soils and providing better soil information to farmers.