Long-term changes in physical properties of paddy soils in Gyeongnam province from 2015 to 2023

Rice is the most important staple crop in South Korea, playing a central role in national food self-sufficiency and food security.To support stable and sustainable rice production, systematic monitoring of the physical condition of paddy soils is critical.This study investigated long-term changes in soil physical properties at 127 representative paddy field sites in Gyeongsangnam-do, with surveys conducted at four-year intervals from 2015 to 2023.The parameters included cultivated layer depth, bulk density, porosity, penetration resistance, and organic matter content.Topographic analysis showed that alluvial valley floors and alluvial fans accounted for 34% of the sites, while alluvial plains and marine plains accounted for 28% each.The results revealed a gradual deepening of the cultivated layer over time.Topsoil bulk density remained relatively stable, ranging from 1.14 to 1.19 Mg m -3 , while subsoil bulk density increased steadily after 2015, reaching 1.52 Mg m -3 in 2023.Soil texture-specific analysis showed that sandy loam and silty clay loam subsoils exceeded critical threshold values for compaction, indicating the necessity for subsoil loosening and deep tillage interventions.Organic matter content peaked in 2015 and slightly declined thereafter, but consistently remained above 25 g kg -3 .While organic matter application and the adoption of larger agricultural machinery may have contributed to the improvement of topsoil physical properties, repeated compaction in subsoil layers below tillage depth appears to have increased bulk density and hardness.