Multivariate assessment of long-term soil fertility dynamics and nutrient accumulation and deficiency in Gyeongnam upland soils from 2001 to 2025

Purpose: This study evaluates the long-term trends and nutritional status of upland soils in Gyeongnam Province to provide scientific guidelines for sustainable soil management and precise fertilizer application.Methods: Soil samples were collected from the same 170 upland sites at four-year intervals from 2001 to 2025, resulting in seven monitoring periods.Soil pH, electrical conductivity (EC), organic matter (OM), available P 2 O 5 , and exchangeable K, Ca, and Mg were determined.Temporal changes in soil chemical properties and nutrient status were evaluated, and relationships among soil chemical properties were examined using correlation and principal component analyses.Results: Analysis over seven monitoring cycles revealed that while pH, EC, OM, and Mg levels generally remained within optimal ranges, mean levels of P 2 O 5 , K, and Ca consistently exceeded recommended thresholds.By 2025, the proportion of soils with excessive nutrient levels had declined; however, deficiencies in OM and Mg were identified in 43% and 46% of the samples, respectively.Notably, the Ca/Mg ratio increased from 4.9 in 2001 to 6.0 in 2025, highlighting an elevated risk of Mg deficiency.Principal component analysis (PCA) demonstrated that PC1 (salt accumulation) and PC2 (base saturation) accounted for 63.7% of the total variance, effectively distinguishing soil characteristics across different monitoring years.Conclusions: These results indicate that long-term nutrient accumulation and deficiency patterns have shifted significantly during the monitoring periods.For sustainable upland soil management in the Gyeongnam region, it is essential to focus on balancing the exchangeable cations, specifically Ca, Mg, and K, to mitigate nutrient imbalances.