<![CDATA[The continuous use of glyphosate herbicides in long-term oil palm monoculture systems has raised significant environmental concerns because of their potential to accelerate Ultisols degradation and prolong herbicide residue persistence across plantation age chronosequences. This study evaluated the physicochemical properties of glyphosate-contaminated Ultisols under oil palm plantations of different ages using a quantitative survey approach with randomized sampling. Soil samples were collected from plantations aged <5, 5-10, 10-15, 15-20, and >20 years, with forest soil as a control, at a depth of 0-20 cm. Long-term oil palm cultivation significantly alters the physical and chemical properties of Ultisols. Conversion from forest to young plantations increases bulk density from 0.85 to 1.31 g cm?³ while reducing porosity, water content, and permeability, indicating severe structural degradation. Although plantations >20 years old show improvements in soil quality, the ecological state of forest soils is not fully restored. Ultisols remain highly acidic (pH 4.43-5.30) and exhibit highly variable loading properties that influence nutrient retention and glyphosate adsorption. Glyphosate residues increase with age, with the highest soil residues in 10-15-year-old plantations (18.07 mg kg?¹) and in oil palm fruits in 15-20-year-old plantations (16.94 mg kg?¹). Plantation age, organic matter dynamics, and herbicide use intensity have been identified as key influences on soil degradation, nutrient imbalance, and glyphosate persistence in tropical oil palm agricultural ecosystems.]]>
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