How long does iron oxide dissolution and transformation require under water-logged conditions? — A perspective from agricultural activity

•Complete magnetic enhancement and reduction was recorded in the studied profile.•Magnetic enhancement occurred in the aerobic layer.•Magnetic reduction occurred under water-logged conditions.•Water-logged condition was caused by agriculture with a history of about 200 years.•The time required for a dissolution of iron oxides was shorter than 200 years. Previous studies have revealed that magnetic enhancement caused by the pedogenic process often occurs in aerobic soils experiencing low to moderate rainfall, while magnetic reduction caused by iron oxide dissolution often occurs in anaerobic soils experiencing high rainfall. To explore the time required for iron oxide dissolution when the soil conditions transform from aerobic to anaerobic, a typical weathering crust profile was selected. The results show the complete process of magnetic enhancement and reduction, and that the former occurred in aerobic soil due to the newborn magnetic minerals during the pedogenic process, while the latter occurred under water-logged conditions caused by rice cultivation with a history of approximately 200 years. Therefore, it can be inferred that the time required for the significant dissolution of iron oxides is probably shorter than 200 years, which is longer than that determined by indoor experiments, but much shorter than the theoretical weathering model.