Human activities drive accelerated soil aggregation in Quaternary red soil

Abstract

Understanding aggregate formation is crucial for enhancing soil fertility and ecosystem quality and promoting the sustainable utilization of soil resources. This study examines the long-term evolution of aggregates and binding agents in Quaternary red soil (QRS) under various anthropogenic land use activities. Using a quantitative soil reconstruction method, dynamics of aggregates, crystalline iron oxides (Fec), poor crystalline iron oxides (Feo), and soil organic carbon (SOC) were analyzed since 91.01 ka BP. Results showed significant decreases in 0.25–0.5 mm (MAA₅), 0.053–0.25 mm (MIA), and <0.053 mm aggregates (SCF), while significant increases in > 5 mm (MAA₁), 2–5 mm (MAA₂), 1–2 mm (MAA₃), and 0.5–1 mm (MAA₄) aggregates under anthropogenic activities. SOC and Feo contents increased in MAA₁–MAA₅ and showed a positive correlation (p < 0.05), whereas Fec decreased in MAA₅, MIA, and SCF, with a notable positive association between Fec loss and MAA₅ content (p < 0.05). A model of aggregate formation in QRS influenced by anthropogenic activities was proposed, encompassing four stages: importation of SOC, activation of Fec, decomposition of SOC, and crystallization of Feo. The primary aggregate formation processes revealed that SCF was bound into MAA₁ while MAA₅ broke up. Aggregate aggregation was more pronounced than breakdown. The cumulative aggregation rate of MAA was higher in sparse forest grassland [0.60 g/(cm²·ka)] and woodland [0.38 g/(cm²·ka)] compared to grassland [0.29 g/(cm²·ka)] and cultivated land [0.27 g/(cm²·ka)]. Thus, anthropogenic land use activities accelerate aggregate aggregation in QRS by promoting the formation of SOC and crystallization of Feo.