Multidimensional effects of arable soil organic carbon distribution: a comparison among terrains

Soil organic carbon (SOC) in arable land directly affects the soil nutrient cycle and biological activity. However, it is unclear how environmental factors influence the processes and mechanisms of SOC distribution in arable soils across different topographies.

Random forest (RF) and piecewise structural equation model (PiecewiseSEM) were used to study the effects of environmental factors in different terrain on SOC content.

Arable soils in mountainous areas exhibited a significantly higher SOC content of 14.35 ± 5.24 g·kg^− 1 compared to that in plains (11.13 ± 4.50 g·kg^− 1) and hilly regions (10.96 ± 4.77 g·kg^− 1) (p < 0.05). Soil pH, soil water content (SWC), and solar radiation (SR) were identified as key factors influencing SOC distribution in all three topographies. Soil properties were the most critical factors directly contributing to SOC distribution in plains and hills, with standardized total effects of 0.30 and 0.33, respectively. The process of SOC distribution in mountainous arable land, however, was primarily determined by climate (0.28).

The results showed differences in SOC content attributed to variations in the processes and levels of influence of climate, soil, and vegetation on SOC accumulation in the three terrains. Hot and humid climates promote direct increases in SOC content in mountainous areas. However, they face challenges in directly affecting SOC levels in plains and hills SOC, but they can still contribute to SOC accumulation in all terrains by fostering high vegetation cover and creating moist acidic soil environments.