Land use change impacts on red slate soil aggregates and associated organic carbon in diverse soil layers in subtropical China.

ABSTRACT

The conversion of natural forests to other land use types generally has a significant influence on soil aggregation and associated soil organic carbon (SOC) concentration, depending on soil depth. However, the dynamics underlying soil aggregate distribution and aggregate-associated SOC concentration after such conversion remain inadequately understood, especially in the red slate soil region of subtropical China, where the stability of soil aggregates is the primary deterrent to soil erosion. This study investigated the effects of land use changes on soil aggregates and aggregate-associated organic carbon content in diverse soil layers in the aforementioned region. Soil samples were collected from seven typical land use types (natural forest, artificial forest, terraced citrus orchard, downhill citrus orchard, kiwifruit orchard, cornfield, and paddy field). Sampling was conducted at a depth of 0 to 100 cm and at 20 cm increments to determine aggregate distribution and aggregate-associated SOC content. Results showed that land use change and soil depth significantly affected aggregate stability and associated SOC concentration. Upon the conversion of natural forests to orchards and croplands, both macroaggregate (>0.25 mm) and SOC concentrations decreased, thereby weakening soil resistance to erosion caused by flowing water. However, the conversion of natural forests to artificial forests did not decrease aggregate stability or aggregate-associated SOC concentration, suggesting that artificial forests are alternative tree species for soil erosion control, aggregate stability enhancement, and SOC fixation. A general linear model indicated that land use changes accounted for 55 % and 56 % of the total variations in SOC concentration in >5 mm and 2.5 mm aggregates, respectively, implying that such changes more significantly affected large-grain aggregates. This study deepens the understanding of SOC accumulation mechanisms and provides valuable information on improving soil quality and physical structure in the red slate soil region of subtropical China.