Factors contributing to aggregate stability at different particle sizes in ultisols from Southern China

Abstract

The main objective of this study was to investigate the effects of abiogenic and biogenic factors, and their interaction, on aggregate stability determined at different particle sizes. Soil samples with the same land use pattern were collected and fractioned into five aggregate sizes: 10–15 mm, 5–10 mm, 2–5 mm, 0.25–2 mm, and < 0.25 mm. Contents of iron/aluminum (Fe/Al) oxides, soil organic carbon (SOC), clay, and mean weight diameter (MWD) values for aggregates at different sizes were determined. The respective contributions of these factors were further estimated using path analysis. The results showed that SOC contents in A horizon declined with the increase of aggregate size. Highest amorphous iron oxide (Feo) contents were observed in 0.25–2 and 2–5 mm aggregates, but highest amorphous aluminum oxide (Alo) contents were found in 5–10 mm aggregates. Abiotic factors (Fe/Al oxides, clay) played a more important role in determining the formation of < 0.25 mm aggregates, whereas both abiotic and biotic factors play an effective role in stabilizing larger aggregates (0.25–2, 2–5, 5–10, and 10–15 mm). The organo-mineral complexes played a certain role in the stability of soil aggregates, especially the larger aggregates. We conclude that abiotic and biotic factors play variable roles in soil aggregates at different sizes, and more studies are needed to better assess their respective roles to improve our understanding of soil aggregation.