Maize residue types and soil fertility levels influence sequestration of newly associated carbon in aggregates with in situ experiments

Soil physical structure plays a key role in the sequestration of organic carbon (C) and affects soil fertility and global climate change. However, the dynamics of the residue-derived C in different aggregate fractions are poorly understood. The objectives of this study were to explore the changes in soil aggregate composition and organic C distribution at different fertility levels after the addition of maize residues (roots, stems, and leaves, labeled with 13C). In this study, soil samples with high fertility (HF) and low fertility (LF) levels were formed through a long-term fertilization experiment (29 years), and different types of maize residues were added to the two types of soils. The 13C abundance was quantified in four fractions of soil aggregates large macroaggregates (>2 mm), small macroaggregates (0.25–2 mm), microaggregates (0.053–0.25 mm), and silt and clay (<0.053 mm) on the 60th, 90th, 180th and 540th day following the addition of residues. The findings indicate that the mass proportions of small macroaggregates and microaggregates in the LF soil were lower, whereas those of the other fractions were higher compared with HF soil. Moreover, greater amount of residue-derived C was found to be associated with soil aggregates in LF soil than that in HF soil, and the residue-derived C in different soil aggregate fractions differed with the residue type. The percentages of residue-derived C distributed in the large macroaggregate fractions averaged 19.9% and 15.3% in the LF and HF soils, respectively. Stem and leaf treatments of HF soil improved the stability of soil aggregates. The addition of roots significantly increased the soil organic C content in the aggregates; the residue-derived C content was the highest in the silt and clay fractions and the lowest in the large macroaggregate fraction (>2 mm). These results suggest that the potential benefits of adding maize residue to regulate SOC sequestration and stabilization of soil aggregates, especially in infertile soils.