Distribution of fresh carbon in different particle-size aggregates of different soil type

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In order to study the effects of application of fresh carbon on distribution in soil aggregate fractions of red soil and lime concretion black soil, the stable carbon isotope (δ13C) technique was used, and explore the dynamic variation and distribution of soil organic carbon(SOC) in soil aggregates during 13C-labelled rice straw decomposition by an indoor incubation experiment. This experiment was put under incubation at 28°C for 120 days, which included two treatments: CK (no straw) and Str (added with 1% straw), all samples were separated into four aggregate-size classes (>2000, 2000~250, 250~53, <53 μm) by wet sieving in the different incubation period, while soil aggregates in different size fraction and organic carbon in soil aggregates were determined. The results showed that the δ13C value of organic carbon in different particle-size water-stable aggregates of Str treatment was significantly higher than that of CK treatment, the δ13C value varied greatly both in red soil and lime concretion black soil, but the turnover rate of native SOC was slow and the degradation degree was relatively close. The quantity of new organic carbon supplied by rice straw found in different levels of aggregates followed a same increasing order of 2000~250 μm < (>2000 μm) < (<53 μm) < 250~53 μm in red soil and lime concretion black soil at 120 days, which further indicates that the added fresh carbon was mainly accumulated in small-sized soil aggregates. The result shows that the addition of rice straw could increase soil organic carbon content in all sizes of aggregates, which provide theory basis for soil quality improvement and organic carbon recycle.