Abstract: 【Objective】 Soil aggregates was not only one of the key structural unit, but also the most important space for soil carbon and nitrogen sequestration. The objective of this study was to explore the retention characteristics of carbon and nitrogen from corn straw and manure amendment in different size soil aggregates, which would be better understanding of the stabilization mechanism of added organic carbon and nitrogen in the aggregate and sustainable soil management.【Method】The treatments was set as follow: (1) Control; (2) straw addition in low rate; (3) straw addition in high rate; (4) manure addition in low rate (with same amount carbon in treatment (2); (5) manure addition in high rate (with same amount carbon in treatment (3). With isotope tracer technique of the natural abundance of ¹³C and labeled ¹⁵N, typical red soil from southern China (dominated by C₃ natural vegetation) was incubated for 300 days indoor on the condition of constant temperature and humidity. The content of organic carbon and nitrogen, isotopic abundance of ¹⁵N and ¹³C in bulk soil and different aggregate size fractions were determined to analyze the distribution of added organic carbon in corn straw and nitrogen in manure, as well as the retention rate of carbon and nitrogen, in macro-aggregate (250-2 000 µm), micro-aggregates (53-250 µm) and silt-clay size fractions (＜53 µm). 【Result】 Results showed that, compared with the control, contents of organic carbon and nitrogen were significantly (P＜0.05) increased after additions of corn straw and manure in red soil after 300-days incubation. It also showed the more amounts of added organic amendments, the higher increments in soil organic carbon and nitrogen content. Compared with the straw addition with same amount of carbon, application of organic manure can significantly increase the content of carbon and nitrogen in different size aggregates. Compared with the Control, the distribution proportion of organic carbon and nitrogen was significantly increased after adding corn straw in macro-aggregate. The proportion of the 1% straw addition treatment was increased by 19.5 and 22.4 percent points, respectively. However, straw treatment significantly reduced the distribution proportion of organic carbon and nitrogen by an average of 11.4 and 10.6 percent points in ＜53 µm aggregates of straw treatment, respectively. For the manure addition treatment, the distribution proportion of organic carbon and nitrogen was significantly increased by 11.6 and 8.3 percent points in 53-250 µm aggregate, respectively, whereas the distribution proportion of organic carbon and nitrogen was reduced by an average of 6.0 and 9.4 percent points in ＜53 µm silt-clay fraction, respectively. In the different aggregate size fractions of corn straws treatment, δ¹³C value of organic carbon in 250-2 000 µm size fractions aggregate was the highest, the second was in the ＜53 µm fraction, and the lowest is in the 53-250 µm size aggregate fraction. Isotope analysis indicated that, the δ¹³C value of the corn addition with high rate treatment was relative high than the corn addition with low rate and the Control CK treatments. But there was no significantly different between the corn addition with low rate and the Control treatment. The retention rate of organic carbon from corn straw was 57.6% in the high corn straw addition treatment, of which the retention rate in the large aggregates (25.9%) was equivalent to 2 times of that in the silt-clay size fraction (13.3%). The nitrogen retention rate from organic manure was averaged as 77.3%, of which the largest proportion of nitrogen was 45.2% in micro-aggregate, was equivalent to 4 times of that in the macro-aggregate (10.4%).【Conclusion】With the same amount of carbon addition, carbon and nitrogen from manure is more efficient for soil carbon and nitrogen accumulation. There is about 50% of the stabilized carbon derived from added corn straw was sequestrated in macro-aggregates, whereas about 58% of stabilized nitrogen from manure allocated in micro-aggregates.

Key words: aggregate fractions, organic carbon, nitrogen, distribution ratio, isotope labeling