Objective  To explore the effect of straw application on stability of soil aggregates and their contribution to organic carbon (C) sequestration can provide a basis for the protection of black soil in northeast China.

  Method  Based on a long-term (43 years) experiment of black soil, five treatments, no fertilization (CK), single application of organic fertilizer (M), single application of nitrogen, phosphorus and potassium fertilizer (NPK), organic fertilizer combined with nitrogen, phosphorus and potassium fertilizer (MNPK) and high amount organic fertilizer combined with chemical fertilizer (M₂N₂P₂) were selected. The same amount of straw (equivalent to the amount of full straw returning in the actual production) was added into silicon tube and was incubated in the field. The soil aggregate stability, organic C contents of soil aggregates and their contribution rate to soil organic C sequestration were analyzed by sampling on the 0, 60^th and 150^th days of incubation.

  Result  The application of straw promoted the formation of > 250 μm macro-aggregate and increased the proportion of macroaggregates. The contents of macroaggregates increased significantly in the treatment of MNPK, which was higher than that in other fertilization treatments. However, the contents of large aggregates decreased with the increase of incubation time, and the stability of aggregates decreased. The straw addition increased the contents of organic C in > 250 μm aggregate, especially in the treatment of M2N2P2. The contribution rates of the added straw to soil organic C of > 250 μm aggregate were more than 80% (P < 0.05) in the treatments of M, NPK and MNPK. The contribution rates of added straw to soil organic C of >250 μm aggregates was decreased gradually with incubation time. However, this contribution rates to 53-250 μm and < 53 μm aggregates showed increasing trends, and organic C would accumulate in smaller soil aggregates. It further indicated that the addition of straw would affect the proportion of aggregate distribution and the contribution rate of organic C.

  Conclusion  The application of straw can improve soil aggregate stability and organic C content. The high fertility black soil combined with straw addition can improve soil organic C sequestration.