Objective  To explore the effects of chemical fertilizer substituted by biogas slurry on characteristics and associated organic carbon (C) of water-stable aggregates in fluvo-aquic soil based on total straw returning, field experiment was conducted to improve soil structure and organic C sequestration as well as the combination of farming and animal husbandry.

  Method  Soil samples from different treatments (no fertilizer control, CK; biogas slurry application alone, BS; chemical fertilizer alone, CF; half substitution chemical fertilizer by biogas slurry, BSCF) were collected and separated by wet sieving method and corresponding aggregate associated organic C was determined.

  Result  All fertilization treatments significantly increased exogenous organic C inputs and mass composition proportion of water-stable macro-aggregates and improved aggregates stability. The greatest WR_0.25, mean weight diameter (MWD) and geometric mean diameter (GMD) were obtained in the treatment of half substitution chemical fertilizer by biogas slurry, which also acquired the lowest percentage of aggregate destruction (PAD) and fractal dimension (D). Aggregate associated organic C contents increased all firstly and then decreased with size increasing and reached the highest in the particle size of 0.25-2 mm. Meanwhile, all fertilization treatments increased aggregate associated organic C contents of different fractions, and organic C contribution rate of aggregates more than 0.25mm at the expense of reducing contribution rate of soil particles less than 0.053 mm.

  Conclusion  Chemical fertilizer substituted by biogas slurry not only improved water-stable macro-aggregates formation and stabilization, but also balances soil organic C maintenance and nutrient release by adjusting organic C contribution rate with different aggregate fractions.