Objective  The aim was to explore the regulation effect of biochar application in non-irrigation season on soil aggregates and carbon sequestration in topsoil of drip irrigation cotton field.

  Method  Five treatments with the biochar applications of 15 t hm⁻² (B₁), 30 t hm⁻² (B₂), 45 t hm⁻² (B₃), 60 t hm⁻² (B₄), and no application (B₀) were set up with three replicates. The effects of biochar in non-irrigation season on soil total carbon (C) and organic C, microbial biomass C, soil respiration rate, aggregate and aggregate-bound total C, and aggregate-bound organic C in the plough layer (0 - 40 cm) of drip irrigation cotton field in Xinjiang were analyzed.

  Result  Compared with the control treatment, the soil total C, aggregate-associated total C, and soil respiration rate increased with the increase of biochar application rate. Total C increased by 6.85% - 18.14%, aggregate-bound total C increased by 6.15% - 17.71%, and soil respiration rate increased by 13.52%-53.88%. > 0.25 mm water-stable aggregate content, aggregate-bound organic C, soil organic C, and microbial biomass C increased first and then decreased with the increase of C application rate. >0.25 mm water-stable aggregate content increased by 11.80% - 21.68%, aggregate-bound organic C increased by 12.64% - 57.54%, soil organic C increased by 17.58% - 55.27%, microbial biomass C increased by 13.02% - 46.96%. By establishing the minimum data set to calculate the soil quality index, the highest soil quality index score was B₃ (0.4632).

  Conclusion  Application of biochar in non-irrigation season is beneficial to increase soil aggregate and soil C content, but also increases C emissions. The optimal application amount of biochar was 45 t·hm⁻² in non-irrigation season of drip irrigation cotton field in Xinjiang.