A one-year short-term biochar application improved carbon accumulation in large macroaggregate fractions

• One-year biochar amendment did not change soil aggregation.
• Higher SOC and black C accumulated in large fractions under one-year biochar amendment.
• Biochar was physically protected within soil aggregates.
• Biochar amendment has potential to improve soil C stabilization.

Biochar amended to soil may improve soil aggregation and in turn increase soil organic carbon (SOC) stabilization. In an intensive wheat–maize rotation system of the North China Plain, we investigated effects of one-year biochar application on soil aggregate-size distribution and structure stability, and aggregate-associated C concentrations. Three biochar (< 1 mm diameter, from corncob at 360 °C for 24 h) treatments were examined as no biochar amendment control, rate at 4.5 (B4.5) and 9.0 t ha− 1 year− 1 (B9.0). Soil samples were collected from 0–10 and 10–20 cm depths and separated into six water-stable aggregate sizes (≥ 5, 2–5, 1–2, 0.5–1, 0.25–0.5 and 0.053–0.25 mm). Results showed that neither soil aggregation nor aggregate stability was significantly affected by biochar amendments. In contrast, more SOC was accumulated in the large fractions (≥ 5 and 2–5 mm) under B9.0 than under the other two treatments. Meanwhile, more C occluded in the large fractions (≥ 5, 2–5 and 1–2 mm) under both B4.5 and B9.0 than under no-biochar control, suggesting that biochar-C was physically protected within these aggregate fractions. Our data indicated that biochar application could be a potential pathway to improve native SOC and black C stabilization in the intensive cropping system of the North China Plain.