Influence of straw, compost, and biochar on soil carbon and aggregates in Chernozem

Crop residue management is a major concern in agricultural ecosystems. These residues can be recycled into biochar and compost to efficiently promote soil organic carbon (SOC) storage in farmlands. However, the influences of straw and its derived materials on SOC (especially on humus fractions) in soil aggregates of varying sizes are largely unknown. To understand these effects, a nine-year field experiment was conducted on calcareous black soil, including five treatments: CK – no fertiliser; NPK – mineral nitrogen, phosphorus, and potassium fertiliser; NPKS – NPK + straw; NPKC – NPK + compost, and NPKB – NPK + biochar. Compared to CK and NPK, the NPKS and NPKC treatments resulted in a noticeable rise (<i>P</i> < 0.05) in the proportion of aggregates with > 0.25 mm size (R0.25), as well as in the mean weight diameter and geometric mean diameter at 0–20 cm depth. The NPKS, NPKC, and NPKB treatments significantly (<i>P</i> < 0.05) increased the contents of large macroaggregates (> 2 mm), small macroaggregates (2~0.25 mm), microaggregates (0.25~0.053 mm), and non-aggregates in the 0–20 cm soil layer, as well as the levels of SOC, humic acid carbon (HAC) and humin carbon (HUC). These treatments also significantly (<i>P</i> < 0.05) enhanced organic carbon storage in the topsoil (0~20 cm). The effects were more pronounced after NPKB treatment relative to NPKS. Compared to CK, the application of mineral fertilisers alone and combined with organic materials significantly (<i>P</i> < 0.05) improved crop yields. The study’s results indicate that the application of organic materials from corn significantly (<i>P</i> < 0.05) enhanced both soil quality and corn yield, with straw-derived biochar showing better effects on soil carbon sequestration.