Biochar and maize stover take different routes to store carbon in soil

Two Amendments, Two Pathways

Maintaining soil organic carbon is important for agricultural productivity and climate mitigation, yet organic amendments do not necessarily build soil carbon in the same way. A 10-year maize field experiment at Shenyang Agricultural University compared annual biochar application at 2.625 t ha⁻¹ with maize stover incorporation at approximately 7.5 t ha⁻¹, alongside an untreated control. The field plots received the treatments for ten consecutive crop seasons before soil was sampled at depths of 0–20, 20–40, and 40–60 cm.

Both amendments significantly increased soil organic carbon across the 0–60 cm profile. In the topsoil, carbon gains were similar for biochar and stover, at 49.70% and 48.87%, respectively. Stover produced larger increases in subsurface and deep-soil carbon, reaching 105.90% in the 20–40 cm layer and 32.35% in the 40–60 cm layer. Biochar produced corresponding increases of 72.81% and 4.74%. These contrasting depth patterns indicate that carbon accumulation depends on amendment-specific transport and stabilization processes.

Molecular Fingerprints of Soil Carbon

The investigators characterized dissolved organic carbon using Fourier transform ion cyclotron resonance mass spectrometry, complemented by lignin phenol analysis, amino-sugar measurements, soil aggregate analysis, and statistical modeling. These approaches enabled assessment of DOC molecular composition, plant-derived carbon, microbial necromass carbon, and the relationships among these pools.

Biochar and stover both increased DOC concentrations, but they altered its properties differently. Biochar lowered the nominal oxidation state of carbon, a pattern associated with lower DOC bioactivity and greater persistence. Stover produced higher DOC bioactivity in topsoil, consistent with a more readily metabolized carbon supply. Stover-derived DOC also showed stronger vertical movement, whereas biochar contributed more stable carbon directly to the soil.

Microbes and Aggregates Shape the Outcome

The carbon sources associated with the two amendments also diverged. Biochar increased microbial necromass carbon while reducing plant-derived carbon in the 0–20 and 20–40 cm layers, a pattern the authors associate with enhanced decomposition of native plant carbon and the substantial input of stable biochar carbon. Stover increased both plant-derived carbon and microbial necromass carbon, particularly through active microbial processing of plant residues.

Soil aggregation contributed to these outcomes. Both amendments increased the proportion of small macroaggregates, but stover exerted the stronger effect across the soil profile. Partial least-squares path modeling indicated that stover enhanced soil organic carbon through a coordinated pathway involving aggregates, plant-derived carbon, and microbial necromass carbon, whereas biochar operated primarily through direct stable-carbon input and indirect accumulation of microbial residues.

Implications and Remaining Questions

The findings support different management roles for the two amendments. Biochar appears better suited to long-term carbon sequestration and stabilization of persistent carbon pools, while maize stover supports active carbon cycling, microbial processing, and the retention of plant-derived carbon. The results therefore favor matching amendment choice to management objectives rather than treating biochar and stover as interchangeable carbon inputs.

Several constraints qualify the interpretation. The experiment used three field replicates, and technical replicates were not performed for FT-ICR-MS because of the high analytical cost. Initial soil physicochemical properties were measured from a composite sample rather than separately by soil layer. In addition, lignin phenols and amino sugars do not capture the entire soil organic carbon spectrum, including highly processed organic matter and black-carbon-like materials. The proposed differences in microbial necromass turnover and DOC transport consequently require further direct testing.

Future work should quantify the differential persistence and turnover of fungal and bacterial necromass carbon and clarify the mechanisms controlling dissolved organic matter transport into deeper soil layers. Longer-term monitoring across soils, climates, crop systems, and amendment properties would also help determine how broadly the observed divergent carbon sequestration pathways apply to agricultural carbon management.

Corresponding Author: Tianyi He

Original Source: https://doi.org/10.1007/s44246-026-00284-2

Contributions: All authors contributed to the study conception and design. Qiang Sun and Hechong Yuan contributed equally to this work. Data curation, investigation, methodology, software, and writing – original draft were performed by Qiang Sun and Hechong Yuan. Methodology and software were performed by Yuanyuan Sun. Investigation was performed by Li Lin, Liqun Xiu, and Yuwei Huang. Writing – review and editing were performed by Xu Yang and Tianyi He. Funding acquisition was performed by Qiang Sun and Jun Meng. Manuscript editing was completed by Han Li and Qi Gao.