Biochar locks carbon in soil for the long haul while stover keeps it cycling

A ten-year field experiment in Northeast China has shown that two popular ways of boosting soil carbon—biochar and maize stover—build soil organic carbon through fundamentally different routes, and that the difference is written into the molecular chemistry of dissolved organic carbon. The study, published in Carbon Research, tracked plots at Shenyang Agricultural University that had received either biochar at 2.63 tonnes per hectare annually, maize stover returned at 7.5 tonnes per hectare annually, or no organic amendment at all, across ten consecutive maize seasons. After a decade, both amendments had significantly raised soil organic carbon in the 0–60 cm profile, but the way that carbon arrived, transformed, and persisted differed sharply between them.

In the topsoil, the two treatments were nearly indistinguishable in their effect on total carbon: biochar raised soil organic carbon by 49.70 percent and stover by 48.87 percent relative to the control, a difference the authors report as not statistically significant. Below 20 cm, however, the paths diverged. Stover outperformed biochar in the subsurface layer, lifting carbon by 105.90 percent versus 72.81 percent, and again in the deep layer at 40–60 cm, where stover added 32.35 percent against biochar’s 4.74 percent. The researchers attribute this vertical advantage to the high solubility of stover-derived dissolved organic carbon, which can leach downward through the profile, whereas biochar particles are too large to migrate effectively and deliver most of their carbon near the surface.

The control plots told their own cautionary tale. Soil organic carbon there fell by 15.4 percent over the decade, from 11.0 to 9.31 grams per kilogram, a decline the authors link to continuous carbon removal through maize harvesting and mineralization of native organic matter under intensive tillage. That loss underscores why some form of organic input is considered necessary to maintain fertility in this region, which sits in China’s golden maize belt and has seen serious SOC depletion from intensive production and limited organic returns.

Dissolved organic carbon, though a small slice of the total soil carbon pool, is among its most active components, connecting nutrient cycling, pollutant transport, and aggregation. Using ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry, the team resolved thousands of individual molecular formulas in the DOC—between 3,382 and 6,462 compounds per sample—and found that lignin-like molecules dominated, making up more than 60 percent of DOC in all layers, with protein-like compounds a distant second. Both amendments raised DOC contents: biochar by 20.66 percent and stover by 48.83 percent in topsoil, with stover again showing the stronger subsurface boost at 118.90 percent.

The molecular fingerprints of that DOC diverged in telling ways. Biochar increased the hydrogen-to-carbon ratio and lowered the nominal oxidation state of carbon, or NOSC, meaning the dissolved pool became more aromatic and less bioactive—harder for microbes to oxidize and degrade. Stover did the opposite, raising NOSC in the topsoil and thereby increasing the bioavailability of the dissolved carbon. Because microorganisms preferentially attack compounds with higher NOSC values, the biochar-treated soil effectively banked its carbon in a chemically resistant form, while stover-fed soil kept its carbon in active circulation. The authors note that NOSC values declined slightly with depth in all treatments, implying lower energy availability for microbes deeper down.

Tracing where the sequestered carbon actually came from required two biomarker systems. Lignin phenols served as proxies for plant-derived carbon, while amino sugars—glucosamine from fungi and muramic acid exclusively from bacteria—quantified microbial necromass carbon, the stable residue of dead microbial cells that emerging research considers a major contributor to stable soil carbon pools. Both amendments increased microbial necromass carbon in the top two soil layers, with fungal necromass dominating over bacterial. But the efficiency of that conversion differed dramatically. The researchers defined microbial carbon pump efficiency as the ratio of necromass carbon gained to DOC gained, and found stover achieved a ratio of 1.57 in topsoil against biochar’s 0.73—evidence that stover-derived dissolved carbon is far more readily converted into microbial biomass.

Plant-derived carbon moved in opposite directions under the two treatments. Stover incorporation raised plant-derived carbon contents, with total lignin phenols in the topsoil reaching 493.71 milligrams per kilogram, more than double the control. Biochar, by contrast, reduced plant-derived carbon in the 0–20 and 20–40 cm layers, lowering it by 16.7 to 36.4 percent relative to control. The explanation lies in microbial ecology: biochar’s porous structure offers shelter to degradative bacteria, whose lignin-degrading enzymes the authors describe as more catalytically active than fungal equivalents, accelerating the breakdown of native plant residues. Biochar also floods the soil with its own stable aromatic carbon—660 grams of total carbon per kilogram of biochar—which dilutes the relative contribution of plant-derived material and shows up in the carbon budget as an ‘other C’ fraction.

A partial least-squares path model formalized these divergent routes. In stover-treated plots, macroaggregates strongly promoted plant-derived carbon, DOC strongly promoted microbial necromass carbon, and necromass carbon showed a significant positive effect on soil organic carbon accumulation—a feedback loop the authors describe as plant carbon input, aggregate protection, and microbial residue retention working in concert. In biochar plots, the model revealed a more chemically driven pathway: direct input of stable aromatic carbon forms a passive pool resistant to decomposition, supplemented by indirect accumulation of microbial necromass, particularly fungal necromass that the authors argue forms a synergistic, chemically resistant pool with biochar’s aromatic structures. Soil aggregates reinforced the contrast: stover significantly increased macroaggregate contents across the whole 0–60 cm profile, while biochar did so only in the deep layer.

The practical upshot, the authors conclude, is that the choice between these amendments should follow regional goals. Biochar, with 60 to 80 percent of its carbon in stable form, outperforms stover for long-term sequestration by elevating what they call the stable carbon ceiling—making it the better candidate for climate change mitigation. Stover, cheaper and more widely available, fosters active carbon cycling through microbial processing and supports soil fertility and biological activity, but the carbon it builds is more susceptible to mineralization. For a region losing topsoil carbon at 15.4 percent per decade under conventional management, the study suggests that neither approach is universally superior; rather, the molecular chemistry of dissolved organic carbon determines whether added carbon is banked or spent.

Subject of Research: Divergent soil carbon sequestration pathways of biochar versus maize stover mediated by dissolved organic carbon chemistry over a decade-long field experiment

Article Title: Divergent carbon sequestration pathways: biochar and maize stover mediate DOC properties and soil carbon accumulation

Article References: Sun, Q., Yuan, H., Sun, Y., Lin, L., Yang, X., He, T., Meng, J., Xiu, L., Huang, Y., Li, H., & Gao, Q. (2026). Divergent carbon sequestration pathways: biochar and maize stover mediate DOC properties and soil carbon accumulation. Carbon Research, 5(1), Article 60. https://doi.org/10.1007/s44246-026-00284-2

Image Credits: AI Generated

DOI: 10.1007/s44246-026-00284-2

Keywords: soil organic carbon, biochar, maize stover, dissolved organic carbon, microbial necromass carbon, FT-ICR-MS, lignin phenols, carbon sequestration, soil aggregates, microbial carbon pump, NOSC, Northeast China