Sustainable agriculture boosted by biogas slurry, reshaping soil carbon dynamics

Beijing, China – A recent field experiment reveals how applying biogas slurry as a topdressing can profoundly influence soil dissolved organic carbon (DOC), a critical component of soil health and carbon cycling, particularly in dryland agricultural settings. Published in Carbon Research, new findings from the Chinese Academy of Agricultural Sciences provide a comprehensive understanding of how this sustainable agricultural practice reshapes carbon transformation and stabilization across different maize growth stages and soil depths.

Biogas slurry, a nutrient-rich byproduct of anaerobic digestion, offers significant potential for sustainable agriculture by recycling organic waste and partially replacing chemical fertilizers. Despite its known benefits, the specific mechanisms by which biogas slurry topdressing (BSTD) regulates soil DOC dynamics under real-world field conditions, considering both crop growth and varied soil layers, remained largely unclear. Soil DOC is a highly mobile carbon fraction that fuels microbial activity and influences nutrient availability, making its precise management vital for robust agroecosystems.

Tracing Carbon's Journey Through Soil

Researchers conducted a multi-year field experiment in Shouyang, Shanxi Province, China, evaluating the effects of different BSTD replacement levels of chemical nitrogen fertilizer on maize plots. Soil samples were collected at critical maize growth stages—tasseling, milk ripening, and maturity—and from three distinct soil depths: 0–10 cm, 10–20 cm, and 20–40 cm. Advanced spectroscopic techniques, including ultraviolet–visible spectroscopy (UV–Vis), excitation-emission matrix (EEM) fluorescence spectroscopy, and Fourier transform infrared spectroscopy (FTIR), were employed to characterize DOC quantity, source, molecular size, humification degree, and functional group composition. Statistical modeling, including partial least squares path modeling, helped unravel the complex interrelationships.

The investigation uncovered that BSTD did not simply increase soil DOC; its effect was dynamic and stage-dependent. While it boosted DOC content at the tasseling stage, it led to a decrease at the milk stage, suggesting rapid microbial consumption and utilization. Crucially, the study showed that BSTD significantly altered the composition of soil DOC by increasing the proportions of humic acid-like substances (5.86%) and soluble microbial by-products (4.97%). Simultaneously, it decreased less humified fractions such as aromatic protein class I and II, and fulvic acid-like substances. These shifts, along with an enrichment of carbon-containing functional groups, indicate that BSTD actively promotes the transformation of more reactive DOC into microbially reprocessed and humified components, rather than causing simple accumulation.

Soil Depth: The Overriding Influence

A pivotal discovery was that soil depth emerged as the most significant factor directly regulating DOC composition and content. This highlights the critical role of vertical heterogeneity within the soil profile in governing how DOC is produced, transformed, retained, and redistributed. Biogas slurry acts as an important external carbon and nutrient source, modifying DOC transformation within this depth-driven soil-crop system, where the crop growth stage regulates the temporal rhythm of carbon input and utilization. The findings emphasize that BSTD optimization should consider not only the fertilizer-replacement ratio but also the timing of slurry application and the retention capacity of different soil layers.

Advancing Sustainable Land Management

This research offers a deeper mechanistic understanding of soil DOC dynamics in dryland maize systems, demonstrating that BSTD is not merely a fertilization strategy but a potent tool for regulating soil carbon turnover and enhancing carbon-resource use efficiency. The insights gained provide a scientific foundation for developing more sustainable and effective biogas slurry management practices. While the study's conclusions are robust, future work combining long-term monitoring, high-resolution mass spectrometry, and functional validation will further clarify these intricate mechanisms at a molecular level.

Corresponding Author: Jiandong Wang or Baoqing Chen

Original Source: https://doi.org/10.1007/s44246-026-00295-z

Contributions: Xiaoyang Liang and Chuanjuan Wang contributed to investigation, formal analysis, data curation, and software; Xiaoyang Liang drafted the original manuscript, and both reviewed and edited the work. Yongxing Wen, Junjie Qin, and Jiandong Wang conducted investigation and reviewed and edited the manuscript. Baoqing Chen and Haitao Wang handled resources, supervision, project administration, and funding acquisition, in addition to conducting investigation and reviewing and editing the work. All authors reviewed and edited the manuscript.