Straw and biochar store carbon differently, scientists find

Advanced carbon materials play a crucial role in soil carbon storage, particularly in salt-affected farmlands. A study published in Biochar by researchers from the Chinese Academy of Agricultural Sciences highlights how straw and biochar, when combined with manure, enhance soil organic carbon through distinct mechanisms. Straw primarily boosts microbial activity and carbon transformation, while biochar improves soil structure and physical carbon protection.

The research team conducted a two-year field experiment in China's Yellow River Delta, an area challenged by high soil salinity and low organic matter. They compared four fertilizer treatments: conventional chemical fertilizer, manure supplementation, and manure combined with either straw or biochar. The study found that both straw and biochar combinations increased soil organic carbon by approximately 19% compared to manure alone in 2023.

Straw, when combined with manure, provided organic materials that stimulated soil microorganisms, increasing carbon-cycling enzyme activities and promoting microbial necromass accumulation. This treatment increased microbial necromass carbon by 10.8% and fungal necromass carbon by 11.2%, indicating the importance of microbial processing in transforming straw-derived carbon into soil carbon.

In contrast, biochar enhanced soil aggregation and pore structure, which helped protect organic carbon within larger soil particles. The biochar treatment increased large soil aggregates by 40.9% and improved aggregate stability by 31.9% compared to manure alone. It also increased soil porosity, creating a favorable environment for carbon retention.

Microbial community analyses revealed that straw reduced certain Actinobacteria-dominated groups, while biochar promoted fungal groups dominated by Ascomycota, which are positively associated with soil carbon storage. These findings suggest two complementary carbon sequestration strategies: biological transformation through straw and physical protection via biochar.

The researchers stress the need for longer-term field observations to assess how these mechanisms affect carbon persistence over time. "Our findings show that selecting organic amendments should involve more than measuring how much carbon they add to soil," said Hongyuan Zhang, a corresponding author of the study. "Understanding how carbon is processed and protected can help guide more effective restoration of degraded agricultural land."

This study provides valuable insights for improving saline soil management, supporting sustainable agriculture, and enhancing soil-based carbon sequestration strategies.