Soils are among the planet's largest carbon reservoirs, yet salinity and land degradation threaten their ability to store carbon and support agriculture. Improving carbon storage in salt-affected farmland could therefore offer a dual benefit: restoring soil health while supporting climate change mitigation.
In a study published in Biochar, researchers from the Chinese Academy of Agricultural Sciences and collaborating institutions discovered that combining manure with straw or biochar significantly increased soil organic carbon, but through two distinct pathways. Straw primarily stimulated microbial activity and carbon transformation, while biochar improved soil structure and the physical protection of carbon.
"Both straw and biochar can improve carbon storage in saline soils, but they work in different ways," said Hongyuan Zhang, a corresponding author of the study. "Understanding these differences is essential for developing soil management strategies that improve fertility and support carbon sequestration."
The researchers conducted a two-year field experiment in China's Yellow River Delta, where high soil salinity and low organic matter levels pose major challenges to agricultural productivity. Four fertilizer treatments were compared, including conventional chemical fertilizer, manure supplementation, and manure combined with either straw or biochar.
The team examined soil carbon, microbial communities, enzyme activities, and soil pore structures to understand how each treatment influenced carbon accumulation.
Both straw and biochar combinations increased soil organic carbon by approximately 19% compared with manure alone in 2023. However, the underlying processes differed substantially.
When straw was combined with manure, it provided readily available organic materials that stimulated soil microorganisms. This increased carbon-cycling enzyme activities and promoted the accumulation of microbial necromass, the remains of dead microorganisms that contribute to soil organic matter.
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