The investigation revealed that biochar and hydrochar alter soil chemistry and biology in opposite directions. Biochar, created by high-temperature pyrolysis of birch wood, increased emissions of nitrous oxide, a powerful greenhouse gas associated with fertilization. In contrast, hydrochar, derived from low-temperature hydrothermal carbonization of birch bark, reduced nitrous oxide emissions and under specific circumstances transformed the soil into a minor nitrous oxide sink.
"Hydrochar appears to promote soil processes that remove nitrous oxide, while biochar can stimulate microbial activity that produces it," lead author Hem Raj Bhattarai of Luke noted.
Both forms of char contributed to greater particulate organic carbon content, supporting soil organic matter buildup. Their influence on carbon dioxide and methane fluxes, as well as on total grass-clover biomass yield, was limited. Notably, biochar used in combination with nitrogen fertilizer caused a modest drop in timothy grass yield, hinting at a potential effect on plant nitrogen uptake.
Hydrochar treatment resulted in higher microbial biomass carbon compared to biochar, suggesting more active soil microbial communities and possibly accounting for reduced nitrous oxide emissions.
"Our results highlight the complex interactions among soil microbes, vegetation, and nitrogen management," Bhattarai stated. "Selecting the right char type for a specific soil and crop system is essential if we want to use these materials to improve soil health and mitigate greenhouse gas emissions."
The study advises further investigation of char effects at field scale and in diverse soil environments to assist sustainable agricultural practice in northern climates.
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