Degradability of raw and post-processed chars in a two-year field experiment

Area of Science:

• Soil science
• Biogeochemistry
• Environmental science

Background:

• Biochar and digestate are soil amendments with potential for carbon sequestration.
• Understanding their degradation dynamics and impact on soil organic carbon (SOC) is crucial for sustainable land management.

Purpose of the Study:

• To analyze the degradation rates of four biochars and one digestate in sandy soil over two years.
• To assess the initial priming effects of these amendments on soil organic carbon mineralization.
• To quantify substrate-derived carbon degradation and soil priming effects using isotopic mixing models.

Main Methods:

• Two-year field experiment with sandy soil amended with biochars and digestate.
• Regular measurements of soil carbon content, soil respiration, and carbon isotopic abundances.
• Application of isotopic mixing models to differentiate substrate-derived and soil-derived carbon in soil and respired CO2.

Main Results:

• Pyrolysis biochar showed slow degradation (half-life ~80 years).
• Hydrothermal Carbonisation (HTC) biochar degraded faster initially, with a slower rate later (half-life 49-61 years).
• Digestate degraded consistently (half-life ~14 years).
• Fermented biochars degraded faster than untreated ones (half-life 11-15 years), comparable to digestate.
• No significant net influence on native soil organic carbon degradation was observed for any amendment after two years.

Conclusions:

• Untreated pyrolysis and HTC biochars exhibit considerable stability under field conditions.
• Fermentation enhances biochar degradation rates.
• Neither biochar nor digestate significantly altered soil organic carbon decomposition over the two-year experimental period.