Epsilon Archive for Student Projects

Abstract

Biochar has potential as a soil amendment and carbon storage material, but its effects on soil microorganisms can vary depending on feedstock and production conditions. This study investigated how biochars derived from manure digestate and produced from different solid fractions and at different pyrolysis temperatures affected soil carbon mineralization and microbial activity.
Two laboratory incubation experiments were conducted using a sandy soil. Experiment 1 compared biochars produced from centrifuge-recovered digestate solids at 400 and 550 °C (BCS400 and BCS550) and used ¹³C-labelled glucose to distinguish glucose-derived from non-glucose-derived carbon dioxide (CO₂). Experiment 2 compared BCS400 with biochar produced from screw-press solids at 400 °C (BSS400) using unlabelled glucose. Carbon dioxide emission, cumulative heat dissipation, calorespirometric ratio (CR), and microbial biomass carbon (MBC) were evaluated.
The BCS400 biochar generally produced greater CO₂ emission and heat dissipation than BCS550, particularly without glucose addition and during the early incubation period, consistent with its less carbonized characteristics. The ¹³C results showed that the pronounced early difference in respiration associated with BCS400 was largely related to the non-glucose-derived CO₂ fraction, whereas by day 65 the control showed greater glucose-derived CO₂ than both biochars. In Experiment 2, BCS400 generally produced greater respiration and heat dissipation than BSS400, despite both biochars being produced at 400 °C. Microbial biomass carbon responses varied with incubation time, with both biochars showing greater microbial biomass than the control at several sampling times. These results indicate that both pyrolysis temperature and digestate separation procedure influenced microbial responses to digestate-derived biochar.
Biochar amendment also altered the relationship between heat dissipation and CO₂ emission. However, many CR values approached or exceeded the theoretical reference value of 469 kJ mol⁻¹, and the difference-based CR represented the net metabolic response following glucose addition rather than glucose metabolism alone. Therefore, the CR results indicated changes in microbial carbon and energy metabolism but did not provide consistent evidence that biochar increased microbial carbon use efficiency (CUE). Overall, digestate-derived biochars should not be considered a uniform group of soil amendments because their microbial effects depend on both digestate processing and pyrolysis conditions.