Biogas liquid digestate application: influence on soil microbial biomass and CO2 respiration

The rapid increase in biogas energy production has led to the accumulation of a significant byproduct, liquid digestate (LD). This study evaluated the effects of various LD dosages on soil CO₂ respiration and microbial biomass through field trials over 1 year and 2 consecutive years. LD was applied to a maize cultivation area at dosages of 10, 30, 50, and 70 t ha⁻¹. The results showed that LD created rapidly diminishing transient effects on soil microbial activity; in long-term applications, microbial stress became apparent at dosages of 30, 50, and 70 t ha⁻¹. Notably, the increase in CO₂ respiration diminished after about 60 days in the 1-year application, while the increase in microbial biomass was sustained for only 30 days. In the 2-year application, the effect on CO₂ respiration disappeared after 30 days, with no significant change in microbial biomass. Initial applications of LD stimulated microbial activity, but high dosages in prolonged applications tended to increase stress factors on microbial communities. These findings indicate that the initial effects of LD on microbial communities can diminish quickly, and soil microorganisms may adapt over time. Additionally, high EC and ammonium concentration in LD may have negatively affected soil microbial communities.