Solid and liquid fractions of digestate: manure or slurry just like any others?
Résumé
Biogas digestates are increasingly used as organic fertilizers. However, their impact on soil microbiota quality remains debated. Indeed, little is known about soil microbial communities responses to a given digestate depending on i) the fraction applied – whole (FYM_WD), liquid (FYM_LD), or solid (FYM_SD) – and/or ii) the physicochemical properties of the receiving soil. In a 42-day microcosm experiment, we applied different fractions of a same digestate to three soils with contrasting physicochemical and climatic characteristics and compared their effects on the abundance and diversity of the soil microbial communities. The experiment also included four additional treatments: cattle manure (CM), cattle slurry (CS), a mineral fertilizer, and an unfertilized control. Forty-two days after application, a significant ‘treatment’ effect was observed on soil microbial indicators for the two coarser-textured soils (P < 0.05). In the sandy loam-textured soil, FYM_SD resulted in a 40 % greater soil microbial biomass than FYM_WD or FYM_LD (P = 0.05). The effect of FYM_SD on soil microbial biomass was equivalent to that of CM or CS (P > 0.05), whereas the effect of FYM_LD more closely resembled that of CS. Moreover, FYM_SD input resulted in a significantly different prokaryotic community structure compared to FYM_LD-fertilized soil, but was equivalent to that of the CM-fertilized soil (P > 0.05). In the loam-textured soil, FYM_SD input resulted in a 20 % lower prokaryotic richness than FYM_LD. Similarly, the fungal community structure was affected the digestate fraction (P = 0.04), and the effects of FYM_SD and CM on fungal community structure were comparable (P > 0.05). Overall, these results demonstrate that digestate fraction influence soil microbial communities in a soil-type dependent manner.