Effects of different biogas slurries on soil microbial carbon metabolism

Biogas slurry is a high-quality organic fertilizer, but different types of biogas slurries have different physical and chemical properties. To explore the effect of biogas slurries derived from different livestock and poultry wastes on the soil microbial community structure, a culture experiment was conducted in the laboratory with the following treatments: soil amended with biogas slurry from chicken manure (FS), pig manure (PS), and cow manure (CS), and an unamended control (CK). The experiment was conducted with equal nitrogen input for each treatment. Samples were collected after incubation of soil for 60 days. Changes in the carbon metabolism of microbial communities subjected to different treatments were examined using the Biolog microplate culture method. Compared to the control, the biogas slurry treatments exerted no significant effect on soil organic matter content, but improved soil pH, electrical conductivity, and contents of inorganic nitrogen, total nitrogen, available phosphorus, and available potassium to varying degrees. Soil microbial biomass carbon was highest in CS, whereas that in PS was significantly lower than that in CK (P<0.05). The highest carbon source utilization intensity was found in FS, while that in CS was similar to that in CK, and lower in PS. Carbohydrate utilization by soil microbes was highest in FS, where it showed a significant increase with respect to that of PS (P<0.05). The utilization of amino acids was inhibited by all biogas slurry treatments; however, such inhibition was significant only in PS when compared with CK (P<0.05). Carboxylic acid utilization was significantly higher in FS than that in the other treatments (P<0.05). The various treatments exerted three distinct effects on amine utilization: on the one hand, FS promoted amine utilization, which showed values significantly higher than those in CK and PS (P<0.05); on the other hand, PS treatment did not significantly affect amine utilization when compared to that of CK; and finally, there was no significant difference in amine utilization between microbial communities subjected to CS and the other treatments. When compared with the other treatments, FS resulted in soil microbial communities with significantly higher values of both Shannon and Simpson indices (P<0.05). The highest value of the McIntosh index was observed in the FS-treated community, with a significant increase with respect to that of PS. Amino acid utilization was the parameter showing the strongest correlations (P<0.05 or P<0.01) with various soil chemical properties. Particularly, significant negative correlations were observed with nitrate nitrogen content, total nitrogen content, available potassium content, and electrical conductivity. In contrast, there were no significant correlations between the diversity indices and soil chemical properties. Soil microbial biomass carbon was negatively correlated with nitrate and available potassium contents (P<0.05). Conversely, soil microbial biomass nitrogen was negatively correlated with the pH and electrical conductivity (P<0.05). Principal component analysis of microbial carbon metabolism showed that the microbial community of PS was differed from that of CK, while CS and FS had relatively small effects on microbial community metabolism. In summary, biogas slurry derived from different livestock and poultry wastes exerted different effects on soil microbial carbon metabolism. Nevertheless, future experiments are required to verify the long-term effects of different biogas slurries in the field.