Soil nitrogen leaching decreases as biogas slurry DOC/N ratio increases

Previous work has measured high rates of nitrogen (N) leaching during biogas slurry irrigation. Here we tested whether increasing the ratio of dissolved organic carbon (DOC) to N in biogas slurry would decrease N leaching by applying biogas slurries with DOC/N ratios of 0.9, 2.3, 7.3, 12.3 and 17.3 to soil columns in the laboratory. Increasing the DOC/N ratio to at least 7.3 reduced N leaching by approximately 91%, likely because denitrification and nitrate (NO3−) consumption were increased in the DOC/N 7.3 treatment and ammonium immobilization increased (and NO3− production decreased) in the DOC/N 12.3 and 17.3 treatments. Additionally, all the detected soil nitrifiers-uncultured Nitrosomonadaceae, Nitrospira, Nitrosospira and Nitrosomonas-were promoted in the DOC/N 0.9-7.3 treatments and inhibited in the DOC/N 12.3 and 17.3 treatments. According to the results of weighted gene co-expression network analysis (WGCNA), it is likely that the soil nitrification was promoted by Acidobacteriaceae (Subgroup_1_uncultured), Rhizomicrobium, Massilia, uncultured Nitrosomonadaceae and Nitrospira but inhibited by Trichococcus.