DNRA and ANRA-centered microbial mechanism of biogas slurry on soil nitrogen leaching: An indication from a laboratory study

Biogas slurry has ammonia (NH4+-N) abundance and is applied in a major production region, Southwest China. This study compared the consequent environmental risk of nitrogen (N) leaching in two major soils, yellow soil and calcareous soil, in Southwest China, and investigated underlying microbial mechanisms. Biogas slurry was applied to soil columns packed with yellow soil and calcareous soil at the rates of 0 to 240 kg N/hm2. Soil N leaching, N contents, and N-related bacteria gene abundances were measured, with their responses to slurry application analyzed through partial least squares-structural equation modeling (PLS-SEM). Nitrate (NO3−-N) dominated in N leaching as a result of soil NO3−-N accumulation and microbial regulation. Nitrification increased yellow soil NO3−-N contents and leaching, however, both were inhibited by dissimilatory nitrate reduction to ammonium (DNRA) and assimilatory nitrate reduction to ammonium (ANRA) in the two soils. Further, NO3−-N leaching was enhanced by biogas slurry in yellow soil by promoting nitrification and preventing DNRA and ANRA; but it was not affected in calcareous soil. Accordingly, yellow soil has higher NO3−-N leaching than calcareous soil. The leaching can be regulated by the DNRA and ANRA in both soils, which were overlooked relative to nitrification but probably reactive to slurry, warranting further exploration. [Display omitted] •Yellow soil has higher nitrate leaching than calcareous soil with slurry application.•Slurry raises yellow soil nitrate leaching via nitrification and nitrate reduction.•Slurry increases calcareous soil nitrate but not the leaching via nitrate reduction.•Nitrification controls yellow soil nitrate leaching but not that in calcareous soil.•Nitrate reduction as DNRA and ANRA regulate both soils' nitrate leaching.