Nitrogen dynamics after slurry application as affected by anaerobic digestion, biochar and a nitrification inhibitor

Animal manures are valuable multi-nutrient fertilizers, but their short-term nitrogen (N) use efficiency (NUE) by plants is low, bearing the potential of harmful N losses to the environment, such as nitrate ( ) leaching. To develop strategies to increase the NUE of cattle slurry, a comprehensive understanding of slurry N dynamics in the soil–plant system is needed. In a 57-day microcosm experiment in the greenhouse, we assessed the effect of different slurry treatments on slurry N turnover in the soil and its uptake by ryegrass (Lolium multiflorum var. Westerwoldicum). Employing a two-factorial design, 15N cattle slurry (SLU), 15N anaerobically digested cattle slurry (SLA), and 15N anaerobically digested cattle slurry plus biochar (SLA+) were combined with and without the nitrification inhibitor 3,4-dimethyl-1H-pyrazole monophosphate (DMPP). As references, a mineral fertilizer (MIN) and an unfertilised treatment (N0) were included. The 15N recovery, hence NUE, in plant biomass was higher for SLA than for SLU, while recovery in soil at 55 days after set-up showed an opposite trend, with over 45% of N from SLU still being recovered in soil. DMPP and biochar only marginally affected NUE and fertilizer N recovery in soil. Although 15N recovery in soil was highest for SLU, residual N leaching from SLU was low (