Improving nitrogen retention of cattle slurry with oxidized biochar: An incubation study with three different soils

The application of livestock slurry in soils can lead to nitrogen (N) losses through ammonia (NH₃ ) emission or nitrate (NO₃ ^- ) leaching. Oxidized biochar has great potential to mitigate N losses due to its strong adsorption capacity; however, the effects of oxidized biochar in different soils treated with slurry are currently unclear. Here, we investigated the effect of untreated and oxidized biochar (applied at a rate of 50 kg C m^-3 slurry) on reducing N losses in a laboratory experiment with three different soils (loamy sand, sandy loam, loam) amended with cattle slurry at an application rate of 73 kg N ha^-1 . Oxidized biochar reduced NH₃ emissions by 64-75% in all soils, whereas untreated biochar reduced NH₃ emissions by 61% only in the loamy sand. Oxidized biochar significantly reduced the NO₃ ^- content in the soil solution of the loamy sand in the early phase of the incubation and led to a significantly higher NO₃ ^- concentration in the same soil compared with the slurry-only treatment at the end of the experiment, indicating a significant increase in NO₃ ^- retention in this organic C-poor soil. We conclude that oxidized biochar can reduce N losses, both in the form of NH₃ emission and NO₃ ^- leaching, from cattle slurry applied to soil, particularly in soil with soil organic carbon content <1% and pH <5 (i.e., oxidized biochar can serve as a means for improving the quality of marginal and acidic soils).