Nitrous oxide emission reduction with greenwaste biochar: comparison of laboratory and field experiments

We compared (i) nitrous oxide (N₂O) fluxes from a 9‐month field experiment established on a temperate, newly sown, intensively managed meadow using automated chambers with fine time resolution, and (ii) fluxes measured at several occasions throughout the experiment under controlled laboratory conditions. Twenty tonnes dry matter ha⁻¹ greenwaste biochar were added to three plots and compared with three control plots. Cumulated N₂O field measurements revealed a reduction of 21.5% in the plots with biochar. The reductions for samples where the biochar was added at the beginning of the experiment in the field and samples which were collected each month and measured in the laboratory were in the same range (11.4–39.2%). Emission reductions from laboratory incubations when biochar was freshly mixed with soil in the laboratory were about twice as large (46.5–58.0%). Our results indicate provisionally that, at our site, biochar controls N₂O emission through its capacity for reducing NO₃ ⁻ availability to denitrifiers, with the efficiency being related to the effectiveness of mixing of biochar in soil.