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Can Biochar or Hydrochar application to soils reduce N2O emissions from soils?

Claudia Kammann1, Daniela Busch1, Sebastian Linsel1, Hans-Werner Koyro1, Ludger Grünhage1, Christoph Müller1
1 Institut für Pflanzenökologie, Uni Gießen

V 1.4 in Neueste wissenschaftliche Ergebnisse

08.07.2010, 14:45-15:05, H 8, GEO

When biochar is applied to soils it is crucial to quantify the subsequent fluxes of all greenhouse gases (CO2, N2O and CH4), because any positive C sequestration effect could be diminished, or even reversed, if the emissions of other potent greenhouse gases increase after biochar application. Neglecting N2O emissions may cause considerable misinterpretation of the real C- (i.e. CO2-equivalent )sink capacity of an ecosystem, be it agricultural (Crutzen et al., 2007) or semi-natural (Kammann et al., 2008). On the other hand, if N2O emissions are significantly reduced by biochar application, this would considerably improve the GHG balance of biochar-grown agricultural products.Rondon et al. (cited in Lehmann 2007) reported reduced N2O emissions after biochar application. Since then, more reports of reduced N2O emissions in the presence of biochar followed (Yanai et al., 2007; Spokas et al., 2009 van Zwieten et al., 2009). However, for hydrochar, a less recalcitrant product from a process called hydrothermal carbonization (HTC), no information is available. In our presentation we would like to show various results from soil incubations of different soils with biochar or hydrochar over several months, or with biochar in the presence of plants, e.g. under conditions that strongly favor denitrification. In all conducted experiments, biochar addition generally reduced the N2O emission sum compared to a non-biochar amended control, in particular after mineral-N addition. In one plant-soil experiment biochar reduced N2O emissions significantly better than the same amount (50 t/ha) of compost. Interestingly, CO2 emissions (plant and soil respiration) were not increased with biochar although the plants were significantly larger (in two very different experiments), indicating that biochar was not mineralized. In soil incubations where the biochar-soil mixtures were set to identical water holding capacity values (e.g. 65% of WHCmax) biochar significantly reduced N2O emissions. However, at very low N2O emission rates, N2O emissions were on some dates non-significantly higher with biochar. Hydrochar, in contrast, reduced N2O emissions during the first 4 weeks but tremendously stimulated N2O emissions later. The hydrochar-amended soil exhibited strong fungal growth (basidiomycetes) that were likely involved in hydrochar decomposition and N2O production. Subsequently, the CO2 emissions in the hydrochar mixtures were several hundred percent higher than in the un-amended control. Although it is premature to draw final conclusions it seems that biochar may be better suited to reduce GHG emissions than hydrochar. However, several more "GHG screening" experiments with various combinations (soil types, chars, and plants) and a sound process understanding are needed.

Letzte Änderung 22.06.2010