Biochar-induced N2O emission reductions after field incorporation in a loam soil.

Biochar addition to soils is heralded to reduce N 2 O emissions, but still, the explanatory mechanisms have not been resolved. Moreover, it is uncertain whether N 2 O emission reductions would persist after prolonged biochar incorporation in the field. In this study, we incorporated four biochar types in a loam textured cropland field and intact soil cores were sampled to investigate the physical control of biochar on denitrification after 7 months. During a first incubation experiment, we measured N 2 O emissions from undisturbed and disturbed (i.e. sieved (2 mm) and grounded) soil cores. Both in the disturbed and undisturbed soil cores biochar at water filled pore space (WFPS) of 80% reduced the N 2 O emissions by 50–90%, refuting the hypothesis that biochar exerts an indirect physical control over soil denitrification several months after incorporation. Secondly, we hypothesized that biochar creates denitrification ‘hotspots’ in soil, where complete reduction of N 2 O to N 2 is promoted compared to non-amended soil. In these hotspots biochar particles could act as microlocations with local anaerobic conditions and local higher pH, stimulating in this way complete denitrification. Via the acetylene inhibition method we did not observe a reduction in the N 2 O/(N 2 O + N 2 ) ratio, which could suggest that biochar did not promote the reduction of N 2 O to N 2 . Manipulations likely to promote labile C bioavailability, here either by glucose addition or by soil particulate OM disclosure after disruption of soil aggregates, resulted in the most prominent biochar-induced N 2 O emission reductions. [ABSTRACT FROM AUTHOR]