Influence of 13 Biochars on N2O Sources during Rewetting-Drying Cycles.

So far, the effects of biochars on microbial sources of N₂O are not well understood. We tested these effects for 12 biochars prepared from cypress, loblolly pine and grape wood produced at four different controlled temperatures (350, 500, 700 and 900°C), respectively, plus a grapevine Kontiki biochar (600-700°C). The biochars were added (2%) to a loamy sand (4 replicates), pre-incubated (40% WHC, 4 days), brought to 80% WHC and 10% enriched ¹⁵N-nitrate was added. During three cycles of (re)wetting – drying (80 to 40% WHC), N₂O concentrations and ¹⁵N-signatures were analyzed. N₂O emissions increased after water additions and decreased during drying to background values. Each rewetting led to larger emissions than measured in the previous cycle for all treatments including controls. Biochars decreased N₂O emissions compared to the control, especially when produced at higher temperatures and from grape feedstocks. Interestingly, the addition of biochars also changed the isotopic signatures of the emitted N₂O, which was less enriched after addition of biochars. Again, this effect was stronger at higher production temperatures of the biochars and with grape feedstocks. The results point to denitrification as an important source for N₂O emissions. Different biochars had differing effects on emission sources: While chars produced from loblolly pine supported denitrification, grape chars, especially Kontiki, shifted sources more to nitrification. Whether potential capture of NO₃^- by biochars could contribute to this, will be further discussed.

Acknowledgements: This contribution was made possible by the ‘DesignChar4Food’ project (D4F) funded by the BLE and FACCE-JPI (German partners), by FACCE-CSA nº 276610/MIT04-DESIGN-UPVASC and IT-932-16 (Spanish partners), and the USDA-National Institute of Food and Agriculture (Project # 2014-35615-21971; US colleagues) plus USDA-ARS CHARnet and GRACENetprograms. CK gratefully acknowledges funding by DFG grant KA3442/1-1 and “OptiChar4EcoVin” (Hessian Ministry for Higher Education, Research and the Arts).