Biochar As a Tool for Nitrogen Management: Increasing Benefits While Reducing Environmental Burdens.

Biochar is a tool to withdraw CO₂ from the atmosphere and convert it into a stable, usable form, i.e. to channel, via carbon farming, C from the atmosphere and the fast terrestrial C cycle into slower cycling C pools. The use of biochar for C sequestration should serve economical value-generating purposes when used in agriculture, in building materials or e.g. paper production, i.e. by using it in in ways that prevent a quick return of C into the atmosphere. C sequestration from the atmosphere is a clear necessity to achieve the 2° or even the 1.5° goal of the Paris agreement (COP21); however, biochar use would clearly offer a larger spectrum of economic incentives which distinguishes biochar use from BE-CCS (bioenergy plus carbon capture and storage), where C sequestration of liquefied CO₂ after biomass burning would only generate costs that make biomass-based energy production even more expensive. However, after ~10 years of biochar research is becomes clear that using large amounts (>2 t ha^-1) of pure biochar without nutrient enrichment in soils does not generate a “return of investment” via yield increases that would be able to “pay” for biochar use. Hence, the environmental benefits associated with biochar use, namely C sequestration, soil organic carbon increase, greenhouse gas emission reductions and nitrate leaching will also not be realized in real-world farming. Recently it was found that biochar shows interesting interactions with nitrogen in its reactive forms such as NO₃^-, NH₄⁺ or organic N. In the talk we will highlight potential future uses of biochar in agricultural systems based on the use of low amounts of biochar as a fertilizer carrier matrix with or without root-zone application or in N-rich organic waste/manure treatment. We show in particular how and when biochar can capture nitrate (i.e. how to promote BNC), demonstrate the positive effect that BNC can have on soil fauna and nitrate protection against leaching in nitrate-polluted soils, and present the results of ¹⁵N biochar field studies on soil N transformations. The latter clearly demonstrated an acceleration of gross nitrification in the presence of biochar, as well as nitrate capture of added ¹⁵N nitrate in biochar particles. Implementing biochar use in surplus N (e.g. manure) management in N-polluted areas, in waste-stream management (composting, manure post-treatment) or as a slowly N-delivering anionic carbon-N fertilizer may open up economically interesting agronomic perspectives to BE-CCS and hence for meeting the 2° goal, by recycling elevated atmospheric CO₂ into anthropogenic usage by smart carbon farming.