A survey of biochars: Interactions with dissolved ammonia and nitrate

Research on biochar, a modern agricultural soil amendment with ancient roots, has revealed crop enhancement capabilities. Studies show biochar adds little to soil in the way of essential plant nutrients. Nevertheless, field experiments with poor soils such as in the Amazon Rain Forest and Australia show increased soil fertility after biochar amendments. A full explanation of the mechanism by which biochar increases soil-fertility may result in how biochar influences soil chemistry and soil processes. Prior published field and in-lab studies substantiate the hypothesis that biochar decreases nitrogen (N) leachate from soil, indicating a biochar-N interaction. Although studies have examined individual biochars/N interactions, no study as of yet has systematically surveyed biochars from various production and parent materials. Results of biochar assessment studies may lead to a more complete understanding of the mechanism by which BC enhances soil quality. Our study examined the ammonia (NH4) and nitrate (NO3) sorption potentials of 30+ biochars produced from different production processes and parent materials. We performed both long and short term sorption experiments, where biochars were submerged in NO3 and NH4 solutions. Results indicate that, in general, biochars in the short term do not interact with NO3, but do decrease NH4 dissolved concentrations significantly. The long term experiment indicates that NH4 concentrations were not significantly affected after the initial short term disappearance. While a majority of biochars behaved similarly to the short term experiment in regards to NO3 results, there were exceptions. A fast pyrolysis macadamia nut shell and a slow pyrolysis switch grass biochar reduced NO3 concentrations to effectively non-detectable levels over the course of the long term experiment. The exact mechanism of this disappearance is still under investigation, but no clear feedstock or pyrolysis technique trends were observed. These results provide evidence for biochar-N interaction.
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Kurt Spokas

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