Biochar Effects On the Terrestrial N Cycle: An Assessment of Various Biochar Feedstocks.

Biochar is a charcoal made from the pyrolysis of agricultural wastes. It has been suggested as an alternative to sequester C and when added to the soil, it has the potential to influence soil properties such as water holding capacity and aeration and therefore N cycling. However, the mechanisms determining biochar interactions in soils are not well understood. Biochar has two important features that may possibly affect the N cycle: (i) High surface area and negative charges, and (ii) biochar may work as a priming material for microbial activities. We hypothesized that the addition of biochar to the soil will increase NH₄⁺ retention, which will decrease nitrification activities, thereby slowing down  N cycling. This means that a reduced pool of mineral N will be available to the plants. We also hypothesized that these effects will be much more pronounced with the addition of high temperature biochar than low temperature biochar. The objective of this study was to determine if the use of biochar as a soil amendment disturbs any of the N transformations (i.e.: mineralization, immobilization, nitrification, denitrification) and the availability of N to the plants. For this study we set up a pot experiment with nine different biochar treatments (High temperature wood, high temperature walnut shell, high temperature mixed wood biochar, low temperature wood, low temperature pine, microbial inoculated biochar, poultry litter biochar, hog waste biochar (woodchip) and, control (no biochar)) at rates equivalent to 10 tons of biochar per hectare. We measured N mineralization and nitrification rates, mineral N immobilization, N₂O fluxes, as well as mineral N pools.  Preliminary results will be presented and discussed.