Biochar Type and Factors Affecting N Transformation, Ammonia Volatilization, and Nitrous Oxide Emissions.

Soil amendment with biochar has shown the potential to improve nitrogen (N) availability for plant uptake and reduce environmental losses via ammonia (NH3) and nitrous oxide (N2O) emissions. There are still many unknowns on how biochar type and soil conditions affect N dynamics and processes associated with these N losses. The aim of this study was to determine effects of biochar type and soil conditions on N transformation and volatilization losses. Laboratory incubation experiments were conducted with urea application rate at 100 mg/kg and four biochar (coconut shell, pine bark/wood chips, wheat midds, and softwood feedstock) amendments in a sandy loam soil under a range of soil temperature and soil moisture conditions. Nitrogen transformation, NH3 volatilization, and N2O emissions were monitored for over 5 weeks. In general, urea hydrolysis occurred immediately following application. Nitrification occurred in 3 days and it was a dominant process. No significant effect of biochar on N transformations was observed. Among the tested biochar materials at 1% (w/w), only coconut shell biochar reduced N2O and NH3 emissions by 22% and 40%, respectively; additional 20% reduction of N2O emissions was observed when the biochar rate increased to 2%. Soil moisture from 5% to 20% (w/w) greatly increased the N2O emissions, but reduced NH3 emissions. Nitrification process was much slower in dry soil (5%, w/w). From 10 to 45 °C, the highest level of N2O emissions occurred at 25 °C, while the highest NH3 emission occurred at 45 °C. Nitrification was much faster at 25 °C, with a much higher nitrite concentration than at 10 or 45 °C. The results suggest that there is a great need to examine the correlations between biochar properties and N losses to define effective materials and develop nitrogen management strategies.