Nitrogen Transformation and Nitrous Oxide Emissions Affected By Biochar Amendment and Fertilizer Stabilizers.

Biochar as a soil amendment and the use of fertilizer stabilizers (N transformation inhibitors) have been shown to reduce N₂O emissions, but the mechanisms or processes involved are not well understood. The objective of this research was to investigate N transformation processes and the relationship to N₂O emissions from biochar amendment and use of the inhibitors. A sandy loam soil was collected from an orchard and incubated with 10% water content (field capacity ~17%) at 25^oC and with application of either urea or urea and ammonium nitrate (UAN). Agrotain® Plus or Ultra (urease inhibitor) and N-Serve® 24 (nitrification inhibitor) were applied at recommended rates with fertilizer. Another potential N transformation inhibitor potassium thiosulfate (KTS) at 0.25-1:1 K₂O/N ratio (w/w), and biochar at 1% (w/w) were also tested. Nitrogen transformation, N₂O emission, and soil pH were monitored for five weeks.  The Agrotain® products, N-Serve®, and biochar were all effective in reducing N₂O emissions. Effective N₂O emission reduction by KTS was only significant at a high ratio (1:1 K₂O/N, w/w). Soil pH corresponded well to urea hydrolysis and nitrification processes. Biochar did not appear to affect either urea hydrolysis or nitrification, but resulted in significantly lower nitrite (NO₂^-, an intermediate product of nitrification) concentrations compared to no biochar amendment. The N₂O emission was highly correlated with the NO₂^- concentration in soil. The inhibitors suppressed the N transformation processes, but their activities were limited to a few weeks after application. This research provides some information for better understanding of how biochar and fertilizer stabilizer can be utilized to mitigate N₂O emissions and/or develop effective N management strategies.