There doesn't seem to be much explanation in the chart, just that denitrifying bacteria ruin the NO3- and it gets lost to the atmosphere.
Couldn't tell you if there is [NO] gas in the atmosphere.
I wonder how much N2 might get fixed into NH4+ if the air was injected directly into the soil. I remember that injectors were used to inject Nitrogen Gas into the soil. The N gas was 80% by volume.