Trying this again because my browser crashed
I looked at video 6 and couldn't catch the name of the place in France, so far haven't found anything on Google either. But did I hear/interpret correctly a statement that there's no conversion of ammonium to nitrate below pH7 (neutral)? That's actually not correct, there is nitrification in acidic soils. Quoting from one research article where they apparently identified a new microorganism (hoping I can quote it without crashing this time!)
"Nitrification rates in acidic soils (pH < 5.5), which comprise 30% of the world's soils, equal or exceed those of neutral soils. Paradoxically, autotrophic ammonia oxidizing bacteria and archaea, which perform the first stage in nitrification, demonstrate little or no growth in suspended liquid culture below pH 6.5, at which ammonia availability is reduced by ionization....."
http://www.pnas.org/content/10...
There's a book called Research on Nitrification and Related Processes by Klotz which has pages viewable on Google that says "...Contrary to previous conceptions that nitrification did not occur at extreme pH values, autotrophic nitrification has now been confirmed on soils with pH values from 3 up to 10....."
I looked this up because if I heard right in the video that there's no nitrification below pH7 then that would mean most of our soils (in the east anyway) are not converting NH4 to NO3. Didn't seem right to me.