Nitrogen Cycle

or (v) the Ammonium can undergo nitrification to become Nitrate which is the other plant-available form of N

YuhaoZhou, regarding bacteria and nitrification, my understanding is that various types of bacteria play different roles in nitrification:

1) Certain types of decomposing bacteria (and actinomycetes) decompose detritus which contains organic N, storing the N in their bodies (pretty sure as NH2¹). This is aminization.
2) Next, the decomposing bacteria are eaten by protozoa and nematodes, which have lower N requirements than most bacteria, and they excrete the excess N as ammonia (inorganic N), as explained here.
3) Next, this ammonia reacts with H+ or H2O to form NH4 (ammonium). This took me a lot of digging to figure out, I hope it's right.
4) Finally, other types of bacteria (and actinomycetes), called nitrifying bacteria, convert this ammonium to nitrite, then nitrate.

¹Somewhere along the way the NH2 becomes NH3, and according to this page that process is part of ammonification (so is step 3). I'm not sure whether it's within the decomposing bacteria, or within the protozoa and nematodes after they eat the bacteria.

See lecture #25 slide 5 and 6. What we are asking you to understand is the major roles of soil organisms. With respect to bacteria, Mitchell is correct that they are a diverse group of organisms and play a range of roles including decomposition of SOM.

If you are interested in knowing more, you may wish to consider APBI 342 / FRST 310 Soil Biology next year.

Thx! Your answer is so clear!