1)rhizobium bacteria fixes atmospheric nitrogen.
2)bodies of animals and plants contains nitrogen, when these r buried in the ground the nitrogen mixes in the soil, and thus used up by plants.
3)when lightening occurs , high temperature of light converts it into it's oxides, these gets mixed in water and forms rain,when this rain falls on ground the nitrogen in it gets mixed in the soil, and thus plants use it.

hope this helps u ......................... plzz mark it as brainliest..........
2 3 2
1 - From bacteria found in their roots. Eg- Rhizobium.
2 - Ur answer is attached!! Prefer this chart!!

Hope it helps ^_^ Mark as brainliest!!
Apologising evrytime wouldn't do ...And again warning too...That not fair..I didn't copy !!
You were right ...@Divyankasc
it should be refer this chart not prefer this chart xD lol
Its a real shame that mods on brainly don't respond