Question

if all nitrogen is absorbed by the plants than where the nitrogen will come from?​

Answer 1

Answer:

Plants can not absorb nitrogen directly from air. Only nitrifying bacteria can convert gaseous nitrogen into nitrites or nitrates in to soil. Plants can absorb nitrate or nitrite from the soil via their root hairs. If nitrate is absorbed, it is first reduced to nitrite ions and then ammonium ions for incorporation into amino acids, nucleic acids, and chlorophyll.  

Answer 2

Answer:

actually there is nitrogen cycle .for more information here is the link