I have studied in my childhood, just recalled while replying the question asked by SS regarding crop rotation.

Plants can not intake the nitrogen from atmosphere, they can take only if they are converted in Nitrate or nitriete. Rhizobium - the bacteria lives in the roots of peas, beans and other (I don't know what to call it falidar) plants, plays a very important roles in Agriculture as the convert Environmental Nitrogen to its oxide in order to easy intake of plants.

Replying to [Deepali]:

Dear Ms. Deepali,

They are the legume crops that can fix the free N in the air to their roots in the soil..

Quoting from [yarenimex]:


Replying to [Deepali]:


Dear Ms. Deepali,


They are the legume crops that can fix the free N in the air to their roots in the soil..

This is one of the reasons that many people plant legumes and at a certain point turn them under.  It is a very good way of improving the soil.  It is sometimes called "green manure".

Replying to [Deepali]:

Hi Deepali et al.,

Just remembered that something similar is done in waste water that requieres more nitrogen to be properly purified. Nitrosomonas and nitrobacter get rid of the nitrogen in the water, but when they are done, there might still be other nutrients that have to be eliminated. In this case you can introduce "azolla" algae, and they fix the needed nitrogen form the air to allow the purification process to continue.

Germex
P.S. Would love to see some discussion in the water recycling and reuse topic! Unless there are people among us who don't need water...