What are different ways by which nitrogen in the air reaches the soil?

Most atmospheric nitrogen (N) exists as N2. Plants cannot use N in this form. The main ways this nitrogen enters soil in a plant usable form include:

• N fixation by bacteria
• Lightening caused atmospheric fixation

Fertilizer manufacturers also use atmospheric N when making N fertilizers.

Most of the N is fixated by bacteria, usually in association with a plant. Legumes, like beans, peas and clover, are especially famous for this. The plants provide the bacteria with food and an environment they can live in, and in exchange, they give the plant usable nitrogen compounds.