Tom wants to incorporate more organic practices on his farm. he wants to enrich the nitrogen content of his soil through biological fixation without adding chemical fertilizers. which plants are best suited for this purpose?

There are multiple factors which controls the nitrogen and other nutrients presence in soil for the good growth of plants, one of them is the selection of right kind of plants which fixes nitrogen more efficiently than others.

These are the few plants which are good nitrogen fixing plants such as:

-Lupines, cowpea, fava bean, alfalfa  

-Tall trees such as black alder, black locust and empress tree  

-Shrubs and shrt trees such as autumn olive, Gumi, Siberieam pea shrub, Russion olive and Sea berry

because the light is a great source of energy for the plants to survive. (i hope this )