Question

why dont legumes (like peanuts and soybeans) need nitrogen - containing fertilizers?

Explanation:

Legumes form a symbiotic relationship with nitrogen - fixing bacteria (such as Rhizobium). These bacteria convert atmospheric nitrogen (\(N_2\)) into ammonia (\(NH_3\)) which can be used by the plant. So, legumes can obtain nitrogen from this biological nitrogen - fixation process instead of relying on nitrogen - containing fertilizers.

Answer:

Legumes have a symbiotic relationship with nitrogen - fixing bacteria that provide them with nitrogen.