Eli5 why plants which need nitrogen from the ground do not take it from the air which is 70% Nitrogen

Question

Eli5 why plants which need nitrogen from the ground do not take it from the air which is 70% Nitrogen

In: 308

Answer 1

Nitrogen, as used by plants, is usually in the form of the nitrate ion. This ion is relatively difficult and expensive to form, so most plants cannot create it from atmospheric nitrogen.