During ${\mathrm{N}}_2$ fixation in root nodule to form $\mathrm{N}{\mathrm{H}}_3$ molecule. How many ATP are consumed?

When nitrogen fixation in plants is done with the help of bacteria then it is called biological nitrogen fixation. It can be represented by the following equation in which one molecule of nitrogen produces two molecules of ammonia at the expense of 16 ATP.

${\mathrm{N}}_2+8\mathrm{H}+8\mathrm{e}+16\mathrm{ }\mathrm{A}\mathrm{T}\mathrm{P}\to 2\mathrm{ }\mathrm{A}\mathrm{m}\mathrm{m}\mathrm{o}\mathrm{n}\mathrm{i}\mathrm{a}+{\mathrm{H}}_2+16\mathrm{A}\mathrm{D}\mathrm{P}+16\mathrm{Pi}$

So, only 8 ATP molecules are consumed to form one molecule of ammonia.