In order to maintain soil fertility you have to add nutrients
back into the soil that plants have used. This could be done by
using organic methods, or by using fertilizers. The amount needed
depends on the type of plant that is being grown and the level of
depletion in the soil
The main use of a leguminous plant is to restore the fertility
of the soil. It is done so by the help of nitrogen fixing bacteria
found in its root nodules.