(i) It is a process of growing leguminous crops such as soybean, chana, tur dal, etc. are grown first. These plants have nodules in which rhizobium bacteria grow which convert nitrogen into nitrogen compounds which are useful for the plants to make proteins.
(ii) After the harvesting, farmer grows non leguminous plant for which nitrogen is already available in the soil. During growth, these crops absorb nitrogen compounds and thus soil is devoid of them.
(iii) Hence the farmer grows leguminous plants again and thus the cycle continues. This is called as crop rotation.