Question

Why do farmers use leguminous crops to provide nitrogen to the soil? Explain.

Answer 1

Hint:- Legumes like alfalfa, clover, beans, peas, lentils, tamarind, etc. belong to the family Fabaceae or Leguminosae. Legumes play a key role in the nitrogen fixation in the soil.

Complete step-by-step solution:-
Nitrogen is an important constituent of fertilizers. It is an important element required by plants for
growth and development as it is the component of amino acids, proteins, enzymes, nucleotides, and
nucleic acids. It is picked up as an inorganic compound and is changed into organic forms by plants and
some prokaryotes.
There are three methods for nitrogen fixation: atmospheric, biological and industrial nitrogen fixation.
In biological nitrogen fixation, some algae, symbiotic bacteria and free-living bacteria pick up the
atmospheric nitrogen, reduce it to ammonia, combines with organic acids to form amino acids. It occurs
by two methods- symbiotic and non-symbiotic.
Leguminous plants help in nitrogen fixation as they have symbiotic nitrogen-fixing bacteria in their root
nodules. The best known nitrogen fixing symbiotic bacteria is Rhizobium leguminosarum.
The steps involved in the formation of root nodules are:
o The Rhizobium bacteria divide and redivides and forms a large colony that gets attached to the
root hairs and epidermal cells.
o The root hairs get curled after the invasion of bacteria. Rhizobium forms an infection thread and
reaches to the cortex of the thread through the infection thread.
o The cortical cells are then stimulated to divide more vigorously to form nodules on the root.
o The nitrogen fixation through this method requires the enzyme nitrogenase which requires an
anaerobic condition for its functioning. Leghemoglobin combines with oxygen and protects
nitrogenase.

Note:- So farmers use leguminous crops to replenish the lost nitrogen back into the soil. They cultivate leguminous plants in between the two main crops. This is called crop rotation.