Nitrogen fixation
Topic: Soils of India: Types, Degradation and Conservation · NCERT: Class 11, Ch 5 "Geomorphic Processes"; Class 12, Ch 3 "Land Resources and Agriculture"
Meaning
Nitrogen fixation turns nitrogen gas from the air into nitrogen compounds that plants can use. In farming, Rhizobium bacteria do this work. They live in small lumps (root nodules) on the roots of legumes, such as pulses. Growing legumes is a natural way to add nitrogen to the soil. When farmers drop legumes from their crop rotations, the soil slowly loses fertility.
Example
In the rice-wheat belt of Punjab and Haryana, pulses have largely been dropped from the rotation. As a result, soil nitrogen is not renewed naturally, and farmers depend heavily on urea.
Don't confuse with
- Chemical nitrogen fertiliser (urea): urea is made in factories and added from outside. Biological fixation adds nitrogen through the bacteria in legume roots, at no cost and without upsetting the soil's nutrient balance.