By Gurbir Dhillon Ph.D.
One of the major long-term goals of the sustainable farming systems is to achieve high crop yields with lower application rates of inorganic nitrogenous fertilizers. Biological nitrogen fixation is one of the major pathways to achieve this goal and promote long-term agricultural sustainability by reducing nitrogenous greenhouse gas emissions and alleviate the overall carbon footprint of crop production systems.
In the biological nitrogen fixation process, certain limited types of microorganisms, such as several species of bacteria, actinomycetes, and cyanobacteria, convert nitrogen gas in the atmosphere to nitrogen-containing organic compounds.
in a symbiotic process, these nitrogen containing compounds plants supply carbohydrates as sources of energy the process to convert organic compounds into nitrogen. An enzyme nitrogenase converts nitrogen gas to ammonia, which in turn, combines with organic acids to form amino acids and proteins.
The enzyme nitrogenase can be destroyed by free oxygen. Thus, it is protected from oxygen inside the root nodules of plants through the formation of a compound known as leghaemoglobin that provides the interior of active nodules with a bright red color. The host plants can use the biologically fixed nitrogen and a portion of it may return to soils as plant residues, and root exudates.
Thus, it becomes available to subsequent crops in rotation. The incorporation of pulses in crop rotations can minimize the overall use of inorganic nitrogenous fertilizers in crop production systems. Biologically fixed nitrogen is less susceptible to loss through volatilization, denitrification and leaching compared to the application of inorganic fertilizers.