Ecology — UPSC Mains Model Answer

Nitrification converts ammonia first to nitrite via Nitrosomonas bacteria, and then to nitrate via Nitrobacter. This two-step aerobic process is critical for making nitrogen available to plants in the nitrate form, which is the preferred uptake form for most crops. Disruption of nitrification — through waterlogging or acidification — directly impairs soil productivity.

Denitrification by bacteria such as Pseudomonas denitrificans converts nitrate back to nitrogen gas, returning it to the atmosphere. Crucially, this process is favoured under anaerobic (oxygen-deficient) conditions, not aerobic ones. Waterlogged soils and poorly drained agricultural fields accelerate denitrification, causing nitrogen loss and reducing fertiliser efficiency.

Anammox (anaerobic ammonium oxidation) uses nitrite as an electron acceptor to oxidise ammonium, producing nitrogen gas under strictly anaerobic conditions. Discovered relatively recently, anammox bacteria contribute substantially to oceanic and wetland nitrogen loss. This pathway is now exploited in wastewater treatment to remove nitrogen without requiring organic carbon.

Excessive nitrogen inputs from synthetic fertilisers disrupt natural cycling, causing eutrophication and nitrous oxide emissions — a potent greenhouse gas. Integrated nutrient management policies, promotion of biological nitrogen fixation, and precision agriculture are essential tools for balancing productivity with ecological integrity.