Bacteria that make nitrogen from the air, instead of fertilizer
Plants need nitrogen, and much of it reaches fields as factory-made fertilizer such as urea. Some bacteria can make it themselves, from the nitrogen gas that is already in the air. We read a desk study on whether that could replace part of the fertilizer a small grower buys.
The two bacteria. Azotobacter and Azospirillum live freely in soil. Both use an enzyme called nitrogenase to turn nitrogen gas into ammonia. Azotobacter does this even in full air, which is unusual because nitrogenase is damaged by oxygen: it breathes very fast to use the oxygen up, and wraps itself in a sugary layer that slows oxygen down. Azospirillum lives near the roots of cereals and also makes a plant growth hormone and helps free up phosphate.
The catch. It is tempting to grow these bacteria in a tank and “draw off” the nitrogen. The study explains why that does not work as hoped: the nitrogen they fix goes mostly into their own cells, not into the water. Strains that leak ammonia grow more slowly and are overtaken by strains that keep it. So the realistic idea is not to extract nitrogen, but to grow the bacteria and use all of them. As the dead cells break down in soil, the nitrogen is released slowly to plants.
Three ways the study compared
- Concentrate the bacterial mass. The simplest, and the one it recommends for a beginner.
- Capture ammonia gas. It needs a strongly alkaline culture and an acid trap, so it demands gloves, goggles and care. Citric acid is a safer trap than sulphuric acid.
- Ferment and filter into a liquid. This resembles the Brazilian “Super Magro” biofertilizer from the 1980s, made from water, fresh cow manure, cane molasses and wood ash.
What does not travel. The study was written for the dry interior of Brazil and prices things there. Costs, shops and climate do not carry over to Canada. Azotobacter likes 25 to 30 °C, so a Canadian winter is a real obstacle.
Where we stand. This is desk research prepared with the help of an AI assistant. We have not grown anything and we do not know whether it works for us. A fair first test would be small: two identical beds, the same soil, water and light, one with a bought inoculant and one without, measured the same way and repeated.
Prepared with AI assistance from a desk study. Not tested by us.