Nitrous oxide

Nitrous oxide (N2O) is a compound of oxygen and nitrogen that can be a product of the reaction that occurs between nitrogen and oxygen during fossil fuel combustion. It is also a major greenhouse gas and air pollutant. Considered over a 100 year period, it has 298 times more impact per unit weight than carbon dioxide. Nitrous oxide also destroys stratospheric ozone, which protects the planet from harmful ultraviolet rays.

Since the year 1750, nitrous oxide levels have risen 20 percent – from below 270 parts per billion (ppb) to more than 320 ppb.

Nitrous oxide, fertilizers, and climate change
A 2012 study published in Nature Geoscience uses nitrogen isotope data to identify the fingerprint of fertilizer use. The researchers say the method proves that increased fertilizer use over the past 50 years is responsible for a dramatic rise in atmospheric nitrous oxide.

Since the year 1750, nitrous oxide levels have risen 20 percent – from below 270 parts per billion (ppb) to more than 320 ppb. Not surprisingly, a steep ramp-up in atmospheric nitrous oxide coincided with the green revolution that increased dramatically in the 1960s, when inexpensive, synthetic fertilizer and other developments boosted food production worldwide.

Tracking the origin of nitrous oxide in the atmosphere, however, is difficult because a molecule from a fertilized field looks identical to one from a natural forest or the ocean if you only measure total concentration. But a quirk of microbial metabolism affects the isotope ratio of the nitrogen the N2O microbes give off, producing a telltale fingerprint that the researchers found can be detected with sensitive techniques.

Nitrous oxide and biochar
The March/April 2011 issue of the Journal of Environmental Quality published a study funded by the Foundation for Research Science and Technology involving scientists at Lincoln University in New Zealand, who determined the effect of incorporating biochar into the soil on nitrous oxide emissions from the urine patches produced by cattle. Biochar was added to the soil during pasture renovation and gas samples were taken on 33 different occasions over an 86-day spring/summer period. They found that addition of biochar to the soil allowed for a 70% reduction in nitrous oxide fluxes over the course of the study. Nitrogen contribution from livestock urine to the emitted nitrous oxide decreased as well. The incorporation of biochar into the soil had no detrimental effects on dry matter yield or total nitrogen content in the pasture.

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