Why is it that agriculture produces so much nitrogen oxides?
Most pastoral systems are based around establishing a clover driven pasture, so that the clover fixes nitrogen for the pasture as a whole to grow. This nitrogen is converted (via urease, an enzyme) to amonium, which is then converted to nitrite (by nitrosomonas bacteria), then nitrate. The plant can take up N in the ammonium and nitrate forms. If there is more nitrate than can be utilised by the plant, there is the risk of it being lost to the atmosphere or leaching. It is not only the clover that fixes the nitrogen, but the excreta from animals also contains nitrogen, which results in the production of some nitrogen oxide. Although nitrogen fertilisers can have an effect, the animal and clover produce a lot more than will ever be applied with fertiliser (a urine patch from a cow applies about 1000kg/ha of nitrogen, compared to “normal” application rates in fertiliser of 20 to 40 kg/ha).
