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Nitrogen glut: Too much of a good thing is deadly for the biosphere
Nitrogen glut: Too much of a good thing is deadly for the biosphere
| Abbreviations in this article CBD UN Convention on Biological Diversity. CO2 carbon dioxide. N nitrogen. N2 dinitrogen (inert nitrogen gas). N2O nitrous oxide. NH3 ammonia. NO, NO2, NOx nitrous oxides. NO3 nitrate. Nr reactive nitrogen. O3 ozone. P phosphorous. PM particulate matter |
Part Two of Ian Angus’s examination of the disruption of the global nitrogen cycle by an economic system that values profits more than life itself.
Part One: Nitrogen Crisis: A neglected threat to Earth’s life support systems
Part One of this article outlined how the metabolic activity of specialized bacteria in soil and oceans drives the nitrogen cycle, by “fixing” inert nitrogen from the air into reactive nitrogen, converting it to forms that plants can use, and eventually returning it to the atmosphere.
As scientists from Germany’s Max Planck Institute explain, the “microbial nitrogen-cycling network” maintained a consistent level of reactive nitrogen in the global biosphere for billions of years.
“There is an astonishing diversity of microorganisms that transform nitrogen, and each of these microorganisms has discrete physiological requirements for optimal growth. As growth conditions in nature are highly variable and seldom optimal, nitrogen turnover by individual microorganisms is bound to be inefficient. However, nitrogen transformations in the environment are carried out by microbial communities that recycle nitrogen more efficiently than single microorganisms. Consequently, very little bioavailable nitrogen escapes to the atmosphere, and the small amount lost as dinitrogen gas is balanced by nitrogen fixation.”[1]
That vital cycle was disrupted in 19th Century Europe, when cities grew so large that the nitrogen and other nutrients consumed in food by the urban population could not return to the land, causing pollution in the cities and reducing soil fertility in the countryside.[2]
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Beware of the N-bomb
Beware of the N-bomb
There are good, and frightening, reasons to closely follow the changes in the nitrogen cycle. We should not be surprised if the effects and costs of disturbing it turn out to be as dramatic as those for the carbon cycle. In addition, greenhouse gas emissions from nitrogen fertilizers are around 3% of global emissions, but they are not visible in greenhouse gas inventories. The abolition or drastic reduction in the use of chemical fertilizers is a pre-condition for a sustainable food system.
In farming, the availability of nutrients, particularly of nitrogen, potash and phosphorus – mostly referred to by their chemical symbols N, P and K – is a major limiting factor. All traditional farming systems have had some strategy for replacing nutrients in the soil. One is to rest the soil and allow a natural re-charge and release of nutrients from the soil and through atmospheric decomposition. Crop rotations with leguminous crops can fix nitrogen from the air and the nutritional demands of the various crops can complement each other. Phosphorous, from deeper layers or bound in the soil, can be ‘mined’ by some crops making it available to others. Nutrients can also come from irrigation water (especially sediments in flood waters), animal manure, human waste, plants, grass and other residues, a plethora of natural organic fertilizers. Farmers have used oil-cakes, feathers, leathers, bone, sea weed and fish as fertilizers. There are even reports that human remains from battlefields and ossuaries have been used as fertilizers. Yet all these methods have some limitations, and in most cases they require a lot of work or other efforts.
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