By Eric Sideman, PH.D.
Ever since humans began to cultivate food, nitrogen has been the most common limit to crop yields. Modern agriculture has answered this limit with synthetic production of nitrogen fertilizers, which has greatly increased global food production and has supported an astonishing growth in the world’s population. However, the environmental problems are just being realized and are not yet being seriously dealt with.
Nitrogen, being a part of DNA, proteins and chlorophyll, is crucial for all life. Nitrogen cycles through living organisms, through the soil and water, and eventually returns to its largest reservoir, the atmosphere. It is the most common component of the atmosphere, making up almost 80%, yet, it is unavailable to plants or animals because of its peculiar chemistry. It exists in the atmosphere in a very stable form (N2) and enters the cycle through living systems only by the initial fixation by bacteria (either free living or symbiotic with such higher plants as legumes). The N2 nitrogen is converted by the bacteria to chemical forms that plants can absorb. The ecosystem is balanced by the stability of nitrogen in the atmosphere that naturally allows only a puny fraction of the reservoir to be fixed at any one time.
Humans have disrupted the natural cycling of nitrogen by burning fossil fuels, growing legumes, and by using nitrogen rich fertilizers. The chief culprit identified by recent studies reported in Scientific American (June and July, 1997) is the industrial fixation of nitrogen gas to make fertilizer. More than half of the nitrogen fertilizer made before 1990 was used during the 1980s.
Traditional farmers provided nitrogen to their crops by enriching their fields with crop residues, animal wastes and human wastes, and by raising legume crops to be plowed into the soil (green manures). A real breakthrough in nitrogen fertilization occurred in the past century with the development of ammonia synthesis. Under high heat and pressure, which of course uses a lot of energy, nitrogen gas and hydrogen gas can be combined to produce ammonia gas. Modern nitrogen fertilizers, such as ammonium nitrate, anhydrous ammonia and urea, are made using ammonia gas. The first ammonia factory was built in Germany in 1913. More recent technical developments allowed cheaper production of ammonia, and the fertilizer industry zoomed ahead.
The ready availability of ammonia and of the nitrogen fertilizers derived from it has effectively eliminated a fundamental restriction on food production. During the 20th century, humanity has almost quadrupled its numbers, and this sudden growth is supported by the food production made possible by nitrogen fertilizer. The fertilizer industry fixes about 80 million tons of nitrogen per year. This will have to increase to support the global population as it zooms to 10 billion during the next century.
Obviously this vast fixation of atmospheric nitrogen leads to a change in the nitrogen cycle, with much more nitrogen pulled out of the atmospheric reservoir. Nitrates from extensive fertilizer use end up in the soil and contaminate ground water through leaching and runoff. Problems range from local health issues such as blue baby disease to global changes. Fertilizer nitrogen that escapes to surface water promotes algal growth and subsequent eutrophication. Nitrous oxide is released into the air. In the low atmosphere nitrous oxide promotes the greenhouse effect, much more so than carbon dioxide does. It also contributes to smog. In the upper atmosphere, reactions of nitrous oxide with excited oxygen contribute to destruction of ozone in the stratosphere.
The Scientific American articles point out that these disturbances receive surprisingly little attention. Carbon dioxide emissions are being reduced and research is supported to continue reduction. A transition away from the use of fossil fuels must eventually happen anyway, because these resources are finite. But there is no way to grow crops without nitrogen, and to grow crops at today’s expected yields per acre to feed the world’s exploding population from a shrinking farm land base takes highly concentrated nitrogen fertilizers. The EPA recognizes the damage caused by nitrous oxides from combustion and has introduced regulations to limit emissions. Cooperative Extension has “Best Management Practices” that reduce fertilizer use and nitrogen leaching and runoff; but not all farmers follow these and no controls exist on the amounts of fertilizers a farmer can use.
An early stabilization of the global population is the best solution to the problems raised by excessive nitrogen fixation. Organic methods of crop production, including crop rotation, using legume green manures, soil conservation, and the recycling of all organic wastes, are management techniques that are needed to reduce the damage that has been done. In land-rich nations these practices can produce enough food to feed today’s population. In land-poor areas nitrogen fertilizers are necessary to maximize production – which leads to devastating environmental disruptions. This is a very strong argument for preserving farm land. Let’s control our population, save our farmland, and farm organically.
Eric is MOFGA’s director of technical services (our “extension agent” You can address your questions to him at the MOFGA office or look for him at the Fair.