CHURCHVILLE, Va.—The latest charge against agriculture is that it puts too much nitrogen into the air. Well, the air has always been 78 percent nitrogen, but ecological activists say too much "fixed" nitrogen is floating into the atmosphere from commercial fertilizer and feedlot wastes.
There is roughly twice as much "man-made" nitrogen going into the air these days as 100 years ago. The activists claim the extra nitrogen is acidifying lakes, causing the world's fish catch to decline and threatening the survival of wild plants that fix their own nitrogen.
They worry about a major ecological collapse.
Fortunately, the charges against nitrogen are essentially groundless. A $500 million federal study of acid rain completed in the late 1980s found virtually no linkage with agriculture.
In fact, the study found that acid rain itself was a small and mostly natural problem. It affects only about 4 percent of the lakes and 3 percent of the forests in the eastern United States, where there isn't enough limestone or other natural buffering to offset the natural acidity of most rainfall.
The World's fish catches are declining because we are catching too many fish with our diesel boats, huge trawl nets and electronic fish-finders. (Fishing is the last vestige of man's old hunting-and-gathering existence.)
The world continues to see periodic algae blooms, which look ugly and can "starve" lakes and coastal waters of their nitrogen. Some of the algae blooms are natural, while some result from humans' overfertilizing the water with manure, fertilizers, nitrous oxide from auto exhausts and detergent phosphates.
But they are not a global problem that can be solved in the pages of Scientific American. They are intensely local problems with necessarily local solutions.
Jesse Ausubel, director of the Program for the Human Environment at Rockefeller University in New York, has presented a better perspective on farming and nitrogen.
Ausubel, whose research team recently published its work in the Proceedings of the National Academy of Science, says he can find no evidence that we are overfertilizing the planet.
That's fortunate, he adds, because without chemical fertilizer it would take twice the world's land area to feed a population of 10 billion people.
Scientific measurements cited by Ausubel shed light on farming and nitrogen.
First, the world's oldest experimental agricultural plots, at Rothamsted in England, showed a one-kilogram per hectare increase in annual nitrogen deposition between 1888 and 1966.
The U.S. National Research Council found only questionable and conflicting evidence of any upward trend in nitrogen deposition from 1965 to 1980.
And third, in high-yield farming regions of Europe and the eastern United States, four to eight kilograms of nitrogen were deposited per hectare annually from 1888 to 1925, while (by way of comparison) six to eight kilograms were deposited in the Northeastern United States during the 1980s.
We shouldn't be surprised at the lack of any alarming trends.
Ausubel says that if all of the world's commercial nitrogen fertilizer—80 million metric tons per year—vaporized completely into the air, it would average less than 1 kilogram per hectare over the earth's surface.
Biologists say it generally takes three to 10 kilograms per hectare to alter wild ecosystems.
Of course, the vast majority of the nitrogen from farms doesn't vaporize into the air at all. Ausubel estimates that two-thirds of the nitrogen applied to fields is harvested through our crops.
In fact, Ausubel says, today's farmers are doing a better job of turning fertilizer into crops.
In the low-yield days of the 1960s, Iowa farmers were "mining the soil." They were putting on only 74 percent of the nitrogen they were harvesting in their corn. During the farm-export boom of the late 1970s, high prices led them to put on twice as much nitrogen as they harvested in their corn.
In recent years, Iowa farmers have put on 120 percent to 160 percent of the nitrogen they harvest.
Ausubel's Rockefeller University team is projecting that the world's farmers will need to use twice as much nitrogen in the 21st century in reaping four times today's yield per hectare.
However, the teams says, the amount of nitrogen leaking from the system is more important than how much is being cycled.
Currently, it believes that farmers are losing about 24 million tons of nitrogen fertilizer per year as well as substantial nitrogen tonnage through livestock and poultry manure that isn't collected and applied to the fields.
The Rockefeller team says the leakage can be reduced by confining more livestock and poultry, by more use of conservation tillage (which sharply reduces runoff and leaching) and by using more slow-release fertilizers that are precision-matched (by microcomputer) to the soil type and slope on each square meter of farmland.
The team says the world may also want to improve urban sewage treatment, which currently releases half of its nitrogen into the air and dumps the other half into streams.
In other words, if the world has a nitrogen problem, it needs modest improvements in farmers' nitrogen efficiency and dramatic improvements in urban sewage treatment.
Ausubel foresees that by 2070 the world will have a stable, declining human population, more wildlands than today and, he hopes, far less nitrogen "leaking" into the environment.
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