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One Hundred Years of Nitrogen Fertilizer from Fossil Fuels

by Ralph C. Martin

In October 1908, Fritz Haber filed his patent on the “synthesis of ammonia from its elements.” This achievement lead to his 1918 Nobel Prize in Chemistry. He collaborated with an industrial colleague, Carl Bosch, to develop the Haber-Bosch process to manufacture large quantities of nitrogen fertilizer as well as explosives. And thus humans faced another “swords and ploughshares” choice.

The implications of Haber’s relentless tinkering in a lab in Germany, one hundred years ago, have been profound.

Since WWI, agriculturalists have applied the energy-intensive Haber-Bosch process with zeal. In the last century, the curve on a graph showing the exponential growth of nitrogen fertilizer use overlaps closely with a curve showing energy use in agriculture and also with another curve indicating the growth of human populations. What will the impact be as energy becomes limiting?

The Haber-Bosch process achieves a temperature of 1000oC and a pressure of 1000 atmospheres to manufacture nitrogen fertilizer. Nitrogen gas molecules, in the form of two N atoms locked together with triple bonds make up 78% of our air. Contained heat and pressure split these N atoms apart and tack on a hydrogen atom to each broken bond of N atoms to form NH3 or ammonia. For this transformation we need fossil fuel energy and also natural gas as a source of hydrogen.

In contrast, Rhizobia, lowly bacteria on legume plants (e.g. peas, beans clovers), use enzymes and very little energy in the form of carbohydrate from their host plants to do the same job. Legume plants receive nitrogen from Rhizobia and Rhizobia receive carbohydrates from legume plants. This ancient trade deal or the symbiosis of millennia is ours to exploit and our example of civility.

In 1798, the dour Reverend Malthus warned that if our human population increased exponentially, food production would still only increase linearly and the race of “man” could not escape from this law. A century or so later, Fritz Haber appeared to give us the key for our escape. With the generous lubrication of energy this key worked well. Human population, nitrogen fertilizer use, food production and energy use all increased exponentially.

Today, as energy supplies dwindle and as green house gas (GHG) emissions increase from the burning of fossil fuels, excess domestic livestock and excess nitrogen fertilizer, we might do well to heed the warning of Malthus from 2 centuries ago. His warning was a warning after all and not a challenge to act as if biological limits do not apply to modern, scientific people. Science based on ecological realism will serve us more effectively than science based on human hubris and fantasies.

In Europe and China, with relatively high nitrogen fertilizer applications per hectare on conventional farms, organic farms yield considerably less. In North America, organic farms produce about 90 – 95% of the yields of conventional farms and in some African countries organic farm yields exceed those on conventional farms. To date, on a global scale, very low proportions of farms are organic.

Will we be able to feed the world without manufactured nitrogen? Many agronomists argue that we cannot, however they tend to assume that we must continue to produce not only similar amounts of food but annually increasing amounts to backstop growth. Others suggest that relying on the use of legume nitrogen while reducing meat consumption, especially from grain-fed animals in feed lots, might address potential food shortages. Additional approaches are to recycle rather than to waste nutrients (including human sewage with safe guards), relying more on urban gardens (recall the Victory gardens of WW II), farming all productive land near cities and adopting organic methods.

What will a retreat from using manufactured nitrogen mean? Vaclav Smil at the University of Manitoba argues that 40% of people in 2000 depended on nitrogen fertilizer and a more recent estimate by Erisman and others, published in Nature in October 2008, is that 48%, almost half of humanity, depend on nitrogen fertilizer for their food supply.

Today, one third of the energy consumed in agriculture goes for nitrogen fertilizer. Even if human populations do not grow, we are also using nitrogen fertilizer to grow bio-fuel and biomass crops. Thus the demand for nitrogen fertilizer is expected to go beyond the savings from improved efficiencies.

One hundred years ago, the miracle of nitrogen fertilizer helped us to crash through restraining boundaries and more became possible. Under prevalent production methods today, many people owe their lives to it, while fossil fuels decline and GHG emissions increase.

Ralph C. Martin, Ph.D., P.Ag. is the Founding Director of the Organic Agriculture Centre of Canada. Please send comments or questions by phone to 902-893-7256 or by email to oacc@dal.ca.

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Posted July 2009


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