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By Jeff Danner Jeff has worked in both the chemical and biotech industries and is the veteran of thousands of science debates at cocktail parties and holiday dinners across the nation. In his Common Science blog, Jeff aims to make technological and scientific concepts accessible to all.

Fun with Fritz and Carl

By Jeff Danner Posted July 17, 2011 at 7:38 pm

When I travel around Orange County I am heartened to see all of the farms. If you have been reading my blog you will know that I believe that areas, like ours, with compact towns surrounded by productive fields are going to outcompete suburban sprawl over the coming decades both economically and for quality of life. To preserve that future we need sustainable farms; which begs the question of “what is a sustainable farm?” To me sustainability essentially comes down to fertilizer.
 

If we are going to talk about fertilizers it’s time to meet Fritz Haber (the picture on the top left) and Carl Bosch (the picture on the top right).  Some surveys list Haber and Bosch as the two most influential people of the entire 20th century. Do you know who they are? If you are interested in farms, food, or population growth you should.
 
Fertilizer is generally described using three numbers, maybe 10-10-10, which correspond to the amount of nitrogen, phosphorous and potassium, the three most essential elements which plants need to grow. Phosphorus and Potassium are the easy part since they come from mines so all you need to do is find them and dig them up. The interesting part of fertilizer is the nitrogen. We live our lives bathed in nitrogen. 78% of the air that we breathe is nitrogen. Unfortunately nitrogen in the air consists of two atoms which are tripled-bonded to each other, a configuration which makes it almost completely inert and not useful to plants.
 
For the nitrogen to be available for plants it must first be converted into ammonia (NH3), and then further in to various nitrates. Until the year 1909, essentially all ammonia in the soil came from either nitrogen-fixing plants or, surprisingly, from lightning strikes. (Note to those of you thinking about manure. Cows don’t make new nitrates they just recycle them.) Some plants, like soy beans and alfalfa, accommodate the growth of a type of bacteria called rhizobia in their root systems which “fix” nitrogen from the air by converting it to ammonia. The essential rationale of crop rotation is based on alternating between plants that remove nitrogen from the soil, like corn, and plants which restore nitrogen to the soil like soy beans.
 
The other main source of ammonia in the soil is lightning. (For some details about lightning read Shelter from the Storm). The air near the lightning gets so hot that nitrogen and the water molecules in the air are torn apart into their constituent atoms. When the air cools back down and the atoms recombine into molecules, some ammonia is formed. This process is efficient enough that some areas which higher storm activity have increased soil fertility.
 
Once people understood that ammonia was necessary for plant growth the search for a synthetic route was on. The timing was also critical because the stores of guano (bird poop) which had been extracted during “guano-mania” to use as fertilizer in the 1800’s were nearly exhausted. (See Advice from George Washington for Orange County for more details on guano-mania.)   In 1909 Fritz Haber and Carl Bosch solved the puzzle by reacting nitrogen and hydrogen at high temperature and pressure over a metal catalyst (ruthenium for the truly curious) to make ammonia. Once you have ammonia you can easily make a number of common fertilizers. Ammonia is also an important raw material for explosives, so the two world wars of the 20th century helped to subsidize ammonia plant construction which, in peace time, led to more fertilizer production. Haber and Bosch won the Nobel Prize for Chemistry in 1918.
 
The Haber-Bosch process revolutionized farming in two key ways. Mother Nature converts about 150 million metric tons per year of nitrogen from the air into ammonia via nitrogen-fixing plants and lightning. Today the Haber-Bosch process coverts an additional 100 million metric tons of nitrogen into ammonia, a 40% increase in nitrogen available to the soil meaning that farmers around the world can grow a lot more food. Secondly, now that you could add the nitrogen to the soil yourself, crop rotation was no longer necessary allowing corn or wheat to be grown on the same field year after year. Or, at least, people thought it was no longer necessary. (More on that later.)
It’s hard to overstate the impact that the Haber-Bosch process has had on the world.  From around 1850 through the early 1900’s a typical acre of farmland could produce around 25 bushels of corn per year. After the introduction of synthetic fertilizers coming from the Haber-Bosch process yields of corn have grown steadily to the level of about 150 bushels per acre today.
 
All of this extra available nitrogen drove what has come to be known as the “Green Revolution”. For many decades food supplies grew by leaps and bounds driving unprecedented world population growth from 2 billion in 1960 to nearly 7 billion today.   Given that nitrogen is a yield limiting factor for plant growth, approximately 40% of the population of the world is dependent on the Haber-Bosch process for sustenance.   This is a troubling statistic given that the Haber-Bosch process and the Green Revolution are unsustainable in two key ways.
 
First, the Haber-Bosch process very energy intensive and is dependent on cheap and plentiful natural gas as the raw material for hydrogen. As natural gas supplies become limited synthetic fertilizer becomes expensive and/or scarce. Read any news story about global food prices today and you can start to see this dynamic coming into play.
 
Secondly the “Green Revolution” through its use of synthetic fertilizers slowly but surely depletes the soil of important micronutrients. When plants grow they use a lot of nitrogen, phosphorous, and potassium (we’ll call them the Big Three), but they also use a lot of other elements in the soil, just in smaller amounts. So if you only regenerate your soil with only the big three each season the soil becomes increasingly depleted of other elements and plant yields start to falter. Fertilizer manufacturers noticed this in the mid 20th century and started adding other elements like iron, copper, zinc and molybdenum. This provided some temporary relief. However, the reality is that plants extract on the order of 50-60 elements (generally referred to as micronutrients in agriculture-speak) from the ground all of which need to be resupplied if soil productivity is to be maintained (essentially the definition of a sustainable farm). Adding compost and manure can help to recycle micronutrients, but every time a food product leaves the farm it carries away micronutrients with it which must be replaced.   Particularly effective micronutrient replacers are organic fertilizers made from seaweed. Mother Nature also helps to resupply micronutrients via volcanic activity. Look for increased crop yields in Western Europe over the next couple of years following the eruptions in Iceland.
 
Effective long term management of farms here in the Chapelboro area will need to focus primarily on soil health, fertilizer, and micronutrient supply. Like most things in life, the best answer probably lies in taking a balanced approach. A farm which depends entirely on synthetic fertilizers from Fritz and Carl will eventually exhaust the soil. However, even an organic farm must replace soil nutrients which leave the farm as produce, by bringing in fertilizer from off the farm. Replenishing some nitrogen from a Haber-Bosch plant seems to me to be a reasonable approach.
 
I’ll close with a note of sad historical irony. Fritz Haber was a patriotic German and was also Jewish. During World War I he supported his country’s efforts by building ammonia plants for explosives and conducting research to produce chemical agents for gas warfare. During WWI Haber invented Zyclon B, which ended up being used as the agent in gas chambers in the Holocaust. Haber died in 1934 so he was spared the horror of seeing what became of this invention.
 
For Common Science readers who have been following this blog since I started in April, I have a comment and a question. For the comment, I know that so far I have focuses heavily global issues of energy and food production at the expense of reserving space for local issues. I wanted to let you know that I am getting there. At least for me, discussions of how we should manage our affairs her in Chapelboro flow from an understanding of the origins and limits of fossil fuels and synthetic fertilizers. I’ve covered a lot of this background now and am ready to shift into a more local focus. As for my question I’d love to get some feedback from you on the blog so far. So if you have a question or comment please log in and comment below or shoot me an e-mail at commonscience@chapelboro.com.
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