How fertilizer may be accelerating global climate change and how a new process may help slow it down

Part 1: Why is fertilizer a problem?

It is not often that one can specifically point to a publication that inspired a whole line of research but it is possible in this case. So, just in case you do not make it to the end of this article, I would like to make one important plug to you. Please read the book “The Alchemy of Air” by Thomas Hager. It’s very readable and he does an excellent job of getting the layman past the technical jargon. It tells you about the development of the Haber-Bosch process, possibly the most significant invention you had never heard of. Reading this book inspired my present line of research which I hope to tell you about in this series.

Why is the Haber-Bosch process so important? To answer this question, we need to revisit why fertilizers are necessary in the first place. In a balanced ecosystem, nutrients needed for plant growth are returned to the soil for use by future generations. The rise of modern agriculture, however, meant that the plant material was instead consumed by humans and not returned to the soil. The resulting depletion of soil nutrients meant that it had to be “fertilized” with nutrients from other sources. The most important of these nutrients is nitrogen, a key component of protein. For a long time, there were very few sources of nitrogen that was in a form fit to be added to soil. Natural sources were limited and difficult to handle. Bat and seabird guano (a polite term for droppings) and naturally occurring deposits of nitrates in the west coast of South America were for a long time the only source of nitrogen fertilizer. The South American nitrate deposits were so valuable that Chile and Bolivia waged the “War of the Pacific” over them. These deposits were getting depleted rapidly and so there was a dire need to find a way to find a cheap and widely available source of fertilizer. 

The difficulty in obtaining nitrogen fertilizers may be puzzling to those who might recall from their high school days that the air consists of 79 percent nitrogen and 21 percent oxygen. The reason for this is the nitrogen molecule is so stable that there only a very few plants that are able to “fix” it from the air and make it available for growth. For most plants, it must be in soluble form (“ammoniums” and “nitrates”) so that it can be taken up with the water. And this essentially is what Fritz Haber and Karl Bosch had the genius to figure out: how to take what is essentially a free raw material (nitrogen in the air) and convert it to a valuable product (ammonia, which can then be easily converted to various forms of soluble nitrogen compounds). The Haber-Bosch process is so effective that it has remained essentially unchanged since the 1920s and now accounts for about 99 percent of the world’s soluble nitrogen production (Dawson CJ and Hilton J, Food Policy, 36, S14-S22, 2011). The use of Haber-Bosch ammonia for synthetic fertilizer is so prevalent that it has been estimated that 50 percent of the world dietary protein can be traced back to Haber-Bosch ammonia.

This wonder process comes at a cost however — costs that were not apparent when energy and hydrocarbons were cheap and global warming was an unknown phenomenon. Because of the inherent nature of the reaction, the Haber-Bosch process must be conducted at high temperature and high pressure. This means that large amounts of energy must be consumed in its manufacture. What’s more, the reaction requires a source of very pure hydrogen. Present day methods for producing this hydrogen requires the consumption of large amounts of natural gas or coal AND the release of considerable amounts of carbon dioxide into the atmosphere. All of these together make fertilizers a major consumer of nonrenewable energy sources and a major contributor to the emissions of greenhouse gases. In 2010, it was estimated that 231,300,000,000 kg of CO2 released into the atmosphere may be attributed to fertilizer manufacture.

This is truly a dilemma of epic proportions. The chemical that the world’s food supply depends on is consuming too much energy to produce and is contributing too much to global climate change. Is there a sustainable process that may provide a substitute for it? In the second part of these series, possible alternatives to Haber-Bosch ammonia will be discussed along with one that this author has studied.

(To be continued)

* * *

Dr. Luis F. Razon is a full professor of Chemical Engineering in De La Salle University. He graduated from De La Salle University in 1980 with a B.S. in Chemical Engineering (magna cum laude). He obtained his M.S. and Ph.D. in Chemical Engineering from the University of Notre Dame in Notre Dame, Indiana under the direction of Prof. Roger Schmitz in 1985. Prior to returning to the academe in 2001, he worked in the food industry for 14 years. He has performed research on a variety of topics, primarily chemical reactor stability and dynamics, and over the past four years, biofuels and life cycle assessment. He is the author or co-author of five out of the 18 Scopus-listed publications from the Philippines about biodiesel.