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Soil Science from the Textbook to the Practical: Nitrogen part 1

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This article comes from the NOFA/Massachusetts 2019 May Issue Newsletter

By Noah Courser-Kellerman, farmer at Alprilla Farm in Essex and NOFA/Mass board member

Nitrogen is one of the most important elements in agriculture, a kind of chemical Jekyll and Hyde, an element of twists and turns and contradictions.  It is usually the most limiting nutrient for plant growth in soils, and yet is one of the most abundant elements in the atmosphere. Nothing is more responsible for the problems and successes of industrial agriculture than Nitrogen. How to responsibly manage Nitrogen is a topic that causes many organic farmers to become philosophical, opinionated and at times self-righteous.  Friendly arguments on the subject have been known to become as heated as an unturned pile of manure and straw. And with good reason!

What other substance has such a profound impact on the health of our soil, the nutrition of our food, our financial bottom line, purity of our groundwater, the formation of dead zones in the Gulf of Mexico and beyond, use of fossil fuels, climate change, global inequality and corporate colonialism? In short, the way we understand and use Nitrogen is important not just to the success of this year’s crop but also to our farms’ relationship to the broader environment. Regenerative agriculture hinges on the responsible management of Nitrogen.

Nitrogen is very reactive as an individual element. Each atom can either give up or gain electrons, allowing for a wide range of possible compounds.

But why is nitrogen so important? Without nitrogen, there would be no life as we know it. The building blocks of proteins are amino acids. Amino acids are composed of carbon, hydrogen and oxygen, like sugars and fats, but have an amino group, (NH2)attached to them. Amino acids can be formed long chains in different sequences, forming proteins. Proteins fold in specific ways to carry out the functions of a cell. Chlorophyll, the green compound that makes photosynthesis possible is a bird’s nest like molecule, which uses four nitrogen atoms to hold a magnesium atom at its center. To function properly, chlorophyll molecules are held in a much larger, complex protein structure. Nitrogen is so important for photosynthesis that the first symptom of nitrogen deficiency in plants is yellowing of the leaves, or chlorosis. DNA contains nitrogen, as do many other compounds: ATP that is crucial for metabolism to function, glucosamine found in our joints and the chitin-containing exoskeletons of insects, crustaceans and fungal cell walls, and countless other compounds crucial for cellular function all contain nitrogen.

"The way we understand and use Nitrogen is important not just to the success of this year’s crop but also to our farms’ relationship to the broader environment." -Noah Courser-KellermanFrom air to plant: Nitrogen fixation

Almost 80% of our atmosphere is dinitrogen, or N2, which is two nitrogen atoms tightly bound together with a triple bond. It takes a large amount of energy to break two nitrogen atoms apart. This can’t be done by most organisms. There are three ways that dinitrogen is broken to form other compounds which are usable to plants, or “fixed”. 


Lightning busts apart N2, which combines with oxygen to form nitrogen oxides. These are brought into the soil in rain, where they form nitrates that plants can use. 5-8% of global N fixation comes from lightning. While it is tempting to go out to the field in a thunderstorm with a kite, Benjamin Franklin style, in an effort to side dress your tomatoes, there are some safety concerns. It is also unclear what the NOP has to say on this subject.

Biological nitrogen fixation

Some types of bacteria can break dinitrogen’s bond to form ammonium (NH4+) and then amino acids. The most important group of these bacteria to agriculture are in the genus Rhizobia and form symbiotic relationships with legumes like alfalfa, peas, beans, vetches and clovers. The plants themselves are incapable of fixing atmospheric nitrogen on their own. Rhizobia enter the plant root from the soil and the plant forms a nodule of tissue around the bacterial colony as it forms. The legume feeds the bacteria some of its sugar produced by photosynthesis in exchange for fixed nitrogen. The enzyme used by the bacteria to break dinitrogen’s bond, nitrogenase, can’t work in the presence of oxygen. Legumes make a type of hemoglobin very similar to the stuff used in our blood cells to carry oxygen to sop up oxygen before it can destroy the all-important nitrogenase enzyme. Fixing nitrogen takes a lot of energy. If there is plenty of nitrogen available to the plant from the soil, it might form nodules, but won’t bother to feed the bacteria or protect them from oxygen. You can test the legumes in your field or garden by carefully slicing open a nodule from the roots of a legume. The inside should be pink. The presence of leghemoglobin indicates that the bacteria are doing their job and your legume crop is fixing nitrogen.

Free-living nitrogen fixers in the genus Azotobacter live in soils and break down high-carbon plant residues. They fix a relatively small amount of nitrogen per acre, though some people have tried commercializing them with limited success. They use slime, soil aggregates, and really fast respiration to protect themselves from oxygen.

In the ocean, photosynthetic cyanobacteria are responsible for nitrogen fixation. Some cyanobacteria protect their nitrogen fixing enzyme from oxygen by forming colonies in which some cells have an extra thick wall, do not photosynthesize and are fed by their neighbors in exchange for nitrogen containing compounds, much like a nodule on a legume root. Others live singly, photosynthesizing aerobically by day and fixing nitrogen anaerobically by night.

Bacterial nitrogen fixation is elegant and beautiful. It exemplifies the way that universal problems in nature —like the scarcity of nitrogen compounds from lightning strikes—are responded to with myriad strategies and cooperative ecological relationships.

Industrial nitrogen fixation

The third way exemplifies the power, brilliance and hubristic inability to anticipate unintended consequences of modern science. It can be argued that synthetic nitrogen fixation was the most influential invention of the 20th century. Not the car, not the internet, but synthetic nitrogen compounds. It is claimed (though perhaps heretical to say in some organic circles) that half of the world’s population owes its existence to the availability of synthetic nitrogen fertilizer.

Fritz Haber was a German Jewish chemist born in 1868 whose life serves as a tragic and complex parable of power and the danger that lies where politics, war and science collide. In the early years of the 20th century he developed a process to synthesize ammonia from hydrogen gas and dinitrogen gas. He found that by using a metal catalyst and heating the gasses under 200 atmospheres of pressure and 5000 Celsius, dinitrogen would break apart and combine with the hydrogen to form ammonia, NH3. Once ammonia was produced, it could be easily turned into nitrate forms and many other chemicals. The process was commercialized by a chemist named Carl Bosch at the chemical company BASF. Nitrates are not just fertilizers, but are also needed for the making of gunpowder and explosives.

When World War One began, the supply of the only other source of large amounts of nitrate, guano (fossilized seabird or bat poop), was cut off in Germany. The utility of the Haber-Bosch process not only for agriculture, but the manufacture of munitions immediately became apparent. It is likely that the Haber Bosch process prolonged the war a great deal by allowing Germany to continue fighting for much longer than would otherwise have been possible without a supply of imported guano.

Fritz Haber’s contribution to the war effort was not limited to the making of explosives and fertilizer. He is also known as the father of chemical warfare. For this work, Haber suffered greatly. His wife, a pacifist, committed suicide in opposition to her husband’s role in the first military use of chlorine gas in the Second Battle of Ypres, which killed 67,000 troops. He justified his work developing chemical weapons by stating that “During peace time, a scientist belongs to the world, but during wartime, he belongs to his country.”

After World War I, Haber continued to develop poison gasses for peacetime use in the nascent pesticide industry. Amid growing anti-Semitism, Haber was forced from the country he loved and for which had made such devastating ethical compromises. He died in exile in 1934, a broken man. In what may be the most bitter irony of this story, members of his family would, years later, fall victim to one of the products he helped develop.  This, of course, was an insecticide, a cyanide-based fumigant sold under the brand name “Zyklon” which was used in the extermination camps of the Third Reich. 

After WWII, chemical factories built to make explosives were repurposed to churn out vast amounts of fertilizers. Farmers, enthralled by the idea of a modern, scientific agriculture based on chemicals, steel and oil bought into this new paradigm enthusiastically, and the so-called Green Revolution began. Global nitrogen fertilizer use increased from a few million tons in the 1940s to over 100 million tons today.

Synthetic nitrogen fertilizers, along with other repurposed wartime technologies like DDT and organophosphate pesticides increased food production and enabled global population to grow. Crop rotation with legumes, cover cropping, and careful management of animals and their manure were suddenly obsolete: All one had to do to grow more wheat, year after year, was to apply some nitrogen from a bag! If the plants got sick, chemicals would save them! A shift took place as we began to wield the power of oil, synthetic fertilizers and pesticides. Values of nurture, care and diversity gave way to those of might, dominance and uniformity.

One might even ask: Was the postwar repurposing of killing technologies an example of “swords into plowshares” or a weaponization of agriculture as a whole?

The dominant reductionist approach to agriculture has dramatically increased the amount of nitrogen “in play” in the global system. This has greatly increased our food supply, but with serious consequences to the biosphere. In the next installment, we will explore how nitrogen cycles from the atmosphere to our soils, crops and bodies and back again.  A better understanding of the nitrogen cycle empowers us to make our farming systems more ecologically sound and financially profitable.

If you enjoyed this article be sure to sign up for the full e-mini series here where you’ll be the first to receive the next individual installation of this monthly “Soil Science- From the Textbook to the Practical”.  Or go back and read the first article in the series here.


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