From Macro to Micro and Back

What do Impossible Burgers, high-powered explosives, the Green Revolution, the air we breathe, and humble beans all have in common? All of these use nitrogen in unique combinations that change our lives. Let’s explore how these very small atoms and molecules affect our world.

Atmospherically speaking

We live in a sea of air. Take a deep breath. Most of what you inhale is nitrogen gas. It makes up 78% of the atmosphere. Yet, unlike the oxygen in the air that is very reactive and loves to combine with all manner of things, nitrogen is fairly resistant to change.

Why? Nitrogen atoms always occur as two partners, N2, bonded very tightly together. Pulling them apart takes substantial amounts of energy, making nitrogen a rather inert material.

How do these partner atoms part ways in nature and form new partnerships that make life on Earth possible?

Nitrogen is an essential nutrient for plants, but it is not readily available in the air or soil. However, there’s a microscopic hero performing atomic miracles: bacteria. Nitrogen-fixing bacteria are able to convert atmospheric nitrogen into a form that plants can use. This process is called nitrogen fixation. Legumes (think beans, peas, soybeans, lentils, etc.) have special nodules on their roots where nitrogen-fixing bacteria can live. These nodules provide the bacteria with a safe place to live and access to food from the legume plant. Bacteria that fix nitrogen often have symbiotic relationships with plants. In return, the bacteria provide the legume plant with nitrogen. This is done by a special enzyme called nitrogenase that is able to break the bond between two nitrogen atoms. These nodules also produce a bright red substance that has become a key ingredient in producing plant-based hamburgers with similar properties to meat.

Meaty plant-based burgers

The Impossible Burger is a plant-based burger that is designed to taste, cook, and look like beef. One of the key ingredients in the Impossible Burger is heme, a protein that is responsible for the meaty flavor and color of beef. This is like hemoglobin in the human body that makes blood red and carries oxygen to all of our cells, but heme is also found in nitrogen-fixing nodules.

The Impossible Foods team realized that they could use heme from nitrogen-fixing nodules to give their plant-based burger a meaty flavor. They developed a process to extract heme from soybean roots, a byproduct of the soybean industry. Extracting heme from soybean nodules is a complex and expensive process, and it would be difficult to produce enough heme to meet the demand for Impossible Burgers on a commercial scale. Instead, Impossible Foods found a new way to engineer plant-based burgers that’s more cost-effective and scalable by developing a process that replicates the heme found in meat from genetically modified yeast.

In traditional farming practices, legumes are planted as cover crops because they fix nitrogen from the air, which can improve soil fertility and reduce the need for nitrogen fertilizer. This helps to suppress weeds, improve soil structure and tilth, and provide food and habitat for beneficial insects and pollinators. There are many different legumes that can be used as cover crops such as clover, alfalfa, vetch, peas, and beans. As a perennial legume, alfalfa produces the most soil nitrogen and can fix up to 200 pounds of nitrogen per acre annually.

Fixing nitrogen on the human scale

Legumes, formed from the nitrogen-containing amino acids that are essential to life, are an important natural, unprocessed, and whole-food source of protein in diverse cuisines around the world. Some edible legumes with the highest protein content are soybeans (36%), lentils (26%), peanuts (26%), tepary beans (24%), chickpeas (19-22%), and black beans (21%).

It requires a lot of energy to break the nitrogen bond and combine them with atoms of hydrogen in water to form ammonia—NH3. In this form, it can be taken up by plants to make chlorophyll, the essential molecule in photosynthesis. It’s what makes plants green and provides for their growth. Natural fertilizers that are rich in nitrogen have been sought out historically by civilizations to sustain their populations, but over time, they faced the prospect of finite natural resources and how to feed their increasing populations.

At the turn of the 20th century, natural sources of ammonia, such as guano and nitrates, were becoming scarce and expensive. Ammonia (NH3) is a crucial component of fertilizers, and there was a pressing need to find a cost-effective method to produce ammonia for agriculture.

As the population increased, there was also a demand for more food. A world war and global pandemic that would decrease the population provided the impetus to develop new sources of nitrogen that helped create chemical weapons and synthetic fertilizers—a curse and a blessing!

As noted, it takes a lot of energy for humans to break the bonds in a nitrogen molecule. When those freed nitrogen atoms found in nitrogen compounds recombine, a large amount of energy is released as heat, and a tremendous amount of gas is produced—an explosion. In particular, a compound of nitrogen and oxygen—a nitrate—provides the explosive punch in gunpowder. But natural deposits of nitrates were found in limited supplies, mainly in the deposits crystallizing from cave walls and the accumulations of bat guano in caves.

With the beginning of World War I, Germany faced a critical shortage of nitrates to create explosive weapons until chemist Fritz Haber came along. Haber was a German national, and his sense of nationalism and patriotism strongly influenced his actions. When World War I broke out in 1914, he saw it as his duty to contribute to the war effort. His development of the Haber-Bosch process for ammonia synthesis was driven, in part, by the need to secure a domestic source of nitrates for explosives production, which was critical for Germany’s military operations during the war.

The primary purpose of the Haber process is to produce ammonia (NH3) from nitrogen (N2) and hydrogen (H2) gases. The Haber process is typically carried out at pressures of 150–200 atmospheres and temperatures of 400–450° Celsius. The nitrogen and hydrogen gases are passed through a reactor containing the iron catalyst. The ammonia gas is then removed from the reactor and cooled.

The Haber process, while crucial to producing synthetic fertilizers, requires substantial energy to convert nitrogen and hydrogen gases into ammonia. This process typically relies on natural gas as a hydrogen source. As a result, the Haber process is closely linked to energy considerations and environmental concerns related to resource utilization and greenhouse gas emissions. Think of the energy sources that are needed to produce such high temperatures and pressures—these are mainly petroleum-based. When their costs are low, fertilizer is inexpensive, but as we see today, their rapidly increasing costs have pushed the price of fertilizer to historically high levels. A good way to think of this is to imagine barrels of oil being dumped on crop fields: The oil is analogous to bags of fertilizer!

This significant production of inexpensive fertilizer partially fueled the Green Revolution. It began in Mexico in the 1920s and spread worldwide, particularly during the 1960s and 1970s. It was characterized by the promotion of certain agricultural technologies, practices, and crop varieties, leading to a substantial increase in crop yields and food production. This agricultural transformation was brought about by:

• The development and introduction of high-yielding crop varieties, particularly for staple crops like wheat, rice, and maize. These new varieties were specifically bred to produce more grains per plant and exhibit greater resistance to pests and diseases.

• Increased use of fertilizers and pesticides to enhance soil fertility and protect crops from pests and diseases. This chemical-intensive approach contributed significantly to increased agricultural productivity.

• Modern farming techniques including mechanization, improved irrigation systems, and efficient crop management practices played a crucial role in boosting crop yields and reducing post-harvest losses.

• Expansion of irrigation, which allowed for more controlled and reliable water distribution to agricultural fields.

The Green Revolution had a profound impact on global agriculture, particularly in countries such as India, Pakistan, and Mexico. These nations experienced significant increases in grain production, which helped alleviate food shortages and reduce hunger.

While the Green Revolution led to increased food production and improved food security, it also raised concerns and controversies. Some of the challenges associated with the Green Revolution include environmental sustainability issues, such as soil degradation and water depletion due to intensive farming practices, as well as concerns about the unequal distribution of benefits among different segments of the population.

Elements like nitrogen are essential down to the level of our DNA; it’s necessary for photosynthesis, which affects every plant on the planet. I hope this journey from the micro to the macro level and back invites you to learn more. Take the first step by making the nutritious and delicious recipe we prepared for you here. Then, explore the nearest green space or farm to observe the superpowers of nitrogen and the rest of the microscopic side of life at work.

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