Fertilisers containing nitrogen

Fertilizers containing nitrogen are widely used in agriculture to help plants grow better. Nitrogen is an essential nutrient for plants, playing a vital role in the formation of proteins, DNA, and other important compounds needed for development. However, the way nitrogen fertilizers are made, used, and managed can create serious environmental problems.

The story of nitrogen fertilizers starts with their production. Most synthetic nitrogen fertilizers are made through the Haber-Bosch process. This is a chemical reaction that combines nitrogen gas from the air with hydrogen, often derived from natural gas, under high temperature and pressure to produce ammonia. Ammonia can then be transformed into other compounds like ammonium nitrate, urea, or ammonium sulfate, which farmers spread on fields. This process revolutionized agriculture by making it possible to add large amounts of usable nitrogen to soils, helping support high crop yields that feed the world's growing population.

However, only a portion of the nitrogen applied as fertilizer is actually taken up and used by crops. The rest can be lost to the environment in several ways. One major pathway is leaching. When it rains or when fields are irrigated, excess nitrates (a form of nitrogen readily dissolved in water) can move downward through the soil and reach groundwater. Nitrate-contaminated groundwater is a health risk for humans, especially infants, because it can interfere with the ability of blood to carry oxygen, a condition known as "blue baby syndrome." In rural areas where people rely on well water, nitrate pollution is a major concern.

Another way nitrogen escapes from fields is through runoff. When fertilizers are over-applied or when heavy rains occur, nitrogen can be washed off fields into rivers, lakes, and eventually oceans. This influx of nitrogen fuels the rapid growth of algae in water bodies—a phenomenon called eutrophication. Algal blooms can deplete oxygen in the water, killing fish and other aquatic organisms and creating so-called "dead zones." One of the largest of these is found in the Gulf of Mexico, triggered by fertilizer runoff from farms in the Midwest carried down the Mississippi River. These dead zones not only harm ecosystems but also threaten fisheries and the people who depend on them.

Nitrogen fertilizers also contribute to air pollution and climate change. Some of the nitrogen applied to fields is converted by soil microbes into nitrous oxide, a potent greenhouse gas. Nitrous oxide is about 300 times more effective at trapping heat in the atmosphere than carbon dioxide, contributing to global warming. In addition, ammonia gas can be released into the air from fertilizers, especially if applied improperly. This can lead to the formation of fine particles in the atmosphere that are harmful when inhaled and can also deposit back onto land or water, further contributing to nutrient pollution elsewhere.

The environmental problems caused by nitrogen fertilizers are made worse by inefficient or excessive use. Farmers sometimes apply more fertilizer than crops can use, either because they are seeking the highest possible yields or because they fear under-fertilizing. Poor timing, such as applying fertilizer just before heavy rain, can also increase losses. Better management practices, such as applying fertilizer in the right amount, at the right time, and in the right place—often called the "4Rs" of nutrient stewardship—can help reduce environmental impacts.

Some solutions include using slow-release fertilizers that make nitrogen available to crops more gradually, which can reduce leaching and other losses. Adding nitrification inhibitors to fertilizers can slow down the conversion of ammonium to nitrate, reducing emissions of nitrous oxide and nitrate leaching. Cover crops planted between main crops can take up leftover nitrogen, keeping it in the soil and out of waterways.

Organic fertilizers, like animal manure or compost, also supply nitrogen but generally release it more slowly and may pose similar risks if mismanaged or overapplied. Even with organic sources, managing the amount, timing, and placement is important to prevent environmental harms.

Finally, society faces a challenge: balancing the need to produce enough food for everyone with the imperative to protect our water, air, and climate. This is especially important as demand for food rises with the growing global population and as climate change itself impacts agriculture. Advances in technology, better policies to encourage responsible fertilizer use, and greater awareness among both farmers and consumers are all part of the solution.

In summary, nitrogen fertilizers are an essential tool in modern agriculture, increasing crop yields and supporting global food security. However, when not managed carefully, they can escape into the environment and cause a range of problems—from polluted drinking water and dead zones in lakes and oceans to greenhouse gas emissions that contribute to climate change. Understanding these dynamics and acting to reduce nitrogen losses is critical for protecting environmental health while sustaining robust food production systems.