The Dark Side Of Inorganic Fertilizers And Greenhouse Gases

The use of inorganic commercial fertilizers has become increasingly common in the last century, with the global agri-food system relying on synthetic nitrogen (N) fertilization to increase crop yields. However, this has come at a cost: the manufacturing and application of fertilizers have a significant emissions toll, contributing to the growing problem of greenhouse gas pollution. The production of synthetic nitrogen fertilizers alone accounts for approximately 2% of the world's energy use, with the process emitting greenhouse gases such as methane and carbon dioxide. The application of fertilizers on fields further contributes to emissions, with crops only taking up about half of the nitrogen they receive. The over-application of fertilizers is a common practice in agriculture, leading to damaging consequences beyond greenhouse gas emissions, such as nitrate pollution and eutrophication. While fertilizers have played a crucial role in boosting crop production, addressing their environmental impact is essential to mitigate their contribution to climate change.

Nitrous oxide emissions

Nitrous oxide (N2O) is a major greenhouse gas that contributes to global warming. It has a warming effect 300 times more potent than carbon dioxide. Nitrous oxide emissions have increased significantly due to human activities, particularly agricultural practices.

The use of synthetic fertilizers in agriculture is a significant contributor to nitrous oxide emissions. When synthetic fertilizers are applied to fields, they increase the amount of nitrogen available to microbes in the soil, which then convert it into nitrous oxide. This process is known as the nitrogen cycle. The over-application of fertilizers, common in modern agriculture, further exacerbates this issue.

According to a study by the University of California, Berkeley, the increased use of fertilizers over the past 50 years is responsible for a 20% rise in atmospheric nitrous oxide since the Industrial Revolution. The study also found that nitrogen-based fertilizers stimulate microbes in the soil to convert nitrogen into nitrous oxide at an accelerated rate.

Agricultural practices, including the use of synthetic fertilizers, account for about 12% of man-made greenhouse gas emissions, according to the International Panel on Climate Change (IPCC). This percentage can increase to 24% when considering land use and change activities. The production and use of synthetic nitrogen fertilizers alone contribute approximately 2% of global energy use and 2.1% to 2.4% of global heat-trapping gas emissions.

Reducing nitrous oxide emissions from agricultural practices is crucial. Experts suggest that using fertilizer more efficiently is key. This includes determining the right amount to use and the optimal time for application. Switching to water-efficient technologies, such as drip irrigation, can also help reduce nitrous oxide emissions by slowing down the release of nitrogen. Additionally, transitioning to organic production methods and utilizing compost, cover crops, and conservation tillage can decrease the need for synthetic fertilizers while improving soil fertility.

Ammonia manufacturing

Ammonia is a nitrogen-containing compound that plants can absorb from the soil. It is the second-most commonly produced chemical in the world, used in huge quantities as a very effective fertilizer. The Haber-Bosch process is the most common method of ammonia synthesis, which involves combining hydrogen and nitrogen gas over an iron catalyst, at high temperatures and pressures. This process uses fossil natural gas, which leads to 2.6 metric tons of life cycle greenhouse gas (GHG) emissions per metric ton of ammonia produced. With ammonia being the second most produced chemical in the world, its production accounts for approximately 2% of worldwide fossil energy use and generates over 420 million tons of CO2 annually.

The hydrogen used in the Haber-Bosch process is often derived from natural gas, coal, or oil through processes that release CO2. According to a 2013 report, CO2 emissions from hydrogen production account for more than half of those from the entire ammonia production process. In total, every NH3 molecule generated releases one molecule of CO2 as a byproduct.

To reduce the carbon intensity of ammonia synthesis, researchers are exploring the use of renewable energy sources and industrial by-products. For example, ammonia synthesis at a wind farm could help solve the problem of intermittency in renewable energy sources. Similarly, a device under development in MacFarlane's lab is about the size of a cell phone and can synthesize ammonia for fertilizer on a small scale, eliminating the need for transport.

Overuse of fertilizers

The overuse of fertilizers has led to an environmental crisis in many parts of the world. Improper use of fertilizers has a detrimental effect on terrestrial, marine, and freshwater ecosystems. This includes soil nutrient depletion, soil acidification, eutrophication, nutrient runoff, and reduced biodiversity.

Fertilizers are essential for modern agriculture, boosting food production and replenishing essential nutrients in the soil, such as nitrogen, phosphorus, and potassium. However, their overuse and mismanagement have resulted in significant environmental challenges. The global agri-food system relies on synthetic nitrogen fertilization to increase crop yields, but the use of synthetic nitrogen fertilizer is unsustainable. The production of synthetic fertilizers is energy-intensive, often relying on fossil fuels, and contributes significantly to greenhouse gas emissions.

Nitrogen-based fertilizers, in particular, are a major source of greenhouse gas emissions. When applied to soil, they release nitrous oxide, a greenhouse gas nearly 300 times more potent than carbon dioxide. While nitrous oxide accounts for only a small fraction of worldwide greenhouse gas emissions, it has a disproportionate impact on warming the planet. The manufacturing and transportation of synthetic fertilizers also contribute to emissions.

The over-application of fertilizers is a common practice in global agriculture. Researchers have found that two-thirds of emissions from fertilizers occur after they are spread on fields, emphasizing the impact of overuse. To address this issue, interventions are needed to reduce fertilizer use without sacrificing crop yields. This includes improving nitrogen management, using slow-release fertilizers, changing the timing of fertilizer application, and utilizing sensors to monitor nutrient absorption by plants.

By implementing a combination of technological and policy solutions, it is estimated that emissions from the fertilizer sector could be reduced by up to 80% by 2050. This includes interventions at both the production and use phases, such as improving nitrogen-use efficiency and decarbonizing fertilizer production.

Nitrogen-based fertilizers

The production of synthetic nitrogen fertilizers alone accounts for approximately 2% of the world's energy use. The most prevalent GHG emissions from nitrogen fertilizers are in the form of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2), accompanied by high emissions of ammonia (NH3). Agriculture is responsible for more than 80% of anthropogenic N2O emissions and 70% of anthropogenic NH3 emissions, which originate predominantly from the application of inorganic fertilizers and livestock manure.

The application of nitrogen fertilizers is the most important factor contributing to direct N2O emissions from agricultural soils. The average application rates of synthetic nitrogen fertilizers for wheat and maize in Chinese croplands during the 2015-2017 period were substantial, at 222 and 197 kg ha-1, respectively. The total consumption of synthetic nitrogen on these crops was 12.63 Mt year-1.

Intervention technologies at both the production and use phases could significantly reduce global greenhouse gas emissions from synthetic nitrogen fertilizers. For example, increasing nitrogen-use efficiency and decarbonizing fertilizer production are effective strategies to reduce emissions. Additionally, improving farm practices, such as better nutrient management and reducing over-application of fertilizers, can help mitigate GHG emissions and have positive economic and environmental impacts.

It is important to note that while nitrogen-based fertilizers contribute to greenhouse gas emissions, they are also crucial for the global food supply chain and sustaining our growing population. Researchers suggest that scalable technological and policy solutions are needed to reduce fertilizer emissions while maintaining food security.

Greenhouse gas footprint

The use of inorganic commercial fertilizers has significantly contributed to greenhouse gas pollution. The global agri-food system heavily relies on synthetic nitrogen (N) fertilizers to increase crop yields. However, their overuse has introduced an environmental crisis in many parts of the world. The manufacturing and application of fertilizers have a substantial emissions toll, with agriculture being responsible for a large portion of anthropogenic non-CO2 GHG emissions.

The production of synthetic nitrogen fertilizers alone accounts for approximately 2% of the world's energy use, with ammonia manufacturing contributing between 1% and 2% of worldwide carbon dioxide emissions. The process of creating ammonia, which plants absorb from the soil, involves high temperatures and pressures, emitting greenhouse gases such as methane and carbon dioxide.

Fertilizers also produce greenhouse gases after being applied to fields. Nitrous oxide, a potent greenhouse gas, is released into the atmosphere when microbes in the soil break down the excess nitrogen. While nitrous oxide accounts for a small fraction of worldwide greenhouse gas emissions, it has a significantly higher warming potential than carbon dioxide.

The over-application of fertilizers is a common issue in global agriculture, and improving farm practices to ensure better nitrogen management is crucial for reducing emissions. Additionally, the use of organic fertilizers instead of chemical fertilizers has shown potential in reducing specific types of GHG emissions, such as nitrous oxide.

According to a 2022 study, the synthetic nitrogen fertilizer supply chain was responsible for 2.1% of global heat-trapping gas emissions, and efforts are being made to reduce emissions from the fertilizer sector. Researchers from the University of Cambridge found that emissions from the fertilizer sector could be reduced by up to 80% by 2050 through a combination of technological and policy solutions.

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