Fertilizers: Air Polluters Or Silent Contributors?

Fertilizers are a major contributor to air pollution. Agriculture is responsible for 92% of volatile ammonia emissions (NH3), with the use of nitrogen fertilizers contributing to 17% of these emissions. The production of artificial fertilizers has skyrocketed from 20 million tons in 1950 to nearly 190 million tons today, with about a third of them being nitrogen-based. While fertilizers are essential for food production, their overuse and mismanagement can lead to environmental and health issues. For example, excess nitrogen from fertilizers can cause an oxygen-less dead zone in water bodies, and ammonia emissions can react with other pollutants to form fine particulate matter (PM2.5), which is harmful to cardiovascular and respiratory health.

Nitrogen-based fertilizers are a major cause of air pollution

Synthetic nitrogen fertilizers, widely used in modern agriculture, are designed to be readily available to plants. However, when not fully utilized by crops, this nitrogen can be lost from farm fields, negatively impacting air and water quality. This excess nitrogen contributes to the formation of ground-level ozone, higher amounts of greenhouse gases, and the thinning of the protective ozone layer. It is also associated with acid rain, which has detrimental effects on aquatic ecosystems and drinking water sources.

The production of synthetic fertilizers also contributes to air pollution, as the process involves petroleum or natural gas, often derived from fracking. The introduction of synthetic nitrogen and other pollutants into the atmosphere during production further exacerbates environmental degradation and public health issues such as asthma.

The impact of nitrogen-based fertilizers on air pollution is evident in California, where researchers from the University of California, Davis, found that agricultural contributions to nitrogen oxide (NOx) pollution may be significantly underestimated. While NOx pollution is typically associated with energy production and vehicle emissions, fertilizer use on crop fields is a significant contributor. The California Air Resources Board (CARB) estimated that only 3.8% of NOx air pollution originates from croplands, but researchers suggested the actual contribution could be as high as 20 to 51%.

To address these issues, advocates urge farmers to reduce their dependence on soluble, synthetic nitrogen fertilizers and adopt insoluble soil amendments that support soil biology and provide plants with nutrients in a more sustainable manner. Additionally, the development of tools to facilitate fertilization decisions and precision farming techniques can help enhance nitrogen uptake by plants, reducing nitrogen losses to the air.

Fertilizer production has increased from 20 million tons in 1950 to 190 million tons today

Fertilizers are a significant contributor to air pollution. Agriculture is responsible for 92% of volatile ammonia emissions (NH3), with the major contributor being livestock and manure management and application (64%). The use of nitrogen fertilizers accounts for 17% of ammonia emissions. These emissions react with other pollutants like nitrogen oxides and sulphur dioxide to form particulate matter (PM2.5), which is harmful to cardiovascular and respiratory health.

The correlation between fertilizer usage and air pollution is evident in China, where a 1g nitrogen increase in fertilizer corresponds to a 0.55 μg/m³ rise in PM2.5 concentrations. Additionally, rice and corn crops tend to worsen air pollution, while the impact of nitrogen fertilizer on wheat is less clear.

The global consumption of chemical fertilizers has witnessed a substantial increase over the decades. In 1965, the consumption stood at approximately 46.3 million metric tons, which rose to about 187.92 million tons in 2022. This massive surge in fertilizer usage, from 20 million tons in 1950 to 190 million tons today, has undoubtedly contributed to the escalating air pollution levels globally.

Nitrogen fertilizers constituted the lion's share of global consumption in 2022, accounting for around 58% of the total. This is particularly concerning given that nitrogen deposited on sensitive habitats, such as peat bogs, can have detrimental effects on the growth of certain plant species. Moreover, nitrogen leaching through soil and surface runoff can contaminate watercourses, causing harm to plants, animals, and water quality.

To address the issue of air pollution caused by fertilizers, governments and organizations worldwide are taking action. For instance, the UK government has proposed options such as stabilizing solid urea fertilizers with a urease inhibitor to slow down the conversion to ammonium and restricting the spreading of solid urea fertilizers to specific periods. These measures aim to reduce ammonia emissions and mitigate their harmful effects on human health and the environment.

Ammonia emissions from fertilizers are harmful to human health

Fertilizers are a significant contributor to air pollution. Agriculture is responsible for 92% of volatile ammonia emissions, with livestock and manure management and application being the major contributors (64%), followed by the use of nitrogen fertilizers (17%). The remaining 19% of ammonia emissions are caused by other sources, including oceans, biomass burning, crops, and fossil fuels.

Ammonia emissions from fertilizers have been shown to have harmful effects on human health. When released into the atmosphere, ammonia reacts with other pollutants, such as nitrogen oxides and sulfur dioxide, to form fine particulate matter (PM2.5). This particulate matter is about 1/30th the width of a human hair and can penetrate deep into the lungs, causing respiratory issues and long-term illnesses such as Chronic Obstructive Pulmonary Disease (COPD) and lung cancer.

The health impacts of exposure to ammonia and PM2.5 can include reduced lung function, irritation to the throat and eyes, and increased coughing and phlegm expulsion. Recent studies have also indicated a potential link between agricultural ammonia emissions and the early onset of asthma in young children.

The impact of fertilizer use on air pollution is time-sensitive and varies across different crops. For example, rice and corn crops tend to exacerbate air pollution, while the effect of nitrogen fertilizer on wheat is less clear. Additionally, while nitrogen fertilizer contributes to higher levels of PM2.5 and SO2, it leads to a reduction in ozone concentrations.

To protect human health and the environment, it is crucial to reduce ammonia emissions from fertilizer use. This can be achieved through improved manure storage techniques, such as using deep, capped pits, and adopting precision farming practices to enhance nitrogen uptake by plants, reducing ammonia losses to the air. Governments and organizations are working to address this issue, with consultations and policies aimed at reducing ammonia emissions from fertilizers and improving air quality.

Fertilizers can cause excess nitrogen in the soil, damaging plant growth

Fertilizers are substances or materials added to the soil to promote plant growth. Most fertilizers contain nitrogen, phosphorus, and potassium. Nitrogen is an essential nutrient for the growth of every organism on Earth. However, plants cannot use the nitrogen gas that makes up about 78% of the air we breathe. Instead, they require nitrogen compounds from the soil, which can be produced naturally or provided by fertilizers.

Excessive nitrogen application can lead to soil acidification and worsen the soil environment, ultimately damaging plant growth and yield. This is supported by a field experiment conducted in China, which revealed that excessive nitrogen fertilization had a negative effect on banana growth and soil fertility. Similarly, a study by Qiao et al. (2012) found that yield reductions in crops with high nitrogen fertilization were caused by physiological disorders associated with excessive nitrogen uptake and soil degradation.

Furthermore, excess nitrogen in the soil can leach into water sources, contaminating drinking water with nitrate. Consuming water with high nitrate levels can pose health risks, especially for those using public water supplies and private wells in areas surrounded by farmland.

To address these issues, scientists are working on improving nitrogen use efficiency in agriculture. This includes promoting the growth of naturally occurring soil nitrogen-fixing bacteria and adopting practices such as drip irrigation, reduced tillage, and the use of cover crops. These measures aim to reduce the environmental impact of excess nitrogen while maintaining high crop yields.

More careful application of fertilizers can reduce air pollution

Fertilizers do contribute to air pollution, and more careful application of fertilizers can help to reduce this.

Nitrogen-based fertilizers, in particular, have been found to negatively impact air quality. When nitrogen is not fully utilized by growing plants, it can be lost from farm fields and negatively impact air quality. This excess nitrogen can be washed from fields into waterways, and it can also leach through the soil and into groundwater over time. High levels of nitrogen can cause eutrophication of water bodies, leading to "dead zones" that decrease aquatic life.

Nitrogen can also be lost from farm fields in the form of gaseous, nitrogen-based compounds such as ammonia and nitrogen oxides. These compounds can have detrimental effects on both human health and the environment. For example, ammonia is harmful to aquatic life, and nitrogen oxides are a significant cause of air pollution, leading to respiratory diseases, circulatory system disorders, and damage to organs such as the liver and spleen.

To reduce the impact of fertilizers on air pollution, farmers can adopt nutrient management techniques. This involves applying nutrients (fertilizer and manure) in the right amounts, at the right time of year, with the right methods, and in the right places. Precision farming, for example, contributes to enhanced uptake of nitrogen by plants and thus reduces losses of ammonia to the air.

In addition, collaboration between a wide range of people, stakeholders, and organizations across an entire watershed is vital to reducing nutrient pollution. Farmers can play a leadership role in these efforts by engaging with their state governments, farm organizations, conservation groups, educational institutions, and community groups.

By carefully managing the application of fertilizers and collaborating with relevant parties, it is possible to reduce the impact of fertilizers on air pollution.

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