Helena Joyce
Fertilisers have been instrumental in improving crop yields and food security, but they can also cause land pollution. When fertilisers are overapplied, excess nutrients are washed off and pollute the natural environment. Nitrogen and phosphorus are the two main fertilisers used by farmers, and nearly two-thirds of the nitrogen applied to crops becomes a pollutant. This excess nitrogen and phosphorus can contaminate water bodies, causing eutrophication, which leads to dead zones and a decrease in aquatic life. Additionally, the manufacturing of synthetic fertilisers emits polluting gases and particles, such as sulphur oxide, ammonia, and nitrogenous by-products, which directly impact the environment and human health. To minimise land pollution, it is essential to apply fertilisers in suitable proportions and adopt nutrient management techniques, such as using organic or ecological fertilisers, which provide a more gradual release of nutrients and reduce the risk of environmental harm.
| Characteristics | Values |
|---|---|
| Excess nutrients from fertilisers enter the natural environment | Nitrogen and phosphorus are the two main fertilisers that farmers add to their fields. Nearly two-thirds of the nitrogen we use on our crops becomes a pollutant; more than half of the applied phosphorus does. |
| Eutrophication | Excess nutrients in water bodies can lead to eutrophication, causing hypoxia ("dead zones") and a decrease in aquatic life. |
| Algal blooms | Algal blooms can deplete oxygen in surface waters, produce toxins harmful to humans, and cause rashes, nausea and respiratory problems. |
| Contamination of drinking water | Nitrates and pathogens in drinking water can be harmful to humans and livestock. |
| Air pollution | Fertiliser manufacturing emits soot, dust particles, sulphur oxide, ammonia, nitric oxide, nitrogen dioxide and volatile solvents, which directly affect the environment and human health. |
| Soil acidification | Nitrate leaching through the soil can contribute to soil acidification and present a serious health hazard if it enters groundwater used for domestic supplies. |
| Loss of biodiversity | Pollution from fertilisers can cause imbalances in ecosystems and affect biodiversity. |
| Habitat loss | Overuse of fertilisers can lead to the destruction of ecosystems and habitat loss. |
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What You'll Learn
Nitrogen and phosphorus pollution
Nitrogen and phosphorus are the two main fertilisers that farmers add to their fields. Research shows that nearly two-thirds of the nitrogen used on crops becomes a pollutant, and more than half of the applied phosphorus does as well.
Excess nitrogen in the atmosphere can produce pollutants such as ammonia and ozone, which can impair our ability to breathe, limit visibility, and alter plant growth. When excess nitrogen returns to the earth from the atmosphere, it can harm the health of forests, soils, and waterways. Nitrogen-based compounds called nitrates in drinking water can be harmful to infants. High levels of nitrates can also be toxic to livestock and humans. Nitrates are not absorbed by soil materials, so they may leach into groundwater.
Excess phosphorus can also have negative effects. For example, the Chesapeake Bay watershed was once mainly composed of forested buffers, wetlands, and meadows that absorbed and filtered nutrients. However, haphazard development has stripped the watershed of these buffers, and now pollution flows undiluted into waterways. As land use patterns change and the watershed's population grows, the amount of nitrogen, phosphorus, and sediment entering the Bay's waters increases. Each year, about 300 million pounds of polluting nitrogen reach the Chesapeake Bay—approximately six times the amount that reached the bay in the 1600s.
Agricultural practices can contribute to nitrogen and phosphorus pollution. China, for instance, generates the most nitrogen pollution, accounting for one-third of the global total. India produces almost one-fifth, followed by the USA, Pakistan, and Brazil. The countries with the largest populations and land masses create the most pollution. However, many countries, particularly poorer countries across Sub-Saharan Africa, do not use enough fertiliser, and their crop yields suffer as a result. This is detrimental to farmers, food security, and the environment, as it means more land is needed for agriculture.
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Eutrophication and hypoxia
Eutrophication is a process in which nutrients accumulate in a body of water, leading to increased growth of organisms that may deplete the oxygen in the water. The term comes from the Greek "eutrophos", meaning "well-nourished". Eutrophication may occur naturally or as a result of human activities. Cultural eutrophication, caused by human activities, occurs when sewage, industrial wastewater, fertilizer runoff, and other nutrient sources are released into the environment. This type of eutrophication has emerged as one of the leading causes of water quality impairment.
Fertilizers, both natural and synthetic, are a major contributor to eutrophication. When fertilizers are overapplied, excess nutrients, particularly nitrogen and phosphorus, are washed off and pollute water bodies. This leads to an over-enrichment of water by nutrients, causing harmful algal blooms and hypoxia (oxygen depletion). Algal blooms can cause fish kills, human illness through shellfish poisoning, and the death of marine mammals and shorebirds. They also contribute to the depletion of oxygen in the water, further exacerbating hypoxia.
Agricultural practices, including fertilizer use, have been identified as a significant contributor to the rise in eutrophic and hypoxic events. Between 1960 and 1990, the global use of synthetic nitrogen fertilizer increased more than sevenfold, while phosphorus use more than tripled. Studies have shown that fertilizers are often applied in excess of crop needs, with nearly two-thirds of nitrogen and more than half of phosphorus becoming pollutants. This excess can be attributed to factors such as improper nutrient management, application of fertilizers in unsuitable proportions, and environmental conditions that allow nutrients to run off into water bodies.
The impact of fertilizer-induced eutrophication and hypoxia is particularly acute in coastal waters, where nitrogen is the key limiting nutrient. Estuaries, which are the interface between freshwater and saltwater, are especially vulnerable to both nitrogen and phosphorus pollution, commonly exhibiting symptoms of eutrophication. In these environments, eutrophication often results in bottom water hypoxia or anoxia, leading to fish kills and habitat degradation.
To mitigate the effects of eutrophication and hypoxia, several strategies have been proposed. These include minimizing point source pollution from sewage and agriculture, as well as reducing nonpoint pollution sources. Seaweed aquaculture has been identified as a potential solution, as seaweed can absorb excess nitrogen, phosphorus, and carbon dioxide, improving water quality. Additionally, direct injection of compressed air has been used to address localized hypoxia, and pump aeration is a standard technique for smaller-scale waters.
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Air pollution
Fertilisers have transformed the way the world produces food, offering benefits for food security and the environment through higher yields and reduced land use. However, the overuse of synthetic fertilisers is having a detrimental impact on the environment. During the manufacturing process, soot and dust particles are emitted into the air, along with polluting gases such as sulphur oxide (SOx), ammonia (NH3), nitrogen oxide (NOx), and nitrogen dioxide (NO2). These emissions directly affect the environment and human health.
Nitrogen-based fertilisers are a significant contributor to air pollution. When nitrogen is not fully utilised by plants, it is lost from farm fields and negatively impacts air quality. Excess nitrogen can be converted into gaseous, nitrogen-based compounds like ammonia and nitrogen oxides, which are released into the atmosphere. Ammonia emissions from fertilised fields and livestock waste can combine with industrial emissions, forming solid particles that contribute to air pollution and pose risks to human health.
Ammonia (NH3) is a harmful pollutant that can affect both aquatic life and human health. High levels of ammonia deposition from the atmosphere into surface waters can harm aquatic ecosystems. Additionally, ammonia emissions can mix with nitrogen oxides and other pollutants from combustion, forming fine particulate matter that contributes to air pollution and respiratory issues.
Nitrogen oxides (NOx) are potent greenhouse gases that contribute to the greenhouse effect and climate change. They are released into the atmosphere when synthetic fertilisers break down, returning excess nitrogen to the environment. Nitrous oxide, in particular, has a significant global warming potential and is long-lasting in the atmosphere.
To mitigate air pollution from fertilisers, farmers can adopt nutrient management techniques. This involves applying the right amount of nutrients, at the right time, using appropriate methods and placement. Encouraging sustainable agricultural practices, such as crop rotation and organic farming, can also help reduce fertiliser residues and their impact on air quality.
Overall, while fertilisers have brought significant benefits to agriculture, the overuse of synthetic fertilisers and improper nutrient management contribute to air pollution. By implementing sustainable practices and reducing nutrient losses, farmers can play a crucial role in mitigating air pollution and protecting the environment and human health.
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Water pollution
Another significant contributor to water pollution is the excess application of fertilisers, which can lead to eutrophication. When nitrogen and phosphorus from fertilisers are not fully utilised by plants, they can be washed into waterways or leach into groundwater. This excess nutrient load causes uncontrolled algae growth, known as algal blooms, which have detrimental effects. Algal blooms reduce water clarity, hindering photosynthesis in oxygen-producing aquatic plants, thereby depleting oxygen levels in the water. This hypoxic condition stresses aquatic life, leading to fish kills and a decline in aquatic biodiversity. Additionally, certain types of algae produce toxins that are harmful to humans and wildlife.
The impact of algal blooms extends beyond ecological consequences. They can degrade drinking water supplies, affecting human health and causing environmental nuisances. Furthermore, the recreational value of water bodies impacted by algal blooms may diminish, along with the value of surrounding properties.
Fertilisers also contribute to water pollution through direct runoff from intensive livestock farming, such as cattle, pig, and poultry farms. Mismanagement of manure applications near wells can result in bacterial contamination of groundwater. High levels of nitrates, which are commonly found in nitrogen fertilisers, can be toxic to both humans and livestock, causing nitrate poisoning and interfering with oxygen uptake.
To mitigate water pollution from fertilisers, proper nutrient management practices are essential. Farmers can play a pivotal role by adopting techniques such as applying the right amount of fertiliser at the appropriate time of year and using the correct methods. Implementing conservation drainage practices, ensuring year-round ground cover, and planting field buffers can also help reduce nutrient runoff into water bodies.
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Soil pollution
Fertilisers have transformed the way the world produces food, bringing large benefits for food security and the environment through higher yields and less land use. However, the overapplication of fertilisers can cause soil pollution. Nitrogen and phosphorus are the two main fertilisers that farmers add to their fields. When nitrogen and phosphorus are not fully utilised by growing plants, they can be lost from farm fields and negatively impact the soil. This excess nitrogen and phosphorus can be washed from farm fields and into waterways during rain events and when snow melts, and can also leach through the soil and into groundwater over time. High levels of nitrogen and phosphorus can cause eutrophication of water bodies, leading to hypoxia ("dead zones") and a decrease in aquatic life.
To prevent soil pollution, farmers can adopt nutrient management techniques by applying nutrients (fertiliser and manure) in the right amounts, at the right time of year, and with the right methods and placement. Conservation tillage can also help improve soil health and reduce erosion, runoff, and soil compaction, thereby decreasing the chance of nutrients reaching waterways through runoff. Implementing conservation drainage practices, such as subsurface tile drainage, is another way to manage water movement on and through the soil.
Additionally, the use of organic and ecological fertilisers should be encouraged. Organic fertilisers, composed of carbonaceous material, can be absorbed more gradually by plants, ensuring the availability of supplementary nutrients in the soil for a longer period. In contrast, synthetic fertilisers immediately provide nutrients to plants, leading to rapid incorporation, which can result in an overabundance of nutrients that can pollute the soil. By avoiding synthetic compounds, organic fertilisers are not harmful and stand out as a crucial alternative to tackle the problematic pollution caused by synthetic fertilisers.
Furthermore, certain practices can help minimise nitrate leaching, a significant contributor to soil pollution. These include maintaining good ground cover around dams and streams, avoiding topdressing bare ground, and applying fertilisers in small amounts frequently rather than all at once. By following these practices and adopting sustainable agricultural techniques such as crop rotation and organic farming, we can mitigate the impact of fertilisers on soil pollution.
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Frequently asked questions
When fertilisers are overapplied, excess nutrients are washed off and pollute the natural environment. This includes the pollution of rivers and lakes, causing imbalances in ecosystems and affecting biodiversity.
Nitrogen and phosphorus are the two main fertilisers that farmers add to their fields. When nitrogen and phosphorus are not fully utilised by the growing plants, they can be lost from the farm fields and negatively impact the downstream water quality. Nitrogen can be lost from farm fields in the form of ammonia and nitrogen oxides, which are harmful to aquatic life.
Organic fertilisers are a crucial alternative to synthetic fertilisers. Organic fertilisers are composed of carbonaceous material and can be absorbed more gradually by plants. Organic farmers use composted manure and other natural materials, as well as crop rotation, to improve soil fertility.
