Air Pollutants: Impacting Crop Health And Agriculture

Air pollution is a pressing issue that poses a significant threat to human health and the environment. Among the various sources of air pollution, agricultural practices, such as the heavy use of fertilizers and livestock waste, are major contributors to fine-particulate air pollution. This has raised concerns about the impact of air pollutants on crop health and productivity. High levels of nitrogen oxide pollution, for example, have been linked to declines in crop yields. Additionally, ground-level ozone (O3), formed from the reaction of nitrogen oxides with other air pollutants, has been identified as a significant pollutant affecting crop growth and productivity. The absorption of O3 by plants leads to the formation of free radicals that attack cell membranes, causing leaf injury, reduced growth, and premature death of the plant. Other air pollutants, such as sulfur dioxide, fluorides, ammonia, and particulate matter, also have detrimental effects on vegetation, further emphasizing the need to address air pollution to ensure sustainable agriculture and food security.

Nitrogen-rich fertilizers and animal waste

Nitrogen is critical for plant growth and reproduction, and nitrogen-rich fertilisers are often used to increase the availability of nitrogen in the soil. However, the use of nitrogen-based fertilisers and animal waste can have negative impacts on crop health and the environment.

Nitrogen-based fertilisers and animal waste (urine and dung) are key sources of nitrous oxide emissions on farms. Nitrous oxide is a powerful greenhouse gas that accounts for 5-7% of global greenhouse emissions, with agricultural practices contributing to 90% of these emissions. The excessive application of nitrogen fertilisers can lead to increased nitrous oxide emissions and other environmental problems such as eutrophication, the greenhouse effect, and acid rain. Consuming crops with high nitrate concentrations, which can result from the use of nitrogen fertilisers, can also have negative effects on human health.

Animal waste from concentrated animal feeding operations (CAFOs) or factory farms is stored in open ponds or pits and is often applied untreated as fertiliser to farm fields. The waste contains not only animal excrement but also bedding waste, antibiotic residues, cleaning solutions, and other chemicals. When applied to fields, the waste can exceed the land's absorption capacity, leading to runoff that pollutes waterways. The high nitrogen content in manure runoff can contribute to the creation of dead zones in downstream waterways, where excessive algae growth consumes all the oxygen, leading to the death of other organisms. Animal waste from CAFOs is also a source of air pollution, releasing greenhouse gases such as methane and nitrous oxide, as well as ammonia, hydrogen sulfide, and other harmful chemicals.

To reduce the negative impacts of nitrogen-rich fertilisers and animal waste on crop health and the environment, farmers can adopt best management practices. This includes carefully planning and implementing the 4 Rs: the 'right' rate, source, timing, and placement of nitrogen fertilisers to match plant needs. By improving agricultural practices, farmers can reduce nitrogen losses, improve crop productivity, and save costs. Additionally, the use of enhanced efficiency fertilisers, such as slow-release products or those with nitrification inhibitors, can help match the fertiliser supply with plant demand for soil nitrogen, reducing nitrogen losses.

Particulate matter

PM10 sources include dust from construction sites, landfills, and agriculture, wildfires, industrial sources, wind-blown dust, pollen, and fragments of bacteria. PM2.5 is largely produced by the combustion of gasoline, oil, diesel fuel, or wood, as well as industrial processes and motor vehicle exhaust.

PM can induce adverse health effects in humans, and the same is true for crops. PM10 exposure has been linked to the worsening of respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). While PM2.5 exposure has been associated with premature mortality, increased hospital admissions for heart or lung causes, acute and chronic bronchitis, asthma attacks, emergency room visits, respiratory symptoms, and restricted activity days.

In crops, PM can enhance production through the redistribution of light from sunlight to shaded leaves. A crop model (pDSSAT) estimated that the global enhancement in crop production due to PM in 2010 was 2.3%, 11.0%, and 3.4% for maize, wheat, and rice, respectively. However, it is important to note that PM emissions from agriculture can also contribute to air pollution, particularly PM10.

Carbon monoxide

Formation and Sources

Impact on Air Quality and Human Health

Contribution to Greenhouse Gas Effects

While not a greenhouse gas itself, carbon monoxide plays an intermediary role in atmospheric chemistry that exacerbates the greenhouse effect. In the atmosphere, CO reacts with hydroxyl radicals (OH), which are crucial for breaking down methane (CH4), a potent greenhouse gas. By reducing the availability of OH radicals, CO indirectly increases methane concentrations, thereby contributing to global warming.

Effects on the Ozone Layer

Impact on Climate Patterns

The increase in carbon monoxide levels has significant implications for global climate patterns. While not a greenhouse gas, CO affects the concentration and longevity of other greenhouse gases, particularly methane. This interaction can lead to an increase in global warming potential. Additionally, CO contributes to the formation of ground-level ozone, which can alter weather patterns and temperature distributions, profoundly affecting ecosystems and biodiversity.

Mitigation Strategies

To mitigate the environmental impacts of carbon monoxide, it is essential to reduce emissions from their primary sources. Strategies include improving fuel combustion efficiency, transitioning to cleaner energy sources, implementing stricter emission standards for vehicles and industrial processes, and enhancing urban air quality monitoring. By taking these steps, we can reduce the indirect environmental effects of CO, improve air quality, and contribute to the global effort to combat climate change.

Ground-level ozone

The impact of ground-level ozone on crops can vary depending on the crop species, cultivar, and environmental conditions. Some crops may be more sensitive to ground-level ozone than others, and the effects may be influenced by factors such as temperature, soil water stress, and nutrient availability.

To mitigate the effects of ground-level ozone on crops, strategies such as reducing precursor emissions and developing crop cultivars with improved ozone tolerance have been proposed. Developing robust crop growth models that incorporate the effects of ground-level ozone can also help improve our understanding and ability to manage this issue.

Nitrogen dioxide

NO2 is produced through the high-temperature combustion of fuels used for heating, transportation, industry, and power generation. It is also a byproduct of household activities, such as the use of furnaces, fireplaces, and gas stoves.

NO2 has direct and indirect effects on crops:

Direct Effects:

Nitrogen oxides (NOx) are phytotoxins, meaning they can directly damage crop cells and reduce yields.

Indirect Effects:

NOx can also affect crops indirectly in two main ways:

• Ozone Formation: NOx is a key precursor to the formation of ground-level ozone (O3), another phytotoxin. O3 is a major component of smog, and high levels can reduce crop yields.
• Aerosol Formation: NOx can react with other compounds in the atmosphere to form particulate matter aerosols. These aerosols can reflect and scatter sunlight, reducing the amount of light available for photosynthesis, which can, in turn, lower crop yields.

The impact of NO2 on crops depends on the local pollution regime. In areas with high levels of volatile organic compounds (VOCs), increased NO2 leads to more O3 formation and decreased yields. However, in areas with low VOC:NOx ratios, increased NOx can actually lower O3 levels, resulting in increased yields.

Studies have shown that reducing NOx levels can have significant benefits for crop production. For example, in China, reducing NO2 levels to the fifth percentile of observed values was estimated to increase yields by 28% for winter crops and 16% for summer crops. Similarly, in Western Europe, yield increases of nearly 10% for both winter and summer crops were projected.

Overall, NO2 has consistent and negative associations with crop growth across different regions and seasons, making it an important factor in agriculture and food security.

Frequently asked questions