How Runoff of Fertilizer Affects the Environment and What You Can Do to Prevent It

Fertilizers are widely used in agriculture to provide essential nutrients for crop growth and yield. However, when excess fertilizer is applied or washed away by rain or irrigation, it can cause serious environmental problems. Runoff of fertilizer is a major source of nutrient pollution in water bodies, such as streams, rivers, lakes, and estuaries. This article will explain what runoff of fertilizer is, how it affects the environment, and what you can do to prevent it.

What is Runoff of Fertilizer?

Runoff of fertilizer is the movement of nutrients, mainly nitrogen and phosphorus, from farm fields to water bodies. Nitrogen and phosphorus are the main components of most fertilizers, and they are essential for plant growth. However, when plants do not use all the nutrients applied, they can be lost from the soil through leaching, erosion, or surface runoff.

Leaching is the process of nutrients moving downward through the soil and reaching groundwater. Erosion is the process of soil particles being detached and carried away by water or wind. Surface runoff is the flow of water over the land surface that can carry nutrients and sediments into water bodies.

How Does Runoff of Fertilizer Affect the Environment?

Runoff of fertilizer can have negative impacts on the environment at different levels. At the local level, runoff of fertilizer can contaminate drinking water sources, reduce biodiversity, and harm aquatic life. At the regional level, runoff of fertilizer can contribute to eutrophication, harmful algal blooms, and hypoxia. At the global level, runoff of fertilizer can increase greenhouse gas emissions and climate change.

Contamination of Drinking Water Sources

Runoff of fertilizer can increase the concentration of nitrate in groundwater and surface water. Nitrate is a form of nitrogen that can be taken up by plants or converted to other forms by bacteria. However, when nitrate levels exceed the safe limit for drinking water (10 mg/L), it can pose a health risk for humans and animals. Nitrate can interfere with the ability of blood to carry oxygen, causing a condition called methemoglobinemia or blue baby syndrome. This condition can be fatal for infants and young children, as well as pregnant women and people with certain diseases.

Reduction of Biodiversity

Runoff of fertilizer can alter the natural balance of nutrients in water bodies, favoring some species over others. For example, excess nitrogen and phosphorus can stimulate the growth of algae and aquatic plants, which can shade out other organisms that need light to survive. Some algae and aquatic plants can also produce toxins that can harm fish and wildlife. As a result, runoff of fertilizer can reduce the diversity and abundance of aquatic life in water bodies.

Harm to Aquatic Life

Runoff of fertilizer can also affect the quality of water for aquatic life. Excess nutrients can lower the pH of water, making it more acidic and corrosive. This can damage the shells and skeletons of some organisms, such as mollusks and corals. Excess nutrients can also increase the turbidity of water, making it more cloudy and reducing visibility. This can affect the ability of some organisms to find food and avoid predators.

How Does Runoff of Fertilizer Contribute to Eutrophication?

Eutrophication is a process where excess nutrients cause excessive growth of algae and aquatic plants in water bodies. Eutrophication can have several negative consequences for the environment:

  • Algae and aquatic plants can block sunlight from reaching deeper waters, reducing photosynthesis and oxygen production.
  • Algae and aquatic plants can die and decompose, consuming oxygen and releasing carbon dioxide.
  • Decomposition can also release nutrients back into the water, fueling more algal growth.
  • Low oxygen levels (hypoxia) or no oxygen (anoxia) can kill fish and other aquatic animals.
  • Some algae can produce toxins that can harm humans and animals that drink or swim in contaminated water.

Eutrophication is a global problem that affects many water bodies around the world. Some examples are:

  • The Gulf of Mexico: The Mississippi River drains about 40% of the US land area and carries large amounts of nutrients from agricultural runoff into the Gulf of Mexico. This causes a large hypoxic zone (also known as a dead zone) every summer, where oxygen levels are too low to support most marine life.
  • The Baltic Sea: The Baltic Sea is one of the largest brackish water bodies in the world, where freshwater from rivers mixes with saltwater from the North Sea. The Baltic Sea receives large amounts of nutrients from agricultural runoff from nine countries that border it. This causes widespread eutrophication and hypoxia in the sea.
  • Lake Erie: Lake Erie is one of the Great Lakes in North America, which contain about 20% of the world’s freshwater. Lake Erie receives large amounts of nutrients from agricultural runoff from four US states and one Canadian province that border it. This causes frequent harmful algal blooms and hypoxia in the lake.

What Can You Do to Prevent Runoff of Fertilizer?

There are many ways that you can prevent or reduce runoff of fertilizer from your farm or garden. Some of them are:

  • Use phosphorus-free fertilizer: Phosphorus is the most limiting nutrient for algal growth in most water bodies, so using phosphorus-free fertilizer can reduce the risk of eutrophication. Most fertilizer bags have a ratio of nitrogen-phosphorus-potassium printed on them. Look for a number like 32-0-25, where the middle number, denoting phosphorus content, is zero.
  • Apply fertilizer at the right time and rate: Applying fertilizer when plants need it and in the right amount can prevent nutrient losses and improve crop yield. Avoid applying fertilizer before heavy rain or irrigation, as this can increase runoff. Follow the instructions on the fertilizer label or consult an extension agent for guidance.
  • Use slow-release fertilizer: Slow-release fertilizer can provide nutrients to plants gradually over time, reducing the risk of leaching and runoff. Slow-release fertilizer can also reduce the frequency of fertilization, saving time and money.
  • Use cover crops and mulch: Cover crops are plants that are grown between crop seasons to protect and improve the soil. Mulch is any material that is spread over the soil surface to conserve moisture and prevent erosion. Both cover crops and mulch can reduce runoff by increasing infiltration, reducing evaporation, and stabilizing the soil.
  • Plant buffer strips and filter strips: Buffer strips are areas of vegetation that are planted along the edges of fields, especially those that border water bodies. Filter strips are areas of vegetation that are planted between fields and drainage ditches or tile outlets. Both buffer strips and filter strips can reduce runoff by slowing down water flow, trapping sediments and nutrients, and enhancing infiltration.
  • Implement conservation tillage: Conservation tillage is a method of preparing the soil for planting that minimizes soil disturbance and maintains crop residues on the surface. Conservation tillage can reduce runoff by increasing organic matter, improving soil structure, and reducing erosion.


Runoff of fertilizer is a serious environmental problem that can affect water quality, biodiversity, and aquatic life. However, by adopting some simple practices, you can prevent or reduce runoff of fertilizer from your farm or garden. This will not only benefit the environment, but also your crop productivity and profitability. Remember, every drop counts!

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