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examBoard: Cambridge
examType: IGCSE
lessonTitle: Overuse of Fertilisers
Farmers around the world use fertilisers to boost crop yields and feed our growing population. But when we use too much, these helpful farming tools can become environmental villains! Let's explore what happens when fertilisers are overused and the problems this creates.
Key Definitions:
Organic fertilisers come from plant or animal sources like manure, compost and bone meal. They release nutrients slowly and improve soil structure.
Inorganic (chemical) fertilisers are manufactured and contain specific amounts of nutrients like nitrogen (N), phosphorus (P) and potassium (K). They work quickly but don't improve soil structure.
Fertilisers boost crop yields by providing essential nutrients that might be lacking in the soil. This helps farmers:
While fertilisers can be beneficial when used correctly, applying too much leads to serious environmental problems. Let's look at the main issues:
One of the biggest problems with fertiliser overuse is how it affects our water systems. When it rains, excess nutrients (especially nitrogen and phosphorus) wash into streams, rivers, lakes and eventually the ocean.
1. Excess fertiliser doesn't stay in the soil
2. Rain washes nutrients into waterways
3. Nutrients cause algae to grow rapidly
4. Algae form "blooms" on water surface
5. Sunlight gets blocked from reaching below
1. Algae die and decompose
2. Decomposition uses up oxygen
3. Water becomes oxygen-depleted
4. Fish and other aquatic life suffocate
5. "Dead zones" form where nothing can live
1. Drinking water contamination
2. Toxic algae can make people ill
3. Fishing industries suffer
4. Tourism affected by smelly, green water
5. Expensive water treatment needed
One of the world's largest dead zones forms every summer in the Gulf of Mexico. Covering up to 18,000 square kilometres (about the size of Wales), this area becomes so depleted of oxygen that marine life either flees or dies.
The cause? Fertiliser runoff from farms along the Mississippi River. Nitrogen and phosphorus wash down the river and into the Gulf, triggering massive algal blooms. When these algae die and decompose, they use up oxygen, creating a hypoxic (low-oxygen) zone where fish, shrimp and other marine creatures cannot survive.
This dead zone has devastating effects on the Gulf's fishing industry, which is worth billions of dollars annually. Despite efforts to reduce fertiliser use in the Mississippi Basin, the dead zone continues to form each year.
Fertiliser overuse doesn't just harm water systems it damages the soil itself and reduces biodiversity both above and below ground.
Fertiliser overuse contributes to air pollution and climate change in ways many people don't realise:
In 2014, the city of Toledo, Ohio in the USA had to shut off drinking water to over 400,000 people for three days because of a toxic algal bloom in Lake Erie. The bloom was caused by phosphorus from agricultural fertilisers washing into the lake.
The algae produced a toxin called microcystin that can cause liver damage, rashes and vomiting. Water treatment plants couldn't remove it safely. Residents had to rely on bottled water for drinking, cooking and even brushing their teeth.
Since then, farmers around Lake Erie have been working to reduce fertiliser runoff through better application methods and timing. However, blooms continue to occur each summer, showing how persistent these problems can be once they develop.
The good news is that we can grow plenty of food without overusing fertilisers. Here are some approaches that help reduce the environmental impact:
Soil testing to apply only what's needed
GPS technology for targeted application
Variable rate technology adjusts fertiliser amounts across fields
Timing applications when plants can best use nutrients
Crop rotation to naturally restore nutrients
Cover crops prevent erosion and add nutrients
Organic farming uses natural fertilisers
Agroforestry combines trees and crops for better nutrient cycling
Riparian buffers - strips of vegetation along waterways
Wetland restoration to filter nutrients
Contour farming to reduce runoff
Slow-release fertilisers that provide nutrients gradually
Addressing fertiliser overuse requires action at multiple levels:
The Netherlands has some of the most productive farms in the world despite drastically reducing fertiliser use. Since the 1980s, Dutch farmers have cut fertiliser application rates by nearly 70% while maintaining or increasing yields.
How did they do it? Through a combination of precise application methods, greenhouse technology, crop selection and innovative farming techniques. The government also implemented strict regulations and provided support for farmers to transition to more sustainable methods.
As a result, water quality in Dutch rivers and lakes has improved significantly, showing that it's possible to grow food abundantly while protecting the environment.
Fertilisers are essential tools for modern agriculture, but their overuse creates serious environmental problems. The challenge is finding the balance using enough to grow the food we need without damaging our water, soil, air and biodiversity.
By understanding the impacts of fertiliser overuse and implementing better management practices, we can work toward more sustainable food production systems that will feed people today without compromising the planet's ability to feed future generations.
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