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examBoard: Cambridge
examType: IGCSE
lessonTitle: Improving Soil Structure with Organic Matter
Soil erosion is one of the biggest threats to sustainable agriculture and environmental management worldwide. One of the most effective ways to combat soil erosion is by improving soil structure through the addition of organic matter. When soil has good structure, it's more resistant to being washed or blown away and it's better at absorbing and retaining water.
Key Definitions:
Organic matter works like glue in the soil, binding particles together to form stable aggregates. This creates spaces (pores) between the aggregates that allow water to infiltrate rather than run off the surface. When rain hits soil with good structure, the water soaks in instead of washing the soil away. Think of it like a sponge versus a brick - which one absorbs water better?
Soils with low organic matter are more vulnerable to erosion because they lack the binding agents that hold soil particles together. When heavy rain falls on poorly structured soil, it can wash away tonnes of topsoil per hectare in a single storm. Wind can also easily pick up and carry away dry, loose soil particles when there's not enough organic matter to hold them in place.
Adding organic matter to soil triggers a cascade of beneficial changes that work together to create erosion-resistant soil. Let's explore the main ways organic matter helps:
When organic matter decomposes in soil, it releases sticky substances that act like natural cement. These substances, along with fungal threads called hyphae, bind soil particles into stable clumps or aggregates. These aggregates create a crumbly, porous structure that's ideal for plant growth and erosion resistance.
Soil with good structure allows water to soak in 10-100 times faster than compacted soil. This means less runoff and erosion during heavy rainfall.
Plant roots can penetrate deeper and spread wider in well-structured soil. These roots help hold soil in place and add more organic matter when they die back.
Organic matter feeds soil organisms like earthworms and beneficial bacteria that further improve soil structure through their movement and waste products.
Different types of organic matter have varying effects on soil structure. Using a mix of materials often gives the best results for erosion control.
Knowing what organic matter to add is only half the battle. How you add it makes a big difference in how effective it will be at preventing erosion.
No-till farming: Leaving crop residues on the surface rather than ploughing them under. This protects soil from raindrop impact and wind while slowly adding organic matter.
Contour planting: Growing crops or applying mulch along the contour of slopes. Combine with organic matter to slow water flow and prevent gully formation.
Mulching: Applying a thick layer of organic material on the soil surface. This protects bare soil immediately while gradually improving structure as it breaks down.
Cover crops are plants grown specifically to protect and improve the soil rather than for harvest. They're one of the most effective ways to add organic matter while actively preventing erosion.
Farmer John Cherry in Hertfordshire transformed his farm's soil health by implementing a no-till system with cover crops and organic matter additions. After five years, his soil organic matter increased from 2.8% to 4.3%, dramatically improving water infiltration rates. During the heavy rains of 2019-2020, neighbouring farms experienced severe erosion and flooding, while Cherry's fields absorbed the rainfall with minimal runoff. His crop yields have remained stable while reducing fertiliser inputs by 30%, demonstrating that improving soil structure with organic matter can be both environmentally and economically beneficial.
It's important to monitor whether your organic matter additions are actually improving soil structure and reducing erosion risk. Here are some simple tests you can do:
Adding organic matter isn't always straightforward. Here are some common challenges and how to overcome them:
Improving soil structure with organic matter is not a quick fix but a long-term investment in soil health and erosion prevention. Natural soils took thousands of years to develop their structure and organic matter content. While we can accelerate this process, it still requires patience and consistent effort.
The good news is that even small improvements in soil structure can significantly reduce erosion risk. Each addition of organic matter builds upon previous efforts, creating a positive cycle where better structure leads to more plant growth, which in turn contributes more organic matter to the soil.
By understanding the crucial role organic matter plays in soil structure and implementing the techniques covered in this guide, you can help combat one of the most serious environmental challenges facing our planet while creating more productive and resilient agricultural systems.
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