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examBoard: Cambridge
examType: IGCSE
lessonTitle: Tree Planting and Mixed Cropping
Soil erosion is one of the most serious environmental challenges facing agriculture worldwide. When topsoil is washed or blown away, it takes with it valuable nutrients that plants need to grow. This section explores how tree planting and mixed cropping can help combat this problem.
Key Definitions:
Soil is a precious resource that takes hundreds of years to form but can be lost in just a few seasons of poor management. Healthy soil:
When soil erodes, it creates numerous problems:
Trees are powerful allies in the fight against soil erosion. Their roots bind soil particles together, while their canopies reduce the impact of rain and wind. Let's explore how strategic tree planting can protect vulnerable soils.
Trees protect soil in multiple ways, creating a complete defence system against erosion:
Tree roots create a network that holds soil in place. They can reach deep into the ground, anchoring soil layers and creating channels that improve water infiltration.
Tree leaves and branches intercept rainfall, reducing its erosive force before it hits the ground. This canopy effect can reduce the impact of heavy rain by up to 80%.
Leaf litter and other plant materials from trees decompose to form humus, which improves soil structure and increases its ability to resist erosion.
Different tree planting strategies can be used depending on the landscape and erosion risks:
Rows of trees planted perpendicular to prevailing winds can reduce wind speed by up to 80%, protecting crops and soil from wind erosion. Effective windbreaks typically consist of:
Trees planted along contour lines on slopes help slow water runoff and trap soil. This technique:
The Great Green Wall initiative is an African-led project to grow an 8,000 km natural wonder across the width of Africa. The project aims to restore degraded landscapes and combat desertification in the Sahel region, where soil erosion has contributed to poverty and migration.
Since its launch in 2007, millions of trees have been planted. In Senegal alone, over 12 million drought-resistant trees have been planted across 40,000 hectares. These trees have helped stabilise soil, improved agricultural productivity and created jobs for local communities.
Mixed cropping (also called intercropping) involves growing two or more crops in the same field. This traditional farming practice has been used for centuries and offers significant benefits for soil conservation.
Mixed cropping systems protect soil through several mechanisms:
Different crops with varied growth patterns ensure the soil is protected year-round. When one crop is harvested, others remain to shield the soil.
Different crop species have varied root structures that hold soil at different depths. This creates a more comprehensive underground network for soil stability.
A diverse canopy of different heights and leaf structures breaks the force of rainfall, reducing splash erosion and allowing water to infiltrate slowly.
Some crop combinations are particularly effective at preventing soil erosion while also providing other benefits:
This ancient Native American system combines maize (corn), beans and squash:
Rows of trees or shrubs alternated with crop rows:
Farmer Managed Natural Regeneration (FMNR) in Niger combines tree management with crop production. Rather than planting new trees, farmers protect and manage naturally occurring tree seedlings in their fields.
Since the 1980s, this approach has led to the restoration of over 5 million hectares of land in Niger. Farmers grow millet, sorghum and other crops between the trees. The results have been remarkable:
Successfully implementing these soil conservation strategies requires careful planning and consideration of local conditions.
While effective, these methods can face implementation challenges:
To determine if tree planting and mixed cropping are successfully controlling soil erosion, several indicators can be monitored:
Tree planting and mixed cropping are most effective when used together as part of an integrated soil conservation strategy. By combining these approaches, farmers can create resilient agricultural systems that protect soil while maintaining or improving productivity.
The evidence from case studies around the world shows that these methods not only prevent soil erosion but also provide numerous co-benefits including improved biodiversity, enhanced climate resilience and better livelihoods for farmers. As climate change intensifies pressure on agricultural lands, these traditional yet scientifically sound approaches will become increasingly important.
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