What is soil made of, what are the main soil types, and how do their properties affect what can be grown?
The four components of soil, the physical characteristics of clay, sand, peat and loam, the factors and profiles behind Northern Ireland's soils, how particle size controls drainage, and how soil pH affects the crops that will grow.
A focused CCEA GCSE Agriculture and Land Use answer on the composition of soils, covering the four soil components, the physical characteristics of clay, sand, peat and loam, soil profiles, particle size and drainage, and how soil pH affects crop choice.
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What this dot point is asking
CCEA wants you to name what soil is made of, describe and compare the main soil types, read a soil profile, link particle size to drainage, and explain how soil pH decides which crops will grow. This is the foundation of Unit 1, so the language here is reused throughout the crop and habitat topics.
The four components of soil
The balance between these components is what gives a soil its character. A soil packed with mineral particles and little air drains badly; a soil rich in organic matter holds water and releases nutrients as it rots down.
The main soil types
Soil types are named after the size of the mineral particles in them.
- Sandy soil. Large, coarse particles with wide air gaps. It is free-draining (water passes straight through), warms up quickly in spring, and is easy to work, but it dries out and loses nutrients as water washes them away.
- Clay soil. The smallest particles, packed tightly with tiny air gaps. It feels sticky, drains poorly and can become waterlogged, is slow to warm, and is easily compacted, but it holds water and nutrients well and can be very fertile.
- Peat soil. Very high in organic matter, dark, holds a lot of water and is naturally acid. Peaty soils are common in upland and boggy parts of Northern Ireland.
- Loam. A balanced mixture of sand, silt and clay plus organic matter. Loam is the ideal farming and gardening soil because it holds enough water and nutrients while still draining freely.
Soils in Northern Ireland and the soil profile
The soil you find depends on the parent material (the rock or sediment beneath), the climate, the organic matter added and time. In Northern Ireland the simplest contrast you need is uplands versus lowlands: uplands tend to have wet, acid, peaty soils, while lowlands tend to have deeper, more workable soils such as loams.
If you dig a pit you see a soil profile: layers from the surface down. The top layer is the topsoil, dark because it is rich in organic matter and where most roots and life are; below it is the lighter subsoil, with less organic matter and more weathered rock.
Particle size and drainage
Soil pH and crops
Soil is described by its pH: acid below pH 6, neutral around pH 7 and alkaline above pH 7. The pH matters for two reasons: different crops prefer different pH ranges, and the pH changes how available the nutrients in the soil are to plant roots. A farmer can add lime to raise the pH of an acid soil towards neutral when they want to grow a crop that dislikes acid conditions.
Examples in context
Example 1. Choosing a field for early potatoes. A grower wants an early crop, so they pick a sandy or sandy loam field rather than a heavy clay one. The sandy soil warms up quickly in spring and drains freely, so the seed potatoes are not sitting in cold, wet soil, and the crop can be planted and harvested earlier, which fetches a better price.
Example 2. Improving a heavy clay field. A farmer with a wet clay field adds organic matter (such as farmyard manure or compost) and improves drainage. The organic matter opens up the soil structure so air and water can move more freely, the field becomes easier to work, and roots can grow more deeply, raising the yield over time.
Try this
Q1. Name the four components of any soil. [4 marks]
- Cue. Mineral (rock) particles, water, air and organic matter.
Q2. Explain why a loam soil is considered the best soil for farming. [2 marks]
- Cue. It is a balanced mix of particle sizes, so it holds enough water and nutrients while still draining freely.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA Unit 1 style4 marksDescribe the physical characteristics of a sandy soil and a clay soil, and explain why each behaves the way it does.Show worked answer →
Four marks need two clear points about each soil, linking a characteristic to the particle size.
Sandy soil has large, coarse particles with big air gaps between them. This makes it free-draining, so water passes through it quickly, and it warms up fast in spring. The drawback is that it dries out and loses nutrients easily because water washes them away.
Clay soil has very small particles packed closely together with tiny air gaps. Water cannot pass through easily, so it drains poorly and can become waterlogged, and it is slow to warm up. The advantage is that it holds water and nutrients well, so it can be fertile if managed.
Markers reward the link between particle size and the property (large particles to free draining, small particles to poor draining and water holding), not just a list of words.
CCEA Unit 1 style3 marksA farmer tests the pH of a field and gets a reading of pH 5. State whether this soil is acid, neutral or alkaline, and explain why the pH matters for crop production.Show worked answer →
One mark for the classification and two for the reasoning.
A reading of pH 5 is below 6, so the soil is acid.
The pH matters because it affects which crops will grow well: some crops only thrive in acid soil while others need neutral or alkaline conditions, so the farmer must match the crop to the soil pH. The pH also affects the availability of nutrients in the soil, so even if nutrients are present they may not be taken up at the wrong pH.
A practical answer adds that the farmer could add lime to raise the pH towards neutral if they want to grow a crop that prefers less acid conditions. Markers reward acid named correctly plus a clear reason linked to crop growth or nutrient availability.
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