Soils and Soil Fertility: notes

Soil Make-up

• Parts of soil: mineral particles, organic matter, water and air.
• Texture: the feel of the soil, set by the sizes of sand, silt and clay. Sand drains fast; clay holds water but drains slowly. Loam is a balanced mix and suits most crops.
• Structure: how particles group into crumbs. Organic matter improves it.
• Profile: layers called horizons: topsoil, subsoil, then parent rock.

Soil pH

• pH: a measure of acidity. Below 7 is acid, 7 is neutral, above 7 is alkaline.
• Liming: lime raises the pH of acid soils.

Nutrients

• Nitrogen (N): leaf growth. Deficiency gives pale yellow leaves.
• Phosphorus (P): roots and early growth. Deficiency gives purple leaves.
• Potassium (K): strong stems and fruit quality.
• Fertilisers: compound D has N, P and K. Ammonium nitrate is a top dressing for N.
• Manure and compost: supply nutrients and humus, and improve structure.