Importance of Soil Composition (Cambridge (CIE) IGCSE Environmental Management): Revision Note

Why is soil composition important for crop growth?

Mineral particles: sand, silt and clay

• The mix of sand, silt and clay affects soil texture, which controls how well crops grow

• Sand drains quickly, preventing waterlogging

• Clay holds water and nutrients but can become waterlogged if too dense

• Silt holds water better than sand and creates a smooth, fertile soil

Nutrient content: organic content and inorganic ions

• Organic content adds humus, which improves soil structure and fertility

  • Humus helps soil hold nutrients and moisture, supporting strong root growth

• Crops need carbon dioxide and water are used to produce sugars like glucose, which they use as a source of energy

• However, crop plants also require certain elements like nitrogen, phosphorus, and potassium

• Plants use these elements to construct proteins and other chemicals they need in order to carry out their life processes

  • They obtain these elements in the form of inorganic ions dissolved in soil water:

    • Nitrate ions (NO₃⁻) for healthy leaf and stem growth

    • Phosphate ions (PO₄³⁻) for root development and energy transfer in plants

    • Potassium ions (K⁺) for flower and fruit formation and disease resistance

• Low nutrient content leads to poor growth and low yields

pH: acidic, neutral and alkaline

• Soil pH affects how easily plants can absorb nutrients

• Most crops grow best in neutral or slightly acidic soils

• Acidic soils may lock up nutrients, making them less available

• Alkaline soils can reduce the uptake of important ions like iron

• Correct pH helps crops take in nutrients effectively

Pore spaces

• Pore spaces are the gaps between soil particles filled with air or water

• Large pores help with drainage and allow crop roots to spread easily

• Small pores hold water, helping crop plants survive dry periods

• A mix of large and small pores supports healthy root systems

Gas content

• Soil must contain oxygen for root respiration

• Oxygen allows roots to release energy for growth and nutrient uptake

• Poor aeration slows growth and may cause root rot

Water content and drainage

• Soil must hold enough water for roots to absorb

• Good drainage prevents waterlogging

  • Waterlogging can be very damaging to crops, as it reduces oxygen availability and damages roots

• Proper water balance supports steady crop growth

Ease of cultivation

• Soils that are easy to cultivate require less energy and labour

• Sandy soils are easier to plough and plant seeds in

• Heavy clay soils are harder to work and may delay planting

• Good cultivation conditions help farmers prepare land quickly and efficiently

Loam soils & crop growth

Why are loam soils a good medium for crop growth?

Ideal combination of mineral particles and pore spaces

• Loam is a type of soil that contains a balanced mix of sand, silt and clay

  • This creates the ideal soil texture for many types of crops

• This balance provides large and small pore spaces, supporting both air flow and water storage

• Roots can spread easily through well-structured loam soils

Retains moisture

• Loam holds enough water for crops during dry periods

• Small pores trap moisture without becoming waterlogged

• Plants have a reliable supply of water for root absorption

Contains organic content and inorganic ions

• Loam contains humus, which improves soil structure and fertility

• Humus helps loam hold nutrients needed for healthy growth

• Loam is effective at storing important inorganic ions such as nitrate, phosphate and potassium

Allows excess water to drain

• Sand particles in loam allow extra water to drain away

• Prevents waterlogging, which can limit oxygen and damage roots

• Good drainage supports strong and healthy crop development

Easy to cultivate

• Loam is crumbly and soft, making it simple to plough and prepare

• Seeds can be planted evenly and germinate well

• Farmers can work the soil efficiently with less labour and machinery