chemical characteristics of soil

• What are the smallest and most chemically active particles in soil?

  Clay and humus particles
• How do clay and humus particles affect plant nutrition?

  They attract ions due to the charges on their surfaces
• What are the chemical properties of soil?

  • Flocculation
  • Cation exchange
  • pH
  • Plant-available nutrients
• What is flocculation in soil?


  It is the clustering together of soil particles to create larger structures called floccules
• What is cation exchange in soil?


  The ability of soil particles to attract, retain, and release cations
• What are examples of cations?


  H⁺, K⁺, Ca²⁺
• What is cation exchange capacity?


  It is the quantity of cations that a soil adsorbs
• Which soil components have the highest rates of cation exchange?


  Colloidal clay and colloidal humus
• What factors affect cation exchange in soil?


  • Humus content
  • Clay content
  • Soil texture
  • pH
• What does pH measure in a solution?


  The concentration of hydrogen ions
• What ions make soils acidic?


  Hydrogen and aluminium ions (H⁺ and Al³⁺)
• What ions make soils alkaline?


  Calcium and magnesium ions (Ca²⁺ and Mg²⁺)
• What is the optimum pH level for crop growth?


  Between 6.5 and 7.5
• What happens to nutrient availability outside the optimum pH range?


  Nutrients can become unavailable to plants
• Why are soils derived from sandstone or granite typically acidic?


  Due to their hydrogen and aluminium content
• Why are soils derived from limestone typically alkaline?


  Because of their calcium and magnesium content
• What is the pH range in which most crops will grow?


  1. 5–8.5
• What is the process of liming in soil management?


  • Spreading ground limestone on the soil
  • Ground limestone contains calcium and magnesium
  • Neutralizes acidic ions in the soil through cation exchange
• What are the specifications for ground limestone used in liming?


  • Moisture content no greater than 2.5%
  • Total Neutralising Value (TNV) no less than 90%
  • Must pass through a 3.35mm sieve
  • Not less than 35% should pass through a 0.15mm sieve