Physical Properties of Soil Class Test

Physical Properties of Soil

• Soil texture is a measure of the proportion of different sized particles (sand, silt, clay) in a soil sample.
• Soil structure is the arrangement of soil particles in a soil.

Particle Size and Soil Types

• Mineral matter is derived from parent material and is classified by size.
• Soil types:
  • Sandy soils: large air pores, free draining, easy to work with, but dries out quickly and has poor nutrient retention.
  • Clay soils: holds water easily, fertile, but has poor drainage and can lead to waterlogging.
  • Loam soil: a soil that contains equal amounts of sand, silt, and clay, with intermediate characteristics of clay and sandy soils.

Organic Matter

• Humus is the product of the breakdown of organic matter (humification).
• Humus is a dark, sticky material that absorbs water, improves soil structure, and is rich in nutrients.

Soil Texture and Drainage

• The breakdown of the parent rock impacts soil texture, making it a fixed property of soil that cannot be changed.
• The ratio of sand, silt, and clay determines the soil texture.
• Methods to determine soil texture include hand testing, sedimentation, and soil sieve analysis.

Soil Structure

• Key points for soil structure:
  • Good structure is necessary for healthy plant growth, nutrient availability, and microbial activity.
  • Floccules contain micropores, while pores between adjacent floccules are larger and called macropores.

Impact of Various Factors on Soil Structure

• Factor 1 – Soil Compaction:
  • Destroys soil structure.
  • Reduces pore space, drainage, and aeration.
  • Plant roots cannot penetrate soil, reducing growth.
  • Less soil organisms (e.g., worms).
• Factor 2 – Organic Matter Loss:
  • Poorer structure.
  • Less nutrient availability.
  • Lower water retention.
  • Lower CEC (cation exchange capacity).
• Factor 3 – Erosion, Sedimentation, and Weathering:
  • Loss of OM-filled topsoil.
  • Sediments can put water quality at risk by carrying excess nutrients (manure) and pathogens.

Soil Water

• Water is held in soil as it is attracted to the negative charges of the clay particle.
• Water forms a thin layer around the soil particle, known as hygroscopic water.
• Capillary water: held in pores within and between soil aggregates.
• Gravitational water: moved through the soil by gravity, available on a temporary basis to plants.

Soil Colour

• Dark brown, black colour: rich in humus, highly fertile soils, and nutrient rich.
• Light colour or grey soils: low fertility, low in nutrients, lacking in humus, and suffers from leaching.

Soil Temperature

• Lower temperature results in lower germination.
• Lower temperature results in lower water and mineral uptake.

Learn about the physical properties of soil, including soil texture, structure, and types. Understand the characteristics of sandy and clay soils.