Module 6:

6.3 Soil science

6.3.4 What are the different soil types?

1  

There are two main soil classifications used in the UK: the SSEW (Soil Survey of England and Wales) and the USDA (United States Department of Agriculture).

The SSEW has 11 soil textural classifications, whilst the USDA has 12.

Each soil textural classification can have quite a variation in the proportions of the three soil particles of sand, silt and clay. For example, a sandy loam soil might contain from 50% to 85% sand, which is a significant difference.

The terms soil texture and soil structure can often be confused with each other, so we are just clarifying each meaning:

Soil texture: The proportion of sand, silt and clay in a soil. Soil texture is a stable feature of a soil and will only change when large quantities of additional mineral particles are mixed into the existing soil.

Soil structure: This is a description of how soil particles are arranged, or clumped together, into aggregates. The pore space within an aggregate and between aggregates is an important aspect of soil structure. A well-structured soil will generally provide good growing conditions, allow for good root growth, improved drainage and a drier surface. Poorly structured soils will provide the opposite of beneficial conditions, including poor drainage, waterlogged surface, poor root growth and increased match cancellations of games where sports are played on the area.

2  

For (natural soil) football pitch purposes the soil classifications could be grouped into light, medium, and heavy soils as follows, being based on the SSEW classification.

Please note that these are very general and subjective groupings.

• Light: Sand; Loamy sand; Sandy loam.
• Medium: Sandy clay loam; Sandy silt loam (to the higher end sand content), Clay loam (to the higher end sand content).
• Heavy: Silt loam; Silty clay loam; Clay loam; Sandy clay; Silty clay; Clay.

2   Particle sizes

Soil particles range from extremely small to quite large and have size diameter ranges as follows:

• Sand: 2mm - 0.06mm.
• Silt has a narrower range from 0.06 - 0.002mm.
• Clay is very fine and dust like particles having diameters of 0.002mm and below.

The following illustration demonstrates the relative size differences between these soil particles.

3   Material purchased for top-dressings

Where material, primarily sand or a very sandy soil, is purchased for use as a top-dressing on a football pitch, it will typically be specified being based on the USDA soil particle descriptors and parameters because there are more categories than exists with the UK version. This allows for a more fit for purpose sand to be purchased for pitch maintenance, renovation or construction. The size ranges are:

• Very Coarse Sand (2 to 1mm).
• Coarse Sand (1 to 0.5mm).
• Medium Sand (0.5 to 0.25mm).
• Fine Sand (0.25 to 0.125mm).
• Very Fine Sand (0.125 to 0.0625mm).
• Silt (0.0625mm to 0.002mm).
• Clay (< 0.002mm).

The majority of sands used for football pitch top-dressings will typically have most of the particle size range within the 0.250-0.500mm size, although there will still be some particles included that are in the 0.125-0.250mm size, as well as some within the 0.500 to 1mm range, although for this latter range the majority of those included would most likely aim to be within the first half of between 0.500 and 0.750mm size. This range provides a balance between appropriate drainage as well as suitable binding strength within a soil profile.