SOIL STRUCTURE

This week we will continue to learn more about Top Soil Selection.

Soil structure is defined by the way individual particles of sand, silt, and clay are held together as clusters. Single particles when assembled appear as larger particles. These are called aggregates or clusters.

Aggregation of soil particles can occur in different patterns, resulting in different soil structures. The circulation of water in the soil varies greatly according to structure, Therefore, it is important for you to know about the structure of the soil when you plan to build a sports field.

GOOD SOIL STRUCTURE

Soils with good structure will have moderate organic matter contents (perhaps 3% or more), some clay, and calcium as the main exchangeable cat ion.

A good structure means that the mineral particles are bound together into crumbs that are then loosely arranged into larger groupings. Cultivation breaks these groupings to give a seedbed of soil crumbs smaller grouping or crumbs. Such soil is said to be friable and when cultivated to have good tilth.

A soil of poor structure may break down either into a powder of individual particles and very small crumbs or into large clods. Tilth is poor, and so maybe seed germination. The crumbs in the soil of good structure resist being broken by cultivation or rain.

A good structure means that there are spaces between crumbs that will have 50% of their bulk as solids, 25% voids for air and 25% pore space for water.

PORE SPACE

The next factor is pore space, also known as porosity. It refers to the volume of soil voids/spaces that can be filled by water and/or air. Loose, porous soils have lower densities and greater porosities than tightly packed soils. Namely clayey and organic soils are more porous than sandy soils. A large number of small particles in a volume of soil produces a large number of soil pores, in comparison to a few large particles that can occupy the same volume of soil so there are fewer pores and less porosity. As noted in the previous section sand particles are the largest therefore the sandy soils are less porous in comparison to clayey and organic soils. The impact on the soil porosity is most noticeable under moist to wet soil conditions, which encourage soil particles to be squashed together resulting in an increase in compaction within the soil. Soil porosity can be divided into Air-Filled Porosity and Water-Filled porosity.

Pore spaces are vital to the health and survival of the grass plant. No two objects can occupy the same space at the same time. If there is no pore space, there are no roots. When pore spaces are squeezed out of the soil, oxygen cannot move down to the root system nor can carbon dioxide, produced by the grassroots and microorganisms, exhaust out of the soil.

Media Department; The RS Group