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Properties of soil

Themes: Texture and Structure | Pores and Soil water | Important Soil Chemistry | Quiz

Very fine soil particles forming a crust over the soil. This crust can even prevent rain soaking in causing water runoff, even flooding. The character and make-up of the soil play an important part in the behaviour of soils and what they can be used for. Two of the most important properties of soils are their texture and structure. By texture, we mean what soils are composed of and how this affects the way they feel and their cultivation. The main components of soil texture are: sand, silt and clay particles and organic matter. For example, soils that are dominantly composed of sand-sized particles feel gritty They contain lots of pores because of the way the grains stack together. This also means that rainwater entering the soil can easily drain away through the soil which leads to the soils being quite droughty. Clay soils by comparison contain many smaller pores which means that water does not pass through the soil as freely and means they can become waterlogged in wet periods and are sometimes difficult to cultivate.

Most soils benefit also from the presence of organic matter which comes from decaying plant remains. Organic matter plays an important part in topsoil structures and is the major 'glue' holding particles together It can improve the workability of most soils whatever their texture. This is why farmers often add farmyard manure to the soil to increase the amount of organic matter. This then leads to the development of well structured soils, easy to work, and ideal for farming. Gardeners also maintain good levels of organic matter in their soil for the same reasons.

The soil jamjar experiment shows clearly the organic matter component in soil. To learn more, see the JamJar experiment in the activities section. The components of soil described above rarely occur as separate particles. There is, for example a strong bond between decomposed organic matter and the clay fraction of soils. In most soils, the particles are moulded together into aggregates to form the architecture of the soil. Compare the architecture of a house - it is built with bricks and mortar and has entrances, rooms and corridors - a soil has the mineral particles, organic matter and these are used to build the architectural structure of the soil. Most soils have a structure which takes the form of aggregates of soil particles separated by pores (holes). Roots pass through these pores in search of water. Depending on the soil texture, amounts of organic matter and the way the soils are managed, the soil structure will vary with depth in the soil and from one soil type to another. The main types of soil structure are crumb, granular, blocky, platy and prismatic.

Themes: Texture and Structure | Pores and Soil water | Important Soil Chemistry | Quiz