Soil is made up of mineral particles which vary in shape, size and chemical composition. Sand particles are quite large because they break down slowly. Other minerals break down more quickly into clay particles. These are extremely small – many thousands of times smaller than coarse sand – and they have an important effect on the physical and chemical properties of the soil. The size of the particles – coarse sand, fine sand, silt and clay – and the proportions in which they occur determine soil texture.
Sandy soils have large particles with large spaces, called pore spaces, between them. They drain readily, have good aeration and are easy to cultivate. For this reason they are often called ‘light’ soils. However, very sandy soils are less effective at retaining water and nutrients than other soil types.
Clay soils have small particles and little pore space. They store water well, often too well for good drainage and aeration, and retain plant nutrients. Clay particles attract and hold nutrients on their surface. Clay soils can be difficult to cultivate and are often called ‘heavy’.
All soils between the extremes of sand and clay are referred to as loams. They are mixtures of coarse and fine particles. They are divided into such categories as sandy loam (more sand than clay) and clay loam (more clay than sand). You can identify the soil in your garden by the feel in your hand when the soil is slightly moist.
This information is from the Yates Garden Guide: fully revised & updated 44th edition, HarperCollins, $39.99. You can have this information and so much more at your fingertips by purchasing the Yates Garden Guide, available at all leading bookstores and Bunnings stores.