Table of Contents
What is Soils Composition
Soils are classified according to the proportions of different sized particles they contain.
In the lab, special ultra fine sieves will be used to separate the particles, but an easy rule of thumb guide can easily be undertaken at home.
The technical term for this subject is “Soil Texture” but I think “Composition” is more expressive, so I will use it.
You will need a small sample of the soil that is typical of the area you want to test, some water (distilled or rainwater is best if your water comes from a source that is hard or produces limescale), and a tall flat bottomed straight-sided glass container at least half an inch or so in diameter. At a pinch, a large test tube will do, but something that shapes with a flat bottom like a tall thin jam jar is ideal. The amount of soil you need depends on the size of the container. It needs to be about half full of soil.
Put the soil in the container and fill to three-quarters full with water
Close the top with a lid or cork and shake it vigorously for a minute or two, so that all the soil particles are broken down into suspension in the water. Then put it somewhere to settle where it won’t be disturbed at all for a day or so, If you have a heavy soil, it might need a few days, and in this case, put it somewhere dark or the algae and bacteria will start to turn it green!
What happens is that the laws of gravity take over
The heaviest (largest) particles sink to the bottom first, and the fine clay particles are the last to settle out of suspension. Organic matter which is not decomposed either floats or sinks to the surface after the clay particles. Occasionally it will settle as a band before the clay.
You will be surprised how easy it is to see the separate bands of particle sizes as they are laid down, and by using a ruler up the side if the tube as a measure and a bit of imagination, you can get a total column height and are often able to measure the individual depths of sand, silt, and clay-sized grains, together with organic matter to give a proportion of each as a percentage of the whole sample.
A few soils cannot be assessed in this way
These are the peat moss or fen soils where the proportion of organic matter is perhaps more than 50% of the total sample. Other groups are the chalk or limestone soils where the overriding factor is that they are almost exclusively composed of chalk or limestone. These are described in the section dealing with the characteristics of different soil types.
Knowing the composition of your soil gives a better understanding of what your soil type is and, if you are an enthusiast, it provides the baseline against which to measure the effect of future improvements. For example: how much organic matter is now left in the soil from that lot you put on two years ago?