There are five main types of soil:- 1. Clay, 2. Sand, 3. Loam, 4. Chalk (or calcareous) 5. Peat,
These are only the basic types, the soil in any location may be a combination of one or more of them; thus there are clayey loams and sandy loams. Also there may be a difference between the soil exposed to the air and the underlying subsoil.
Clay may be likened in some ways to putty. It is very fine-grained, and smooth and silky to the touch. Even when it is well drained, it is wet, and so is difficult to cultivate during rainy periods and in the winter months. In fact, if it is dug or forked when wet, it has the nasty habit of settling down - or " panning," as it is called - like cement, and then it is very difficult to work afterwards.
Clays should be dug in the autumn, if possible, and left rough, so that the action of the frost and wind can pulverise them, and make them into an easily workable condition in the spring. These soils are said to be `late`, because it is impossible to get on them as early as sandy soils in the spring, and so the crops produced are later also. On the other hand, clay soils are much richer in plant food than sand, and this, in addition to their water-retention properties, makes them valuable in a dry season.
It is most important to see that clay soils are drained, and this is one of the best ways of improving them. Lime should be applied to clay soils regularly, as it prevents them from becoming so " sticky," and "opens" them up. During periods of draught, clay can become `rock hard` and crack, it`s not uncommon to see cracks 2 inches wide and 3 foot deep on lawns laid on clay.
2. Sandy soils
Sandy soils contain less than 10 per cent of clay, and consist of very small particles of silica and quartz. The amount of humus present will alter the colour and the texture.
Sand is a light and dry soil. It is one of the warmest soils as it warms up much more quickly in the spring due to its dryness. For this reason it is useful in producing early crops.
One of the advantages of a sandy soil is that it can be worked at any time of the year and it is comparatively easy to cultivate. On the other hand it is poor in plant foods, coarse-grained, and does not retain moisture.
The best way of describing loam is to say that it is an ideal blend of sand and clay. The sand being present to keep the soil open, and the clay, in its turn, ensuring that sufficient moisture-retention properties are there.
Obviously there are various types of loams, depending on the proportion of clay or sand present. Loam is generally considered the best soil for large numbers of plants. The ideal loam has all the advantages of sandy and clay soils, and none of their disadvantages. The sand present allows the plant roots to work easily throughout it ; the clay present helps to look after the plant food side, and prevents rapid drying out. In wet weather the water can percolate through quite quickly, and so the soil does not become waterlogged, and in dry weather it does not become too hard for the roots to work through.
4. Calcareous or chalky soils
Calcareous or chalky soils, more often than not, are very deficient in plant food and rather shallow. They are often very lacking in humus, and as much organic matter as possible should be added every year. They are more often calcareous by reason of the fact that they overlie chalk or limestone, and the fine particles of these substances may be found every time the land is cultivated. When wet, they are often very sticky and unpleasant, and so are difficult to work during rainy periods. In dry seasons they are disappointing, as they soon suffer from lack of water.
Because of the chalk present, the leaves of plants often become bright yellow in colour, owing to what is known as chlorosis. This yellowing may not affect the plants in any other way, but it usually means stunted growth. Chalky soils have the advantage that it is seldom necessary to lime them, and in them the clubfoot disease of cabbages, etc., does not flourish.
Into this group we can include the marls, though these are really a chalky clay. In the garden they are therefore treated in the same way as clay soils, except that, again, lime will not usually be necessary.
5. Peat soil
Peat soil has usually been derived from marsh land where there has been continuous growth and decay over thousands of years. The most outstanding feature of them is that they are usually absolutely free of lime and so are very " sour ". This sourness is produced by the decaying of the vegetable matter present, as peat soils contain more than 20 per cent of humus.
Peat is usually found in low-lying areas, and so may be waterlogged and may need pipe draining. Certain crops, like celery, for instance, do very well on peat soils. Brown peat is more easy to work than the black, heavy bog-like peat. Once peat soils are well worked and limed, they can prove very valuable - in fact some plants (acid lovers), like rhododendrons and azaleas, prefer these soils to any other.
Most soils are about a foot in depth, though many of them are no deeper than eight or nine inches. Below this is what gardeners call the subsoil, which may be similar in character to the material above, and yet which may not contain available plant foods. It is important to try and get the soil to as great a depth as possible.
Of course there are places where the layer of soil may be only a few inches over hard rock, and, in others the soil type may go down as far as you can dig. Subsoil affects the gardener, chiefly because it either allows or impedes drainage of the top soil. For instance, if you have a light loam over gravel or sand, you can be assured that all excessive moisture will be quickly carried away. It is unfortunate to have an easily workable loam over clay, as then the movement of water is stopped and the surface can become waterlogged.
Therefore you must take notice of both the soil and the subsoil, as the one is the complement of the other.