Types of Soil
Sands are not necessarily all sand, nor are clays necessarily all clay. In between these two extremes, both of which would be most unfavourable to plant growth, there are a number of different textural classes, of which 12 are commonly recognized in Great Britain. These 12 classes can be placed in three broad groups-coarse soils, medium-textured soils and fine-textured soils. Chalky soils may be coarse, medium or fine, depending on the other constituents.
The coarse-textured soils which include sands, loamy sands and sandy loams are valuable not only for their ease of cultivation but for their ‘earliness’, for they warm up quickly in spring.
Soon after wet weather they can be cultivated — hoeing and sowing can be carried on.
Poor drainage is rarely a problem. But it is often only a matter of a few days after rain that they dry out, and, unless there is a good water supply, young-soon die of drought. They are also very hungry soils, because bulky manures rot quickly and some plant nutrients are quickly washed out of reach of plant roots. Lime, also, is readily washed out, thus making such soils very prone to acidity.
MANAGEMENT OF COARSE SOILS
Coarse soils are best managed by heavy manuring with spongy humus-forming manures, and feeding little and often with fertilizers. The addition of clay or marl (a chalky clay) can work wonders provided the two soils are mixed thoroughly. But this treatment is rarely feasible, and it is usually necessary to depend onin large amounts for the improvement of sandy soils.
In the medium-texturedgroup are loams which contain sand, silt and clay in such well-balanced proportions that none produces a dominating influence. When moist they feel neither gritty, silty, nor sticky, and when a moist lump is rubbed with the thumb it leaves only a rough smear. They are among the most fertile soils, and with proper management almost any crop can be grown in them. They are apt to become cloddy when worked too soon after rain, but break down into a good tilth fairly easily when dry.
MANAGEMENT OF MEDIUM-TEXTURED SOILS
These soils are easy to manage, for they do not need any of the careful treatment required by either coarse- or fine-textured soils.
As the amounts of silt and clay in the soil increase, so the soil becomes more difficult to work. Such soils are slow to drain, the rain lies about in puddles for a long time, and the soils, being wet, are cold and cause delay in spring sowing and planting.
Care must be taken to choose the right time to cultivate them, for if they are dug or worked while they are too wet their structure will, be ruined for the whole season. When wet they are like plasticine, and when dry like concrete. They must be caught just at the right moment when they are neither too wet nor too dry, and then work on them must be done at full speed. The advantages of these soils are that they do not dry out as quickly as sandy soils do, and though plants take a long time to establish themselves in them, once they are established large yields of high-quality crops can be expected.
MANAGEMENT OF FINE-TEXTURED SOILS
Corrective treatment often includes artificial drainage or the mixing in of coarse organic matter such as peat oror strawy manure, in order to open up the soils and so let air into them and water through them. Where possible dig clay soils roughly in the autumn and allow them to remain in a rough state throughout the winter so as to expose the biggest surface area possible to frost action, which will pulverize the lumps into smaller pieces by the spring.
It is possible to decide whether a soil is clay or not by rolling a little when moist between thumb and finger. Moist clay will roll into long threads which bend into a ring without fracturing, and will polish if rubbed lightly with the thumb. Silt, although often simulating the heaviness of clay, feels smooth and lacks its stickiness. Clay soils are not necessarily acid. If, however, they do become acid, very large quantities of lime are necessary to counteract the acidity.