"That trouble always comes from a lack of one or the other is quite sufficient to prove to us that these are essential. Just see how sand lacks water, as does lime soil too! But there is plenty of air space, unless these soils are too finely powdered. Now look at clay! plenty of water, but how about the air? When clay begins its packing, then air is excluded.
"So one of the questions to be asked in soil improvement concerns the water and air problem. We must have air spaces, and we must have water-holding capacity.
"Before we go home I must just speak of soil and subsoil. When you strike your spade down into the earth and lay bare a section of the soil this is what you see: on top is the plant growth, the soil beneath this, dark in texture and about our locality of a depth of from six to eight inches. This layer is called the topsoil. In sections of the West it is several feet in depth. Now below the topsoil is a lighter coloured, less fertile, more rocky layer, the subsoil. Beneath comes a layer of rock.
"And finally you may be a bit confused by the word loam. It is often given as one of the classes of soils. By loam we mean clay, sand and humus. You will often hear people speaking of a sandy loam or a clayey loam according as there is a greater percentage of sand or clay in the soil.
"Next Friday I shall talk about soil fertility. So trot home lively now!"
II
PLANT FOOD
A soil, as I have said before to the boys, may contain all the food necessary for plant growth and still not support any good growth at all. That means then we ought to be able in some way or other so to understand the soil that it will be possible to unlock these good things for the plants to live on.