We conclude, then, that the soil forms the real wealth of the world. All our comforts and luxuries come in the first place, as we have seen, from the soil. The more crowded people become upon the earth, and the greater the number that engage in manufacturing and trade, the more important becomes the care and cultivation of the soil. If we do not take the best of care of the soil, there may come a time when there will not be food enough for us all.
CHAPTER NINE
THINGS OF WHICH SOIL IS MADE
Let us take a spadeful of soft, dark earth from the garden and see if we can find of what it is made.
We will first put the earth in a dish of water and stir it thoroughly. We notice that the water at once becomes muddy and that little particles of a dark substance rise to the surface. These particles appear to be pieces of stems and leaves.
This crumbling vegetation is peat, a substance which fills many swamps and, when cut into blocks and dried, is used for fuel. When scattered through the earth peat has a very different use. As the leaves and stems of plants die and slowly mingle with the earth, they give it the dark color, which usually extends down for two or three feet. As this vegetation changes, or decays, as we usually say, it furnishes a number of substances which supply food to the roots of growing plants. One of the most important of these is nitrogen, an invisible gas.
The decaying vegetation which we find mixed with the soil has other uses. It holds water and so helps to keep the soil moist. It makes the soil loose and more easy to cultivate. It absorbs heat from the sun and so helps to warm the soil. This vegetable matter, when it is completely decayed, we call humus. Soils that are rich in humus are usually very fertile.
We will now turn the muddy water into another dish, pour more clear water upon the material that remains in the bottom of the dish, and wash it again, repeating the work until the water is no longer muddied. We will set aside the dish containing the muddy water and examine what remains in the bottom of the dish that once contained the earth or soil. This is mostly sand, but with it are rough fragments of rock which can be crumbled in the hand. The greater number of the little sand grains are quartz. Some of them are clear like glass, others are reddish. In this quartz sand are a few grains of iron which the magnet picks out, and a number of scales of yellow mica.