The Soil

Teacher’s Story

The soil is the sepulcher and the resurrection of all life in the past. The greater the sepulcher the greater the resurrection. The greater the resurrection the greater the growth. The life of yesterday seeks the earth to-day that new life may come from it tomorrow. The soil is composed of stone flour and organic matter (humus) mixed; the greater the store of organic matter the greater the fertility.—John Walton Spencer.

Because the child, after making mud pies, is told that his face is dirty, he naturally concludes that all soil is dirt. But it is only when out of place that it is dirt; for, in place, it is the home of miracles—the matrix from which comes that wonderful force which we call life. After the study of the brook, the crystals, the minerals and the rocks, the pupils are ready for a more careful study of the soil. However, most of the study in soils belongs to agriculture rather than to nature-study.

The Soil Makers

If we could go back to the very beginning, we should find that the soil consisted solely of broken off particles of rock—particles so finely ground by nature’s forces that we might properly call them “rock flour.” In our study of the brook, we noted that those stones with sharp corners were just beginning their experience in the brook mill, and those that were rounded out, forming pebbles, had their corners ground off in the making of the soil grist. And in the work of the brook we saw how this grinding was done, and how the soil grist is sifted, sorted, carried and dropped.

But there are other agencies besides water that help in grinding the stone flour. If we visit some rocky cliff, we are sure to find at its base a heap of stones, gravel and soil, which the geologists call talus. In our eastern country we know that these pebbles and soil were pried loose by Jack Frost with his ice wedges. The water filters into all the cracks and crevices of the rock, and since water, when freezing, is obliged to expand, the particles of rock were thereby torn loose and forced off and fell to the bottom of the cliff. Moreover, rocks expand when hot, and are often thus broken without the aid of water and frost. In the rocks of the desert, the changes in temperature pry off the rock particles, which the winds carry away to make up the sands of the desert. The winds hurl these sands against other rocks which are still standing, and hurl them with such force that more particles are torn off, making more sand. In fact, the wind, in some regions, grinds the rocks into stone flour as effectually as does the water in other places. Then, too, the gases of the air also cause rocks to decay. We know how iron rusts and falls to pieces through contact with the gases of the air. Some rocks decompose in a similar way. We often see that the inscriptions on old headstones have been almost obliterated, because the gases in the air have so decomposed the marble.

In addition to the other soil makers, there are the little plants which we call lichens. The spores of these plants are so minute that we cannot see them, and they drift about in the air until they find resting place upon some rock. Here they begin to grow, and as they grow they become strongly acid; they are thus enabled to eat a foothold into the rock, softening its surface and powdering it into stone flour. And in these situations other plants grow later, sending their roots down into every crack and crevice and thus prying off more of the rock.

The Soil Carriers

In the study of the brook we have seen how the water lifts, carries and deposits the soils; and since, at one time or another, the entire surface of the earth has been under water, we can see that water has been the most important of the soil carriers and has done the greatest work. The wind carries much soil, especially in the arid regions; the movements of the sand dunes in the deserts and on the seashores bear witness to what the wind can do as a soil carrier. But in the northern United States, from New England to the Dakotas, much of our soil has been carried by a great ice river that once upon a time flowed down upon our lands from the North. This great, slow-moving river, perhaps a mile or more high, plowed up the soil and stones, and freezing them fast carried and shoved them along under its great weight. After a time the ice melted and dropped its burden. Many of the stones were of granite taken up from the old mountains of northern Canada and ground off and rounded during their journey. We call these stones which were brought down to us from the North, “boulders;” and the soils which were brought along on the bottoms of glaciers and dropped and pressed down by the tremendous ice weight and thus made compact although unsorted, we call “hardpan.”

The Kinds of Soil

By the work of these soil makers and soil carriers, the rock flour was made. But if we should take some of it and plant our seeds in it, we should find that they would not grow thriftily, even though we watered them and gave them every care. The reason for this is that most rock flour does not have in it the substances which the plants most need for their growth. But if we should go to the woods and get some of the black woods-earth and mix it with rock flour, we should find that our plants would thrive. This rich, earth mold in the forest is almost wholly made up of matter once alive, but which is now decayed, and which we call “humus.” The more humus that we have in the rock flour, the richer it is in plant food, and the more plant growth it will support.

In general, soils may be divided into clay, sand, gravel, loam and humus.

Clay in its purest state is kaolinite, the result of weathering of feldspar, or mica. It is finely powdered and is used for pottery, while the less pure clays are used for brickmaking. Clayey soil is sticky and slippery when wet, and bakes hard and cracks when dry. It is hard to cultivate, but it absorbs moisture from the air and holds fast to its fertility, and is especially good for permanent pastures and meadows.

Sand, in a pure state, is made up mostly of finely broken particles of quartz and feldspar, and is used for the making of glass. A sandy soil is light and open and easy to work. It absorbs little water from the air and has little power for holding plant food, since the water washes it out. It is especially valuable for truck gardening, because it is a warm soil. It is warm because water does not evaporate from its surface rapidly.

Humus is composed of decayed animal and vegetable matter. It is very rich in plant food. Wherever there is humus in the soil it is likely to be darker in color than the stone flour.

Loam is a mixture of clay, sand and humus. For many crops it is the most desirable soil.