Lessons on Soil

by Edward J. Russell

Fig. 23. Pieces of grass, leaves, etc. change into plant food in the surface but not to any great extent in the subsoil. Mustard is growing in surface soil (Pot 3), in surface soil and pieces of grass (Pot 6), in subsoil (Pot 4), and in subsoil and grass (Pot 7)

Now let us look at these results carefully. The experiment with surface soil shows that the pieces of stem and leaf have furnished a good deal of food to the mustard and have caused a gain of 24.3 grams in the crop. If we knew what the pieces were made of we could push the experiment still further and find out more about plant food, but this involves chemical problems and must be left alone for the present. We can, however, say that plant remains are an important source of plant food, and since we suppose the black material of the soil to be made of plant remains (see p. 36), it will be quite fair to say also that this black material, the humus, is a source of plant food. We have therefore answered the question we set, and we can explain some at any rate of the differences between the surface soil and the subsoil. The surface soil contains a great deal of the black material, which forms plant food, while the subsoil does not. Thus plants grow well on the surface soil and starve on the subsoil. We can also explain why gardeners and farmers speak of black soils as rich soils; they contain more than other soils of this black material that makes plant food. Still further, we can explain why the farmer often sows plants like mustard, tares or clover, and then ploughs them into the ground. They are not wasted, but they make food for the next crop that goes in.

Now let us turn to the results of the subsoil experiments. The leaves and stems have increased the crop, but only by 5.4 grams: they have not been nearly so effective as in the surface soil. It is evident that the mustard did not feed directly on the leaves and stems put in; if it had there should have been an equal gain in both cases. The leaves and stems clearly have to undergo some change before they are made into plant food and the soil has something to do with this change. After the crops are cut the soils should be tipped out and examined. More of the original pieces of leaf and stem are found in the subsoil than in the surface soil. That is to say, there has been more change in Pot 6 containing surface soil than in Pot 7 containing subsoil. The "something," whatever it may be, that changes plant remains like leaves, stems, pieces of grass, roots, etc. into plant food therefore acts better in the surface soil than in the subsoil. Here then we have another difference between surface and subsoils.

SUMMARY. The experimental results obtained in this chapter may now be summed up as follows:—

(1) Plant food is present in the top soil only and not to any extent in the subsoil.

(2) There is not much present, so little indeed that we could not detect it by weighing.

(3) It is, however, always being made in the top soil, if water is present. Only little is made from the subsoil.

(4) The remains of leaves, stems, roots, etc. furnish an important source of plant food.

(5) But they have first to undergo some change, and the agent producing this change is more active in the top soil than in the subsoil.

(6) The top soil is much the most useful part of the soil and should never be buried during digging or trenching, but always carefully kept on top.

CHAPTER VII

THE DWELLERS IN THE SOIL

Apparatus required.

Garden soil. Six bottles and corks [1]. Twelve Erlenmeyer flasks, 50 c.c. capacity [2]. Cotton wool. Milk (about half a pint). Leaf gelatine. Soil baked in an oven. Six saucers [3]. The apparatus in Fig. 28 (two lots). Wash bottle containing lime water (Fig. 27, also p. 19).

In digging a garden a number of little animals are found, such as earthworms, beetles, ants, centipedes, millipedes and others. There are also some very curious forms of vegetable life. By carefully looking about it is not difficult to find patches of soil covered with a greenish slimy growth; they are found best under bushes where the soil is not disturbed, or else where the soil has been pressed down by a footmark and not touched since. Any good soil left undisturbed for a time shows this growth.

Put some fresh moist garden soil into a bottle and cork it up tightly so that it keeps moist. Write the date on the bottle and then leave it in the light where you can easily see it. After a time—sometimes a long, sometimes a shorter time—the soil becomes covered with a slimy growth, greenish in colour, mingled here and there with reddish brown. The longer the soil is left the better. Often after several months something further happens; little ferns begin to grow and they live a very long time indeed. There is at Rothamsted a bottle of soil that was put up just like this as far back as 1874. For a number of years past a beautiful fern has been growing inside the bottle, and even now it is very healthy and vigorous. If, instead of being kept moist, the rich garden soil is left in a dry shed during the whole of the winter so that it gradually loses its moisture, it will generally show quite a lot of white fluffy growth.

All of these living things are very wonderful, and some, especially earthworms, are very useful to gardeners and farmers.

After a shower of rain look carefully in the garden or else on a lawn, common, or pasture field where the grass is closely grazed by cattle or does not naturally grow long, and you will find numbers of tiny heaps of soil scattered about. Carefully brush away a heap and a little hole is seen, now hit the ground near it a few times with a stick or stamp on it with your foot and the worm, if he is near the top, comes up. When he is safely out of the way dig carefully down with a knife or trowel so as to examine the hole or "burrow." At the top you generally find it lined with pieces of grass or leaves that the worm has pulled in; lower down the lining comes to an end, but the colour of the burrow is redder than that of the rest of the soil wherever the soil has a greenish tinge. These holes are useful because they let air and water down into the soil.