Читать книгу The First Book of Farming - C. L. Goodrich - Страница 19

The proper place to begin this study is in the field or garden. So we will make another excursion, and this time we will take with us a pick-axe or mattock, a shovel or two, a sharp stick, a quart or half-gallon pitcher, and several buckets of water. Arrived in the field, we will select a well-developed plant, say, of corn, potato or cotton. Then we will dig a hole about six feet long, three feet wide, and five or six feet deep, close to the plant, letting one side come about four or five inches from the base of the plant. It will be well to have this hole run across the row rather than lengthwise with it. Then with the pitcher pour water about the base of the plant and wash the soil away from the roots. Gently loosening the soil with the sharpened stick will hasten this work. In this way carefully expose the roots along the side of the hole, tracing them as far as possible laterally and as deep as possible, taking care to loosen them as little as possible from their natural position. (See Figs. 8 and 9.) Having exposed the roots of one kind of plant to a width and depth of five or six feet, expose the roots of six or eight plants of different kinds to a depth of about eighteen inches. As this may require more time than we can take for it in one day, it will be well to cover the exposed roots with some old burlaps or other material until we have them all ready, in order to keep them from drying and from injury.

When all is ready we will study the root system of each plant and answer these four questions:

In what part of the soil are most of the roots?

How deep do they penetrate the soil?

How near do they come to the surface of the soil?

How far do they reach out sidewise or laterally from the plant?

To the first question, "In what part of the soil are most of the roots?" you will give the following answers: "In the upper layer." "In the surface soil." "In the softer soil." "In the darker soil." "In the plowed soil."

These are all correct, but the last is the important one. Most of the roots will be formed in that part of the soil that has been plowed or spaded.

The second question, "How deep do the roots penetrate the soil?" is easily answered. Roots will be found penetrating the soil to depths of from two to six feet or more. (See Fig. 8.) The author has traced the roots of cowpea and soy bean plants to depths of five and six feet, corn roots four and five feet, parsnips over six feet. The sweet-potato roots illustrated in Fig. 8 penetrated the soil to a depth of over five feet. The roots of alfalfa or lucern have been traced to depths of from thirteen to sixteen feet or more.

How near to the surface of the soil do you find roots? Main side or lateral roots will be found within two or three inches of the surface, and little rootlets from these will be found reaching up as near the surface as there is a supply of moisture. After a continued period of wet weather, if the soil has not been disturbed, roots will be found coming to the very surface and even running along the top of the soil.

As to the fourth question, How far do roots reach out sidewise or laterally from the plant? you will find roots extending three, four, five and even six or more feet from the plant. They have numerous branches and rootlets, which fill all parts of the upper soil. Tree roots have been found thirty or forty feet in length.

We started on this observation lesson to find out something about the habit of growth of roots, so that we could tell how the roots do their work for the plant. But before going on with that question, let us stop right here and see whether we cannot find some very important lessons for the farmer and plant grower from what we have already seen. Is a knowledge of these facts we have learned about roots of any value to the farmer? Let us examine each case and see.

Of what value is it to the farmer to know that the larger part of the roots of farm plants develop in that part of the soil that has been plowed or spaded? It tells him that plowing tends to bring about the soil conditions which are favorable to the growth and development of roots. Therefore, the deeper he plows, the deeper is the body of the soil having conditions best suited for root growth, and the larger will be the crop which grows above the soil.

Of what value is it to the farmer to know that the roots of farm plants penetrate to depths of five or six feet in the soil? To answer this question it will be necessary for us to know something of the conditions necessary for root growth. So we will leave this till later.

Of what value is it to the farmer to know that many of the roots of his farm plants come very near the surface of the soil? It tells him that he should be careful in cultivating his crop to injure as few of these roots as possible. In some parts of the country, particularly in the South, the tool commonly used for field cultivation is a small plow. This is run alongside of the row, throwing the soil from the crop, and then again throwing the soil to the crop. Suppose we investigate, and see how this affects the roots of the crop.

FIG. 8.

Sweet potato roots. The great mass of the roots is in the plowed soil. Many of them reach out 5 to 7 feet from the plant.

Some reach a depth of more than 5 feet, and others come to the very surface of the soil.ToList

FIG. 9.

Soy-bean roots showing location, extent and depth of root-growth.ToList

Let us visit a field where some farmer is working a crop with a plow, or get him to do it, for the sake of the lesson. We will ask him to stop the plow somewhere opposite a plant, then we will dig a hole a little to one side of the plow and wash away the soil from over the plow (see Fig. 10), and see where the roots are. We will find that the plow-point runs under many strong-feeding lateral roots and tears them off, thus checking the feeding power of the plant, and consequently checking its growth. Now, if we can get a cultivator, we will have that run along the row and then wash away the loosened soil. It will be found that few, if any, of the main lateral roots have been injured.

Is it of any value to the farmer to know that roots extend laterally three to six feet and more on all sides of the plant, and that every part of the upper soil is filled with their branches and rootlets? This fact has a bearing on the application of manures and fertilizers. It tells the farmer that when he applies the manure and fertilizers to the soil he should mix the most of them thoroughly all through the soil, placing only a little directly in the row to start the young plant.

To find out how quickly the roots reach out into the soil, wash the soil away from some seedlings that have been growing only a few days, say, seven, ten and fifteen. (See Fig. 11.)

From our observations, then, we have learned the important lessons of deep, thorough plowing, careful shallow after-cultivation, and that fertilizers should be well mixed with the soil.

We are now ready to go back to our study of the habit of growth of roots, and can perhaps tell something of how the root does its work for the plant.

It is very easy to see how the roots hold the plant firmly in place, for they penetrate so thoroughly every part of the soil, and to such distances, that they hold with a grip that makes it impossible to remove the plant from the soil without tearing it free from the roots.

It is also on account of this very thorough reaching out through the soil that the roots are able to supply the plant with sufficient moisture and food.

We have doubtless observed that most of these roots are very slender and many very delicate. How did they manage to reach out into the soil so far from the plant? Or where does the root grow in length? To answer this question I will ask you to perform the following experiment:

Experiment.—Place some kernels of corn or other large seeds on a plate between the folds of a piece of wet cloth. Cover with a pane of glass or another plate. Keep the cloth moist till the seeds sprout and the young plants have roots two or three inches long. Now have at hand a plate, two pieces of glass, 4 by 6 inches, a piece of white cloth about 4 by 8 inches, a spool of dark thread, and two burnt matches, or small slivers of wood. A shallow tin pan may be used in place of the plate. Lay one pane of glass on the plate, letting one end rest in the bottom of the plate and the other on the opposite edge of the plate. At one end of the piece of cloth cut two slits on opposite sides about an inch down from the end and reaching nearly to the middle. Wet the cloth and spread it on the glass. Take one of the sprouted seeds, lay it on the cloth, tie pieces of thread around the main root at intervals of one-quarter inch from tip to seed. Tie carefully, so that the root will not be injured. Place the second pane of glass over the roots, letting the edge come just below the seed, slipping in the slivers of wood to prevent the glass crushing the roots. Wrap the two flaps of the cloth about the seed. Pour some water in the plate and leave for development. (Fig. 12.) A day or two of waiting will show conclusively that the lengthening takes place at the tip only, or just back of the tip. Is this fact of any value to the farmer? Yes. The soft tender root tips will force their way through a mellow soil with greater ease and rapidity than through a hard soil, and the more rapid the root growth the more rapid the development of the plant. This teaches us again the lesson of deep, thorough breaking and pulverizing of the soil before the crop is planted.

We have learned that the roots grow out into the soil in search of moisture and food, which they absorb for the use of the plant. How does the root take in moisture and food? Many people think that there are little mouths at the tips of the roots, and that the food and moisture are taken in through them. This is not so, for examination with the most powerful microscopes fails to discover any such mouths. Sprout seeds of radish, turnip or cabbage, or other seeds, on dark cloth, placed in plates and kept moist. Notice the fuzz or mass of root hairs near the ends of the tender roots of the seedlings (Fig. 13). Plant similar seed in sand or soil, and when they have started to grow pull them up and notice how difficult it is to remove all of the sand or dirt from the roots. This is because the delicate root hairs cling so closely to the soil grains. The root hairs are absorbing moisture laden with plant food from the surface of the soil particles. The root hairs are found only near the root tips. As the root grows older, its surface becomes tougher and harder, and the hairs die, while new ones appear on the new growth just back of the root tips, which are constantly reaching out after moisture and food. The moisture gets into the root hairs by a process called osmose. The following interesting experiment will give you an idea of this process or force of osmose.

FIG. 10.

A plow stopped in the furrow, to show what it does to the roots of plants when used for after-cultivation. Notice the point of the plow under the roots.ToList

FIG. 11.

A corn-plant ten days after planting the seed. To show how quickly the roots reach out into the soil. Some of the roots were over 18 inches long.ToList

Experiment.—Procure a wide-mouthed bottle, an egg, a glass tube about three inches long and a quarter-inch in diameter, a candle, and a piece of wire a little longer than the tube. Remove a part of the shell from the large end of the egg without breaking the skin beneath. This is easily done by gently tapping the shell with the handle of a pocket-knife until it is full of small cracks, and then, with the blade of the knife, picking off the small pieces. In this way remove the shell from the space about the size of a nickel. Remove the shell from the small end of the egg over a space about as large as the end of the glass tube. Next, from the lower end of the candle cut a piece about one-half inch long. Bore a hole in this just the size of the glass tube. Now soften one end of the piece of candle with the hole in it and stick it on to the small end of the egg so that the hole in the candle comes over the hole in the egg. Heat the wire, and with it solder the piece of candle more firmly to the egg, making a water-tight joint. Place the glass tube in the hole in the piece of candle, pushing it down till it touches the egg. Then, with the heated wire, solder the tube firmly in place. Now run the wire down the tube and break the skin of the egg just under the end of the tube. Fill the bottle with water till it overflows, and set the egg on the bottle, the large end in contact with the water (Fig. 14). In an hour or so the contents of the egg will be seen rising in the glass tube. This happens because the water is making its way by osmose into the egg through the skin, which has no openings, so far as can be discovered. If the bottle is kept supplied with water as fast as it is taken up by the egg, almost the entire contents of the egg will be forced out of the tube. In this way water in which plant food is dissolved enters the slender root hairs and rises through the plant.

Experiment.—This process of osmose may also be shown as follows (Fig. 15): Remove the shell from the large end of an egg without breaking the skin, break a hole in the small end of the egg and empty out the contents of the egg; rinse the shell with water. Fill a wide-mouthed bottle with water colored with a few drops of red ink. Fill the egg-shell partly full of clear water and set it on the bottle of colored water. Colored water will gradually pass through the membrane of the egg and color the water in the shell. Prepare another egg in the same way, but put colored water in the shell and clear water in the bottle. The colored water in the shell will pass through the skin and color the water in the bottle. Sugar or salt may be used in place of the red ink, and their presence after passing through the membrane may be detected by taste.