Agriculture for Beginners Part 3
If people in those days, with new and fertile soils, could use manures profitably, how much more ought we to use them in our time, when soils have lost their virgin fertility, and when the plant food in the soil has been exhausted by years and years of cropping!
To sell year after year all the produce grown on land is a sure way to ruin it. If, for example, the richest land is planted every year in corn, and no stable or farmyard manure or other fertilizer returned to the soil, the land so treated will of course soon become too poor to grow any crop. If, on the other hand, clover or alfalfa or corn or cotton-seed meal is fed to stock, and the manure from the stock returned to the soil, the land will be kept rich. Hence those farmers who do not sell such raw products as cotton, corn, wheat, oats, and clover, but who market articles made from these raw products, find it easier to keep their land fertile. For ill.u.s.tration: if instead of selling hay, farmers feed it to sheep and sell meat and wool; if instead of selling cotton seed, they feed its meal to cows, and sell milk and b.u.t.ter; if instead of selling stover, they feed it to beef cattle, they get a good price for products and in addition have all the manure needed to keep their land productive and increase its value each year.
[Ill.u.s.tration:FIG. 14. RELATION OF HUMUS TO GROWTH OF CORN 1, clay subsoil; 2, same, with fertilizer; 3, same, with humus]
If we wish to keep up the fertility of our lands we should not allow anything to be lost from our farms. All the manures, straw, roots, stubble, healthy vines--in fact everything decomposable--should be plowed under or used as a top-dressing. Especial care should be taken in storing manure. It should be watchfully protected from sun and rain. If a farmer has no shed under which to keep his manure, he should scatter it on his fields as fast as it is made.
[Ill.u.s.tration: FIG. 15. THE COTTON PLANT WITH AND WITHOUT FOOD In left top pot, no plant food; in left bottom pot, plant food scanty; in both right pots, all elements of plant food present]
He should understand also that liquid manure is of more value than solid, because that important plant food, nitrogen, is found almost wholly in the liquid portion. Some of the phosphoric acid and considerable amounts of the potash are also found in the liquid manure.
Hence economy requires that none of this escape either by leakage or by fermentation. Sometimes one can detect the smell of ammonia in the stable. This ammonia is formed by the decomposition of the liquid manure, and its loss should be checked by sprinkling some floats, acid phosphate, or muck over the stable floor.
Many farmers find it desirable to buy fertilizers to use with the manure made on the farm. In this case it is helpful to understand the composition, source, and availability of the various substances composing commercial fertilizers. The three most valuable things in commercial fertilizers are nitrogen, potash, and phosphoric acid.
The nitrogen is obtained from (1) nitrate of soda mined in Chile, (2) ammonium sulphate, a by-product of the gas works, (3) dried blood and other by-products of the slaughter-houses, and (4) cotton-seed meal.
Nitrate of soda is soluble in water and may therefore be washed away before being used by plants. For this reason it should be applied in small quant.i.ties and at intervals of a few weeks.
Potash is obtained in Germany, where it is found in several forms. It is put on the market as muriate of potash, sulphate of potash, kainite, which contains salt as an impurity, and in other impure forms. Potash is found also in _unleached_ wood ashes.
Phosphoric acid is found in various rocks of Tennessee, Florida, and South Carolina, and also to a large extent in bones. The rocks or bones are usually treated with sulphuric acid. This treatment changes the phosphoric acid into a form ready for plant use.
These three kinds of plant food are ordinarily all that we need to supply. In some cases, however, lime has to be added. Besides being a plant food itself, lime helps most soils by improving the structure of the grains; by sweetening the soil, thereby aiding the little living germs called _bacteria_; by hastening the decay of organic matter; and by setting free the potash that is locked up in the soil.
CHAPTER II
THE SOIL AND THE PLANT
SECTION VIII. ROOTS
[Ill.u.s.tration: FIG. 16. ROOT-HAIRS ON A RADISH]
You have perhaps observed the regularity of arrangement in the twigs and branches of trees. Now pull up the roots of a plant, as, for example, sheep sorrel, Jimson weed, or some other plant. Note the branching of the roots. In these there is no such regularity as is seen in the twig.
Trace the rootlets to their finest tips. How small, slender, and delicate they are! Still we do not see the finest of them, for in taking the plant from the ground we tore the most delicate away. In order to see the real construction of a root we must grow one so that we may examine it uninjured. To do this, sprout some oats in a germinator or in any box in which one gla.s.s side has been arranged and allow the oats to grow till they are two or more inches high. Now examine the roots and you will see very fine hairs, similar to those shown in the accompanying figure, forming a fuzz over the surface of the roots near the tips. This fuzz is made of small hairs standing so close together that there are often as many as 38,200 on a single square inch. Fig. 17 shows how a root looks when it has been cut crosswise into what is known as a cross section. The figure is much increased in size. You can see how the root-hairs extend from the root in every direction. Fig. 18 shows a single root-hair very greatly enlarged, with particles of sand sticking to it.
[Ill.u.s.tration: FIG. 17. A SLICE OF A ROOT Highly magnified]
These hairs are the feeding-organs of the roots, and they are formed only near the tips of the finest roots. You see that the large, coa.r.s.e roots that you are familiar with have nothing to do with _absorbing_ plant food from the soil. They serve merely to _conduct_ the sap and nourishment from the root-hairs to the tree.
When you apply manure or other fertilizer to a tree, remember that it is far better to supply the fertilizer to the roots that are at some distance from the trunk, for such roots are the real feeders. The plant food in the manure soaks into the soil and immediately reaches the root-hairs. You can understand this better by studying the distribution of the roots of an orchard tree, shown in Fig. 19. There you can see that the fine tips are found at a long distance from the main trunk.
[Ill.u.s.tration: FIG. 18. A ROOT-HAIR WITH PARTICLES OF SOIL STICKING TO IT]
You can now readily see why it is that plants usually wilt when they are transplanted. The fine, delicate root-hairs are then broken off, and the plant can but poorly keep up its food and water supply until new hairs have been formed. While these are forming, water has been evaporating from the leaves, and consequently the plant does not get enough moisture and therefore droops.
[Ill.u.s.tration: FIG. 19. DISTRIBUTION OF APPLE-TREE ROOTS]
Would you not conclude that it is very poor farming to till deeply any crop after the roots have extended between the rows far enough to be cut by the plow or cultivator? In cultivating between corn rows, for example, if you find that you are disturbing fine roots, you may be sure that you are breaking off millions of root-hairs from each plant and hence are doing harm rather than good. Fig. 20 shows how the roots from one corn row intertangle with those of another. You see at a glance how many of these roots would be destroyed by deep cultivation. Stirring the upper inch of soil when the plants are well grown is sufficient tillage and does no injury to the roots.
[Ill.u.s.tration: FIG. 20. CORN ROOTS REACH FROM ROW TO ROW]
A deep soil is much better than a shallow soil, as its depth makes it just so much easier for the roots to seek deep food. Fig. 21 ill.u.s.trates well how far down into the soil the alfalfa roots go.
[Ill.u.s.tration: FIG. 21 ALFALFA ROOT]
=EXERCISE=
Dig up the roots of several cultivated plants and weeds and compare them. Do you find some that are fine or fibrous? some fleshy like the carrot? The dandelion is a good example of a tap-root.
Tap-roots are deep feeders. Examine very carefully the roots of a medium-sized corn plant. Sift the dirt away gently so as to loosen as few roots as possible. How do the roots compare in area with the part above the ground? Try to trace a single root of the corn plant from the stalk to its very tip. How long are the roots of mature plants? Are they deep or shallow feeders? Germinate some oats or beans in a gla.s.s-sided box, as suggested, and observe the root-hairs.
SECTION IX. HOW THE PLANT FEEDS FROM THE SOIL
Plants receive their nourishment from two sources--from the air and from the soil. The soil food, or mineral food, dissolved in water, must reach the plant through the root-hairs with which all plants are provided in great numbers. Each of these hairs may be compared to a finger reaching among the particles of earth for food and water. If we examine the root-hairs ever so closely, we find no holes, or openings, in them. It is evident, then, that no solid particles can enter the root-hairs, but that all food must pa.s.s into the root in solution.
An experiment just here will help us to understand how a root feeds.
[Ill.u.s.tration: FIG. 22. EXPERIMENT TO SHOW HOW ROOTS TAKE UP FOOD]
=EXPERIMENT=
Secure a narrow gla.s.s tube like the one in Fig. 22. If you cannot get a tube, a narrow, straight lamp-chimney will, with a little care, do nearly as well. From a bladder made soft by soaking, cut a piece large enough to cover the end of the tube or chimney and to hang over a little all around. Make the piece of bladder secure to the end of the tube by wrapping tightly with a waxed thread, as at B. Partly fill the tube with mola.s.ses (or it may be easier in case you use a narrow tube to fill it before attaching the bladder). Put the tube into a jar or bottle of water so placed that the level of the mola.s.ses inside and the water outside will be the same. Fasten the tube in this position and observe it frequently for three or four hours. At the end of the time you should find that the mola.s.ses in the tube has risen above the level of the liquid outside. It may even overflow at the top. If you use the lamp-chimney the rise will not be so clearly seen, since a greater volume is required to fill the s.p.a.ce in the chimney. This increase in the contents of the tube is due to the entrance of water from the outside. The water has pa.s.sed through the thin bladder, or membrane, and has come to occupy s.p.a.ce in the tube. There is also a pa.s.sage the other way, but the mola.s.ses can pa.s.s through the bladder membrane so slowly that the pa.s.sage is scarcely noticeable.
There are no holes, or openings, in the membrane, but still there is a free pa.s.sage of liquids in both directions, although the more heavily laden solution must move more slowly.
A root-hair acts in much the same way as the tube in our experiment, with the exception that it is so made as to allow certain substances to pa.s.s in only one direction, that is, toward the inside. The outside of the root-hair is bathed in solutions rich in nourishment. The nourishment pa.s.ses from the outside to the inside through the delicate membrane of the root-hair. Thus does food enter the plant-root. From the root-hairs, foods are carried to the inside of the root.
From this you can see how important it is for a plant to have fine, loose soil for its root-hairs; also how necessary is the water in the soil, since the food can be used only when it is dissolved in water.
This pa.s.sage of liquids from one side of a membrane to another is called _osmosis_. It has many uses in the plant kingdom. We say a root takes nourishment by osmosis.
SECTION X. ROOT-TUBERCLES
Tubercle is a big word, but you ought to know how to p.r.o.nounce it and what is meant by root-tubercles. We are going to tell you what a root-tubercle is and something about its importance to agriculture. When you have learned this, we are sure you will want to examine some plants for yourself in order that you may see just what tubercles look like on a real root.
Root-tubercles do not form on all kinds of plants that farmers grow.
They are formed only on those kinds that botanists call _legumes_. The clovers, cowpeas, vetches, soy beans, and alfalfa are all legumes. The tubercles are little knotty, wart-like growths on the roots of the plants just named. These tubercles are caused by tiny forms of life called, as you perhaps already know, bacteria, or _germs_.
[Ill.u.s.tration: FIG. 23. TUBERCLES ON CLOVER ROOTS The specimen at the right was grown in soil inoculated with soil from an old clover field. The one at the left was grown in soil not inoculated]
Instead of living in nests in trees like birds or in the ground like moles and worms, these tiny germs, less than one twenty-five thousandth of an inch long, make their homes on the roots of legumes. Nestling snugly together, they live, grow, and multiply in their sunless homes.
Through their activity the soil is enriched by the addition of much nitrogen from the air. They are the good fairies of the farmer, and no magician's wand ever blessed a land so much as these invisible folk bless the land that they live in.