EXPERIMENTTake a lamp-chimney and fill it with fine, dry dirt. The dirt from a road or a field will do. Tie over the smaller end of the lamp-chimney a piece of cloth or a pocket handkerchief, and place this end in a shallow pan of water. If the soil in the lamp-chimney is clay and well packed, the water will quickly rise to the top.By filling three or four lamp-chimneys with as many different soils, the pupil will see that the water rises more slowly in some than in others.Now take the water pan away, and the water in the lamp-chimneys will gradually evaporate. Study for a few days the effect of evaporation on the several soils.
EXPERIMENT
Take a lamp-chimney and fill it with fine, dry dirt. The dirt from a road or a field will do. Tie over the smaller end of the lamp-chimney a piece of cloth or a pocket handkerchief, and place this end in a shallow pan of water. If the soil in the lamp-chimney is clay and well packed, the water will quickly rise to the top.
By filling three or four lamp-chimneys with as many different soils, the pupil will see that the water rises more slowly in some than in others.
Now take the water pan away, and the water in the lamp-chimneys will gradually evaporate. Study for a few days the effect of evaporation on the several soils.
A wise man was once asked, "What is the most valuable improvement ever made in agriculture?" He answered, "Drainage." Often soils unfit for crop-production because they contain too much water are by drainage rendered the most valuable of farming lands.
Drainage benefits land in the following ways:
1. It deepens the subsoil by removing unnecessary water from the spaces between the soil particles. This admits air. Then the oxygen which is in the air, by aiding decay, prepares plant food for vegetation.
2. It makes the surface soil, or topsoil, deeper. It stands to reason that the deeper the soil the more plant food becomes available for plant use.
3. It improves the texture of the soil. Wet soil is sticky. Drainage makes this sticky soil crumble and fall apart.
4. It prevents washing.
5. It increases the porosity of soils and permits roots to go deeper into the soil for food and moisture.
6. It increases the warmth of the soil.
7. It permits earlier working in spring and after rains.
Fig. 9.Fig. 9. Laying a Tile Drain
8. It favors the growth of germs which change the unavailable nitrogen of the soil into nitrates; that is, into the form of nitrogen most useful to plants.
9. It enables plants to resist drought better because the roots go into the ground deeper early in the season.
A soil that is hard and wet will not grow good crops. The nitrogen-gathering crops will store the greatest quantity of nitrogen in the soil when the soil is open to the freecirculation of the air. These valuable crops cannot do this when the soil is wet and cold.
Sandy soils with sandy subsoils do not often need drainage; such soils are naturally drained. With clay soils it is different. It is very important to remove the stagnant water in them and to let the air in.
When land has been properly drained the other steps in improvement are easily taken. After soil has been dried and mellowed by proper drainage, then commercial fertilizers, barnyard manure, cowpeas, and clover can most readily do their great work of improving the texture of the soil and of making it fitter for plant growth.
Fig. 10.Fig. 10. A Tile in Position
Tile Drains.Tile drains are the best and cheapest that can be used. It would not be too strong to say that draining by tiles is the most perfect drainage. Thousands of practical tests in this country have proved the superiority of tile draining for the following reasons:
1. Good tile drains properly laid last for years and do not fill up.
2. They furnish the cheapest possible means of removing too much water from the soil.
3. They are out of reach of all cultivating tools.
4. Surface water in filtering through the tiles leaves its nutritious elements for plant growth.
EXPERIMENTSTo show the Effect of Drainage.Take two tomato cans and fill both with the same kind of soil. Punch several holes in the bottom of one to drain the soil above and to admit air circulation. Leave the other unpunctured. Plant seeds of any kind in both cans and keep in a warm place. Add every third day equal quantities of water. Let seeds grow in both cans and observe the difference in growth for two or three weeks.To show the Effect of Air in Soils.Take two tomato cans; fill one with soil that is loose and warm, and the other with wet clay or muck from a swampy field. Plant a few seeds of the same kind in each and observe how much better the dry, warm, open soil is for growing farm crops.
EXPERIMENTS
To show the Effect of Drainage.Take two tomato cans and fill both with the same kind of soil. Punch several holes in the bottom of one to drain the soil above and to admit air circulation. Leave the other unpunctured. Plant seeds of any kind in both cans and keep in a warm place. Add every third day equal quantities of water. Let seeds grow in both cans and observe the difference in growth for two or three weeks.
To show the Effect of Air in Soils.Take two tomato cans; fill one with soil that is loose and warm, and the other with wet clay or muck from a swampy field. Plant a few seeds of the same kind in each and observe how much better the dry, warm, open soil is for growing farm crops.
We hear a great deal about the exhaustion or wearing out of the soil. Many uncomfortable people are always declaring that our lands will no longer produce profitable crops, and hence that farming will no longer pay.
Now it is true, unfortunately, that much land has been robbed of its fertility, and, because this is true, we should be most deeply interested in everything that leads to the improvement of our soils.
When our country was first discovered and trees were growing everywhere, we had virgin soils, or new soils thatwere rich and productive because they were filled with vegetable matter and plant food. There are not many virgin soils now because the trees have been cut from the best lands, and these lands have been farmed so carelessly that the vegetable matter and available plant food have been largely used up. Now that fresh land is scarce it is very necessary to restore fertility to these exhausted lands. What are some of the ways in which this can be done?
Fig. 11.Fig. 11. Clover is a Soil-Improver
There are several things to be done in trying to reclaim worn-out land. One of the first of these is to till the land well. Many of you may have heard the story of the dying father who called his sons about him and whispered feebly, "There is great treasure hidden in the garden." The sons could hardly wait to bury their dead father before, thud,thud, thud, their picks were going in the garden. Day after day they dug; they dug deep; they dug wide. Not a foot of the crop-worn garden escaped the probing of the pick as the sons feverishly searched for the expected treasure. But no treasure was found. Their work seemed entirely useless.
Fig. 12.Fig. 12. Increasing the Productive Power of the SoilSecond crop of cowpeas on old, abandoned land
"Let us not lose every whit of our labor; let us plant this pick-scarred garden," said the eldest. So the garden was planted. In the fall the hitherto neglected garden yielded a harvest so bountiful, so unexpected, that the meaning of their father's words dawned upon them. "Truly," they said, "a treasure was hidden there. Let us seek it in all our fields."
The story applies as well to-day as it did when it was first told. Thorough culture of the soil, frequent and intelligent tillage—these are the foundations of soil-restoration.
Along with good tillage must go crop-rotation and good drainage. A supply of organic matter will prevent heavy rains from washing the soil and carrying away plant food. Drainage will aid good tillage in allowing air to circulate between the soil particles and in arranging plant food so that plants can use it.
But we must add humus, or vegetable matter, to the soil. You remember that the virgin soils contained a great deal of vegetable matter and plant food, but by the continuous growing of crops like wheat, corn, and cotton, and by constant shallow tillage, both humus and plant food have been used up. Consequently much of our cultivated soil to-day is hard and dead.
There are three ways of adding humus and plant food to this lifeless land: the first way is to apply barnyard manure (to adopt this method means that livestock raising must be a part of all farming); the second way is to adopt rotation of crops, and frequently to plow under crops like clover and cowpeas; the third way is to apply commercial fertilizers.
To summarize: if we want to make our soil better year by year, we must cultivate well, drain well, and in the most economical way add humus and plant food.
EXPERIMENTSelect a small area of ground at your home and divide it into four sections, as shown in the following sketch:Fig. 13.Fig. 13.On SectionAapply barnyard manure; on SectionBapply commercial fertilizers; on SectionCapply nothing, but till well; on SectionDapply nothing, and till very poorly.A,B, andCshould all be thoroughly plowed and harrowed. Then add barnyard manure toA, commercial fertilizers toB, and harrowA,B, andCat least four times until the soil is mellow and fine.Dwill most likely be cloddy, like many fields that we often see. Now plant on each plat some crop like cotton, corn, or wheat. When the plats are ready to harvest, measure the yield of each and determine whether the increased yield of the best plats has paid for the outlay for tillage and manure. The pupil will be much interested in the results obtained from the first crop.Now follow a system of crop-rotation on the plats. Clover can follow corn or cotton or wheat; and cowpeas, wheat. Then determine the yield of each plat for the second crop. By following these plats for several years, and increasing the number, the pupils will learn many things of greatest value.
EXPERIMENT
Select a small area of ground at your home and divide it into four sections, as shown in the following sketch:
Fig. 13.Fig. 13.
On SectionAapply barnyard manure; on SectionBapply commercial fertilizers; on SectionCapply nothing, but till well; on SectionDapply nothing, and till very poorly.
A,B, andCshould all be thoroughly plowed and harrowed. Then add barnyard manure toA, commercial fertilizers toB, and harrowA,B, andCat least four times until the soil is mellow and fine.Dwill most likely be cloddy, like many fields that we often see. Now plant on each plat some crop like cotton, corn, or wheat. When the plats are ready to harvest, measure the yield of each and determine whether the increased yield of the best plats has paid for the outlay for tillage and manure. The pupil will be much interested in the results obtained from the first crop.
Now follow a system of crop-rotation on the plats. Clover can follow corn or cotton or wheat; and cowpeas, wheat. Then determine the yield of each plat for the second crop. By following these plats for several years, and increasing the number, the pupils will learn many things of greatest value.
In the early days of our history, when the soil was new and rich, we were not compelled to use large amounts of manures and fertilizers. Yet our histories speak of an Indian named Squanto who came into one of the New England colonies and showed the first settlers how, by putting a fish in each hill of corn, they could obtain larger yields.
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 illustration: 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 butter; 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.
Fig. 14.Fig. 14. Relation of Humus to Growth of Corn
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.
Fig. 15.Fig. 15. The Cotton Plant with and without Food
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 quantities 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 inunleachedwood 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 calledbacteria; by hastening the decay of organic matter; and by setting free the potash that is locked up in the soil.
Fig. 16.Fig. 16. Root-Hairson a Radish
Fig. 17.Fig. 17. A Slice of a RootHighly magnified
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 glass 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.
Fig. 18.Fig. 18. A Root-Hairwith Particles of Soilsticking to it
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, coarse roots that you are familiar with have nothing to do withabsorbingplant food from the soil. They serve merely toconductthe 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.
Fig. 19.Fig. 19. Distribution of Apple-Tree Roots
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.
Fig. 21.Fig. 21.Alfalfa Root
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 bedestroyed 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.
Fig. 20.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 illustrates well how far down into the soil the alfalfa roots go.
EXERCISEDig 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 glass-sided box, as suggested, and observe the root-hairs.
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 glass-sided box, as suggested, and observe the root-hairs.
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 pass into the root in solution.
An experiment just here will help us to understand how a root feeds.
EXPERIMENTFig. 22.Fig. 22. Experimentto show how Rootstake up FoodSecure a narrow glass 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 molasses (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 molasses 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 molasses 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 space in the chimney. This increase inthe contents of the tube is due to the entrance of water from the outside. The water has passed through the thin bladder, or membrane, and has come to occupy space in the tube. There is also a passage the other way, but the molasses can pass through the bladder membrane so slowly that the passage is scarcely noticeable. There are no holes, or openings, in the membrane, but still there is a free passage of liquids in both directions, although the more heavily laden solution must move more slowly.
EXPERIMENT
Fig. 22.Fig. 22. Experimentto show how Rootstake up Food
Secure a narrow glass 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 molasses (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 molasses 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 molasses 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 space in the chimney. This increase inthe contents of the tube is due to the entrance of water from the outside. The water has passed through the thin bladder, or membrane, and has come to occupy space in the tube. There is also a passage the other way, but the molasses can pass through the bladder membrane so slowly that the passage is scarcely noticeable. There are no holes, or openings, in the membrane, but still there is a free passage 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 pass in only one direction, that is, toward the inside. The outside of the root-hair is bathed in solutions rich in nourishment. The nourishment passes 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 passage of liquids from one side of a membrane to another is calledosmosis. It has many uses in the plant kingdom. We say a root takes nourishment by osmosis.
Tubercle is a big word, but you ought to know how to pronounce 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 calllegumes. 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, orgerms.
Fig. 23.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.
Just as bees gather honey from the flowers and carry it to the hives, where they prepare it for their own future use and for the use of others, so do these root-tubercles gather nitrogen from the air and fix it in their root homes, where it can be used by other crops.
Fig. 24.Fig. 24. Soy Beans and Cowpeas, Two Great Soil-Improvers
In the earlier pages of this book you were told something about the food of plants. One of the main elements of plant food, perhaps you remember, is nitrogen. Just as soon as the roots of the leguminous plants begin to push down into the soil, the bacteria, or germs that make the tubercles, begin to build their homes on the roots, and in so doing they add nitrogen to the soil. You now see the importance of growing such crops as peas and clover on your land, for by their tubercles you can constantly add plant food to the soil. Now this much-needed nitrogen is the most costly part of the fertilizers that farmers buy every year. If every farmer, then, would grow these tubercle-bearing crops, he would rapidly add to the richness of his land and at the same time escape the necessity of buying so much expensive fertilizer.
EXPERIMENTTake a spade or shovel and dig carefully around the roots of a cowpea and a clover plant; loosen the earth thoroughly and then pull the plants up, being careful not to break off any of the roots. Now wash the roots, and after they become dry count the nodules, or tubercles, on them. Observe the difference in size. How are they arranged? Do all leguminous plants have equal numbers of nodules? How do these nodules help the farmer?
EXPERIMENT
Take a spade or shovel and dig carefully around the roots of a cowpea and a clover plant; loosen the earth thoroughly and then pull the plants up, being careful not to break off any of the roots. Now wash the roots, and after they become dry count the nodules, or tubercles, on them. Observe the difference in size. How are they arranged? Do all leguminous plants have equal numbers of nodules? How do these nodules help the farmer?
Doubtless you know what is meant by rotation, for your teacher has explained to you already how the earth rotates, or turns, on its axis and revolves around the sun. When we speak of crop-rotation we mean not only that the same crop should not be planted on the same land for two successive years but that crops should follow one another in a regular order.
Many farmers do not follow a system of farming that involves a change of crops. In some parts of the country the same fields are planted to corn or wheat or cotton year after year. This is not a good practice and sooner or later will wear out the soil completely, because the soil-elements that furnish the food of that constant crop are soon exhausted and good crop-production is no longer possible.
Why is crop-rotation so necessary? There are different kinds of plant food in the soil. If any one of these is used up, the soil of course loses its power to feed plants properly. Now each crop uses more of some of the different kinds of foods than others do, just as you like some kinds of food better than others. But the crop cannot, as you can, learn to use the kinds of food it does not like; it must use the kind that nature fitted it to use. Not only do different crops feed upon different soil foods, but they use different quantities of these foods.
Now if a farmer plant the same crop in the same field each year, that crop soon uses up all of the available plant food that it likes. Hence the soil can no longer properly nourish the crop that has been year by year robbing it. If that crop is to be successfully grown again on the land, the exhausted element must be restored.
Fig. 25.Fig. 25. Grass following Corn
This can be done in two ways: first, by finding out what element has here been exhausted, and then restoring this element by means either of commercial fertilizers or manure; second, by planting on the land crops that feed on different food and that will allow or assist kind Mother Nature "to repair her waste places." An illustration may help you to remember this fact. Nitrogen is, as already explained, one of the commonest plant foods. It may almost be called plant bread. The wheat crop uses up a good deal of nitrogen. Suppose a field were planted in wheat year after year. Most of the available nitrogen would be taken out of the soil aftera while, and a new wheat crop, if planted on the field, would not get enough of its proper food to yield a paying harvest. This same land, however, that could not grow wheat could produce other crops that do not require so much nitrogen. For example, it could grow cowpeas. Cowpeas, aided by their root-tubercles, are able to gather from the air a great part of the nitrogen needed for their growth. Thus a good crop of peas can be obtained even if there is little available nitrogen in the soil. On the other hand wheat and corn and cotton cannot use the free nitrogen of the air, and they suffer if there is an insufficient quantity present in the soil; hence the necessity of growing legumes to supply what is lacking.
Fig. 26.Fig. 26. Cowpeas and Corn—August
Let us now see how easily plant food may be saved by the rotation of crops.
If you sow wheat in the autumn it is ready to be harvested in time for planting cowpeas. Plow or disk the wheat stubble, and sow the same field to cowpeas. If the wheat crop has exhausted the greater part of the nitrogen of the soil, it makes no difference to the cowpea; for the cowpea will get its nitrogen from the air and not only provide for its own growth but will leave quantities of nitrogen in the queer nodules of its roots for the crops coming after it in the rotation.
Fig. 27.Fig. 27. Cowpeas and Corn—October
If corn be planted, there should be a rotation in just the same way. The corn plant, a summer grower, of course uses a certain portion of the plant food stored in the soil. In order that the crop following the corn may feed on what the corn did not use, this crop should be one that requires a somewhat different food. Moreover, it should be one that fits in well with corn so as to make a winter crop. We find justsuch a plant in clover or wheat. Like the cowpea, all the varieties of clover have on their roots tubercles that add the important element, nitrogen, to the soil.
From these facts is it not clear that if you wish to improve your land quickly and keep it always fruitful you must practice crop-rotation?
Here are two systems of crop-rotation as practiced at one or more agricultural experiment stations. Each furnishes an ideal plan for keeping up land.
First YearSecond YearThird YearSummerWinterSummerWinterSummerWinterCornCrimson CloverCottonWheatCowpeasRye for pastureorSummerWinterSummerWinterSummerWinterCornWheatClover and grassClover and grassGrassGrass for pastureor meadow
In these rotations the cowpeas and clovers are nitrogen-gathering crops. They not only furnish hay but they enrich the soil. The wheat, corn, and cotton are money crops, but in addition they are cultivated crops; hence they improve the physical condition of the soil and give opportunity to kill weeds. The grasses and clovers are of course used for pasturage and hay. This is only a suggested rotation. Work out one that will meet your home need.
EXERCISELet the pupils each present a system of rotation that includes the crops raised at home. The system presented should as nearly as possible meet the following requirements:1. Legumes for gathering nitrogen.2. Money crops for cash income.3. Cultivated crops for tillage and weed-destruction.4. Food crops for feeding live stock.
EXERCISE
Let the pupils each present a system of rotation that includes the crops raised at home. The system presented should as nearly as possible meet the following requirements:
1. Legumes for gathering nitrogen.2. Money crops for cash income.3. Cultivated crops for tillage and weed-destruction.4. Food crops for feeding live stock.
If you partly burn a match you will see that it becomes black. This black substance into which the match changes is calledcarbon. Examine a fresh stick of charcoal, which is, as you no doubt know, burnt wood. You see in the charcoal every fiber that you saw in the wood itself. This means that every part of the plant contains carbon. How important, then, is this substance to the plant!
You will be surprised to know that the total amount of carbon in plants comes from the air. All the carbon that a plant gets is taken in by the leaves of the plant; not a particle is gathered by the roots. A large tree, weighing perhaps 11,000 pounds, requires in its growth carbon from 16,000,000 cubic yards of air.
Perhaps, after these statements, you may think there is danger that the carbon of the air may sometime become exhausted. The air of the whole world contains about 1,760,000,000,000 pounds of carbon. Moreover, this is continually being added to by our fires and by the breath of animals. When wood or coal is used for fuel the carbon of the burning substance is returned to the air in the form of gas. Some large factories burn great quantities of coal and thus turn much carbon back to the air. A single factory in Germanyis estimated to give back to the air daily about 5,280,000 pounds of carbon. You see, then, that carbon is constantly being put back into the air to replace that which is used by growing plants.
The carbon of the air can be used by none but green plants, and by them only in the sunlight. We may compare the green coloring matter of the leaf to a machine, and the sunlight to the power, or energy, which keeps the machine in motion. By means, then, of sunlight and the green coloring matter of the leaves, the plant secures carbon. The carbon passes into the plant and is there made into two foods very necessary to the plant; namely, starch and sugar.
Sometimes the plant uses the starch and sugar immediately. At other times it stores both away, as it does in the Irish and the sweet potato and in beets, cabbage, peas, and beans. These plants are used as food by man because they contain so much nourishment; that is, starch and sugar which were stored away by the plant for its own future use.
EXERCISEExamine some charcoal. Can you see the rings of growth? Slightly char paper, cloth, meat, sugar, starch, etc. What does the turning black prove? What per cent of these substances do you think is pure carbon?
EXERCISE
Examine some charcoal. Can you see the rings of growth? Slightly char paper, cloth, meat, sugar, starch, etc. What does the turning black prove? What per cent of these substances do you think is pure carbon?
The root-hairs take nourishment from the soil. The leaves manufacture starch and sugar. These manufactured foods must be carried to all parts of the plant. There are two currents to carry them. One passes from the roots through the young wood to the leaves, and one, a downward current, passes through the bark, carrying needed food to the roots (see Fig. 28).
Fig. 28.Fig. 28 Movementof the Sap Current
If you should injure the roots, the water supply to the leaves would be cut off and the leaves would immediately wither. On the other hand, if you remove the bark, that is, girdle the tree, you in no way interfere with the water supply and the leaves do not wither. Girdling does, however, interfere with the downward food current through the bark.
Fig. 29.Fig. 29. A ThickeningAbove the Wire thatCaused the Girdling
If the tree be girdled the roots sooner or later suffer from lack of food supply from the leaves. Owing to this food stoppage the roots will cease to grow and will soon be unable to take in sufficient water, and then the leaves will begin to droop. This, however, may not happen until several months after the girdling. Sometimes a partly girdled branch grows much in thickness just above the girdle, as is shown in Fig. 29. This extra growth seems to be due to a stoppage of the rich supply of food which was on its way to the roots through the bark. It could go no farther and was therefore used by the tree to make an unnatural growth at this point. You will now understand how and why trees die when they are girdled to clear new ground.
It is, then, the general law of sap-movement that the upward current from the roots passes through the woody portion of the trunk, and that the current bearing the food made by the leaves passes downward through the bark.
EXERCISELet the teacher see that these and all other experiments are performed by the pupils. Do not allow them to guess, but make them see.Girdle valueless trees or saplings of several kinds, cutting the bark away in a complete circle around the tree. Do not cut into the wood. How long before the tree shows signs of injury? Girdle a single small limb on a tree. What happens? Explain.
EXERCISE
Let the teacher see that these and all other experiments are performed by the pupils. Do not allow them to guess, but make them see.
Girdle valueless trees or saplings of several kinds, cutting the bark away in a complete circle around the tree. Do not cut into the wood. How long before the tree shows signs of injury? Girdle a single small limb on a tree. What happens? Explain.
Fig. 30.Fig. 30. Partsof the Pistil
Some people think that the flowers by the wayside are for the purpose of beautifying the world and increasing man's enjoyment. Do you think this is true? Undoubtedly a flower is beautiful, and to be beautiful is one of the uses of many flowers; but it is not the chief use of a flower.
You know that when peach or apple blossoms are nipped by the spring frost the fruit crop is in danger. The fruit of the plant bears the seed, and the flower produces the fruit. That is its chief duty.
Do you know any plant that produces seed without flowers? Some one answers, "The corn, the elm, and the maple all produce seed, but have no flower." No, that is not correct. If you look closely you will find in the spring very small flowers on the elm and on the maple, while the ear and the tassel are really the blossoms of the corn plant. Every plant that producesseed has flowers, although they may sometimes seem very curious flowers.
Fig. 31.Fig. 31. A Buttercup
Fig. 32.Fig. 32. A Plum Blossom
Let us see what a flower really is. Take, for example, a buttercup, cotton, tobacco, or plum blossom (see Figs. 31 and 32). You will find on the outside a row of green leaves inclosing the flower when it is still a bud. These leaves are thesepals. Next on the inside is a row of colored leaves, orpetals. Arranged inside of the petals are some threadlike parts, each with a knob on the end. These are thestamens. Examine one stamen closely (Fig. 33). On the knob at its tip you should find, if the flower is fully open, some fine grains, or powder. In the lily this powder is so abundant that in smelling the flower you often brush a quantity of it off on your nose. This substance is calledpollen, and the knob on the end of the stamen, on which the pollen is borne, is theanther.
The pollen is of very great importance to the flower. Without it there could be no seeds. The stamens as pollen-bearers, then, are very important. But there is another part to each flower that is of equal value. This part you will find in the center of the flower, inside the circle of stamens. It is called thepistil(Fig. 32). The swollen tip of the pistil is thestigma. The swollen base of the pistil forms theovary. If you carefully cut open this ovary you will find in it very small immature seeds.
Fig. 33.Fig. 33. Stamensa,anther;f, filament