Agriculture for Beginners Part 4
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.
[Ill.u.s.tration: 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.
=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?
SECTION XI. THE ROTATION OF CROPS
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 quant.i.ties 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.
[Ill.u.s.tration: FIG. 25. GRa.s.s 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 a.s.sist kind Mother Nature "to repair her waste places." An ill.u.s.tration 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 after a 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 quant.i.ty present in the soil; hence the necessity of growing legumes to supply what is lacking.
[Ill.u.s.tration: 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 quant.i.ties of nitrogen in the queer nodules of its roots for the crops coming after it in the rotation.
[Ill.u.s.tration: 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 just such 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?
AN ILl.u.s.tRATION OF 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 YEAR || SECOND YEAR || THIRD YEAR ----------+----------++-----------+----------++-----------+---------- Summer | Winter || Summer | Winter || Summer | Winter ----------+----------++-----------+----------++-----------+---------- Corn | Crimson || Cotton | Wheat || Cowpeas | Rye for | clover || | || | pasture ----------+----------++-----------+----------++-----------+----------
or
----------+----------++-----------+----------++-----------+---------- Summer | Winter || Summer | Winter || Summer | Winter ----------+----------++-----------+----------++-----------+---------- Corn | Wheat || Clover | Clover || Gra.s.s | Gra.s.s for | || and gra.s.s | and gra.s.s|| |pasture or | || | || | 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 gra.s.ses 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.
=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.
CHAPTER III
THE PLANT
SECTION XII. HOW A PLANT FEEDS FROM THE AIR
If you partly burn a match you will see that it becomes black. This black substance into which the match changes is called _carbon_. 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 quant.i.ties of coal and thus turn much carbon back to the air. A single factory in Germany is 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 pa.s.ses 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.
=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?
SECTION XIII. THE SAP CURRENT
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 pa.s.ses from the roots through the young wood to the leaves, and one, a downward current, pa.s.ses through the bark, carrying needed food to the roots (see Fig.
28).
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.
[Ill.u.s.tration: FIG. 28 MOVEMENT OF THE SAP CURRENT]