Calcium, a yellowish solid. Found in limestone.
Magnesium, a silver white solid.
Iron, a silver gray solid.
Of these elements the nitrogen, sulphur, phosphorus, pota.s.sium, calcium, magnesium, and iron must not only exist in the soil but must also be there in such form that the plant can use them. The plant does not use them in their simple elementary form but in various compounds.
These compounds must be soluble in water or in weak acids.
Of these seven elements of plant food the nitrogen, phosphorus, and pota.s.sium and calcium are of particular importance to the farmer, because they do not always exist in the soil in sufficient available quant.i.ties to produce profitable crops. Professor Roberts, of Cornell University, tells us that an average acre of soil eight inches deep contains three thousand pounds of nitrogen. The nitrogen exists largely in the humus of the soil and it is only as the humus decays that the nitrogen is made available. Here is another reason for keeping the soil well supplied with organic matter. The decay of this organic matter is hastened by working the soil; therefore good tillage helps to supply the plant with nitrogen.
If the nitrogen becomes available when there is no crop on the soil it will be washed out by rains and so lost. Therefore the soil, especially if it is sandy, should be covered with a crop the year through. Many lands lose large amounts of plant food by being left bare through the fall and winter, especially in those parts of the country where the land does not freeze. The phosphorus, pota.s.sium and calcium also exist in most soils in considerable quant.i.ties, but often are not available; thorough tillage and the addition of organic matter will help to make them available, and new supplies may be added in the form of fertilizers. Calcium is found in nearly all soils in sufficient quant.i.ties for most crops, but sometimes there is not enough of it for such crops as clover, cowpea, alfalfa, etc. It is also used to improve soil texture. The entire subject of commercial fertilizers is based almost entirely on the fact of the lack of these four elements in the soil in sufficient available quant.i.ties to grow profitable crops. The plant gets its phosphorus from phosphoric acid, its pota.s.sium from potash, and its calcium from lime.
There is a cla.s.s of plants which have the power of taking free nitrogen from the air. These are the leguminous plants; such as clover, beans, cowpeas, alfalfa, soy bean, etc. They do it through the acid of microscopic organisms called bacteria which live in nodules or tubercles on the roots of these plants (Figs. 34-35). Collect roots of these plants and find the nodules on them. The bacteria take nitrogen from the air which penetrates the soil and give it over to the plants.
Here is another reason for good soil ventilation.
This last fact brings us to another very important property of soils.
Soils have existing in them many very small plants called bacteria.
They are so very small that it would take several hundred of them to reach across the edge of this sheet of paper. We cannot see them with the naked eye but only with the most powerful microscopes. Some of these minute plants are great friends to the farmer, for it is largely through their work that food is made available for the higher plants.
Some of them break down the organic matter and help prepare the nitrogen for the larger plants. Others help the leguminous plants to feed on the nitrogen of the air. To do their work they need warmth, moisture, air, and some mineral food; these conditions we bring about by improving the texture of the soil by means of thorough tillage and the use of organic matter.
CHAPTER IX
SEEDS
CONDITIONS NECESSARY FOR SEEDS TO SPROUT
In the spring comes the great seed-planting time on the farm, in the home garden and in the school garden. Many times the questions will be asked: Why didn"t those seeds come up? How shall I plant seeds so as to help them sprout easily and grow into strong plants? To answer these questions, perform a few experiments with seeds, and thus find out what conditions are necessary for seeds to sprout, or germinate.
For these experiments you will need a few teacups, gla.s.s tumblers or tin cans, such as tomato cans or baking-powder cans; a few plates, either of tin or crockery; some wide-mouth bottles that will hold about half a pint, such as pickle, olive, or yeast bottles or druggists" wide-mouth prescription bottles; and a few pieces of cloth.
Also seeds of corn, garden peas and beans.
=Experiment.=--Put seeds of corn, garden peas, and beans (about a handful of each) to soak in bottles or tumblers of water. Next day, two hours earlier in the day, put a duplicate lot of seeds to soak.
When this second lot of seeds has soaked two hours, you will have two lots of soaked seeds of each kind, one of which has soaked twenty-four hours and the other two hours. Now take these seeds from the water and dry the surplus water from them by gently patting or rubbing a few at a time in the folds of a piece of cloth, taking care not to break the skin or outer coating of the seed. Place them in dry bottles, putting in enough to cover the bottoms of the bottles about three seeds deep; cork the bottles. If you cannot find corks, tie paper over the mouths of the bottles. Label the bottles "Seeds soaked 24 hours," "Seeds soaked 2 hours," and let them stand in a warm place several days. If there is danger of freezing at night, the bottles of seeds may be kept in the kitchen or living room where it is warm, until they sprout.
Observe the seeds from day to day. The seeds that soaked twenty-four hours will sprout readily (Fig. 36), while most, if not all, of those that soaked only two hours will not sprout. Why is this? It is because the two-hour soaked seeds do not receive sufficient moisture to carry on the process of sprouting.
Our experiment teaches us that seeds will not sprout until they receive enough moisture to soak them through and through.
This also teaches that when we plant seeds we must so prepare the soil for them and so plant them that they will be able to get sufficient moisture to sprout.
=Experiment.=--Soak some beans, peas or corn, twenty-four hours; carefully dry them with a cloth. In one half-pint bottle place enough of them to cover the bottom of the bottle two or three seeds deep; mark this bottle A. Fill another bottle two-thirds full of them and mark the bottle B (Fig. 37). Cork the bottles and let them stand for several days. Also let some seeds remain soaking in the water. The few seeds in bottle A will sprout, while, the larger number in bottle B will not sprout, or will produce only very short sprouts. Why do not the seeds sprout easily in the bottle which is more than half full?
To answer this question try the following experiment:
=Experiment.=--Carefully loosen the cork in bottle B (the bottle containing poorly sprouted seeds), light a match, remove the cork from the bottle and introduce the lighted match. The match will stop burning as soon as it is held in the bottle, because there is no fresh air in the bottle to keep the match burning. Test bottle A in the same way. What has become of the fresh air that was in the bottles when the seeds were put in them? The seeds have taken something from it and have left bad air in its place; they need fresh air to help them sprout, but they have not sprouted so well in bottle B because there was not fresh air enough for so many seeds. The seeds in the water do not sprout because there is not enough air in the water. Now try another experiment.
[Ill.u.s.tration: FIG. 36.
To show that seeds need water for germination. The beans in bottle _A_ were soaked 2 hours, those in bottle _B_ were soaked 24 hours. They were then removed from the water and put into dry bottles.]
[Ill.u.s.tration: FIG. 37.
To show that seeds need air for germination. The beans in both bottles were soaked 24 hours, and then were put into dry bottles Bottle _A_ contained sufficient air to start the few seeds. Bottle _B_ had not enough. The water in the tumbler _C_ did not contain sufficient air for germination. See experiment, page 72.]
[Ill.u.s.tration: FIG. 38.
To show that seeds need air for germination. Corn planted in puddled clay in tumbler _A_ could not get sufficent air for sprouting. The moist sand in tumbler _B_ admitted sufficient air for germination.]
=Experiment.=--Fill some tumblers or teacups or tin cans with wet sand and others with clay that has been wet and then thoroughly stirred till it is about the consistency of cake batter or fresh mixed mortar.
Take a tumbler of the wet sand and one of the wet clay and plant two or three kernels of corn in each, pressing the kernels down one-half or three-quarters of an inch below the surface; cover the seeds and carefully smooth the surface. In other tumblers plant peas, beans, and other seeds. Cover the tumblers with saucers, or pieces of gla.s.s or board to keep the soil from drying. Watch them for several days. If the clay tends to dry and crack, moisten it, fill the cracks and smooth the surface. The seeds in the sand will sprout but those in the clay will not (see Fig. 38). Why is this? Water fills the small s.p.a.ces between the particles of clay and shuts out the fresh air which is necessary for the sprouting of the seeds.
This teaches us that when we plant seeds we must so prepare the soil, and so plant the seeds that they will get enough fresh air to enable them to sprout, or, in other words, the soil must be well ventilated.
=Experiment.=--Plant seeds of corn and beans in each of two tumblers; set one out of doors in a cold place and keep the other in a warm place in the house. The seeds kept in the house will sprout quickly but those outside in the cold will not sprout at all. This shows us that seeds will not sprout without heat.
If the weather is warm place one of the tumblers in a refrigerator.
Why don"t we plant corn in December?
Why not plant melons in January?
Why not plant cotton in November?
The seeds of farm crops may be divided into two cla.s.ses according to the temperatures at which they will germinate or sprout readily and can be safely planted.
Cla.s.s A. Those seeds that will germinate or sprout at an average temperature of forty-five degrees in the shade, or at about the time the peach and plum trees blossom:
Barley Beet Parsley Oats Carrot Parsnip Rye Cabbage Onion Wheat Cauliflower Pea Red Clover Endive Radish Crimson Clover Kale Turnip Gra.s.ses Lettuce Spinach
These can be planted with safety in the spring as soon as the ground can be prepared, and some of them, if planted in the fall, live through the winter.
Cla.s.s B. Those seeds that will germinate or sprout at an average temperature of sixty degrees in the shade, or when the apple trees blossom:
Alfalfa Soy Bean Squash Cow Pea Pole Bean Cuc.u.mber Corn String Bean Pumpkin Cotton Melon Tomato Egg Plant Okra Pepper
We are now ready to answer the question: What conditions are necessary for seeds to sprout or germinate? These conditions are:
The presence of enough moisture to keep the seed thoroughly soaked.
The presence of fresh air.
The presence of more or less heat.
This teaches us that when we plant seeds in the window box or in the garden or on the farm we must so prepare the soil and so plant the seeds that they will be able to obtain sufficient moisture, heat, and air for sprouting. The moisture must be film water, for if it is free water or capillary water filling the soil pores, there can be no ventilation and, therefore, no sprouting.
SEED TESTING
In a previous experiment (page 73) the seeds planted in the wet clay did not sprout (see Fig. 38). In answer to the question, "Why is this?" some will say the seeds were bad. It often happens on the farm that the seeds do not sprout well and the farmer accuses the seedsman of selling him poor seed, but does not think that he himself may be the cause of the failure by not putting the seeds under the proper conditions for sprouting. How can we tell whether or not our seeds will sprout if properly planted? We can test them by putting a number of seeds from each package under proper conditions of moisture, heat and air, as follows: