The Apple. VariousЧитать онлайн книгу.
the air is distributed through the soil; seeds are dropped; the living animal forms begin to multiply; the soil is enriched, and gradually it begins to be in a condition suitable to bear the simpler forms of vegetable life, which in turn decaying, add to the richness of the soil.
Furthermore, the mechanical condition of the soil has much to do with the successful growth of the plant. If the soil is extremely fine, it is liable to become so compact that the rootlets cannot easily penetrate it, when it is of such a composition as to bake readily in the sun; if very coarse, like gravel, there is not a sufficient capacity to retain moisture. It should, however, be porous enough to allow the air to penetrate it, for upon the aeration of the soil depends much of its fertility. We loosen the soil about the roots of plants to allow the air to penetrate and give an opportunity for the chemical changes constantly undergoing in the soil. Then, too, the work of the earthworms in loosening the soil, and thus adding to its porosity, should not be overlooked. In this soil workshop, too, live and labor certain minute organisms that make it their business to enrich the soil by helping the rootlets to assimilate the nitrogen of the air.
Since the soil is composed mostly of ingredients that come from the decomposition of rocks, it follows that is must be of very complex composition. Fortunately, however, there are only a few of the ingredients of the soil that are of interest to the agriculturist, as only a few of the elements, as they are called, go to make up the plant structure, or at least only a few are essential ingredients of the plant. Nitrogen, though very abundant in the air, is not abundant in the soil. In fact, the soil has to depend largely on the nitrogen compounds that are washed out of the atmosphere in small quantities by the rain. Another source of nitrogen is the action of certain bacteria, that make little sacs on the rootlets and, living on the juices of the plants, fix the nitrogen of the air, and thus fertilize the soil; especially on plants of the leguminous family, as peas, beans, and clover.
Silicon, which with oxygen makes ordinary sand, is essential to the growth of plants and is everywhere found in abundance. Sulphur, united with oxygen and the metals to form sulphates, is generally abundant enough. The same may be said of chlorine, which, united with sodium or potassium, is always present in our prairie soils. Phosphorus, as it occurs in the phosphates, is one of the most essential ingredients of a fertile soil. Calcium and magnesium are found in combination as carbonates and sulphates, and, though essential, are usually abundant, especially where limestone rocks underlie the soil and outcrop in so many places. Potassium is found united with chlorine or sulphuric acid. It is one of the elements that is most liable to be exhausted from the soil by a succession of crops. Sodium exists almost everywhere. It is one of the elements of common salt, and, though much like potassium, cannot take the place of the latter in plant nurture. Iron is abundant and at the same time necessary in small quantities. The elements above mentioned, together with oxygen, are to be found in the ashes of plants. Besides, there are two elements that come largely from the atmosphere, namely carbon and hydrogen, which, united with oxygen, make up the bulk of the plant. Thus, wood is a substance containing carbon, hydrogen, and oxygen, with small quantities of nitrogen and mineral salts. The mineral salts represent about one per cent. of air-dried wood.
Having considered in a general way the constituents of the plant, and having noticed the source of each of these constituents, it may be of interest to look at the composition of the soil as revealed by chemical analysis. "A" is the analysis of a soil from Finney county, as made in the laboratory of the Kansas State University, by the author. "B" is a soil from Wyandotte county, as reported in the report of the Kansas State Board of Agriculture for 1874. "C" is a prairie soil from Dakota, as reported by Prof. E. Richards, of the department of agriculture.
| "A" | "B" | "C" | |
| Silica and insoluble | 71.66 | 82.16 | 69.82 |
| Iron and aluminum oxides | 6.55 | 6.70 | 12.05 |
| Calcium oxide | 4.41 | .68 | .85 |
| Magnesium oxide | 1.02 | .06 | .87 |
| Phosphoric anhydride | .18 | .08 | .11 |
| Chlorine | .01 | .03 | .03 |
| Potassium oxide | .75 | .05 | .72 |
| Sodium oxide | .25 | .11 | .94 |
| Sulphuric anhydride | .06 | .39 | .12 |
| Volatile and organic matter | 3.98 | 5.44 | 8.90 |
| Moisture | 9.67 | 3.80 | 6.27 |
| Undetermined, carbonic acid, etc. | 1.48 | .30 | .22 |
| 100.00 | 100.00 | 100.00 |
In some cases it happens that there is a sufficient quantity of an ingredient in the soil, but it is not in a sufficiently soluble form to be available. It will be noticed that in the analyses quoted above the amount of the necessary constituents of the soil to plant growth is not in any case large. The nitrogen may be present in the volatile and organic matter, and upon the proportion of this complex organic matter very often depends to a great extent the fertility of the soil.
Some experiments made at one of the agricultural experiment stations upon the effect of "apple stock," that is, young trees raised for nursery purposes, on the soil, showed that in eleven tons of such stock the following quantities of ingredients were removed from the soil:
| Silica | 50.6 | lbs. |
| Phosphoric acid | 21.4 | " |
| Sulphuric acid | 14.3 | " |
| Chlorine |
|