The weight of the whole crop from which these figures were taken was eight hundred and forty-seven pounds, so that cotton exhausts land less than any staple crop, if the roots, stems, leaves, etc., be turned under and only the lint and seed be removed. Of these the lint (one hundred pounds) takes 1.17 pound from the soil, and the seed 13.89 pounds, making 15.06 pounds net loss.[47] But ignoring returns that may be made in the shape of cotton-seed meal, etc., and lime, with which our soils are abundantly supplied, we see that nitrogen, phosphoric acid, and potash have been removed. Suppose the owner puts bone meal on his exhausted land: the phosphoric acid in the bone will supply one need, and an improvement results. On the strength of this, bone meal will be loaded into the soil again, and let us suppose the deficit not yet made up, the crop again shows improvement. Now, phosphoric acid abounds in the soil, though the deficiency in nitrogen and potash has become steadily greater; so, when the customary bone meal is applied, the crop falls back, because the plants are starving for potash and nitrogen. They are like scurvy-smitten sailors, but many thoughtless farmers would attribute the decline to the maker of the bone meal, and say that its quality was not so high as formerly—an opinion similar to that of a sea captain who would ascribe to the poor quality of salt beef an outbreak of scurvy on his vessel.
As crops of any description extract potash, nitrogen, and phosphoric acid from soils, the question how they are to be replaced is an important matter, and its answer may be most readily found by studying Nature's methods. In parts of the Old World there are fields that are fertile in the extreme after thousands of years of tillage, and it is apparent that mere cultivation does not prove injurious. The tropical forests have something growing wherever a plant can find foothold—a population in which the struggle for food is secondary to that for light and air, and yet the soil supporting this vegetation is marvelously rich. Every leaf that falls remains where it fell until in the warm, moist, half-lighted forest it becomes a little heap of mold. The bacteria of decomposition require warmth and moisture for their life; light is deleterious to them, but they thrive in the dense shade of the jungle. The tangled web of roots, weeds, and vines retains the rainfall, retarding evaporation, and preventing both droughts and freshets. Receiving dead and broken leaves, boughs, and other vegetable products, and spared the washing of violent torrents, the forest is inestimably fertile.
On a smaller scale this goes on universally. The annual weeds, deciduous leaves, and such matter, fall prey to molds and bacteria, by which they are made soluble. Snows and rains bear the products into the soil, and there other bacteria, clustering around the roots, form the acids needed to complete solution. Every one knows that "well-rotted" manure is better than that which is fresh, and many wonder at this, but the reason is apparent. In feeding delicate patients, physicians often prescribe predigested foods or the digestive ferments to aid enfeebled assimilation; and similarly the manures that have been thoroughly acted on by bacteria, or containing those capable of producing the matters that plants need, are of most value for nourishing vegetation.
In producing an article of any sort, the cheapness and ease with which it can be made is largely dependent on the shape in which the raw material reaches the factory. If a foundry can procure iron that needs only to be melted and cast, the owner can fill his orders more readily than would be possible if he had to reduce the metal from the ore; and Nature uses this principle over and over again. The importance of nitrogen to plants and its abundance in Nature have been mentioned, but it has also been said that plants can not use it directly, as most animals do with oxygen. The tiny bacteria intervene, and this they do in two ways: first, by causing decay of animal or vegetable matter containing nitrogen, and by this decay producing substances that plants can absorb; and, secondly, by producing little nodules or "tubercles" on the rootlets, through which the plant can take up nitrogen.[48] Now, when a plant is sated with nitrogen, it ceases to form these tubercles, and their formation is a sure sign that the plant is craving this article of food. When it is supplied, and its own life is ended, these form reservoirs from which other plants may be supplied, as new castings may be made from broken wheels. The great value of "green manuring" depends on the store of available nitrogen so laid up, but it is open to failure in one direction. The liability of fermentation to go to the acid stage from contamination with acid-forming ferments has been mentioned, an accident the possibility of which is impressed on us from time to time by sour bread; and similarly the organic matter turned under may undergo acid fermentation, rendering the ground "sour" and unfit for cultivation.
The limits of this paper forbid the consideration of special fertilizers, but from the general principles laid down the rules for any special case may be deduced. A soil should contain a sufficient amount of potash, soda, lime, iron, and a few other minerals; phosphoric acid, nitrogen, organic matter, and, for some special crops, some other ingredients may be needed. When the soil needs renewing, there are two ways of accomplishing it. One way is to guess at what is needed; to buy fertilizers at high prices, without inquiring whether the soil needs the substances in that particular brand or not. Though very common, this is not a good plan. It is as though a physician were to give a patient any drug that was convenient, without inquiring into the disorder or the needs of the system, and it is followed by much the same result. That acid phosphate gave Farmer A a good crop, is no reason that Farmer B's land is also deficient in phosphorus. The same reasoning would teach that a heart stimulant that rouses a patient from shock would benefit one in danger of apoplexy, where the least increase in heart force might be fatal. A physician using such reasoning as the basis of his practice would not be considered a master of his art; and were he to attribute the fatal outcome of his logic to the poor quality of his stimulant, he would display criminal ignorance of drugs as well as disease; yet it is very common to see farmers put guano on a soil begging for potash, and then heap execration on the head of the dealer who sold the guano when the crop failed. To revert to a simile used above, a captain must not blame the salt pork for scurvy.
The other way to buy and use fertilizers is to ascertain what a certain crop needs; then find out whether these be in the soil, and to what extent. With these data the deficiency may be made good without the wasteful cost of the former method. State and Federal Departments of Agriculture furnish their aid freely and gladly, and already the signs are seen of the day when agriculture will take its place among the semiexact sciences, and the present haphazard methods will become obsolete.
SKETCH OF AUGUST KEKULÉ.
"This news," said Herr H. Landrelt, president, announcing Kekulé's death in the German Chemical Society at Berlin, "will be received with sorrow not only by our society but by the whole chemical world. Science has again lost one of its greatest representatives, one of those extremely rare spirits who were called upon to found a new epoch in it and push it mightily forward."
Friedrich August Kekulé was born at Darmstadt, September 7, 1829, and died, after a long illness, at Bonn, July 13, 1896. He was originally destined by his father for the profession of an architect; and some houses, he told his students in a festival address, still existed (in 1892) in Darmstadt of which he drew the plans when, a youth, he was attending the gymnasium. The leading events of his life were very tersely told by himself in an address responding to an ovation from the students of the University of Bonn on the twenty-fifth anniversary of his professorship there; a translation of which, from the Kölnische Zeitung, was published by Mr. J. E. Martin in Nature, June 30, 1892.