ROTATION OF CROPS (Continued)

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CHAPTER XLI. ROTATION OF CROPS (Continued)

“When soil is spoken of as worn out and needing rest, the speaker uses a figure of speech meaning that the soil has been exhausted by the crops it has borne. The crops do indeed take from the land a great quantity of substances necessary for plant-life; and when these substances are no longer present in sufficient amount, the soil refuses to produce; it is exhausted. To restore its original fertility would require a large outlay in fertilizer and hence it is often more advantageous to accomplish this object by one of the following methods.

“Sometimes the land is allowed to lie fallow; that is to say, it is left to itself without any care whatever for whole years. Weeds spring up freely, and at the same time water, air, and frost act on the soil, disintegrating and mellowing it and inducing the formation of certain substances necessary to vegetation. The weeds are converted into mold, and finally the land, rested and recuperated, is ready to bear a new crop. Restoration by this process is very slow, taking several years, and hence it is customary to shorten the period of waiting by working the soil and even manuring it, although it may not [209]yet be the intention to sow any seed. In these circumstances the land is called fallow land.

“There is, however, one way to obtain an uninterrupted succession of crops from the same land unless the soil is very poor. All plants derive their nourishment from the soil and the atmosphere; but some take more from the atmosphere, others from the soil. The plants that get their sustenance chiefly from the air are those that have luxuriant foliage. The potato is one of these. You know that it is through their leaves that plants obtain the carbonic acid gas diffused in the air. The greater the spread of foliage, the more abundant will this absorption be. The plants that depend almost wholly on the soil are those with only a few small, slender leaves, thus taking but little carbonic acid gas from the air. Such is wheat.

“Moreover, from the potato plant we take only the tubers, which form but a small part of the whole, and we turn under the stalks and leaves, which are thereupon converted into humus. Thus the potato has the property of enriching the soil at the expense of the atmosphere, and it gives back more than it takes. It is, then, one of the enriching rather than impoverishing plants in respect to its action on the soil. Cereals, on the contrary, are utilized by the harvester both as to seed and haulm, nothing but the meager roots being left in the ground; and as, on account of their very scanty foliage, cereals derive almost their entire sustenance from the soil, they take from it much more than they give back to it. [210]They accordingly belong to the class of plants that impoverish rather than enrich the soil in which they grow.

“It is impossible, thus, except by a ruinous expenditure of fertilizer, to raise a crop of grain every year on the same land. But if we should let potatoes succeed wheat, and wheat succeed potatoes, what would be the result? The latter crop, deriving a large part of its nourishment from the air, would flourish in soil comparatively exhausted by wheat; and on having its leaves and stalks turned under it would give back to the soil a part of its former fertility. Wheat could then be successfully raised again on the same land.

“This practice of raising successively on the same land different crops as little harmful to one another as possible and capable of utilizing to the utmost the dressing put on to the land, is nothing but that very rotation of crops that I have already told you something about. Its purpose is to economize fertilizer and at the same time to secure an uninterrupted succession of crops. The underlying principle consists in making an enriching plant succeed an impoverishing one; that is to say, a plant with luxuriant foliage is made to succeed one with scanty foliage. The chief enriching plants are clover, lucerne, sainfoin, potatoes, turnips, and beets. Cereals, on the contrary, are all impoverishing plants. It is a general custom to raise on the same land a more or less extended series of different crops, the series running four, five, or six years, or [211]even longer, after which it begins over again in the same order. This rotation of crops is designated according to the number of years the series covers, as for instance a five-year or a six-year rotation. A six-year rotation might run, we will say, somewhat as follows:

1st year—potatoes—enriching crop.2nd year—wheat—impoverishing crop.3rd year—clover—enriching crop.4th year—wheat—impoverishing crop.5th year—sainfoin—enriching crop.6th year—oats—impoverishing crop.

“Let us examine in detail this series that we have taken as an example. The first year the soil is thoroughly manured. One of the effects of manuring is to start a great crop of weeds that would infest the land and impoverish the crop were they not carefully removed. Hence the necessity of weeding. To weed a piece of ground is to destroy the weeds either by hand or with some implement. But it is not every crop that admits of weeding: the plants must be a certain distance apart, as otherwise they will be trampled under foot, cut off, or uprooted in the weeding process. Wheat cannot be weeded, its stalks are too close together; but potatoes are far enough apart for weeding without difficulty. Now, weeding destroys all useless, injurious grasses and other unwelcome intruders; their future reappearance is prevented by pulling them up before their seeds [212]ripen, and thus at last the ground is cleaned and made ready for a choice crop. This will explain to you the great advantage of letting the potato or some other crop that can be weeded take precedence of the cereals.

“The second year comes wheat. Cleaned by the tillage that has gone before, the ground is no longer covered with grass and weeds. Nor does it need fresh manure, for if the potatoes have consumed certain elements in the soil, these are not exactly the same that wheat requires; and, furthermore, the dead plants, turned under and reduced to vegetable mold, compensate by what they have derived from the atmosphere for what the tubers may have taken from the soil. Wheat is therefore just the crop to raise now.

“But it would be much against one’s interest to exact from the soil another crop of wheat the third year. Exhausted by the grain it has just produced, the soil would yield but a scanty harvest unless it were freshly manured, a process that would make of the whole operation, not a piece of farming, but an example of gardening, and would also entail too great expense. For that reason the third year is devoted to the raising of an enriching crop, such as clover. After furnishing a supply of fodder, what is left of the clover is turned under, and all its remnants of roots, stems, and leaves are reduced to mold, which renders the soil fit for another wheat harvest the fourth year. A third enriching crop to be turned under after the final mowing, is likewise [213]needed for the fifth year; and this crop may be sainfoin. At the end of the series comes another cereal, oats, for example. The rotation is now complete, and the program begins all over again.

“Crop-rotation is capable of innumerable variations, and the series may be longer or shorter, but there should be the slightest possible departure from the rule that a cereal crop ought always to be preceded by some crop that enriches the soil.”

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