“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 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 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.