“After clover we can try a fourth crop, of a different kind; but it is evident that as the guests succeed one another at the same table the remnants become more and more scanty and difficult to utilize. Accordingly we must choose a hardy plant and one that is content with little. Finally a time will come, and at no very distant date, when the board will be bare: the coating of manure will have given up its last particle of nutritious matter. Then the table must be garnished afresh, the field fertilized anew before beginning again with the same crops or attempting others. Let us demand no more. You understand, my young friends, that in order to utilize to the utmost this precious substance that gives us every kind of food, such as bread, vegetables, forage, meat, fruit, dairy products—to make the very best use of this we must, instead of raising the same crop in the same field year after year, adopt the plan of varying our crops, changing from one of one kind to another of a different character, so that what earlier plantings have left in the soil may be turned to account by later ones. This succession of different sorts of farm produce is called rotation of crops.” 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 yet be the intention to sow any seed. In these circumstances the land is called fallow land.