(S) Rotation is a cleaning process. Cer tain weeds follow certain crops. Chess and cockle are common weeds in old wheat-lands.
The life-cycle of these plants is so similar to that of wheat that they thrive with the wheat ; and the seeds may not be removed from wheat-seed in the ordinary cleaning process. These weeds are soon eliminated by the grass-course in the rotation, or by some clean-tillage course. Most weeds are eradicated in the course of a good rotation ; in fact, a rotation cannot be considered to be good unless it holds the weeds in check. With crops which are not grown as a part of a rotation, as rice, it is sometimes necessary to interject another crop for a year or two in order to clean the land.
Insects a n d plant diseases follow certain crops. There are no insects or diseases that follow all crops. Therefore a rotation cleans the fields of many of these troubles and pests.
Nearly all continu- ous-cropping schemes run into these difficulties sooner or later. A short and sharp rotation, for example, is the best means of contending with wire worms. It is not uncommon sometimes to find onions failing year after year in the best onion regions. The trouble is likely to be due to pests or diseases. Two or three years of celery or other crop may clean up the difficulty. The horticulturist is particularly liable to suffer from insects and plant diseases, especially if he is an orchardist, because he cannot well practice a definite rota tion. The larger part of the spraying devices and materials are devised to meet the necessities of the horticulturist.
(9) A rotation allows the farmer to meet the needs of the staple markets by providing a continuous and predictable output.
(10) Rotation-farming develops a continuous and consecutive plan of business. It maintains the continuity of farm labor, and reduces the economic and social difficulties that arise from the employing of many men at one time and few men at another time.
Rotation practices.
Just what rotation scheme shall be adopted in any case must depend on many local and special considerations. What some of these considerations are may be briefly discussed.
(a) The rotation must adapt itself to the farmer's business—to the support of live-stock if he is a dairyman or stock-farmer, to the demands of the grain trade if he is a grain-farmer, to the cotton market if he is in a cotton region.
(b) It most adapt itself to the soil and the fertility problem. Often the chief purpose of a rotation is to recuperate worn and depleted lands. In such ease, the frequent recurrence of leguminous humour crops is preeminently desirable.
(c) The fertilizer question often modifies the rotation —whether manure can be pur chased cheaply and in abundance or whether it must be made on the place.
(d) The kind of soil and the climate may dictate the rotation.
(e) The labor supply has an important bearing on the character of the rotation course. The farmer must be careful to plan to keep the number of plowings and the amount of cultivating within the limits of his capabilities.
(f) The size of the farm, and whether land can be rented for pasturage, are also determinants. It is not profitable to grow the cereals and some other crops on small areas ; in fact, rotation-farming is chiefly successful with large-area crops.
(g) In the future more than in the past, the rotation must be planned with reference to the species of plants that will best serve one another, or produce the best interrelationship results.
(h) The rotation must consider in what condition one crop will leave the soil for the succeeding crop, and how one crop can be seeded with another crop. One reason why wheat is still so generally grown in the East is because it is a good "seeding crop "; grass and clover are seeded with it, and it therefore often makes a rotation practicable.
In some parts of the East, rye takes the place of winter-wheat in the rotation course. Every careful farmer soon comes to know that a cer tain tilth or condition of soil may be expected to result from certain crops. Thus buckwheat has a marked effect on hard-pan soils, leaving them mellow and ash-like. The explanation of this action of buckwheat is unknown. Potato growers who have hard land like to grow buckwheat as a preparation for potatoes, although buckwheat is rarely a regular part a rotation. Winter-wheat commonly follows oats, for the reason that the oats are harvested early enough to allow the sowing of wheat in the fall. However, barley is considered to be a better preparation crop for wheat, as it comes off the land earlier and does not deplete the moisture content of the soil so much ; it therefore usually allows the making of a better seed-bed for the wheat.