The Encyclopedia Americana (1920)/Rotation of Crops
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Rotation of Crops
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|Edition of 1920. See also Crop rotation on Wikipedia, and the disclaimer.|
ROTATION OF CROPS, the order in which crops are grown during a series of years on the same land. The advantages of this practice are: (1) All plants tend to exhaust the soil, but in different degrees, hence a rotation tends to maintain a balance. Thus at the Rothamsted Experiment Station, England, where wheat has been grown on the same land for 62 successive years without manure or fertilizers, the average yield is about 13 bushels per acre, or nearly the same as the average yield in the United States, while where grown in a four-course rotation of rutabagas, barley, beans or clover, wheat, the average yield during a period of 52 years is nearly 27 bushels per acre, without manuring or fertilizing. (2) All plants do not take up the same ingredients in the same proportion; thus, crops rich in carbonaceous matter take up relatively small amounts of food from the soil, but large quantities from the air, the latter costing nothing. (3) Some crops give better opportunity for cleaning land, as corn, potatoes. Others cannot be tilled and favor the growth of weeds, as wheat, oats. (4) When several crops are grown on a farm the labor is distributed over a greater portion of the year and it is more economical. The social evils consequent on temporary emplovment at high wages for a short period of the year, and idleness the rest of the time, cannot be overlooked. (5) Plants vary in their ability to assimilate the plant food in the soil; thus buckwheat and rye are able to flourish where wheat and cabbages could hardly live. (6) The legumes enrich the soil in nitrogen. (7) A variety of crops is essential where cattle and other livestock are kept. (8) In a rotation the increase of destructive insects and diseases is hindered, owing to their not having the necessary crop to prey upon. (9) Some crops permit the sowing of others among them, thus saving time; clover and grass seeds being sown among barley and wheat, wheat sown among corn. (10) Some crops permit the aggregation of the soil particles when they become excessively reduced by tillage, hence land is laid down to grass, alfalfa. (11) Certain crops aid in accumulating humus, as grass, hence such should follow two or three years of exhaustion by tillage. Admitting air to the soil tends to destroy humus and to reduce the water-holding capacity. The loss of humus has converted garden-spots in New York and other Eastern States, northern Africa, Asia Minor and Spain into wastes, and Sicily, the granary of Italy in the time of the Romans, is now comparatively sterile.
Rotations are described according to the number of years required to complete a circuit, as three-course, four-course, etc. In the latter the tillable land is divided into four parts and each crop is grown on part of the farm each year. The folly of growing the same crop on the same land for several successive years was noted by the Romans and others, as also the benefits derived from growing a leguminous crop, as alfalfa or clover, previous to a grain crop, as wheat. These observations remained unutilized until a comparatively recent date. Rotations have gradually grown into their present forms according to circumstances, and have been and are modified as required and as our knowledge increases. Attention was first drawn to their value in 1777, in a treatise by Dickson of Edinburgh, Scotland.
One of the earliest recorded systems was the “outfield” and “infield,” in which part of the land was used for growing grain until its crop-producing power was so reduced that it became unprofitable, when it was allowed to lie idle for a number of years. Increase of population caused a modification, the land being rested or “fallowed” a year at intervals; thus, among the Jews, this was repeated every seventh year. A system of continuous single cropping has been pursued in the Western States with distinct loss to the nation. Where land is weedy and in dry districts, as parts of California, the east of England, etc., bare fallowing or the cultivation of the soil without growing a crop is still considered good practice, sufficient moisture being conserved to ensure a profitable crop the succeeding year. A development from this system consisted of the introduction of green crops, either intertillage crops, as corn, turnips, potatoes, cabbages, etc., if the land was weedy and needed cleaning, or of legumes, as clover. The advantages of a crop-fallow are that the land is turned to profitable use; it is cleaned and the available nitrogen present as nitrates is not so liable to be lost by percolation, being taken up by the crops; that humus is produced from the root-residue; and that if a leguminous crop is grown it enriches the soil in nitrogen by means of the bacteria on its roots.
In 1788 Marshall of England stated that a common rotation was: 1st year, wheat, barley or bigg; 2d year, oats, beans and pulse; 3d year, bare fallow. A distinct advance was made with the realization of the value of the Norfolk four-course, which was practised on light land and originally consisted of roots, barley, clover, wheat. The principles involved are (1), that a deep-rooted crop shall succeed a shallow-rooted one, barley being shallow-rooted and clover deep-rooted; (2) that crops of the same natural order and somewhat like tendencies, as wheat and barley, both being straw-crops and more or less subject to similar enemies, shall not succeed each other; (3) that a weedy crop shall be followed by a cleaning one, as the roots after the wheat; and (4) that a leguminous crop shall have a place in each rotation. The advantages of this system were: (1) The wheat was grown after a nitrogen-gathering crop; the clover stubble was readily prepared for wheat in the fall, or if stock feed was scarce it could be pastured late and spring wheat or oats grown instead. The wheat was harvested in time to permit the land being fall-plowed and cleaned for the succeeding root crop. (2) The fallow crop, roots, received manure and intertillage, and gave an opportunity to clean the land and stir it deeply. It furnished work for the horses in summer in cultivating, and a bulky crop of succulent feed for stock, which with the hay furnished considerable manure. (3) A grain-crop follows well after a root crop, and generally little or no plowing is needed. Barley is a good crop to seed with, as it occupies the land but a short time and is not so exacting on the soil moisture as oats. (4) The clover requires a firm seed-bed, and if the roots were consumed on the land and shallow tillage given in fitting the land for the barley, such was secured. The barley permitted a good growth of clover which enabled it to withstand the winter. This crop supplied the hay. The disadvantages of this system are that it is too short, the land being liable to become both clover and turnip sick, and the turnips affected with “club-root.” Under these circumstances clover and turnips could be taken every eighth year, substituting beans, peas or cowpeas for the former, and potatoes, etc., for the latter. Such close cropping renders the rotation expensive, the labor bill being high, but the cost may be reduced by leaving the grass and clover seeding down for two or three years, thus making a five or six years' rotation, or it may be used as the basis for a seven or eight course. This rotation is capable of adaptations as follows: (1) Grain — wheat, oats, barley, rye, corn, buckwheat; (2) cleaning or fallow crop — corn, potatoes, sugar beets, mangels, tobacco, cabbages, turnips, rutabagas, rape, cowpeas, soy beans, sorghum, etc.; (3) Grain — barley, oats, rye, wheat, corn; (4) Legume — clover, grass and clover, cowpeas, soy beans; (5) Legume— grass and clover, mown once and pastured, or pastured all the year.
In the United States the rotations of crops vary considerably in different sections. In many places the succession of crops is dictated rather by accident or convenience than by any well-considered principles. Corn and wheat or oats formed a common two-course rotation with the early settlers, until the land failed to produce a crop of wheat when corn was grown every second year, the land going to weeds in the interval. The “Eastern Shore rotation,” which is a two-course, consists of corn followed by oats, with a secondary crop of Magothy Bay beans. The growth of this leguminous crop, while curtailing the yield of oats, furnishes considerable green manure for plowing in. The first system on the best cultivated farms in Virginia was a three-course, beginning with corn, and succeeded by wheat in which the grass and weeds were allowed to grow and be grazed the third year. One well-known farmer in Virginia grew clover in place of the weeds the third year to furnish green manure. A later rotation was: (1) corn or oats; (2) wheat and clover sown; (3) clover grown and plowed under in August, and the land seeded to wheat for the fourth year.
An old and successful rotation recorded for New England is corn, oats and timothy and clover, the latter remaining down for three years; thus two plowings are required in five years, one for corn, and a light plowing for oats, the grass and clover seed being sown among the oats. A modern three-course rotation for the Eastern States is potatoes, winter rye, clover. This is a modification of a well-known Middle Western rotation, potatoes, winter wheat, clover. It embraces a root crop, a cereal and a leguminous crop. It is well suited to light and medium soils and is economical in labor, but one deep plowing being required in three years, that for the potatoes, the land being prepared for the rye by discing. The potatoes are a cash crop, the rye furnishes bedding and feed for stock, and the clover furnishes hay, and is not left down long enough to be seriously injured by the clover-root worm. The rotation is too short for many places, and probably the land would become clover-sick. It may be converted into a four-course by growing a crop of corn after the clover, and into a five-course by sowing grass with the clover and leaving them down for two years, thus corn, potatoes, rye, grass (timothy, redtop, etc. clover), mown, grass mown and grazed. In this way two-fifths of the tilled land is plowed each year, that for corn and potatoes; the land for potatoes may be plowed in fall after the rye is sown in September, thus reducing the spring work. If milch cows are kept, the corn furnishes grain, and stover or may be cut for silage, the rye may be cut green for fodder or allowed to mature, and the area in potatoes might be reduced and cowpeas, soy beans, peas and barley, or some other fodder or silage crop substituted.
For a dairy farm having half the land in permanent pasture, a satisfactory four-course is (1) corn (cut for silage); (2) oats, the land being fall-plowed, the crop furnishing grain and bedding; (3) wheat (sown in fall, the grain being sold or consumed, the straw used for bedding); (4) clover (sown in spring in the wheat). This rotation permits of carrying the maximum amount of livestock and having a large supply of manure, thus enabling the crop-producing power of the soil to be maintained or increased. The livestock furnish constant employment and enable the farmer to make two profits, that of the grower and the manufacturer.
A common rotation in the Middle West is corn, wheat and clover. The wheat is sown in the corn with a one-horse drill before the latter is mature, the clover being sown in the wheat. Labor is a serious problem, and this system economizes it, but one plowing being required. Consult Wheeler, ‘A Rotation of Crops,’ Bull. 74, 75, 76, Agr. Exp. Sta., Rhode Island (1900); Gilbert, ‘Memoranda of the Rothamsted Experiments’ (1901); Parker, E. C, ‘Field Management and Crop Rotation’ (Saint Paul 1915). Consult also works referred to in article Agriculture In The United States, all of which emphasize the imperative necessity of rotation if our lands are to be saved from exhaustion.