A rotation of crops, according to the Cyclopedia of American Agriculture, is "a recurring succession of plants covering a regular period of years and maintained on alternating fields on the farm." Crop rotation can best be explained, perhaps, by giving an example of it which is common in many sections. A cultivated crop, as corn or potatoes, is grown on one part of the farm the first year; a grain crop, as wheat, oats, or barley, on another; and a grass crop, as timothy, clover, or brome grass, on a third part. The following year the grain will occupy the land where the cultivated crop was grown; the grass crop, which was sown with the grain the first year, will occupy that land; while the land in grass the first year will be broken and planted to a cultivated crop. This regular sequence of cultivated crops, grain crops, and grass crops, is called a rotation of crops. Unless there is some definite plan and reason for such a sequence, it can not properly be called a rotation. For instance, the alternating of oats or barley or flax with wheat in a spring-wheat region can hardly be called a rotation, for it does not conform to the principles on which crop rotation is based.
The system of farming which was originally followed was to grow a crop on a piece
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of land continuously until the yields decreased below the point where production was profitable. Then the land was allowed to "rest;" i.e., it reverted to a state of nature, growing up to weeds, brush, or trees, while a new field was cleared for the farm operations. If the old piece was again cleared after a few years, its original fertility would be found to be largely restored, for the plants which grew on it during the interval drew the plant food from the soil as it became available and returned it with each recurring season.
After a time, the practice became common of resting the land for but a single season, allowing it to grow up to weeds and then plowing them under. This was less expensive and laborious than clearing new land, while its effect on crop yields was nearly as good. As agriculture advanced, the land was cultivated during this resting period to prevent the growth of weeds and what was known as the "summer fallow" was developed. Still later, a cultivated crop was substituted for the summer fallow, for land was constantly becoming more valuable and it was not profitable to allow it to lie idle every alternate year. Crop rotation was thus eventually developed. This same process of evolution from continuous cropping to a systematic rotation of crops is repeated in more or less detail in practically every newly-settled country. It is now taking place in a large part of our western territory, though here the lack of rainfall may interfere in some degree with the adoption of logical rotation systems.
A rotation of crops improves the physical condition of the soil, helps to conserve moisture and vegetable matter in the soil, lessens the damage from insects and plant diseases, aids in the control of weeds, increases crop yields, distributes the necessary
How Rotations Help 595
labor of crop production, and helps to systematize farm operations.
The roots of all plants do not penetrate the soil to the same depth. Deep-rooting plants like clover and alfalfa enter the lower layers of the soil; when their roots decay they open channels for the passage of air and moisture and make it easier for the crops which follow to draw on the stores of plant food in the subsoil. Constant cultivation and the growing of cultivated crops tend to decrease the supply of vegetable matter in the soil, because favorable conditions for its decomposition are provided. Grain crops add little in the way of vegetable matter unless the straw is returned in manure, as the roots and stubble are not bulky. The grasses, however, grow for two or more years and accumulate a large quantity of fibrous material, which tends to reastore the supply of vegetable matter. If a portion of this matter is in the lower soil layers, as in the case of deep-rooting plants, it further improves the physical condition. The varying cultivation which is given to different crops is also of benefit, for the soil is stirred to different depths and aerated.
Practically all systems of rotation include, at some time during their course, one or more cultivated crops. Cultivation, by maintaining a surface mulch and lessening evaporation, helps to hold the moisture in the soil. Moisture passes very readily from stubble land, or from any bare, untilled field, but the tillage given a cultivated crop conserves moisture for the crop which follows.
Constant cultivation and the removal of crops rapidly reduce the vegetable matter in the soil. A rational system of rotation includes the keeping of more or less live stock to turn the
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bulkier and less valuable products of the farm into more concentrated and more readily salable products. With proper care given to the manure, a large part of this vegetable matter may be returned to the soil. While grain crops and cultivated crops are exhaustive of vegetable matter, grass crops, because they have extensive root systems, materially increase the vegetable matter in the soil.
[Illustration: Fig. 150. Samples of soil from (1) a grass plot, and (2) from one which has been in corn continuously for a number of years. Note the absence of vegetable matter in the sample from the corn field.]
Most of the plant diseases and injurious insects are decidedly limited in the number of plants on which they can live. Many of them are destructive to only one of the crops commonly grown. They are not generally capable of movement for any considerable distance during a season, but increase very rapidly from year to year if a single crop is
Rotations Keep Down Weeds 597
grown repeatedly on the same land. The change of crops from one field to another helps to keep these pests under control. As most plant diseases are unable to maintain themselves for more than three or four years in the soil without their particular host crop on which to grow, the crop may be returned to the land at the end of such a period with little fear of injury. The same statement is true to a lesser extent of insects; some of them will go from field to field, but the greater part of them will die for lack of suitable food if crops on which they do not feed are introduced.
Some weeds grow best in certain crops or under certain conditions; others thrive unde rtotally different conditions. The small grains offer particularly favorable conditions for the growth of many weeds. The spring grains are sown before many of the weed seeds germinate, and ordinarily no effort is made to control weeds which come up in them, so that they are allowed to grow unmolested till harvest. Even less opportunity is afforded to combat weeds in fall grain, except that the grain begins growth earlier in the spring than many of the weeds and is harvested earlier than some of them mature their seed. By harvest, most of the annual weeds have ripened their seeds and have thus had every chance to increase. Meadows and pastures offer less favorable conditions for annual weeds, as the crops and weeds are cut or eaten off by stock, and when a good sod is established it affords little opportunity for weeds to get a start. Biennial and perennial weeds, however, often thrive in meadows and pastures, if the field is left undisturbed for several years and there is no chance to destroy them by stirring the soil. Cultivated crops offer opportunities for the destruction of weeds of all classes. In other words, weeds increase rapidly in grain crops, some classes decrease while others may increase in
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meadows and pastures, and all classes decrease in fields on which cultivated crops are grown and given proper attention.
A rotation of crops, with the diversification which it necessarily implies, insures some return for the season's labor. Seasonal conditions may be such as to cause the total failure of one crop, but it is very seldom, at least east of the 100th meridian, that all the crops on the farm fail to yield a profitable return. Conditions that are unfavorable to oats or wheat may be quite suitable for corn or hay, so that if one has several crops he is much surer of some return for his labor than if he depends entirely on one. The old caution, "Do not put all your eggs in one basket," applies as well to crops as to anything else. Plant diseases or insect pests may destory one crop, but they are seldom destructive to all crops in any one year. The diversification of crops has been the best means of preventing financial disaster in the sections of the South which have been invaded by the cotton boll weevil, just as it has been under similar circumstances in other sections.
One crop helps to prepare the soil for the one which follows. Clover opens the subsoil and adds nitrogen and vegetable matter for the corn or potato crop which comes after it. A cultivated crop preceding one of small grain puts the soil in the best physical condition, conserves moisture, and cleans the land of weeds. If the crops which are produced are largely fed on the farm and the manure returned to the land, crop yields will be further increased, because each crop, except perhaps the small grains, increases the available supply of plant food. The grasses and clovers add vegetable matter to the soil, while cultivation unlocks a part of the store of plant food and makes it available for the use of plants.
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Growing a single crop or a single class of crops limits the seasons at which farm work can be done. The growing of small grains requires a rush of work during a few weeks while the land is being prepared and the crops seeded, and again during harvest, with little employment during the remainder of the year. Cultivated crops in general are planted later than the small grains and most of the work of cultivation is done before grain harvest, while they are not ready to gather until the grain crops are safely housed. Hay crops require little labor except at the haying season, which usually comes when other crops do not require much attention, except that it may sometimes conflict with the harvest of small grains , or the cultivation of intertilled crops. The harvest of such crops as alfalfa, which yield several cuttings during the season, may conflict with the handling of other crops, but such conflicts can hardly be avoided. A diversity of crops usually encourages the keeping of more live stock than single-crop farming, and live stock usually requires more attention during the season when the crops require least care, thus distributing labor throughout the year. The system of farming which provides employment for the farm labor throughout the greater part of the year is the one which is most likely to prove stable and profitable, other things being equal.
A rotation implies a definite system of operations. The following of a rotation allows the farmer to plan his work more definitely during the season and to figure more definitely on crop yields and income. Rotations tend to the division of the farm into regular units of uniform size, and decrease rather than increase the number of fields on most farms. By effecting a more uniform distribution of farm labor throughout the season, a smaller and much more permanent force is
510 Field Crops
required, which in itself tends to place the work of the farm on a stable and systematic basis.
Many people hold that rotations conserve soil fertility. While crop yields will decrease much more slowly where several crops are grown in a rotation than where any one is grown continuously, crop rotation is just as certain to exhaust the supply of available fertility eventually, if no fertilizers are used, as is a single cropping system. The various crop plants all use
[Illustration: Fig. 151. Good plowing is essential to the production of good crops.]
the same elements of plant food, though some draw more heavily on one and some on another. The three which are most largely used and which are most likely to become depleted are nitrogen, phosphorus, and potassium. The legumes take the nitrogen from the air and store it in the soil in a form available for other plants, so that if a leguminous crop is grown as often as once in three years there is
The Crops in a Rotation 511
little danger of the exhaustion of this element, but Nature's supply of potassium and phosphorus must eventually be supplemented.
Live stock farming aids in conserving these elements, for live stock products remove much less of them than grains, hay, and cotton. If the manure is properly handled and returned to the land, the exhaustion of the soil will be very slow, but it will be constantly taking place. The products which are sold will remove some of the potassium and phosphorus, while there will also be a considerable loss by leaching from the soil and from the manure. Some phosphorus and potassium should occasionally be added from outside sources in the form of purchased feeds or of fertilizers in order to maintain or to increase the fertility of the soil.
So far as their arrangement in a rotation is concerned, field crops may be divided into grass, grain, and intertilled, or "fallow," crops. Grass crops include all the plants which are grown in meadows and pastures, such as the perennial forage grasses, clovers, and alfalfa. These remain on the land for two or more years and increase the supply of vegetable matter by the mass of stubble and roots which they produce. All annual crops not intertilled will be designated in this discussion as grain crops. They are sown too thickly to allow intertillage, and occupy the land but a few months. They exhaust the supply of humus and plant food elements, and are also exhaustive of soil moisture. This class of crops includes wheat, oats, barley, rye, flax, buckwheat, millet, and all annual forage crops similarly produced. Intertilled crops are planted in rows wide enough apart to be tilled during a large part of the growing season. They are also exhaustive
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[Illustration: Fig. 152. A corn-wheat-clover rotation (on the left) vs. continuous corn growing (on the right). Note the difference in growth of the crop as shown in the upper pictures, also in soil texture and content of vegetable matter as indicated in the lower views. A good rotation pays.]
The Essentials of a Rotation 513
of soil fertility, and while the cultivation tends to "burn out" or hasten the decomposition of vegetable matter, it aids in the changing of plant food from insoluble to soluble forms and also conserves moisture. Intertilled crops include corn, cotton, potatoes, sugar beets, tobacco, and many others of less importance. The annual leguminous forage crops may be cultivated like corn or sown broadcast. Their effect on the soil is very similar to that on other crops, except for their ability to add nitrogen.
The essentials of a good rotation are:
An intertilled crop,
A crop for cash returns,
A crop for feeding to live stock, and
A crop to increase the supply of vegetable matter and nitrogen.
Two or more of these essentials may be embraced in a single crop. Thus clover supplies a crop for live stock feeding, and is one which increases the supply of humus and nitrogen. Corn is a cultivated crop, and may be either a cash crop or one for feeding to live stock.
As already stated, weeds increase when grain crops are grown, and the methods of destroying them are limited. Some classes of weeds increase in meadows and pastures. An intertilled crop is needed at intervals to subdue weeds and to keep them from overrunning the land. Tillage aids in retaining the soil moisture and in liberating supplies of plant food. Stirring the soil allows the air to penetrate to the roots of the plants and enables them to grow better than in hard, cloddy ground. The aeration of the soil also improves its texture and provides more favorable conditions for the growth and work of some of the beneficial bacteria.
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It is essential, if the work of the farm is to be made profitable, that at least one crop be grown for cash returns. It need not necessarily be one which is sold in its natural state, for it may be converted on the farm into animal products and then marketed. On many farms, however, some crop is grown for direct sales for cash or its equivalent. If no cash crop is grown, there is no opportunity to increase the available funds for necessary improvements or for the purchase of food and clothing and other necessities of life which can not be produced on the farm. It might be possible to follow a rotation of crops which would rapidly increase the available supply of plant food by growing only such crops as clover, rye, and cowpeas and continually plowing them under as green manure crops, but this practice would yield no cash returns and could only be followed where there was some source of income from outside the farm. In general, the growing of a cash crop is a necessity. Cotton, wheat, potatoes, tobacco, flax, barley, and sugar beets are important crops which are grown for direct sales. Hay and corn frequently become cash crops indirectly by marketing them through live stock.
At least one crop should be included in the rotation which can be used for feedign to live stock. The necessary work stock should be fed, as far as possible, on products grown on the farm, for it is usually cheaper to grow their feed than to purchase it. It is generally profitable to keep some cattle, hogs, and sheep, or at least one of these clases of animals, to convert much that is grown on the farm into more readily marketable or more valuable products, and at the same time to return to the land in the manure a large part of the fertility which is removed by the crops. Livestock farming will postpone soil exhaustion much longer than grain farming
Crops to Supply Nitrogen 515
if no fertility is brought to the farm from outside sources. Among the crops which may be grown for live stock feeding are corn, grass, clover, alfalfa, oats, and barley.
It is necessary to conserve the supply of vegetable matter in the soil, in order to maintain profitable crop yields. The exhaustion of the vegetable matter makes the soil "hard to work;" it becomes stiff and lifeless, bakes and clods badly and dries out very quickly. Vegetable matter improves the physical condition of the land and increases its moisture-holding capacity. The acids formed through the decay of this organic matter also help to unlock the unavailable supply of some of the elements of plant food by changing the nature of the compounds and by acting as a stronger solvent than water. Nitrogen, the most expensive of the three elements of plant food usually purchased in the form of commercial fertilizers, can be added to the soil very cheaply through the medium of leguminous crops. The grasses increase the supply of vegetable matter; the legumes increase the supply of both vegetable matter and nitrogen. Vegetable matter is also added to the soil in corn and cotton stalks, straw, stubble, and manure. The more important crops to supply vegetable matter are clover, alfalfa, the perennial grasses, cowpeas, soy beans, field peas, and green manure crops such as rye, vetch, and rape.
The crops which are included in the rotation depend entirely on the kind of farming which is followed, the crops which succeed best in the locality, and the individual preferences of the farmer. All the farm need not necessarily be included in a single rotation. It may be advisable to have a primary rotation for the greater part of the land, and a secondary one for a smaller portion of it which is different in texture or fertility, or to supply crops
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for a special purpose. Thus the greater portion of the farm may be devoted to the production of wheat and potatoes, with clover to complete the rotation. A rotation which includes these three crops embraces two cash crops, wheat and potatoes; and intertilled crop, potatoes; a crop for live stock, clover, with the wheat straw as roughage and bedding; and a crop to add humus and nitrogen, clover. Such a system would not supply enough feed other than clover hay for any large number of live stock. If the section is adapted to the production of corn, either for grain or for forage, that crop might be added to the rotation, or a secondary rotation might be devised on another part of the farm, in which corn, oats, and clover may be grown. Here all three crops would be sutiable for feeding to live stock; all might be considered as cash crops, as they would be marketed through the live stock products; corn would supply the intertilled crop, and clover the vegetable matter.
Many of the best systems of crop rotation, as already stated, include the feeding on the farm of a large proportion of the crops which are produced, and the return of the fertility in the form of manure. As a general thing, this manure may be applied to best advantage to the grass crop or to the cultivated crops. Whenever it is practicable, it should be hauled to the field during the winter as it is made, as the loss from leaching there is less than if it is left in the barnyard. If the manure can be stored under cover where it will not leach away, it may be left to decay. Well-rotted manure is less bulky and less likely to contain dangerous weed seeds than fresh manure; but under most other conditions it should be applied to the field as soon as possible, because there is less waste than in rotted manure, and the active rotting of fresh manure in the soil warms it and aids bacterial and chemical action. Manure may be
Length of the Rotation 517
applied to meadows at any time except during a few weeks before haying, while it may be spread on pastures throughout the year, though it is usually best to apply it to them during the winter. In the South, where a perennial grass crop is not often grown, manure is usually put on the land before planting the principal crop, which is generally cotton or corn.
The length of the rotation depends on the crops which it includes and the system of
[Illustration: Fig. 153. The manure spreader distributes the manure evenly over the soil so that it can be plowed under without trouble and placed where it will be most easily reached by crops. The easiest way to handle manure is to load it directly into the spreader from the stable.]
farming which is followed. It may be a two-year, three-year, or four-year rotation, or it may be planned for a much longer period. The most common rotations are three-, four-, and five-year ones.
It is not possible to outline a single rotation or even several rotations which
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will fit all cases, for that must be left to the needs, facilities, and inclinations of the individual farmer. Those that are suggested here are some that are in more or less common use, and that include the principal crops of the sections specified. They may be varied in almost innumerable ways.
In New England, special crops are grown or special lines of farming are followed in the different sections, and the rotations depend entirely on the particular system in vogue in the locality. Where potatoes are the main crop, the rotation is often as follows: 1, potatoes; 2, oats, with clover seeded in the oats; 3, clover.1 The clover may be left for two years, or the potatoes may be grown for two years in succession. In the dairy sections, fodder corn is one of the principal crops. Here the rotation may be: 1, corn, cut for silage, followed by rye; 2, rye, plowed under for green manure, followed by corn and rye as before; 3, rye, with clover seeded in it; 4, clover. In the tobacco district, tobacco may take the place of the second crop of corn.
In the North Atlantic States, dairying is generally important. Here a common rotation is: 1, corn; 2, wheat, seeded to clover and grass; 3, meadow; 4, pasture. The pasture may be left for one or more years. A little farther south, where cowpeas and crimson clover can be grown, the rotation may be: 1, corn; 2, wheat, followed by cowpeas; 3, cowpeas, cut early for hay, followed by grass; 4, meadow; 5, pasture. The simple three-year rotation of corn, wheat, clover, or corn, oats, clover, may also be followed.
In the Southeastern States, rotations are less common, for the land is kept pretty constantly in cotton. Because
1 In this discussion of rotations, the figures refer to the year in the rotation. Thus, in the one just given, a crop of potatoes is grown on a given piece of land the first year; the second year it is sown to oats, with clover seeded in the oats, while the third year it is a clover meadow or pasture. If potatoes are grown for two years, it would be: 1, potatoes; 2, potatoes; 3, oats; 4, clover.
Rotations in the Central States 519
of the possibility of growing several crops during the year, many different combinations of crops may be made. One which includes the two most important crops, corn and cotton, and also embraces all the features of a good rotation, is: 1, cotton, followed by rye or bur clover; 2, corn, with cowpeas sown in the corn, followed by winter oats or winter barley; 3, winter grain followed by cowpeas cut for hay, the land then being sown to rye or some other winter cover crop. A more simple rotation, but one which lacks an essential feature of all cropping systems for the South, the winter cover crop, is: 1, corn and cowpeas; 2, winter grain, followed by cowpeas; 3, cotton; 4, cotton or corn. A simple alternation may be followed in some sections, such as cotton and bur clover or winter wheat and cowpeas. With the addition of phosphorus and potassium, this is very successful.
[Illustration: Fig. 154. The arrangement of the fields and crops in a three-year rotation of corn, oats, and clover.]
In the Central states, in what is commonly known as the corn belt, the one crop on which all systems of farming are based is corn. The three principal crops are corn, wheat, and grass or corn, oats, and grass, and they are arranged in the rotation in the order named. Two crops of corn may be grown in succession or the land may be left in grass for one, two, or more years, either as meadow or pasture. A very common form of this rotation is the five-year one, as follows: 1, corn; 2, corn; 3,
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oats (or wheat); 4, meadow; 5, pasture. It is possible in the southern part of the corn belt to grow a crop after grain if the land is not seeded to grass. A rotation embracing this feature might be devised like this: 1, corn; 2, oats, followed by cowpeas or soy beans; 3, wheat; 4, meadow; 5, pasture.
In Minnesota, Wisconsin, and the Dakotas, some of the rotations used in New York and New England may be profitably followed. In the Dakotas and farther west, rotations are not commonly practiced, only small grain crops being extensively grown. A system of farming based on a single class of crops can hardly be called a rotation. The land is usually sown to flax when it is first broken; wheat is then grown for a period of years, when one or two crops of oats or barley
[Illustration: Fig. 155. An expansion of the roation in Fig. 154. inot a four-year rotation. Timothy is sown with the clover and is cut for hay the first year after seeding; the second year, it is pastured.]
may be introduced, to be followed again by wheat. Under this system, weeds increase rapidly, and it is often necessary to resort to the bare fallow or to introduce a cultivated crop to control them; the latter is preferable. The crops which are commonly introduced are corn and potatoes, and both are usually grown with success.
In the Great Plains, Rocky Mountains, and Pacific states the systems of farming are yet too new for any general series of rotations to have
References on Rotations 521
been adopted. One which may be followed in the irrigated districts embraces three or four successive crops of alfalfa, followed by one or two crops of potatoes or sugar beets and perhaps one or more of barley, wheat, or oats, when the land is again seeded to alfalfa. In California, on the dry lands where grain is grown, a more or less definite squence of wheat, barley, and oats is sometimes followed, but rotations which embrace all the desirable features are little known.
1. Draw a plan of the home farm or of some farm in the neighborhood and show the crops which are now grown on it. If a definite rotation is now followed, tell whether it is a good one. If it is not, show how it may be improved to more nearly meet the four essentials of a good rotation. If no rotation is followed, plan one which is suitable for the type of farming which is followed.
2. Plan a three-year rotation, using the more important crops of your community and taking care that the four essentials are included. In the same way, plan four-year and five-year rotations.
3. Plan a rotation which will be suitable for a dairy farm in your section; for a hog and beef-cattle farm; for the production of the leading cash crop.
242. An Example of Model Farming.
272. A Successful Hog and Seed-Corn Farm.
312. A Successful Southern Hay Farm.
325. Small Farms in the Corn Belt.
326. Building up a Run-Down Cotton Plantation.
337. Cropping Systems for New England Dairy Farms.
355. A Successful Poultry and Dairy Farm.
454. A Successful New York Farm.
Bailey's Cyclopedia of American Agriculture, Vol. II, pp. 81-109.
Burkett's Farm Crops, pp. 16-26.
Hays' Farm Development, pp. 96-116.
Hopkins' Soil Fertility and Permanent Agriculture, pp. 226-235.
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