Excerpt: The term "cover-crop," which, until 1893, was not distinguished from "catch-crop," or from "green-manure crop," is now applied to a crop grown to prevent injury and losses to soils, and either directly or indirectly to improve them, and often to afford protection to trees or other plants, rather than to secure the proceeds or products of the crop itself.
The term "cover-crop," which, until 1893, was not distinguished from "catch-crop," or from "green-manure crop," is now applied to a crop grown to prevent injury and losses to soils, and either directly or indirectly to improve them, and often to afford protection to trees or other plants, rather than to secure the proceeds or products of the crop itself. A catch-crop is one that is grown between the periods of other crops, as after early potatoes and before winter wheat; or, sometimes the word is used to designate companion-crops, or those that are grown between the rows of other crops, as turnips grown between potatoes. The purpose of the catch-crop is to utilize the land to the utmost, securing an incidental crop. Green-manure crops are those grown for the purpose of enriching the land, whereas cover-crops are grown to protect the land, or trees, or other plants that may be growing on it. Cover-crops may or may not be green-manure crops. Cover-crops usually remain on the ground in winter. [See the article on Fruit-growing for another discussion of cover-crops.]
Cover-crops are used, (1) to prevent the loss of soluble plant-food, which occurs when lands are left uncovered during the late fall and winter, especially in the case of corn, potato and tobacco lands, and for small-fruits or cultivated orchards; (2) to prevent the galling or surface erosion of hillsides or slopes by winter rains; and (3) to prevent root injury by excessive freezing of orchard lands, which danger, however, is apparent chiefly in the North and West, from Nebraska to North Dakota, Minnesota, Wisconsin and Canada. In all of these cases, the benefits, in addition to those mentioned, are due to the introduction into such soils of vegetable matter.
The advantages of cover-crops in conserving and increasing fertility may be stated more in detail as follows: They absorb the plant-food from insoluble sources, and convert it into organic forms; they retain plant-food, particularly of a nitrogenous character, that would be carried away from a bare soil by leaching; and they regulate temperature and moisture conditions, thus promoting nitrification when seasonal conditions are favorable. Cover crops improve physical character by providing roots to break up the soil particles and make them finer, besides adding vegetable matter or humus-forming material to the land, thus making the moisture conditions more favorable. They encourage the deeper rooting of orchard trees and prevent deep freezing by acting as a mulch. The effect of the cover-crop on the land will depend, to some degree, on the root habit of the crop. The clovers are very deep rooters (Fig. 369), and are prized for this reason as well as for other merits.
Crops that are used as a cover to accomplish these results should not be confused with those which are used for green-manures. If they are made to serve as green-manures the real advantage of the cover-crop may be lost, for if a cover-crop is left too late in the spring it may cause injury by robbing the main crop of the needed moisture; and when plowed down, after making too large a growth, it will injure spring-sown crops by cutting off the capillary supply of ground-water. These points should be carefully observed, for while many cover-crops may serve a specially useful purpose as green-manures, the direct manurial effect should be
regarded as an incidental gain, secondary to that secured from their use as cover-crops.
A very large number of plants have been used for cover-crops in the United States. These may be divided into two groups, viz., the legumes, or nitrogen-gatherers, and the non-legumes, or those which are sometimes distinguished as nitrogen-consumers. Of the legumes, the following have been used with considerable success: the several varieties of red clover and Canada field-peas, widely useful in the northern tier of states; alfalfa, in the western states and California; soybeans, cowpeas and crimson clover in the central and southern states; velvet bean and beggarweed, especially
Fig. 368. Crimson clover as an orchard cover-crop. Usually it should be plowed under before it blooms.
useful only in the South; hairy vetch and spring vetch, most successfully used in the South, though rather generally grown in the northern states; sweet clover and sometimes, for peculiar conditions, serradella. Of the non-legumes, rye, wheat, oats and barley of the cereals are probably more commonly used than any others; rape and turnips of various varieties are used commonly; though they are not hardy in the northern sections of the country; buckwheat, white mustard and spurry have also been used with satisfaction under special conditions. Various mixtures and combinations of these plants are sometimes used, in order that the cover may extend through a longer period, or to insure a covering of the land should conditions, be unfavorable for one or more members of the combination.
The knowledge gained through experiment station work as to the usefulness of cover-crops, is constantly increasing, and they are now considered an important part of rational agricultural practice.
The principle that should govern in the use of cover-crops is to employ such crops as may accomplish the special purposes desired. To get the best
results, a cover-crop should be used when there is a period in a succession of crops in a rotation when the land would be likely to lie bare for any considerable period, or, as in the case of orchards, when it is desirable to increase the vegetable matter in the soil and to retard the vegetative growth of the trees and bushes, and thus to encourage a more complete maturity of the plant.
The kind of crop to plant must be determined by the local conditions and the local needs; that is, whether a grass, cereal, legume, or cruciferous plant shall be used, will depend on whether the habits of growth and characteristics of the plant will accomplish the purpose desired. For example, in the southern states, Bermuda-grass is admirably adapted to prevent erosion of land, yet this crop would not be recommended for northern conditions. In Delaware, and in certain other of the middle states, crimson clover is generally seeded in corn as a cover-crop. It is hardy, grows well in the fall, and protects the soil during the winter; in addition, it starts early and grows rapidly in the spring, accumulating a large mass of vegetable matter containing nitrogen, in time to plow down for a spring crop. The conditions in these states are favorable for the use of crimson clover as a cover-crop, whereas farther north the plant is not hardy and may serve as a cover-crop only in the fall. In the more northern sections; therefore, wheat or rye would be more desirable, as it will serve as a cover during the fall and continue to grow through the winter and early spring, absorbing and retaining soluble plant food and gathering useful vegetable matter.
In market-gardening, when it is necessary to plant early in spring, such crops as turnips, rape, oats, Canada peas, cowpeas, or soybeans, which die after freezing weather, are serviceable as fall cover-crops, because they accumulate large quantities of vegetable matter, cover the land with a mulch during the late fall and early winter, and are in condition to decay rapidly when the ground is plowed, which frequently may be done in early March.
The following bibliography of some of the experiments conducted in this country will serve as a guide to the kind of crop to be grown under the varying conditions of climate, location and cropping: Tennessee Experiment Station, Bulletin No.4; Nebraska Experiment Station, Report 1899, pp. 50-61; Canada Experimental Farms, Ottawa, Canada. Report 1901, pp.140-152; Ontario Agricultural College and Experiment Station, Report 1904; Cornell Experiment Station, Bulletin No. 198; Report of the Secretary of Agriculture, Nova Scotia. 1902, Part I, pp. 70-90; Massachusetts Experiment Station, Bulletin No. 82; Missouri Fruit Experiment Station, Bulletin No.4; Delaware Experiment Station, Bulletins Nos. 60 and 61; Michigan Experiment Station, Special Bulletins Nos. 27 and 30; Connecticut Experiment Station, Bulletin No. 149; Proceedings of Western New York Horticultural Society, 1901, pp. 12-17; American Agriculturist, 1902, pp. 79 and 100. The term cover-crop was first used in this signification by Bailey in 1893, Cornell Bulletin No. 61.
Fig. 369. Root habit of (top) crimson, (middle) mammoth clover, (bottom) winter vetch. Cornell Exp. Sta.