COVER-CROPS. Figs. 368-370.
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.] Uscs 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 hill sides 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 Can ada. 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 insolu ble sources, and convert it into organic forms; they retain plant-food, particu larly 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 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.
• Plants used 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-con sumers. Of the legumes, the following have been used with considerable success : the several varie ties 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 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 com monly used than any others ; rape and turnips of various varieties are used commonly, though they are not hardy in the northern sections of the coun try ; buckwheat, white mustard and spurry have also been used with satisfaction under special con ditions. 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.