All the varieties of clover discussed in this
volume may be grown in certain rotations. Their adaptation for this use,
however, differs much. This increases as the natural period of the life
of the plant lessens and vice versa. Consequently, the medium red
the mammoth, the crimson, the Japan and the burr varieties stand high in such adaptation. The alsike, living longer, is lower in its adaptation, and alfalfa, because of its long life, stands lowest in this respect. The small, white variety is almost invariably grown or found growing spontaneously along with grasses, hence no definite place has been or can be assigned to it in the rotation. Sweet clover being regarded by many as a weed has not had any place assigned to it in a regular rotation, although in certain localities it may yet be grown for purposes of soil renovation. (See page 306.) All these crops are leguminous without any exception. This fact is of great significance where crops can be rotated. They have power to gather nitrogen from the air and store it in the soil in tubercles which form on their roots, in all soils in which they produce a vigorous growth. This fact indicates where they should come in the rotation. They should be grown with a view to gather food for other crops made to follow them, which have not the same power. They should, therefore, be made to precede such crops as the small cereals, corn, the sorghums, the millets and cotton. But since these clover plants have the power to bring nitrogen from the air, it must not be supposed that they will grow with sufficient vigor in soils destitute of this element. They must be able to appropriate enough from the seed soil to give them a good start before they can draw nitrogen from the air, hence, though they may be made to follow almost any kind of crop, it may sometimes be necessary to apply some nitrogenous fertilizer before they will make a vigorous growth. The clovers, unless in the case of some of the smaller varieties, are more commonly sown to provide hay than pasture in the first crops obtained from them. The value of the hay is increased or lessened in proportion as weeds are present. To insure cleanliness in the hay crop, therefore, the system which aims to sow clover seed on land to which clean cultivation has been given while growing on them a cultivated crop, as corn or field roots, meets with much favor. The mechanical condition of the soil immediately after growing these crops also favors the vigorous growth of the young clover plants, more especially when they are sown upon the surface of the land after some form of surface cultivation, rather than upon a surface made by plowing the land after cultivation has been given to it, but to this there may be some exceptions. Clover in some of its varieties is frequently grown from year to year in orchards and for the two-fold purpose of gathering food for the trees and providing for them a cover crop in winter. The medium red and crimson varieties are preferred for such a use. The latter is the more suitable of the two, since it does not draw on soil moisture needed by the trees, owing to the season at which it is grown. Enough of the seed of these crops may be allowed to mature to re-seed the land from year to year, and thus keep it producing. The clover plants not only gather nitrogen for the fruit trees, but in their decay they increase the power of the soil to retain moisture for the benefit of the trees. Some varieties of clover may be grown as catch crops, that is, as crops which are grown in addition to some other crop produced the same season. When thus grown, it is usually for purposes of soil improvement rather than to furnish food. The varieties best adapted for this purpose in the Northern States and Canada are the medium red and the crimson, the latter being much more circumscribed in the area where it will grow successfully than the former. When medium red clover is thus grown, it is commonly sown along with one of the small cereal grains, and is buried in the autumn or in the following spring. (See page 75.) The extent of the advantage is dependent chiefly on the amount of the growth made, and this in turn is influenced by the character of the soil, the season, and the nurse crop. In certain areas favorable to the growth of clover some good farmers sow clover along with all the small cereal grains which they grow. Crimson clover is usually sown in the late summer after some crop has been reaped and it is plowed under the following spring. (See page 250.) In the Southern States Japan clover and burr clover will serve the purpose of catch crops better than the other varieties. The former will follow a winter crop (see page 284), and the latter a summer crop. (See page 294.) Although alfalfa is not usually looked upon as a rotation crop in the Rocky Mountain valleys, it may be made such a crop. In these it grows so vigorously as to fill the soil with its roots in one or two seasons, hence it may be made to rotate profitably with other crops. (See page 135.) In such instances, however, medium red clover would probably answer the purpose quite as well, and possibly better, since the labor of burying it with the plow would be less difficult. While some varieties of clover may be grown in various rotations and with profit, one of the best of these, where the conditions are favorable, is a three years' rotation. The first year some small cereal grain is grown and clover is sown along with it or, at least, on the same land. The next year the clover is grown for hay or pasture. The third year a crop of corn, potatoes or vegetables is grown, and the following year small cereal grain and clover. The clover may thus be made to furnish nitrogen indefinitely for the other crops, but in some instances it may be necessary to add phosphoric acid and potash. =Preparing the Soil.=--Clovers are usually sown with a nurse crop. The exceptions are crimson clover, and in many instances alfalfa. When thus grown, the preparation of soil for the nurse crop will usually suffice for the clovers also. But there may be instances in which it would be proper to give more attention to cleaning and pulverizing the soil to properly fit it for receiving the clover seed. The leading essentials in a seed-bed for clover are fineness, cleanness, moistness and firmness. Ordinarily black loam soils, sandy loam soils, sandy soils, humus soils and the volcanic ash soils of the West are made sufficiently fine without great labor. Clay soils may call for the free use of the harrow and roller used in some sort of alternation before they are sufficiently pulverized. Excessive fineness in pulverization of these soils is also to be guarded against in rainy climates, lest they run together, but this condition is present far less frequently than the opposite. Cleanness can usually be secured when clovers follow cultivated crops by the labor given to these when the land is not plowed in preparing it for the clovers. In other instances the longer the land is plowed before putting in the seed and the more frequently the surface is stirred during the growing part of the season, the cleaner will the seed-bed be. In the spring the land is usually sufficiently moist for receiving the seed. In the autumn moisture is frequently deficient. Stirring the surface of the soil occasionally with the harrow will materially increase the moisture content in the soil near the surface, even in the absence of rain. As crimson clover is usually sown in the late summer and alfalfa is frequently sown in the autumn, it may sometimes be necessary to give much attention to securing sufficient moisture to insure germination in the seed. When clovers are sown in the spring on land which is also growing a winter crop, no preparation is necessary in preparing the land for receiving the seed. On some soils the ground becomes sufficiently honeycombed through the agency of water and frost to put it in a fine condition for receiving the seed. When this condition is not present, the seed will usually grow if sown amid the grain and covered with the harrow. When clovers are sown on sod land for the purpose of renewing pastures, disking them will prepare them for receiving the seed. The extent of the disking will depend on such conditions as the toughness of the sod and the nature of the soil. Usually disking once when the frost is out a little way from the surface, and then disking across at an angle will suffice, and in some instances disking one way only will be sufficient. On newly cleared lands the clovers will usually grow without any stirring of the land before sowing, or any harrowing after sowing. Clovers that are grown chiefly for pasture, as the small white, the Japan and the burr, will usually obtain a hold upon the soil if scattered upon the surface which is not soon to be cultivated.
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