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that it may come to be used for purposes of soil renovation.
Soils.—But little can be gleaned from American sources on this subject. Notwithstanding, it may be said with safety that it has greater power to grow on poor, worn and hard soils than any forage plant that has yet been introduced into America for economic uses.
It will probably be found true of it, as of other clovers, that it will thrive best on soils that have produced timber, and more especially timber of the hardwood varieties. This means, therefore, that it will grow well in probably all kinds of clay soils and also in loam soils underlaid with clay: It has high adaptation for soils abounding in lime. It can be made to succeed on hard clay subsoils from which the surface soil has been removed. But it will also grow well on sandy soils and even on gravels when a reasonable amount of moisture is present. The author succeeded in growing it in good form in 1897 and 1898 in a vacant lot in St. Paul, from which 6 to 8 feet of surface soil had been removed a short time previously. The subsoil was so sandy that it would almost have answered for building uses. .
This clover will probably grow with least success on soils of the prairie so light in texture as to lift with the winds, and in which the underlying clay is several feet from the surface, also in slough soils that are much saturated with water.
Since it grows vigorously on road sides, in rocky waste places and even in brick yards when sown without a covering, the idea has gained currency that the harder the soil, the better the plants will grow, and the more surely will they be established in the soil; but this view does not seem to be in accord with the principles which usually govern plant growth. It will, however, send its roots down into hard subsoils so deeply that in certain seasons the plants could not be dug up without the aid of a pick.
Place in the Rotation. Since sweet clover seed is more commonly scattered in byplaces, or is self-sown from plants that have run wild, it can scarcely be said that it has ever been grown as a regular crop and in a regular rotation. Nor is it ever likely to become a factor in such a rotation unless its properties shall be so modified that it can be grown acceptably as a pasture plant. In such an event it would have the same place in the rotation as other clovers; that is, it would naturally follow a cultivated, that is, a cleaning crop, and precede some crop or a succession of crops that would profit from the nitrogen and humus which it had brought to the soil, and also from the influence which the roots would exercise mechanically upon the same. But the necessity for sowing it on clean ground would not be so great as with the other clovers, since it has greater power than these to overshadow weeds when the two grow together.
In the meantime, this plant will probably continue to be grown as in the past; that is, if sown, it will be sown: 1. In byplaces to provide pasture for bees, in which case in time it will be superseded by other plants. 2. On worn lands so poor that they refuse to grow valuable food products sown, partly, at least, with a view to renovate them. And 3. In cuttings made by railroads and in gullies that have been made in fields, with a view to prevent soil movement. It may also come to be sown in grain crops in localities where other varieties of clover will not grow, to be plowed under the following spring.
Preparing the Soil. —Since sweet clover will grow on the firmest and most forbidding soils, even when self-sown, it would not seem necessary, ordinarily, to spend much time in specially preparing a seed-bed for it. The fact stated is proof of its ability to grow on a firm surface. It does not follow, however, that such a condition of the seedbed will give a better stand of the plants than a pulverized condition of the same; as some have contended. It may be that on soils that are quite loose near the surface, and under conditions that incline to dry a seed-bed firm and even hard, may be more conductive to growth in the plants than one in which the conditions are the opposite. Much rolling of loose soils has been recommended when preparing the seed-bed with a view to firm them.
When the seed is sown along with grain, the preparation of the soil needed for grain would be ample preparation also for the clover. When sown on stubble land, in many instances no preparation by way of stirring the soil would seem necessary. And when sown on railroad embankments, road sides, rocky situations and byplaces generally no preparation of the soil would be possible.
Sowing. - In the North sweet clover is best sown in the spring. In fact, it can only be sown then with the assurance that it will survive the winter north of a certain limit. That limit will vary with altitude, but it will probably run irregularly across the Middle States, from the Atlantic westward to the Cascade Mountains, beyond which it will veer away to the North. In the Southern States, it may be sown fall or spring, but if sown late in the fall the young plants will in some instances succumb to the frost of winter. Early fall sowing, therefore, is much to be preferred to sowing late.
The method of sowing may be the same as in sowing medium red clover (see page 78); that is, when the seed is sown with grain crops. When sown in byplaces, it will ordinarily be sown by hand. In such places it will re-seed itself and will likely grow in these for successive seasons. On railroad embankments, the seed is scattered more commonly on the upper portion, and from the plants which grow there the seeds produced scatter downward. The plants not only lessen washing in the soil, but they prepare the same for the growth of grasses. They also aid thus in the introduction of grasses into rocky and very hard soils..
Sweet clover may be sown with almost any kind of a nurse crop desired, which does not destroy it with an over-abundant shade. Or it may be sown alone where such a necessity exists. But the instances are not numerous in which it would be desirable or necessary to sow it alone on arable soils. There may be conditions when it could be sown successfully at the time of the last cultivation given to corn and with a view to soil enrichment.
Since sweet clover is seldom sown for the purpose of providing food for live stock, it is not sown in mixtures, nor is it well adapted for being sown thus, because of the large and luxuriant character of the growth, which would tend to smother other plants sown along with it.
The amount of seed to sow has been variously stated at from 15 to 20 pounds per acre. The smaller amount should be enough for almost any purpose, and a much smaller amount should suffice for sowing in byplaces and along road sides, where the plants retain possession of the ground through selffeeding.
Pasturing. Because of the bitter aromatic principle which it contains, known as commarin, stock dislike it, especially at the first. And it is questionable if they can be educated to like it in areas where other food, which is more palatable, grows abundantly. In an experiment directed by the author at the Minnesota University Experiment Station, sheep pastured upon it, and did not take kindly to it; but by turning them in to graze upon it in the morning, they cropped it down. In localities where good grazing is not plentiful, if live stock have access to it, especially when the plants are young, they will so crop it down that in a few years it will entirely disappear. But where other pastures are abundant, it will continue to grow indefinitely. It would not