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subsoil as they grow. From the tap roots branch off lateral roots in an outward and downward țirection. From these laterals many rootlets penetrate through the soil. When the plants are numerous, these roots and rootlets fill the soil. When it is broken up, therefore, particles of soil are so separated that they tend to fall apart, hence the soil is always made more or less friable, even when it consists of the stiffest clays. The shade furnished by the clover also furthers friability. This friability makes the land easier to work, and it is also more easily penetrated by the roots of plants. The influence on aeration is also marked. The air can more readily penetrate through the interstices in the soil, and, in consequence, chemical changes in the soil favorable to plant growth are facilitated.
The roots of clovers are usually so numerous that they literally fill the soil with vegetable matter. This matter, in process of decay, greatly increases the power of the soil to hold moisture, whether it falls from the clouds or ascends from the subsoil through capillary attraction. The moisture thus held is greatly beneficial to the plants that immediately follow, especially in a dry season and in open soils, and the influence thus exerted frequently goes on, though with decreasing potency, for two, three or four seasons.
Reference has already been made to the tap root which clover sends down into the soil and subsoil. In the strong varieties this tap root goes down deeply. When the crop is plowed up, the roots decay, and when they do, for a time at least, they fur
nish channels down which the surface water percolates, if present in excess. Thus it is that clover aids in draining lands under the conditions named. The channels thus opened do not close immediately with the decay of the clover roots, hence the downward movement of water in the soil is facilitated for some time subsequently.
It has been stated that clovers have more power than some other plants to gather plant food in the soil. In some instances they literally fill the soil with their roots. When other plants are sown after the clover has been broken up they feed richly on the decaying roots of the clover. Thus it is that clover gathers food for other plants which they would not be so well able to gather for themselves, and puts it in a form in which it can be easily appropriated by these. The nitrogen in clover is yielded up more gradually and continuously as nitrates than it could be obtained from any form of top dressings that can be given to the land. In this fact is found one important reason why cereal grains thrive so well after clover.
Since the roots of clovers act so beneficently on soils, it is highly important that they be increased to the greatest extent practicable. Owing to the relation between the growth of the roots of plants and the parts produced above ground, development in root growth is promoted much more when the clover is cut for hay than when it is fed off by grazing. Experiments have also demonstrated that the development of root growth is much enhanced in medium red clover by taking a second cutting for hay or seed. They have also demonstrated that more nitrogen is left in the soil by clover roots after a seed crop than after a crop of hay.
From what has been said, it will be apparent that the extent to which clovers enrich the soil will depend upon the strength of the growth of the plants and certain other conditions. It will not be possible to reduce to figures the additions in plant food which clovers add to the soil other than in a comparative way. Dr. Voelker has stated that there is fully three times as much nitrogen in a crop of clover as in the average produce of the grain and straw of wheat per acre. Dr. Kedzie is on record as having said that in the hay or sod furnished by a good crop of clover, there is enough nitrogen for more than four average crops of wheat, enough phosphoric acid for more than two average crops and enough of potash for more than six average crops. He has said, inoreover, that the roots and stubble contain fully as much of these elements as hay.
It will also be apparent that where clover grows in good form no cheaper or better way can be adopted in manuring land, and that in certain areas the judicious use of land plaster on the clover hastens the renovating process. It is thought that in some instances the mere loading and spreading of barnyard manure costs more than the clover and plaster. Especially will this be true of fields distant from the farm steading. It is specially important, therefore, that in enriching these, clover will be utilized to the fullest extent practicable.
Clover as a Weed Destroyer.- Where clover is much grown, at least in some of its varieties, it becomes an aid in reducing the prevalence of many forms of weed growth. It is thus helpful in some instances, because of the number of the cuttings secured; in others because of its smothering tendencies, and in yet others because of the season of the year when it is sown and harvested or plowed under, as the case may be.
Alfalfa and medium red clover are cut more frequently than the other varieties and, therefore, because of this, render more service than these in checking weed growth. The former is cut so frequently as to make it practically impossible for most forms of annual weed life to mature seed in the crop. The same is true of biennials and also perennials. But there are some forms of perennial weeds which multiply through the medium of their rootstocks that may eventually crowd alfalfa. Medium red clover is usually cut twice a year, hence, in it annuals and biennials cannot mature seed, except in exceptional instances, and because of the short duration of its life, perennials have not time to spread so as to do much harm.
The clovers that are most helpful in smothering weeds are the mammoth, the medium and the alsike varieties. These are thus helpful in the order named. To accomplish such an end they must grow vigorously, and the plants must be numerous on the ground. When grown thus, but few forms of weed life can make any material headway in the clover crop. Even perennials may be greatly weakened, and in some instances virtually smothered by such growth of clover. To insure a sufficient growth of clover it may be advantageous to top dress the crop with farmyard manure sufficiently decayed, and in the case of medium red clover to dress the second cutting with land plaster. If the second growth is plowed under, subsequent cultivation of the surface will further aid in completing the work of destruction.
The crimson variety is sown and also harvested at such a time that the influence on weed eradication is very marked. The ground is usually prepared in the summer and so late that weeds which sprout after the clover has been sown cannot mature the same autumn. In the spring it is harvested before any weeds can ripen. When plowed under, rather than harvested, the result is the same.
When clover is grown in short rotations, its power to destroy weeds is increased. For instance, when the medium red or mammoth varieties are grown in the three years' rotation of corn or some root crop, followed by grain seeded with clover, the effects upon weed eradication are very marked, if the cultivation given to the corn or roots is ample. Under such a system weeds could be virtually prevented from maturing seeds at any time, especially if the medium variety of clover were sown, and if the stubbles were mown some time subsequent to the harvesting of the grain crop. Such a system of roi tation faithfully carried out for a number of years should practically eradicate all, or nearly all, the noxious forms of weed life.