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Cover-crops. Green temporary crops, grown for the purpose of improving the soil, either as protection or to be turned down as green manure; word used chiefly in speaking of fruit-growing operations.

The use of cover-crops has become an essential part of orchard management. The name is derived from the fact that the seed is sown in the fall or late summer, and sufficient growth results so that the ground is covered and protected during the winter. The crops are grown for their effect upon the orchard, not for the direct value of the crop. The term was first used in this connection by Bailey, Bulletin No. 61, of the New York Station at Cornell, p. 333, December, 1893.

Cover-crops make use of the available plant-food at a time when the trees are beginning to use it less and less. In this way, food that otherwise might be lost is stored up until it becomes available to the trees the following spring through the rotting of the cover-crops. The presence of the coyer-crop, with its mat of roots, also prevents soil-washing and erosion with its accompanying loss of plant-food. The legumes, through the action of the bacteria found in their root-nodules, are able to add to the total amount of nitrogen present in the soil. This is the only way in which cover-crops increase the total supply of the plant-food elements, but the decay of the cover-crops increases the humus in the soil and, by the activities thus set up, the locked- up plant-food is released in a soluble form and thus the total available plant-food is increased. The ability of a soil to absorb and retain water is greatly increased in proportion to the humus that the soil contains. For this reason, soils rich in humus are less likely to be injured by erosion from the rapid run-off of the rainfall and less liable to suffer from drought. In soils plentifully supplied with moisture and plant-food, the trees are likely to continue growth so long that the wood does not mature and harden before winter, thus rendering them liable to injury during a severe winter. Such trees usually bear fruit that is poor in quality and in color. To produce mature, well-colored apples, it is essential that excessive growth after midsummer be prevented. The best means of doing this is to grow a crop in the orchard that will compete with the trees for the food and water. Soil protected by a cover-crop does not freeze so quickly or so deeply as when uncovered, and therefore the tree roots under a cover-crop are less likely to be injured by freezing and by heaving. Many of our best fruit soils contain a large proportion of clay. When the humus-content of such soils becomes low, they are stiff and difficult to work and they dry out and bake quickly. Plowing under cover-crops restores the needed humus. This is important from the farm- management point of view. The period of time during which a clay field may successfully be plowed may frequently be doubled by thus increasing the humus supply. As the physical condition of the soil is bettered, the rootlets of the tree can more easily penetrate it in their search for food, and this larger feeding area means a greater supply of food. Orchards that are to be cultivated should be plowed as early as the land can be worked, in order to prevent excessive loss of moisture through evaporation and the demands of any growing cover-crop. This is especially true when rye, clover, or vetch are grown. Fall plowing is seldom advisable, as much of the benefit of the cover-crop is then lost. The time of seeding depends upon the needs of the fruit and the supply of moisture available. In seasons of plentiful rainfall the cover-crop should be put in early, but in a period of drought the trees need all the moisture there is in the soil and the seeding should be late. In the North Atlantic States, the cover-crops are planted from the latter part of July to the middle of August.

Kinds of cover-crops.
In general, cover-crops may be divided into the leguminous or nitrogen-gathering, and the non-leguminous crops.

1. Leguminous cover-crops.—Red and mammoth clover, Canada field peas, and winter vetch are used in the northern states; soybean, cowpea, crimson clover, and vetch in the central and southern states.

2. Non-leguminous cover-crops.—Rye, oats, wheat, and barley; rape and turnips; Duck wheat and nearly all weeds.

Average quantity of seed per acre.
Barley………………………….2 to  2½ bushel.
Buckwheat…………………..          1   bushel.   
Clover, red……………………10  to 15 pounds.
Clover, mammoth…………..10 to 15 pounds.
Clover, crimson……………..15 to 20 pounds.
Cowpea………………………...1½ to 2 bushel.
Millet………………………….         to 1½ bushel.
Oats…………………………….2 to 3 bushel. 
Peas…………………………….2 to 3 bushel. 
Rape…………………………….2 to 5 pounds. 
Rye………………………………1½ to 2 bushel. 
Soybean………………………..1 to 1½ bushel. 
Turnip…………………………….     4pounds. 
Vetch …………………………….1½ to 1bushels.
Wheat…………………………….2 to 2½ bushels.

3. Combinations of cover-crops.—An ideal cover-crop should possess certain characters. It should make a vigorous vegetative growth by fall so as to furnish an abundance of humus and to hasten the maturity of the trees. The seed should be of such a nature that it will catch well when planted at a time of year when the soil is very dry. Preferably, the cover-crop should winter over. All these characters are seldom found in a single crop and, hence, combinations are desirable. Thus buckwheat, which makes a quick growth, does not live through the winter as does the slower-growing rye, so the two combine well. The following combinations are frequently used:
   Clover (red or mammoth)………10  pounds.
1. Winter vetch………………..……..15 pounds.
   Oats…………………………………½ bushel
   Cowhorn turnips…………….... ½ pound.
   Buckwheat………………………...½ bushel.
2. Oats………………………………..1 bushel.
   Rye………………………………….1 bushel.
3. Oats………………………………..1½ bushel.
   Clover……………………….………15  pounds.
4. Buckwheat………………………...¾ bushel.
   Oats………………………………..1 bushel.
5. Oats………………………………..1½ bushel.
    Rye………………………………….1 bushel.

In the peach orchard, where large annual growth is not desirable, or in apple orchards making excessive growth, the leguminous crops should be used sparingly, if at all C. S. Wilson.

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