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COVER CROPS.

A cover crop is one which is used for the particular purpose of securing its mulching and physical effect upon the land in the intervals between the regular crops or the normal seasons of tillage. A sowed crop in the orchard may be valuable in two ways: by affording a cover to the land, and by improving the soil when it is plowed in. As a cover, it may keep down weeds, and protect the land. from injurious effects of frost. As a green manure, it may add fiber to the soil, and thus augment its power of holding fertility and moisture, and it may add directly to the fertility of the land. This late crop catches and holds the leaching nitrates which the tree-roots utilize earlier in the season. Taken as a whole, the cover crop may be said to improve the soil in nine ways:

I. It directly improves the physical condition of the land;

Prevents hard soils from cementing or puddling;

Holds the rains and snows until they have time to soak away into the land;

Dries out the soil in spring, making early tillage possible;

Sometimes serves as a protection from frost.

II. It catches and holds some of the leaching ni

*Term first used in this connection in Bull. 61, Cornell Exp. Sta. 333 (Dec. 1893).

Cover Crops and Moisture.

185

trates, of which the roots of trees are in little

need late in the season ;

Adds humus to the soil;

Renders plant-foods available;

Appropriates nitrogen, if it is a leguminous

crop.

As a rule, crops grown for cover alone should be sown not earlier than midsummer. The most thorough tillage can then be given early in the season, and the benefits of the cover can be secured for the early fall and winter. It is generally advisable to grow a crop which answers for both a cover and green manure, although it is easily possible to make the soil too nitrogenous for some fruits by the extravagant use of such fertilizers. It will also be observed, from the above enumeration of the benefits arising from cover crops, that crops which are killed by the winter may still be exceedingly useful. The reader must also be reminded, in passing, that much of the value of the cover crop depends upon its being plowed under very early in spring, as explained in the last chapter.

There is much confusion in the popular mind concerning the relation of cover crops to moisture. Some contend that any crop which shades the ground will keep the surface moist and conserve moisture, whilst others, knowing that all plants exhale water, consider that any crop tends to make the land dry. Both these opinions are partly correct. A crop which occupies the soil the entire season, and which does not allow of cultivation, will make the land

dry, whilst one sowed late in the season upon land which has been thoroughly tilled during May, June and July, does not seriously rob the soil of moisture. At all events, there need be no fear of drying out the soil by sowing a late crop, for the serious injury of drought is usually effected before such crops are established, and rainfall is then becoming abundant; and the tree needs to be checked, rather than stimulated, at this season, by the transfer of the nitrates and moisture to other plants. The most marked way in which such crops conserve moisture is by means of the fiber and humus which they impart to the soil when plowed under; but even this humus cannot compete with cultivation as a retainer of moisture.

An experiment at Cornell illustrates the value of cultivation over a green crop occupying the land the entire season, in a dry year. The orchard is a hard clay,-just the soil which is benefited by the loosening effects of green manures. The orchard was divided into three portions in 1890, a year after the trees were set. One-third has received liberal annual dressings of commercial fertilizers, and has been well tilled; another third has had no treatment except good tillage; and the remaining third has had liberal applications of potash, and has then been sown early to a nitrogenous (leguminous) green crop. This third portion has simply been plowed

*Bull. 72, Cornell Exp. Sta. This experiment has not yet progressed far enough for report upon methods of fertilizing, and is mentioned here only for the purpose of contrasting methods of cultivation.

Cover Crops vs. Tillage.

187

and fitted well each spring, and then sown, having received no subsequent tillage. The crops were all plowed under the following spring. The following are the crops :

1890.

Mixed beans. Sowed June 16.
1891. Field peas. Sowed June 24.
1892. Vetch. Sowed June 16.
1893. Cow peas. Sowed June 19.

Sowed June 14.

1894. Field peas. Here, then, is a chance to compare the effects of tillage with humus in a season of almost unprecedented drought. Upon September 1, 1894, the green manured strip was much the driest portion of the orchard. The tree growth in this portion was much less vigorous, and the leaves were perceptibly lighter colored, than on the adjacent plots. Even the unfertilized but well tilled tract showed a better foliage. In this green manure portion, leaves on peach trees were then beginning to yellow and fall from the effects of drought, whilst the same rows, when they struck the other plots, showed perfect foliage. In apricots the effects were also marked. Pears and plums also showed the differences. In the cultivated portions one could easily stir up loose earth with the toe of his boot, while in the green manured part one had to dig from six to ten inches in a hard soil before he could find visible moisture. Careful tests showed the same fact. Samples of soil were taken to the depth of one foot on September 1, by means of a soil sampler, eight samples being lifted from representative parts of both the tilled and untilled areas.

Four of these samples were combined into one, and this mixture constituted the complete sample which was used in a test for moisture; that is, there were two samples of untilled soil and two of tiled soil, but each of these was made up of four other samples selected from various parts of the areas. These samples were carefully weighed, and were then equally fire-dried and weighed again. The loss in weight represents the comparative content of free water in the different samples. The results are as follows:

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In addition to this difference in moisture between the two areas, it should be said that in the tilled land it was distributed to within two inches or less of the surface, while in the untilled land the first few inches was exceedingly dry. In other words, in the tiled land nearly the entire soil was in condition to part with its fertility, while in the other the uppermost and richest soil was inactive.

All this emphasizes the fact that tillage alone is better than green manuring alone; but the best results would no doubt have been obtained if good tillage had been given for two or three months, and if the green crop had been sown in July or August. In general, this combination is an excellent one for orchards, particularly for such lands as lack nitrogen and vegetable matter, and for those fruits which are benefited by winter protection of the soil.

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