CHAPTER VI[ToC]
MANURING AND FERTILIZING
Cover crops may be said to be supplementary to tillage. In the previous chapter this function has been discussed. It now remains to point out another important function—that of a green manure crop adding humus and plant food to the soil. Not only do some cover crops add plant food and all humus to the soil, but they tend to conserve these by preventing leaching, especially of nitrates, and they help to render plant food more available by reworking it and leaving it in a form more available for the tree. They sometimes act as a protection against winter injury by holding snow and by their own bulk. They also help to dry out the soil in spring, thus making the land tillable earlier.
There are two great classes of cover or green manure crops, leguminous and non-leguminous. A non-leguminous crop merely adds humus and improves the physical condition of the soil. In itself it adds no plant food, although it may take up, utilize, and leave behind plant food in a more available form for the tree's use. But in addition to these benefits, leguminous crops actually add to the soil plant food in the form of nitrogen which they have the ability to assimilate from the air by means of bacterial organisms on their roots.
Non-Leguminous Crops.—The most important of the non-leguminous crops are rye, buckwheat, turnips or rape, barley, oats, and millet. The first mentioned are the most commonly used. Also in order of importance the following are the usual leguminous cover and green manure crops to be used: clovers, winter vetch, soy beans, alfalfa, cow peas (first in the South). In order to determine the relative advisability of the use of these various crops let us now look at some of their characteristics and requirements.
Rye is one of the best non-leguminous cover crops, especially in the young orchard, as it does not grow as well in shade as in the open. A particularly strong point about rye is that it grows rapidly quite late in the fall and starts early in the spring. Starting earlier than most crops in the spring, it makes a considerable amount of growth before the land is fit to plow. Especially in warmer climates rye should not be sown too early in the fall—not usually before September 1st—because of this too heavy growth. Rye is also adapted to a great variety of soils and hence will often grow where other crops will not do well. About two bushels of seed are required per acre.
Buckwheat is probably about equally as good as rye for an orchard cover crop, although it does not produce quite as much organic matter. It will germinate at almost any season of the year even if it is very dry. It is a great soil improver because of its ability to feed and thrive on soils too poor for other crops, due to its numerous shallow feeding rootlets. It grows rapidly and covers the ground well, but like rye does not thrive as well in shade. Buckwheat should not be used to excess on the heavier types of soil as it is rather hard on the land. One bushel of seed to an acre makes a good seeding.
Turnips or rape often make good pioneer cover or green manure crops. They are great soil improvement crops and it is comparatively easy to secure a good stand of them even in dry weather. Sown in late July in the North they will produce a great bulk of humus and add much moisture to the soil, especially if they cover the ground well. Their broad, abundant leaves and high tops also hold the snow well in winter. Cow Horn is the best variety of turnips to use, as it is a large, rank grower. Use one to two pounds of seed to the acre. Rape makes an excellent pasture crop in an orchard both for sheep and hogs, but especially for the former. Eight or nine pounds of seed are necessary to the acre.
Barley, oats, and millet are not as good crops as the foregoing, because, with the possible exception of millet, they make their best growth early in the season. Moreover they take up too much moisture from the soil at a time when the tree most needs this moisture. In fact they are sometimes used for this specific purpose on wet land in too wet seasons. Two to two and one half bushels of oats or barley and one to one and one half bushels of millet to the acre are necessary for a good seeding.
Although weeds can hardly be classified as cover crops, they are often valuable ones. They grow rapidly and rank, making a large bulk of humus, without the expense of seeding. If they are not allowed to go to seed so as to scatter the seed about the farm, they often make the best of cover crops. This necessitates a mowing in September. Weeds are plants out of place, and when these plants are in place they are not necessarily weeds, as they have then become serviceable.