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.
LEGUMES.--In general, legumes are more valuable as cover and green
manure crops than non-leguminous plants, because as a rule they are
more rank growers and more deeply rooted, as well as because they add
nitrogen to the soil. But it is rather more difficult to secure a good
stand of most legumes than it is of the crops previously mentioned for
several reasons. As a rule the seeds are smaller and a large seed
usually has greater germinating power than a small one. This often
means much at the time of the year when the cover crop is sown. Then
legumes are more difficult to grow, requiring better soil conditions.
Still these should be present in good orchard soils. Drainage must be
good, the soil must be at least average in fertility and physical
condition, it must not be sour--hence it is often necessary to use
lime--and soils frequently require inoculation before they will grow
legumes satisfactorily.
Where the clovers grow well they make excellent cover crops as well as
green manure crops. The chief difficulty with them is that of
obtaining a good stand in a dry midsummer. The mammoth red and the
medium red clovers are probably the best of their genus on the heavier
soils, while crimson clover is best on sandy soils and where it will
grow, on the lighter gravel loams. The latter is especially well
adapted to building up run down sandy soils. Although it is somewhat
easier to secure a stand of this clover, alsike does not grow rank
enough to make a good cover or green manure crop. Most clovers are
deep rooted plants and therefore great soil improvers physically as
well as being great nitrogen gatherers. The amounts of seed required
per acre for the different kinds are about as follows: mammoth fifteen
to twenty pounds; red (medium) twelve to fifteen pounds; crimson
twelve to fifteen pounds; and alsike ten to twelve pounds.
Where it can be readily and successfully grown alfalfa is really a
better cover and green manure crop than the clovers. It is deeper
rooted, makes a better top growth, and therefore adds more nitrogen
and more humus to the soil than the clovers. It cannot be recommended
for common use, however, as it is so difficult to grow except under
favorable conditions. It requires a more fertile soil than clover, a
soil with little or no acidity, good drainage, and usually the soil
must be inoculated. Only where these conditions prevail can alfalfa be
generally recommended.
Vetch is an excellent cover and green manure crop, forming a thick,
close mat of herbage which makes a good cover for the soil. It is very
quick to start growing and a rapid grower in the spring. It also adds
larger quantities of nitrogen. The hairy or winter vetch lives through
the hard freezing winters. Summer vetch, although an equally good
grower, is killed by freezing. One bushel of seed is required per acre
and the seed is expensive, which is the greatest objection to the use
of this excellent crop.
Two other less well known and used leguminous crops are well worth
trial as cover crops--soy beans in the North and cow peas in the
South. Both are great nitrogen gatherers and as they are rank and
rapid growers add large quantities of humus to the soil. Under
favorable conditions they will cover the ground with a perfect mat of
vegetation in a very short time. Being larger seeded, it is
considerably easier to obtain a stand on dry soils and in dry seasons
than it is of the smaller seeded clovers. It is usually best to sow in
drills the ordinary width, seven inches, apart.
Cow peas are universally used as a cover and green manure crop in the
South, but they do not thrive so well in the North. One and one half
to two bushels of seed are required per acre. In the North the earlier
maturing varieties of soy beans are almost equally good. One to one
and one half bushels of seed are sown per acre.
Leguminous cover crops are also the best and the cheapest source of
nitrogen for the apple orchard, after they are well established. Their
use may be overdone, however. Too much nitrogen results in a growth of
wood at the expense of fruit buds. To avoid this it is often advisable
to use non-leguminous and leguminous crops alternately, when the
orchard is making a satisfactory growth. Sometimes also these two
kinds of crops, as buckwheat and clover for example, may be combined
with good results. When this is done one half the usual amount of seed
of each should be used.
EARLY PLOWING.--Many people make the common mistake of thinking that
a green manure crop must be allowed to grow until late in June in
order to secure the maximum amount of growth. There are several
reasons why this is not good practice. In the first place cultivation
is most essential in the early spring as has been pointed out. Then
moisture is better conserved by plowing under the crop early and a
better physical condition of the soil secured. Plowing early in the
spring warms up the soil and sets plants to work more quickly. Lastly,
material rots much more quickly in the early spring when moisture is
more abundant, which is very important.
An apple tree is as much a crop as anything grown on the farm and must
be so regarded by those who would become successful orchardists. When
it is not properly fed and cared for, good yields of fruit may not
justly be expected. Especially is this true of an orchard which is
being intercropped. But because of the fact that an apple tree is not
an annual crop but the product of many years' growth, because its root
system is deeper and more widely spread out than those of other crops,
and because the amount of plant food removed in a crop of fruit is
comparatively small, fertilization is less important than many
persons would have us think. It is a fact that where orchards receive
good cultivation and a liberal supply of humus commercial fertilizers
give but medium results.
ELEMENTS OF FERTILITY.--Three elements are necessary for the growth of
apple trees, nitrogen, phosphoric acid, and potash. To these lime may
be added, although its benefit is indirect rather than direct as a
plant food. How badly any of these elements may be needed depends on
the soil, its previous treatment, and on the system of management. By
learning what are the effects of these elements on the tree and fruit
we may determine under what conditions, if any, their use is
advisable.
Nitrogen promotes the growth of new wood and leaves, giving the latter
a dark green color. In fact the color of the leaves and the amount of
the wood growth are usually good indicators of the need of nitrogen.
Nitrogen in excess develops over vigorous growth and prevents the
maturity of wood and buds. It always has a tendency to delay the
maturity of the fruit by keeping it growing late. On many varieties it
tends to produce poorly colored fruits.
When trees are making a normal amount of growth in a year--say a foot
to three feet or more--and when the leaves are of good size and a
dark green in color, there is little need of nitrogen. But when trees
are not growing satisfactorily and the leaves have a sickly yellow
color, then the need of nitrogen is evident. On early soils and in
long growing seasons nitrogen may be more freely and safely used than
under other conditions.
The effect of phosphoric acid and potash on the tree and fruit is much
more uncertain. They are supposed to influence the quality and the
flavor of the fruit, giving better color and flavor, and this they
undoubtedly do to some extent. Potash probably gives the leaves a
darker green color. The precise effect of these two elements is at
present a subject of much discussion, one set of investigators
maintaining after a long and careful investigation that these effects
are too small to be worth while, and the other claiming that they have
a marked effect in the ways above indicated. The only safe guide is
the actual local result. If the fruit is satisfactory in every way it
will be of little use to try fertilizers. On the other hand, if it is
not, then it will pay to experiment with them. The needs of and the
results on different soils are so variable that it is always wise to
experiment on a small scale before using fertilizers extensively.
STABLE MANURE.--The necessary plant food is best supplied by stable
manure applied at the rate of ten loads per acre for a light
application to twenty loads per acre for a heavy application. This
amounts to a load for from two to five mature trees. Such an
application will not only go far toward supplying the necessary
nitrogen, phosphoric acid, and potash, but especially if coarse will
add considerable humus and improve the physical condition of the soil.
Except on land which washes badly, manure should be applied in the
fall and winter. It should not be piled near the trunk of the tree but
spread uniformly over the entire surface of the ground. It is
particularly important to spread the manure under and beyond the
farthest extent of the branches as this is the most important feeding
root area of the tree.
COMMERCIAL FERTILIZERS.--Where manure is not available or where it
cannot be applied in sufficient amounts, commercial fertilizers may be
resorted to, after they have been experimentally tested out.
Leguminous cover crops are the best source of nitrogen, as has been
indicated, but where these do not grow well, or in seasons when they
have for some reason failed, nitrate of soda or dried blood are good
substitutes. From two hundred to three hundred pounds of one or the
other of these may be applied broadcast in the spring soon after
growth is well started and all danger of its being checked by frost or
cold weather is past. It is well to apply the nitrate of soda in two
applications a few weeks apart, especially on soils which are leachy
and in wet seasons, as part of the nitrogen may leach away if all is
applied at once. These should be thoroughly worked into the soil with
a spring-tooth harrow.
To supply the other two elements, from two hundred to four hundred
pounds of treated rock phosphate or basic slag for the phosphoric
acid, and the same amount of sulphate of potash for the potash, should
be applied at any time in the early part of the season, preferably
just before a light rain, and worked into the soil as before.
Home-made wood ashes are a good source of both these elements, and
especially of the potash. They cannot be purchased economically in any
quantity, but on the general farm there could be no better way to
utilize the wood ashes made around the place than by applying them two
or three bushels to a full grown tree every year or two. Wood ashes
are also a good source of lime, being about one-third calcium oxide.
Thus a large amount of available plant food will be supplied to the
tree, and where it is needed should result not only in better wood
growth but in the formation of vigorous leaf and fruit buds for the
following year.
Lime is not usually considered as a fertilizer except on soils
actually deficient in it. But it will usually be advisable to apply
from one thousand five hundred to two thousand pounds of fresh burned
lime or its equivalent, in order to correct any natural soil acidity,
to hasten the decay of organic material, to increase the activity of
the soil bacteria, and to improve the physical condition of the soil
by floculating the soil particles and helping to break up lumpy soils.
Lime also helps to liberate plant food by recombining it with certain
other elements in the soil. All these effects make a more congenial
medium for the leguminous crops to grow in, and it is frequently
advisable to use lime for this purpose alone. After this first heavy
application about 800 pounds of lime should be applied per acre every
four or five years.