Written specially for "The Kansas Apple," By Prof. E. H. S. BAILEY,
Chemist at the Kansas State University.
In the cultivation of the apple tree, which, like most plants, gets its
nourishment from two sources, the soil and the atmosphere, these must be
first considered. From the soil come the mineral ingredients, those that
are given back to the soil when the plant is burned, and from the
atmosphere come the ingredients of no less importance in the growth of
the tree, but which mostly disappear as invisible gases upon combustion.
Upon the character of this soil, and upon the climate, a general term
that may be said to cover the conditions of the atmosphere, depend the
success of the horticulturist. In addition to this, insect pests are
liable to constantly menace the crop.
In the making of soils, a process that is constantly going on, the most
important agents are water, air, frost, sunshine, and the action of
living organisms. By this combined action, the mountain, with its rich
store of mineral matter, is disintegrated, its constituents are partly
dissolved in the water and partly carried mechanically to the plains
below; the air is distributed through the soil; seeds are dropped; the
living animal forms begin to multiply; the soil is enriched, and
gradually it begins to be in a condition suitable to bear the simpler
forms of vegetable life, which in turn decaying, add to the richness of
the soil.
Furthermore, the mechanical condition of the soil has much to do with
the successful growth of the plant. If the soil is extremely fine, it is
liable to become so compact that the rootlets cannot easily penetrate
it, when it is of such a composition as to bake readily in the sun; if
very coarse, like gravel, there is not a sufficient capacity to retain
moisture. It should, however, be porous enough to allow the air to
penetrate it, for upon the aeration of the soil depends much of its
fertility. We loosen the soil about the roots of plants to allow the air
to penetrate and give an opportunity for the chemical changes constantly
undergoing in the soil. Then, too, the work of the earthworms in
loosening the soil, and thus adding to its porosity, should not be
overlooked. In this soil workshop, too, live and labor certain minute
organisms that make it their business to enrich the soil by helping the
rootlets to assimilate the nitrogen of the air.
Since the soil is composed mostly of ingredients that come from the
decomposition of rocks, it follows that is must be of very complex
composition. Fortunately, however, there are only a few of the
ingredients of the soil that are of interest to the agriculturist, as
only a few of the elements, as they are called, go to make up the plant
structure, or at least only a few are essential ingredients of the
plant. Nitrogen, though very abundant in the air, is not abundant in the
soil. In fact, the soil has to depend largely on the nitrogen compounds
that are washed out of the atmosphere in small quantities by the rain.
Another source of nitrogen is the action of certain bacteria, that make
little sacs on the rootlets and, living on the juices of the plants, fix
the nitrogen of the air, and thus fertilize the soil; especially on
plants of the leguminous family, as peas, beans, and clover.
Silicon, which with oxygen makes ordinary sand, is essential to the
growth of plants and is everywhere found in abundance. Sulphur, united
with oxygen and the metals to form sulphates, is generally abundant
enough. The same may be said of chlorine, which, united with sodium or
potassium, is always present in our prairie soils. Phosphorus, as it
occurs in the phosphates, is one of the most essential ingredients of a
fertile soil. Calcium and magnesium are found in combination as
carbonates and sulphates, and, though essential, are usually abundant,
especially where limestone rocks underlie the soil and outcrop in so
many places. Potassium is found united with chlorine or sulphuric acid.
It is one of the elements that is most liable to be exhausted from the
soil by a succession of crops. Sodium exists almost everywhere. It is
one of the elements of common salt, and, though much like potassium,
cannot take the place of the latter in plant nurture. Iron is abundant
and at the same time necessary in small quantities. The elements above
mentioned, together with oxygen, are to be found in the ashes of plants.
Besides, there are two elements that come largely from the atmosphere,
namely carbon and hydrogen, which, united with oxygen, make up the bulk
of the plant. Thus, wood is a substance containing carbon, hydrogen, and
oxygen, with small quantities of nitrogen and mineral salts. The mineral
salts represent about one per cent. of air-dried wood.
Having considered in a general way the constituents of the plant, and
having noticed the source of each of these constituents, it may be of
interest to look at the composition of the soil as revealed by chemical
analysis. "A" is the analysis of a soil from Finney county, as made in
the laboratory of the Kansas State University, by the author. "B" is a
soil from Wyandotte county, as reported in the report of the Kansas
State Board of Agriculture for 1874. "C" is a prairie soil from Dakota,
as reported by Prof. E. Richards, of the department of agriculture.
"A" "B" "C"
Silica and insoluble 71.66 82.16 69.82
Iron and aluminum oxides 6.55 6.70 12.05
Calcium oxide 4.41 .68 .85
Magnesium oxide 1.02 .06 .87
Phosphoric anhydride .18 .08 .11
Chlorine .01 .03 .03
Potassium oxide .75 .05 .72
Sodium oxide .25 .11 .94
Sulphuric anhydride .06 .39 .12
Volatile and organic matter 3.98 5.44 8.90
Moisture 9.67 3.80 6.27
Undetermined, carbonic acid, etc. 1.48 .30 .22
------ ------ ------
100.00 100.00 100.00
In some cases it happens that there is a sufficient quantity of an
ingredient in the soil, but it is not in a sufficiently _soluble_ form
to be available. It will be noticed that in the analyses quoted above
the amount of the necessary constituents of the soil to plant growth is
not in any case large. The nitrogen may be present in the volatile and
organic matter, and upon the proportion of this complex organic matter
very often depends to a great extent the fertility of the soil.
Some experiments made at one of the agricultural experiment stations
upon the effect of "apple stock," that is, young trees raised for
nursery purposes, on the soil, showed that in eleven tons of such stock
the following quantities of ingredients were removed from the soil:
Silica 50.6 lbs.
Phosphoric acid 21.4 "
Sulphuric acid 14.3 "
Chlorine 1.3 "
Carbonic-acid gas 94.9 "
Iron oxide 6.1 "
Lime 138.6 lbs.
Magnesia 23.7 "
Soda 21.3 "
Potash 27.1 "
-----------
Total 399.3 lbs.
This is no inconsiderable quantity of material to be removed by a single
crop.
Professor Goessmann, in discussing the ash of fruits, gives the
following analysis of the ash of the Baldwin apple; this would represent
the mineral matter taken from the soil by the fruit: Potash, 63.54 per
cent.; soda, 1.71; lime, 7.28; magnesia, 5.52, and phosphoric acid,
20.87. Comparing this with the ash of other fruits, it is seen that the
amount of potash required is larger than in the case of other fruits
except plums and peaches, and the amount of phosphoric acid is high, but
not as high as in the case of some berries. The application is obvious;
in order to successfully raise apples there must be an abundance of
potash and of phosphoric acid in the soil, and these ingredients must be
in an available form.
If we compare the apple and the pear by an analysis for fertilizing
constituents, or such constituents as are usually introduced into
deficient soil by means of fertilizers, we have the following table:
1000 parts of the fruit contain, in the case of each,
H2O N Ash K2O Na2O CaO MgO P2O5 SO3 SiO2
Apple 831 0.6 2.2 0.8 0.6 0.1 0.2 0.3 0.1 0.1
Pear 831 0.6 3.3 1.8 0.3 0.3 0.2 0.5 0.2 0.1
When we study the composition of the apple, to determine the "proximate
principles," as they are called, it is noticed that we have the
constituents mentioned in the discussion of the elements contained in
the fruit combined to form various substances; thus:
Apples. Pears. Cherries. Peaches.
Water 82.04 83.95 75.73 84.99
Sugar 6.83 7.00 13.11 1.58
Free acid .85 .07 .35 .61
Albuminous substances .45 .26 .90 .46
Pectous substances .47 3.28 2.29 6.31
Soluble 14.96 10.90 17.25 9.39
Free acid in fruits is not neutralized by sugar, but it is well known
that an abundance of sugar will cover up the sour taste of a fruit. The
constituents above noted are mostly found in the expressed juice of the
fruit, and give it its characteristic flavor. Without the sugar in these
juices it would not be possible to make any alcoholic beverages from
them. In the process of fermentation, in the case of apple juice, we
have first the change of the sugar to alcohol and carbonic-acid gas,
which imparts to cider its characteristic taste and tang. Afterwards,
the alcoholic solution, in the presence of the organic matter, is
subjected to what is called acetic fermentation; that is, the vinegar
plant grows at the expense of the organic matter in the cider, and this
beverage is converted into vinegar, containing acetic acid. It is a
familiar fact that the change does not readily take place except when
cider is exposed to the air, and this is shown to be true from a
chemical standpoint, as the cider really is oxidized to make the
vinegar; that is, it takes up oxygen from the air.
The greater the proportion of sugar, the greater the quantity of
alcohol, the stronger the vinegar will be. Grapes contain more than
twice as much sugar as apples; hence, a wine that is made from them is
stronger in alcohol than a cider made from apples. Cherries, as will be
seen by reference to the table above, contain a large amount of sugar;
hence their use in making cherry brandy, which contains a large per
cent. of alcohol. It should be said, however, that in order to make
brandy the cherry juice must be distilled. In this respect the process
is similar to that employed in making apple brandy.
After the juice has been extracted from the apples the pomace that
remains is sometimes used as a fertilizer. This is valuable chiefly on
account of the mineral salts contained in it. An analysis of the pomace
shows that it contains: Water, 69.90 per cent.; ash, .71; albuminous
substances, 1.58; fiber, 4.87; nitrogen, free extract, 21.24; fat,
1.71.
The acid of the apple is usually considered to be malic acid, but really
there are several acids mixed together. It is a mild and agreeable
vegetable acid, and its presence adds much to the flavor of the fruit.
The pectous and albuminous substances are those that assist in the
formation of fruit jellies. Some of these substances are liquid when
hot, and gelatinize on cooling; by too long boiling they lose this
property of gelatinizing; hence the precaution that is taken in the
making of fruit jellies not to boil the juice too long.
The subject of the ripening of fruits like the apple has been
extensively studied, as has also that of the subsequent decay. According
to recent researches, early varieties of apples contain little starch
when picked, and do not keep well. The season, soil, and age of the tree
affect the composition of the fruit. It has been shown that sugar is
sure to be formed from the starch in the process of ripening, after the
fruit is taken from the tree, and during the winter the cane sugar is
gradually, and finally almost entirely, changed to directly-reducing
sugar. The maximum sugar content is reached earlier the earlier in the
season the apple ripens. Late winter varieties reach this point as late
as November. There is much starch in the latter when picked, which
gradually changes to sugar on keeping. This process is analogous to the
ripening of the banana. This fruit is picked while green, and from it is
made by the natives of South America a flour which is a good farinaceous
food, and readily answers the place of the starchy grains. We are
familiar with the fact that as the fruit ripens it contains large
quantities of sugar, and is edible uncooked, which fact is usually not
true of starchy foods.
The subject of the decay of the apple has been discussed in a very
interesting way in the _Popular Science Monthly_ for May, 1893, by Byron
D. Halsted. Though chemical changes take place here, also, and the apple
is finally resolved mostly into carbonic-acid gas, water, and mineral
salts, yet these changes are brought about by the action of various
fungi which find a soil favorable to their growth in the apple pulp.
Though apples are considered digestible and wholesome, their
digestibility is much increased by cooking. This is especially true if
some of the starch is not converted to sugar, for, as noted above,
starch, to be readily assimilated in the system, should be cooked. There
is probably no fruit that is so uniformly wholesome and so deservedly
popular with all classes as the apple. The apple and pear were known in
England before the conquest, and, indeed, probably before the Saxon
invasion. They have been gradually "improved" from the wild crab-apple
of Europe. It is stated on good authority that there is no country on
the globe so well adapted to the growth of this fruit as the temperate
regions of North America, and this seems to be demonstrated by the fact
that the apples of the United States are superseding the native fruit in
most of the civilized countries.