Pocahontas star herald., 1915-12-03
Il.-How PLANTS FEED.


Cooperative Extension for Arkansas.
Plants require for their growth. me.
ehanieal support, air. heat, light, wa
ter and food. All OF these, with the
exception OF light, are supplied wholly
or in part by the soil. Composed as
IL is OF rock fragments and decaying
vegetable matter. the soil offers a
place for root development and af.
fords physical support for the plant.
The air present in the spaces be
tween the soil particles Is used by the
roots of plants. Heat is supplied in
part by the soil as a result of its
physical condition. Water, while not
a component part of soil, is furnished
TO the plant by Il, and the physical
condition of the soil determines the
amount Of water that may be reserved
for use by plants. The water sur.
rounding the soil particles dissolves
plant food and the solution is absorb
ed by the plant roots. Thus the soil
must not only furnish a physical sup
port for plants. but II must supply
plant food and afford a means for
transferring the food to the plant.
Ten elements OF plant food are con.
sidered to be absolutely essential for
the growth Of plants. Three of these.
carbon, oxygen and hydrogen. are OBJ
tanned from the air. while phospho-
rus, potassium. calcium (lime). mag
nesium, iron and sulphur are obtained
directly from the soil itself.
Carbon and oxygen are obtained
from the air. where carbon is pres.
ent in the form of carbon-dioxide gas
and where oxygen exists in free con-
dition. These gases are taken into
the plant through the leaves, and
there combine with water TO form
the complex vegetable compounds.
The nitrogen used by plants is
secured through the soil Through
decay OF the vegetable matter in the
soil the nitrogen-bearing compounds
in II are broken down into more sim
pie forms, which, through the action
OF various soil bacteria, are soon
changed into a form that can be used
by plants. With these processes GO
ing on all the time Except when the
soil is frozen or waterlogged), a con-
stant supply OF available nitrogen is
provided. The content OF vegetable
matter in the soil must be kept up
at all times to insure a sufficient
quantity Of nitrogen for good crops.
Nitrogen from the air can only be
secured by growing leguminous crops
on the roots Of which nodules are
formed. The bacteria living in the
nodules gather nitrogen from the air
in the soil, and store It in organic
combination in the nodules. Some OF
this is used by the host plant, but
most of it is left in soil TO become
available through decay OF nodules.
The mineral clements essential for
plant growth are supplied by the soil.
They are a part, to a greater or less
degree, of the rock fragments which
constitute the body OF the soil.
Lime in soils becomes soluble so
readily, and our rainfall is so heavy,
that it has been washed from even the
best limestone soils in Arkansas.
Most of our soils, therefore, are
lacking in lime sufficient for the sat
isfactory growth of many lime loving
crops. This, with other changes in the
soil, has led TO soil acidity.
Phosphorus and potash are present
in all soils, usually in quite insoluble
form. They form a part of certain
minerals found in the rock fragments
of the soil. These minerals are brok-
en- down and the phosphorus and pot
ash made soluble through exposure to
weather, the atmosphere, the decay OF
vegetable matter, and a slight solv-
ent effect of plant roots. Potash in
many of our soils is present in suf-
ficient quantities to last for hundreds
of years, but because of improper til
lage and an insufficient amount of de-
caying vegetable matter it does not in
all cases become soluble fast enough
to support good crops
Phosphorus is the mineral element
most seriously lacking in Arkansas
soils. For satisfactory crops of any
kind it is necessary to replentish the
phosphorus supply by the application
of a phosphorus bearing fertilizer,
raw rock phosphate, acid phosphate,
or bone meal.
When the supply of any one of the
ten elements of plant food is limited,
the crop is limited Since all of these
are furnished either by the air or
by the soil we know where to look
for the cause of an unsatisfactory
crop. AS pointed out in the above
paragraphs, nitrogen, phosphorus and
potash are the essential elements to
which most attention must be given.