Pullman herald. [volume] (Pullman, W.T. [Wash.]) 1888-1989, 1910-06-17
AVAILABLE FERTILITY

n This naturally depends upon many
aifferent things. For example a soil
NIGHT be abundantly supplied with
al the necessary elem ents of plant
food in proper form yet if the soil
,,ora 70 remain dry throughout the
.oaeon. no crops would grow in it.
AGAIN a soil might contain abundant
available fertility and plenty of mois-
trre but remain frozen through an
ontire season, in which case no crop
would grow In broad sense, there
fore fertility requires favorable con-
ditions of moisture supply, tempera-
tire. state OF tillage, sufficient sup
nIv of plant food of proper kind, etc
As commonly used, however, the
term fertility means a sufficient sup
ply of plant food in available form.
What is available plant food? A
little thought will show that it is
plant food in such form that it will
dissolve in soil water or plant root
iuices. Plants have no power or abb
Htv to absorb food in solid form.
plant food is taken from the soil
through the roots and circulates in
the sap. 1t must, therefore, be in Ii
uuid form and available food is only
that form of plant food which can
be dissolved from the soil and so be
taken up in liquid form. The avail
ability of plant food is, therefore,
measured by its solubility in plant
juices.
All the chemical elements in the
soil (of which there are about fiji
teen) may be taken up by plants but
not all of them are of equal use or
value. Some are not necessary at all
to plant growth. Others which are ne
cessary for plant growth are always
present in soil in abundance A few
which are absolutely necessary for all
plant growth are commonly present
in the soil in comparatively small
proportions. These are the SO call
ed critical elements" of fertility;
namely, nitrogen, phosphorus, potash
and lime. The element nitrogen is
used by plants in building up its
green growing foliage. Phosphorus is
essential for the production of seeds
Potash aids in the building up of
starches or sugars which are essen
tial parts of all plants. Lime is in
some obscure way connected with the
building of woody fiber Obviously
then all these elements are necessary
for every kind of farming crop al
though different amounts are needed
by different crops. Lime in addition
to its value as a direct plant food has
much to do with the physical condi-
ton of the soil and the availability
of plant food. Fertility from the
standpoint of plant food, therefore,
requires a sufficient supply of each
of these four critical elements in
proper or available form.
Lime, potash and phosphorus are
all found in rocks. They are the min
eral elements of fertility. Nitrogen is
not mineral element and is not
found in rocks. Nitrogen comes or
ginally from the air but must be
converted into liquid or available
form by the decay of plant tissue CON
tanning it. 1t can be taken from the
air only by the bacteria which grow
on the roots of leguminous clover
plants Gncluding alfalfa, cloyers,
vetches, peas, beans, etc. These bac-
terra take nitrogen from the air and
when they die and decay the nitro
gen which they contain is available
for other plants.
Most soils contain considerable
supplies of all the essential elements
of fertility, generally enough to last
for hundred years or more. The
problem of fertility is that of getting
this plant into available form. The
chief agencies for dissolving mineral
plant food materials are the bacteria
and acids which are developed in de-
caying vegetable or animal matter.
Rotting vegetation Cor "humus'O is,
therefore, the best agency for main
tanning or increasing the availability
of plant food. This accounts for the
well known beneficial effect of ma
nure. The actual benefit of manure
when applied to soils is at least
double the value of the plant food,
which was already present in the soil
IN unavailable form.
One of the best means of increas-
Ing fertility of soils is, therefore, the
blowing under of some "humus form
ing material. For this purpose barn
yard manure is best Next in value
are the so-called green manures" or
green crops plowed under. OF these
ne legumes are by far the best be-