Wheat 51
mately 22 pounds of phosphoric acid, 57 pounds of nitrogen
and 35 pounds of potash. It is evident that the nitrogen
supply cannot be kept up by the use of fertilizers of this
, description. To buy sufficient nitrogen to meet the require-
ments of the crop would render it unprofitable. - .
The solution of the problem of fertility, then, is, as stated, A
to keep up a good humus supply bya good rotation containing
clover and other legumes and_by the use of manure, supple-
mented by the purchase, in sufficient quantity, of the
element which may be deficientjwhich is usually phosphor-
ous. It is no doubt profitable, on many soils, to use a high
grade complete fertilizer to give the crop a good start, but it
should always be borne in mind that the use of it alone will
not keep up the fertility of the soil. .
‘ Any soil, no matter how abundantly supplied with the
mineral elements of plant food, may become so deficient in
organic matter that the availability of the mineral plant food i
will not be sufficient to meet the needs of the crop. In such
cases the use of commercial fertilizers may give profitable
results, and may be used until a supply of organic matter is
restored to the soil. V
(For a further discussion of the use of fertilizers see
Bulletin No. 140.)
Aside from the fertilizing value of humus it has other ’
important functions. Humus increases the capacity of the
soil to hold water and increases its ability to retain water.
These are important considerations in the growing of the
wheat crop, because wheat requires a large amount of water,
and the soil cannot be cultivated successfully to retain it.
A good humus content prevents to a large degree the
“freezing out" of wheat. Two years ago there was much
complaint of winter killing of wheat. The writer made
limited observations of wheat fields and found invariably that
where the wheat was frozen out there was a low humus
content. In looking over one large field, there were numer-
' ous spots where the wheat was good, while in other places it
was frozen out. The good places were well supplied with
humus, while the poor places were deficient. This field was
  wfs;»g