is inactive. The
need of nitrogen for grass in the early spring, before nitrification in
the soil is active, is an illustration. Let the causes be what they
may, the fertilizer formulas that call for plant-food in a fertilizer
in the same proportions that it is found in plants are disappointing in
their results. The analysis of the plant is not a dependable index.

The Multiplication of Formulas.--Fertilizer manufacturers have made all
possible combinations of fertilizer materials, using them in various
quantities. Each manufacturer has given a mixture a brand of his own,
and confusion reigns. There is no formula for a soil or crop that will
remain absolutely the best, even for one particular field. It
represents one's judgment of the present need, and is employed subject
to change, just as is the prescription of a physician. It is usually
only an approach toward the most profitable amount and kind of
plant-food that may be supplied. The one important consideration is
that no manufacturer can know the need nearly so well as the
intelligent farmer who knows the history of his field and constantly
tests its ability.

[Illustration: On the productive farm of Dr. W. I. Chamberlain, in
Northern Ohio.]

A Few Combinations are Safest.--It is the best judgment of scientists
to-day that greater results would be obtained from the use of
commercial fertilizers if the number of formulas could be reduced to
ten, or even a less number. The satisfactory fertilizers fall into
three classes:

1. The phosphatic fertilizer, carrying phosphoric acid to land that
gets its nitrogen from clover or stable manure, and that continues
to supply its own potash. Such a fertilizer should have a high
content of phosphoric acid in order that the freight charge, per
pound of plant-food, may be as low as possible. Acid phosphate,
basic slag, and bone are chief in this group.

2. The combination of phosphoric acid and potash that is needed by
soils obtaining all required nitrogen from clover or manure. In
most instances the phosphoric acid should run higher than the
potash, but the percentage of potash should never run lower than 4.
A lower percentage of potash is not as profitable as a higher one,
provided any potash is needed. The potash content should be greater
than that of the phosphoric acid in case of some sandy soils and of
some crops of heavy leaf growth, including various garden cro