--------------------+
| 5 pounds nitrate of soda. |
| 18 pounds 14 per cent acid phosphate. |
| 4 pounds muriate of potash. |
+---------------------------------------+
| Nothing. |
+---------------------------------------+

Variation in Soil.--The difficulty in determining the character of
fertilizer for a field, due to variation in the soil, is overestimated.
Very often a land-owner says, "I have a dozen kinds of soil in every
field." This is true in a way, it may be, but if all the field has had
the same treatment in the past, the probability is that the fertilizer
which is best for one part of the field will be quite good for the
other parts. The likeness in characteristics that permits the land to
be cropped as one field gives some assurance of likeness in plant-food
needs, even where the proportion of clay and sand varies and the color
is not the same.

There may be wide variation in the productive power of the fields of a
farm, due to the treatments they have received. The land that grows
heavy clover in a close rotation, or receives all the stable manure,
may need neither nitrogen nor potash, while another field, hard-run by
timothy and corn, may need a complete fertilizer. When a careful
fertilizer test on land of only average productive power has been made,
the owner has some definite knowledge of his soil that enables him to
give more intelligent treatment to all his fields than was possible
before the test had been made. He observes the appearance and yield of
plants where the plant-food requirement was fully met, and makes
allowance in other fields for gains or losses in the soil due to
different treatment. It is out of the question to become discouraged
before a beginning has been made. If yields are limited by absence of
plant-food, fertilizers must be used. If money must be expended for
fertilizers, it is only good business to know that the money is
expended to the best advantage.

CHAPTER XVII

COMMERCIAL SOURCES OF PLANT-FOOD

Acquaintance with Terms.--The hesitation of many users of commercial
fertilizer to master the few technical terms used in analyses of the
goods, for which over one hundred million dollars annually are expended
in this country, is to be deplored. The number of the materials
available for any large use as sources of plant-food in a commercial
fertilizer is small, and something of their charact