Ingredients In The Mixture
The matters of interest to the farmer are
the determination of the amounts of nitrogen, phosphoric acid, and
potash that he should apply to a particular field, their availability,
and their cost. Let us assume that he has found 300 pounds of a
fertilizer containing 3 per cent nitrogen, 10 per cent phosphoric acid,
and 6 per cent potash to be an excellent application for wheat on a
thin soil that is to be seeded to clover and timothy. This fertilizer
contains 3 pounds of nitrogen to each 100 pounds. He applies 300 pounds
of the fertilizer per acre, or 9 pounds of nitrogen. The fertilizer
contains 10 pounds of phosphoric acid to the 100 pounds. He thus
applies 30 pounds of phosphoric acid per acre. The fertilizer contains
6 pounds of potash per 100 pounds, and he therefore applies 18 pounds
per acre. What he has really learned, then, is that an acre of this
land, when seeded to wheat, needs 9 pounds of nitrogen, 30 pounds of
phosphoric acid, and 18 pounds of potash. It is in these terms he
should do his thinking, and the matter of fertilization becomes simple.
In the general farming of the Pennsylvania experiment station, it is
the practice to depend upon nitrate of soda as the source of a
fertilizer for wheat. Manufacturers claim that sulphate of ammonia and
tankage would be better. The farmer soon will learn what he prefers for
his soil, provided he practices home-mixing.
Let us assume that he uses nitrate of soda, which never varies much
from 15 per cent in its content of nitrogen. If 100 pounds of nitrate
contain 15 pounds of nitrogen, the 9 pounds wanted for an acre will be
found in 9/15 of 100 pounds or 60 pounds.
Thirty pounds of phosphoric acid are wanted for an acre. If the acid
phosphate contains 14 per cent of phosphoric acid, or 14 pounds to the
100, the required amount will be 30/14 of 100, or 214 pounds.
Eighteen pounds of potash are wanted for an acre. The muriate of potash
on our markets never varies much from 50 per cent in its content of
potash. If 100 pounds of muriate contain 50 pounds of potash to the
100, the required amount wanted will be 18/50 of 100, or 36 pounds.
Adding the 60, 214, and 36 pounds, we have 310 pounds for the acre of
land. If the field contains 20 acres, the order will call for 20 times
the 60 pounds of nitrate of soda, 20 times the 214 pounds of acid
phosphate, and 20 times the 36 pounds of potash.
If the farmer prefers to use sulphate of ammonia, which varies little
from 20 per cent of nitrogen, or 20 pounds in the 100, he will get his
9 pounds of nitrogen for an acre by buying 9/20 of 100 pounds, or 45
pounds, and the substitution of the 45 pounds of sulphate of ammonia
for the 60 pounds of nitrate of soda will reduce the total application
of fertilizer per acre from 310 pounds to 295 pounds. The important
fact is that in either case there is the required amount of nitrogen.
Let us assume that the field contains enough nitrogen, but other needs
remain the same. In such case, the nitrogen is dropped out, and the
application becomes 250 pounds per acre.
The home-mixer may substitute tankage of guaranteed analysis for part
of the nitrogen and phosphoric acid. Let us assume that the tankage
runs 9 per cent nitrogen and 20 per cent phosphoric acid. If half the
required nitrogen per acre, or 4-1/2 pounds, is wanted in tankage, 50
pounds of the tankage will supply it. At the same time the 50 pounds of
tankage supplies 10 pounds of phosphoric acid, replacing one third of
the 214 pounds of acid phosphate. We thus have for the acre 30 pounds
of nitrate of soda, 50 pounds of tankage, 143 pounds of acid phosphate,
and 36 pounds of potash, or 259 pounds. The content of plant-food
remains the same, but one half of the nitrogen is only slowly
available. The farmer who buys unmixed materials will incline to use
only a few kinds, and at first he will confine himself chiefly to
materials whose composition varies little. In this way he quickly sees
in a ton of the material, not the whole bulk, but the definite number
of pounds of nitrogen and other constituents of plant-food contained in
it, and the calculations in home-mixing become simple.
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