Making Phosphate Available

If the natural rock is used it should be ground so that at least 90
per cent will pass through a sieve with 10,000 meshes to the square
inch, and of course its content of phosphorus (from 12 to 15 per
cent) or of so-called "phosphoric acid" (from 27 to 34 per cent)
should also be guaranteed. Moreover it should be used liberally and
in connection with plenty of decaying organic matter. People
sometimes ask, "How much of the phosphorus in raw phosphate is
available?" The best answer to this question is, "None of it; and,
if you are not going to make it available, don't use it."

On my own farm I use about one ton per acre of raw phosphate once
every six years, thus adding at least 250 pounds of phosphorus at a
cost of less than $8; whereas 200 pounds of the common "complete"
fertilizer per acre yearly would cost $12 every six years, and would
supply only 40 pounds of phosphorus. I do not use "complete"
fertilizers, because there is plenty of nitrogen in the air and
plenty of potassium in the soil; and because, by growing and plowing
under plenty of clover, I not only secure nitrogen from the air and
liberate potassium from the soil but also liberate the phosphorus
from the raw rock phosphate applied to the soil. In beginning the
use of raw phosphate where the supply of organic manures is limited,
I apply one ton of phosphate and 600 pounds of kainit in intimate
connection, turn them under, preferably with organic matter, then
add ground limestone if needed, and thus prepare to grow clover.

By far the most important agencies under the farmer's control for
the liberation of plant food are the decomposition products of
fermenting or decaying organic matter, such as green manures, crop