is direction is not great
enough to be a very material factor in deciding upon a carrier of
phosphoric acid. If a soil has little lime in it, a state of acidity
soon will come anyway, and the increase in amount of required lime will
be small. The cheapness of acid phosphate, as compared with animal
bone, is the decisive factor.

The ill-effects usually attributed to acid phosphate are not due in any
great degree directly to the sulphuric acid used in its making, but to
the bad farming methods that so often attend its use. When the need of
commercial fertilizers is first recognized, acid phosphate seems to
meet the need. The soil's store of available phosphoric acid gives out
first, and this fertilizer brings a new supply. If the available potash
is in scant amount, the acid phosphate helps in this direction by
freeing some potash. The phosphoric acid has peculiar ability in giving
impetus to the growth of a young plant, and that enables it to send its
roots out and obtain more nitrogen than it otherwise would do. The
farmer thus may come to regard it as a means of securing a crop, and
there is neglect of manure and clover. If a field is thin and fails to
make a sod, there is no immediate compulsion to use manure or to grow a
catch crop to get organic matter, but the field is cropped again with
grain. Soon the supply of humus is exhausted, the soil lies lifeless,
and the stores of available nitrogen and potash are in a worse depleted
state than formerly.

The fault lies with the method. The phosphoric acid in the acid
phosphate was needed. Profit from its use was legitimate, but the
necessity of supplying organic matter became even greater than it would
have been otherwise. Tens of thousands of our most successful farmers
use heavy applications of acid phosphate, but they keep their soils in
good physical condition by the use of manure or clover, and they apply
potash and nitrogen when needed. The clover is assured by using lime
wherever it is in too limited supply, and that is the case in most
instances, regardless of the use of any kind of commercial fertilizer.

Basic Slag.--When iron ores contain much phosphorus, its extraction by
use of lime gives a by-product in the making of steel that has
agricultural value. The ores of the United States usually do not give a
slag sufficiently rich in phosphorus to be valuable. Nearly all the
basic slag used as a fertilizer is imported from Germany, and usually
contains 17 to