FLORIDA STATE HORTICULTURAL SOCIETY 
109 
of lime, is often less efficient than it 
would be if it were entirely dissociated 
from carbonate of lime. 
When soluble phosphoric acid reacts 
with lime, it first forms dicalcium phos¬ 
phate or, in other words, a two-lime, or 
reverted, phosphate. This is still very 
available to plants; for even though it is 
not directly soluble in water, it is readily 
dissolved by the action of plant roots and 
by water containing carbonic acid, such, 
for example, as rain water and the nat¬ 
ural soil waters, which derive their car¬ 
bonic acid from the decomposition of the 
organic matter of the soil. 
The chemist determines in the labora¬ 
tory the amount of water-soluble phos¬ 
phoric acid and also the amount of re¬ 
verted phosphoric acid and refers to the 
sum of the two as “available” phosphoric 
acid. 
Another source of phosphoric acid, 
which was used in this country somewhat 
extensively before the war, is basic slag 
meal, or Thomas phosphate. This was 
produced in the manufacture of steel 
from phosphate of iron by what is known 
as the “basic” process. The phosphoric 
acid in this material is largely combined 
with lime in a different combination from 
any of the other phosphates mentioned, 
and some iron, manganese, and free lime 
are also present. As concerns the avail¬ 
ability of its phosphoric acid, it is some¬ 
what inferior to superphosphate. It is, 
however, superior in this respect to un¬ 
treated bone meal and is much superior 
to raw rock phosphate or soft phosphate. 
Its availability to plants depends very 
largely upon the conditions under which 
it is manufactured, and certain basic 
slag meals produced in some European 
works before the war had a very low 
availability as compared with that pro¬ 
duced in others. Thus the source of the 
basic slag meal, or Thomas phosphate, 
may be a very important consideration 
from the purchaser’s standpoint. 
Another new source of phosphoric acid 
is the so-called “ammo-phos,” which is a 
combination of ammonia and phosphoric 
acid. This is a material which is as yet 
but relatively little known in agricultural 
circles. It must be used experimentally 
under varying conditions and with a large 
number of different kinds of plants be¬ 
fore one can state definitely the condi¬ 
tions under which it can be used to the 
best advantage, or can be sure of its .real 
desirability and of the efficiency of its 
phosphoric acid as compared with phos¬ 
phoric acid in superphosphate. ' 
During and since the war many pro¬ 
cesses have been patented for the prepara¬ 
tion of phosphates for agricultural use 
from raw rock phosphate by different 
methods involving fusion with various 
substances; but as yet none of these prod¬ 
ucts has apparently been able to hold its 
own in competition with superphosphate, 
either by way of efficiency in crop pro¬ 
duction or economy of manufacture. 
In connection with my experiments, 
especially in the Middle West, I have been 
astonished to find that as small amounts 
as 90-150 pounds of a relatively low- 
grade fertilizer, containing high percent¬ 
ages of phosphoric acid, have given in¬ 
creases of 8-15 bushels of wheat to the 
acre, 15-40 bushels of oats, and 10-25 
bushels of corn. In one case 100 pounds 
of fertilizer were used to the acre for 
