108 
FLORIDA STATE HORTICULTURAL SOCIETY 
acid phosphate, or dissolved bone, is often 
of some use to plants. It may not only 
serve as direct plant food, but, to a cer¬ 
tain extent, the gypsum may act as a lib¬ 
erator of potash; and if ammonia happens 
to be present in the soil in the form of 
carbonate, it may react with the ammonia 
so as to change a part of it temporarily 
into sulphate, in which form it is non¬ 
volatile and cannot escape into the air 
and be lost. 
Two great advantages are derived 
from the use of superphosphate, whether 
made from bone or rock, namely: (i) 
it is soluble in water and hence can be 
taken up immediately by the plants, and 
(2) it becomes better distributed in the 
soil if applied in soluble form than if ap¬ 
plied in its untreated natural condition. 
To be sure, much of the soluble phos¬ 
phoric acid, upon application of a super¬ 
phosphate to the soil, is soon changed into 
less soluble forms, known as “reverted” 
or “back-gone” phosphoric acid. Its ef¬ 
ficiency, after this reversion has taken 
place, is determined to a considerable ex¬ 
tent by the character of the soil and the 
relative proportions of the various sub¬ 
stances with which the soluble phosphoric 
acid can combine. For example, if the 
soil contains large quantities of aluminum 
and iron oxides, and little or no available 
lime, there is a tendency for much of the 
phosphoric acid to enter into combination 
with the iron and aluminum and for but 
little of it to enter into combination with 
lime. It is on this account that it is ad¬ 
vantageous to make small or moderate 
applications of lime from time to time to 
soils where superphosphates are to be 
used, provided crops are grown which 
are not subject to injury by liming. For 
citrus fruits, unfortunately, lime must 
for other reasons be used with exceeding 
care and in very small quantities if at all. 
Much has been said and written in re¬ 
cent years about raw rock phosphate, or, 
in other words, regarding phosphate rock 
which has not been subjected to treatment 
with sulphuric acid; and many extrava¬ 
gant claims have been made concerning 
its efficiency as plant food. It is of some 
agricultural value even without treatment, 
on certain soils, and its greatest efficiency 
is observed when it is used on acid peat 
or muck soils. The next best soils on 
which to use it would be upland soils 
which contain large amounts of acid or¬ 
ganic matter. However, for most crops 
and soils throughout the greater portion 
of the United States and especially in the 
east along the Atlantic seaboard, no other 
form of phosphoric acid has proved equal 
to superphosphate prepared from bone or 
rock phosphate by treatment with sul¬ 
phuric acid. It has been found, for ex¬ 
ample, that if the raw rock phosphate is 
used on land which has been recently 
limed or which naturally contains a con¬ 
siderable amount of carbonate of lime, its 
efficiency is very greatly reduced or in 
some cases practically nullified, for the 
reason that the acids of the soil or those 
contained in the rain water or produced 
as a result of nitrification and fermenta¬ 
tion are likely to attack the carbonate of 
lime before they can exert any material 
solvent action on the raw rock phosphate. 
It is for this reason that soft phosphate, 
which generally contains much carbonate 
