66 
FLORIDA STATE HORTICULTURAL SOCIETY 
The consensus of opinion is that. A. P. 
is likely to increase soil acidity, but the 
authorities do not agree as to just why it 
should. Popular opinion fastens on the 
use of sulfuric acid in manufacture, but 
A. P. does not contain any free acid unless 
very carelessly made. That is the point 
guarded against—less than actually need¬ 
ed to dissolve the tricalcium being used 
since an excess is expensive to the manu¬ 
facturer and injurious to the product. 
Van Slyke lays the possible acidity to the 
interaction of the gypsum with other com¬ 
pounds present, thus leaving the sulfuric 
radical in the soil. At any rate this possi¬ 
ble acidity is not a serious objection if the 
soil be well supplied with lime. Gypsum 
is partially soluble, but is not in any sense 
a fertilizer or a soil corrective. Then if 
we use large quantities of lime we are 
likely to cause a more speedy reversion of 
the soluble P. A., perhaps there may final¬ 
ly be present more tricalcium phosphate 
(floats) than either other form of P. A. 
Possibly A. P., along with other fertil¬ 
izer sources, has been made to suffer for 
the sins of its users. It is not unreason¬ 
able to presume a possible corrosive action 
from a large quantity—twenty to thirty 
pounds per tree—of fertilizer largely wa¬ 
ter soluble—applied at one time. Many 
growers believe that little but often means 
better results for the same or less money. 
We know that less phosphoric acid is lost 
in the soil drainage than either N. or K., 
but it may readily be carried below the 
reach of the roots. The use of more sol¬ 
uble sources in winter and less soluble in 
summer is advised by some who fertilize 
twice or three times a year, but we cannot 
depend on having a wet summer or a dry 
winter. It is matter of record that Jan¬ 
uary may be wetter than July or August 
(1912), or December than June (1913). 
The facts are that we have not any 
complete data on the use of different 
forms of P. under Florida conditions and 
in citrus groves. The usual recommenda¬ 
tion of some grower is seldom of weight 
because, in the first place, the tests have 
not been carried through a number of 
years, and secondly, they have not em¬ 
braced several different sources, nor have 
they been checked by black plots. Neither 
have records of temperature and rainfall 
been kept. 
Prof. Hopkins, of the Illinois Experi¬ 
ment Station, has made an excellent case 
for floats, and farmers in Illinois by fol¬ 
lowing his advice get good results at little 
expense for P. The satisfactory use of 
floats is conditional upon thorough incor¬ 
poration in the soil with large amounts of 
decaying vegetable matter and plenty of 
lime. We may say in passing that ad¬ 
vantageous fertilizing necessitates lime 
either in the fertilizer or applied sepa¬ 
rately. And it takes limestone to fill the 
bill. Present indications are that floats 
cannot be used to advantage in a bearing 
grove, but I do believe that a new grove 
can be easily and cheaply made by plowing 
under on land previously well dressed with 
floats and limestone. The grower would 
really need to buy little fertilizer in addi¬ 
tion, except potassium, which if used as 
low grade sulfate would also supply Mg. 
Most sources of the fertilizing elements 
have some possible objection, sometimes 
more theoretical than practical. All the 
