104 
FLORIDA STATE HORTICULTURAL SOCIETY. 
mean to say that all our troubles are due 
to these unnatural and unfavorable con¬ 
ditions which we have created; but we 
do know that unfavorable conditions 
often tend towards a weakened plant, 
and that a weakened plant is more sus¬ 
ceptible to diseases and insect attacks. 
To state the idea in a different way: 
Fertilizers cannot give their best results, 
no matter how lavishly or how carefully 
applied, if the crop must encounter other 
unfavorable conditions, any more than 
a powerful locomotive with a heavy train 
of cars can give its best results over a 
track with light rails and a poor roadbed. 
In the latter case the light rails and poor 
roadbed become the limiting factor, while 
in the former case any one of several 
conditions may prove a limiting factor. 
SOME FACTORS LIMITING THE EFFICIENCY 
OF FERTILIZERS. 
/. Deficiency of Water .—Perhaps I 
can make this clearer by giving some il¬ 
lustrations of what I mean by limiting 
factors. 
Not many days ago while passing over 
one of the lines of the Atlantic Coast 
Line Railway I saw citrus groves where 
the leaves were curling. Under such 
conditions no kind or quantity of fertil¬ 
izer could do much for those trees. There 
must be water to bring the fertilizer into 
solution before the plant can use it, and 
when the leaves begin to curl we know 
that the supply of moisture is failing. 
Here the efficiency of the fertilizer is lim¬ 
ited, and that too, at a most critical time, 
by a deficiency of water. To get the ben¬ 
efit of fertilizers at such times we must 
either irrigate or put the soil in such con¬ 
dition that the moisture from beneath 
may be brought up by capillary action. 
This latter, however, is impossible if at 
a depth of four or five inches or a foot 
beneath the surface there is a plow sole 
or hard stratum of earth. This hard 
stratum becomes the limiting factor (in 
the case of trees) for it prevents the roots 
from going in search of food and moist¬ 
ure and also prevents the moisture from 
coming up near the surface where it is 
needed to dissolve the fertilizer. 
2. Deficiency of Humus .—The effi¬ 
ciency of fertilizers may be further lim¬ 
ited by a deficiency of humus in the soil. 
White sand is a poor material to hold 
moisture and plant food. On the other 
hand, if this sand is well supplied with 
humus its capacity to hold these materials 
is greatly increased. This in itself may 
mean handsome profits; for although the 
soil may be well supplied with fertilizers, 
if the moisture necessary to bring these 
into solution is wanting the crop will suf¬ 
fer. Many instances could be cited where 
the crop yield has been greatly increased 
by incorporating with the soil an abun¬ 
dant supply of humus. We have heard 
much in recent years of the failure of 
groves to put on a full crop of fruit; and 
undoubtedly much of this trouble is due, 
not to a lack of fertilizers, but as has al¬ 
ready been pointed out to the lack of suf¬ 
ficient water to bring the fertilizer into 
solution at a critical time. Irrigation will 
help to solve this problem but where ir¬ 
rigation is not practicable the next best 
step is to increase the supply of humus, 
which will in turn increase the water sup¬ 
ply. Indeed it is well to have an abun- 
