104 
FLORIDA STATE HORTICULTURAL SOCIETY 
of their growth, than if they are supplied 
with properly balanced plant food which 
does not carry an excess of ammonia. 
Another point in connection with le¬ 
gumes ought to be mentioned. Everyone 
recognizes the importance of getting ni¬ 
trogen out of the air and of utilizing 
legumes wherever they can be utilized to 
advantage. Until quite recently some 
mistaken notions have existed in regard 
to the amount of nitrogen which they fix 
from the air; since, as long as there is 
present in the soil an abundant supply of 
combined nitrogen in forms which the 
plants can utilize, they take it up instead 
of assimilating atmospheric nitrogen to 
any considerable extent. Recent experi¬ 
ments in the Middle West have shown 
where legumes and non-legumes have 
been grown side by side and then removed 
from the land, that the soil has been made 
poorer in nitrogen where the legumes 
were grown than where the land was de¬ 
voted to non-legumes. Even if the crops 
are left on the farm and are returned in 
manure, a large percentage of the ammo¬ 
nia is finally lost before the plant residues 
in the form of liquid and solid manure 
are returned to the land. On this ac¬ 
count, if one wishes to add to the soil the 
greatest amount of nitrogen from atmos¬ 
pheric sources, the legumes must be 
grown on land which is not already rich 
in combined nitrogen, and they must then 
be plowed under. 
When plant residues are applied to the 
soil, the complex nitrogenous compounds 
which are contained in them are soon 
broken up through the activity of bac¬ 
teria and the other naturally-existing mi¬ 
cro-organisms of the soil. While these 
changes are taking place, some plants are 
able to assimilate directly certain of the 
more simple organic nitrogenous com¬ 
pounds, comparable to those produced 
from hair, wool, and other complex or¬ 
ganic nitrogenous compounds when sub¬ 
jected to suitable factory preparation and 
treatment for fertilizer uses. The greater 
portion of the nitrogen, however, is trans¬ 
formed into ammonia by the agencies just 
mentioned, which in turn is transformed 
in the soil into nitrous acid and finally 
into nitric acid. This nitric acid then en¬ 
ters into combination with potash, soda, 
lime, or magnesia, from which it is taken 
up by plants unless lost in the drainage 
waters. In Indiana even aluminum ni¬ 
trate has been known to be formed in soils 
to such an extent that it became poison¬ 
ous to vegetation. In other words, this 
compound may act in the same way as 
certain of the other soluble aluminum 
salts. 
The various changes in plant residues 
take place more readily in soil well sup¬ 
plied with moisture, and at fairly high 
temperatures, than in rather dry soil, es¬ 
pecially when the temperature is low. 
The formation of nitrates is said to oc¬ 
cur most actively at a temperature of 
about 98° F.; hence, in many cases soil 
near the surface in summer becomes too 
hot for the most rapid formation of ni¬ 
trates. 
It is not necessary from the standpoint 
of the plant that all of the nitrogen, aside 
from the small amount which is taken up 
in simple organic forms, be changed into 
nitrates; for at least many kinds of plants 
at certain stages of their growth are able 
to use some nitrogen while still combined 
