THE HAWAIIAN 
FORESTER I AGRICULTURIST 
Vol. V APRIL, 1908 No. 4 
NEW NITROGEN FERTILIZERS. 
By L. G. Blackman. 
The principal constituents of plant food are present in greater 
or less proportion in most soils. As the latter are formed by the 
disintegrating and general weathering process of rocks, the com- 
position of a particular soil is dependent to a great extent upon 
the nature of the rock from which it has been derived. Inter- 
mingled with the inorganic decomposed rock there is present in 
every fertile soil a variable proportion of decomposed organic 
matter, the accumulation of former generations of animal and 
vegetable growths. It is the latter ingredient, termed "humus," 
which gives a soil much of its agricultural value and upon which 
to a great extent plants feed, for vegetation, as well as animals, 
is incapable of supportly life directly from inorganic substances 
alone. 
In a natural state the earth's successive growths of vegetation 
contribute to the accumulation of the soil's humus. Each gen- 
eration returns to the earth an added deposit of matter in a form 
readily available as plant food. The continual cultivation of 
crops and their removal from the soil by man, however, depletes 
the soil of much of its valuable plant food, and this process being 
continued, a time is soon reached when the land becomes so ex- 
hausted that it cannot be profitably cultivated without artificial 
reinforcement. 
In order that a plant may grow to advantage, it is of prime im- 
portance that a sufficient supply of all the elements of its food 
be present in an assimilable form. At times, although such ele- 
ments are contained in the soil, they are locked up in some chemical 
combination with other elements, which renders them unavailable 
by vegetation. Speaking broadly, the main necessary food of 
plants may be said to be Carbon, Hydrogen, Oxygen and Nitro- 
gen, and in less degree Potash, Lime, Magnesia and Phosphoric 
Acid. 
