HINTS ON SOILS AND FERTILIZERS 13 
elements. These elements are nitrogen, phoi- 
phorus, potassium and, in many cases, calcium. 
In fact, when commercial fertilizers are sold, 
they are sold on the basis of the first three 
named elements; nitrogen, phosphorus and 
potassium. Consequently, these are the ele¬ 
ments that are provided most by the farmer 
who is interested in keeping up the fertility of 
his land. 
The nitrogen is used by the plants in the 
manufacturing of protein, a form of food 
relished by all animals. Phosphorus is used 
by the plant largely in filling out the grain or 
fruit of the plant. Obviously, the greatest need 
for this element is during the later stages of 
plant growth. Potassium is used largely for 
protein and starc'h formation by the plants. 
This element is especially desirable in the 
growing of root crops, such as potatoes, beets, 
etc., which contain a high percentage of starch. 
Calcium (or “lime”) is regarded as being es¬ 
sential for leaf and stalk growth. It has a 
double function, however, in that it sweetens 
the soil, or neutralizes it, so that bacteria that 
are beneficial to the soil can exist, as it is a 
well-known fact that certain crops cannot thrive 
on acid, or “sour” soils. 
The nitrogen that is used by the plant is not 
in the form of the gas that is so abundant in 
the air. While it is true that carbon and oxy¬ 
gen can be taken in by the plant as a gas in 
the form of carbon dioxide, a gas, the plant is 
unable to take in the free nitrogen from the air, 
but must take it in through the roots of the 
plant, in a soluble form. Because of this fact, 
