HINTS ON SOILS AND FERTILIZERS 11 
usually provided, unless the soil is so full of 
water that the air is crowded out. 
Water, to a certain extent, is an absolute re¬ 
quirement for plant growth, and is usually 
found in the soil to some extent, at least. The 
form of water that the plant uses for growth 
is not the form that we ordinarily understand 
water to be. What we really mean here, is 
moisture, in a form that surrounds the soil 
grains. 
Finally, we usually find more or less inor¬ 
ganic substances in the soil, such as the chem¬ 
ist would classify as “salts.” These are found 
in greater amounts in dry climates than in wet, 
as the more frequent rains of the moist cli¬ 
mates tend to wash or bleach these salts from 
the soil. 
CHEMICAL COMPOSITION OF SOILS 
We have now learned that soil, as we ordi¬ 
narily understand the term, is composed of 
humus and mineral elements, chiefly. Now we 
may well ask “What are these materials com¬ 
posed of?” The mineral matter is obviously 
composed of minerals. There are a few min¬ 
eral elements contained in the decaying or¬ 
ganic matter also. Hence, we have consider¬ 
able mineral elements contained in the ordi¬ 
nary soil. There are ten elements that are 
absolutely required to produce plant growth, 
but a few of these are gases, rather than min¬ 
eral elements. These ten elements are as fol¬ 
lows: carbon, hydrogen, oxygen, phosphorus, 
potassium, nitrogen, sulphur, calcium, iron and 
