4 8 FLORIDA GEOLOGICAL SURVEY—FOURTH ANNUAL REPORT. 
FERTILIZERS AND FERTILIZATION. 
Fertilizers are plant foods added to the soils to supplement the 
natural plant foods. Of the ten elements essential to plant growth, 
three, carbon, oxygen, and hydrogen, making up 95 per cent, of the 
plant structure, are derived from sources other than the soil, namely, 
from water and from the air. The supply of these three elements 
is ample to meet all requirements. Of the seven elements 
taken from the soil four, calcium, iron, magnesium, and sulphur, are 
sufficiently abundant in soils to meet the requirements of plants. 
The three remaining elements, nitrogen, phosphorus, and potassium, 
frequently become deficient in soil, and require to be added. The 
application of fertilizer is commonly understood to refer to the addi¬ 
tion of nitrogen, phosphorus, or potassium, in a form available to 
the plant. 
The application of water to crops is known as irrigation. The 
application of calcium, as limestone, or lime, is known as liming the 
soil. Tn neither case, ordinarily, is the application intended to supply 
plant food, the water being applied as a carrier of food and the lime¬ 
stone or lime as a soil treatment. 
CHEMICAL ANALYSES. 
A number of chemical analyses of various Florida soils have been 
included in the body of this report. The interpretation of isolated 
analyses, however, must be applied with caution as they may lead 
through insufficient evidence to erroneous conclusions. The physical 
properties of soils, which can not be adequately indicated from 
isolated samples, are equally as important as their chemical prop¬ 
erties. The soil moisture, the drainage and the possibilities of irri¬ 
gation, the tilth of the soil and the climatic conditions are all im 
portant factors that must not be overlooked in rating the agricul¬ 
tural value of soils. 
