8 
SOIL SURVEY OF BUFFALO COUNTY. 
character and chemical composition, and by offering suggestions 
for their management, based upon the work of the Soil Survey 
within the area, covered in the report, and upon the results of 
field tests made by the Experiment Station. 
Soil fertility depends upon two factors: first, upon the physi¬ 
cal characteristics of the soil, such as water holding capacity, 
workability, etc., and second, upon the chemical composition of 
the material composing the soil. The chemical composition de¬ 
pends upon the mode of origin of the soil, and the source of mate¬ 
rial from which the soil is derived. 
Water holding capacity, and other physical properties of soil 
all depend chiefly upon texture, which refers to the size of the 
individual soil grains, or particles. A coarse sandy soil, for ex¬ 
ample, will not retain moisture so long as a loam soil, or clay 
loam, because the finer the soil grains, the greater will be the 
total soil-grain surface area to which moisture may adhere. Tex¬ 
ture is determined in the field by rubbing the soil between the 
thumb and fingers, and with experience one soon becomes expert 
at judging the size of soil grains. This field judgment is verified 
in the laboratory by a mechanical analysis, which is made by a 
simple method of separating soil grains into different groups, of 
which there are seven. These are known as clay, silt, very fine 
sand, fine sand, medium sand, course sand, and fine gravel, and 
the following table gives the size of the soil particles of which 
each group or separate is composed. 
TABLE SHOWING SIZE OF SOIL PARTICLES 
Fine gravel . 
Coarse sand . 
Medium sand . 
Fine sand . 
Very fine sand . 
Silt . 
Clay . 
1 millimeter equals .03937 ol an inch. 
Millimeters 
2.000-1.000 
1.000- .500 
.500- .250 
.250- .100 
.100- ;050 
.050- .005 
.005- .000 
A chemical analysis is also made of the soil to determine the 
amounts of various essential plant-food elements which are pres¬ 
ent. A chemical analysis shows whether the soil contains a large 
store of plant food, or only a small quantity, and it indicates 
which kinds of plant food will probably be needed first. The 
amount of organic matter in the soil is also determined, and tests 
are made to show conditions relative to soil acidity. 
