HINTS ON SOILS AND FERTILIZERS 53 
these plants, especially when the season is 
moist during the time that these diseases are 
prevalent. As a matter of fact, every crop that 
the farmer raises, has to fight a struggle 
against these insidious enemies. Many farmers 
are aware of the chinch bug, boll weevil, grass¬ 
hoppers, cutworms, as good examples of insect 
pests, and of rust, smut and other fungus dis¬ 
eases that play havoc with the farm crops dur¬ 
ing the growing season. 
We have discussed the benefits of humus, or 
organic matter, in the soils. We have learned 
that this material is simply decaying vegetable 
matter in the soil. No soil is very productive 
that lacks any appreciable amount of this ma¬ 
terial, as this humus is a great factor in im¬ 
proving the tilth of the soil, and its fertility. 
When a field is sow r n to certain cultivated 
crops, and these crops are removed from the 
land, and nothing is put back into the soil, 
then we have a soil soon deficient in organic 
matter. The soil becomes hard and difficult to 
work. This can be remedied by a method 
known as “rotation of crops,” whereby differ¬ 
ent crops are raised on the same field in suc¬ 
cessive years, and one of these crops should 
be a hay crop, such as clover, for instance. The 
clover can be raised on the piece for two or 
three years, and finally plowed under, thus 
providing a good supply of vegetation to sup¬ 
ply this organic matter, and incidentally fur¬ 
nishing considerable nitrogen. 
Besides the factors already mentioned deter¬ 
mining the yields of farm crops, we might men¬ 
tion a few other requisites that are essential 
