GENERAL AGRICULTURE AND CLIMATE. 
65 
A good rotation should necessarily include crops belonging 
to each of these three classes. The value of such practice is 
apparent in its effect on the physical condition of the soil, on 
weediness, on organic matter supply, on plant diseases, and 
on nitrogen supply of the soil. Better yields are, therefore, 
obtained when crops are rotated than when a single cropping 
system is followed. 
Again, crop rotation permits raising livestock and means di¬ 
versified farming. No one will deny the benefits of this type 
of farming in stabilizing farm business and making best use 
of labor and equipment the year around. 
It should not be understood, however, that crop rotation 
means maintaining the supply of plant food better than where 
a single cropping system is practiced. It is often said that 
certain crops are “hard” on the soil in the sense that they 
remove more plant food than other crops. In part that is true, 
but a more important difference is that some plants remove 
more of certain elements than others. Again, a crop like corn, 
because of its root development and length of growing season, 
may utilize plant food that is less soluble. 
Potatoes require relatively more potassium; corn draws 
heavily on nitrogen; while legumes are heavy feeders of lime 
(calcium) and also require large amounts of phosphorus, po¬ 
tassium, and nitrogen (some of which may be extracted from 
the air in the soil). Again, grain crops and roots require 
plant food that is readily available, while corn is less par¬ 
ticular in this respect. 
By properly rotating crops, therefore, the soil is subjected 
to these different “feeding characteristics”. One crop com¬ 
pensates for the other, and there is maintained more nearly 
a balanced condition than with the single crop system. 
It is of great importance that in selecting crops to grow, 
careful consideration be given to the question of climate. This 
is about the only factor which the farmer cannot control. A 
poor soil may be improved, better markets may be found, and 
better labor secured; but the farmer is powerless to change 
climatic conditions. He must, therefore, select such crops 
as are suited to his climate. 
The soil is also a factor of great importance. As a general 
rule, small grain crops do better on heavy than on light soils, 
and the same is true of grasses grown for hay. On the other 
