62 PRACTICAL CORN CULTURE 
not permanently maintain the fertility of the soil. All 
crops require more or less phosphorus and potash as a part 
of their plant food. Each year a drain is made on the supply 
of phosphorus and potash. When these elements of plant 
food are taken from the soil they must be returned in the 
form of stable manure, commercial fertilizer or rock phos- 
phate. No plant can put phosphorus and potash in the soil; 
instead, they all take it out. 
For nearly fifteen years we have followed with slight 
variation a rotation consisting of corn two years, then oats, 
wheat and clover successively. This is the popular rotation 
in Central Illinois and is followed to a greater or lesser 
extent on nine-tenths of the farms in this latitude. 
Since oats are a heavy drain on the land and often an 
unprofitable crop, we have, for the last two years, substituted 
soy beans largely for oats. Each year we sow about 100 
acres to soy beans. Before adopting soy beans this ground 
was sown to oats. By following this method we are including 
two leguminous crops in the rotation instead of one. 
The soy bean is a wonderful crop for improving the phys- 
ical condition of the soil. An ideal seed bed for winter 
wheat can be made on soy bean fields with very little work. 
Remember to return the straw to the land if you wish to 
increase the nitrogen content of the soil. (More will be said 
of soy beans in the next chapter.) 
Alfalfa is one of the most profitable of the legume crops 
but it is not a good crop to work in a rotation. This is due 
to the fact that it is difficult and expensive to secure a good 
stand and when once secured it is profitable to leave the 
ground in alfalfa from three to five years. A good stand 
of alfalfa will generally grow better each year for the first 
three years. Alfalfa will grow on most of the well drained 
soils of the Corn Belt. It will grow on thin land but it will 
do much better on strong land. That alfalfa will build up 
