LEGUMINOUS CROPS 69 
tent of the soil is to be rapidly increased, it is necessary 
that the nitrogen in the stem and leaves should be returned 
by plowing under the crop or, at least, by returning the 
straw to the land after the seed has been removed. 
The legumes we have used in restoring and maintaining 
a sufficient supply of nitrogen and humus in the soils of our 
own farms have been clover, soy beans, cowpeas and alfalfa. 
We have not used vetches or sweet clover but we intend to 
sow eighty acres of the latter. Our reasons for giving sweet 
clover a trial will be mentioned under ‘‘The Culture of 
Sweet Clover.’’ 
CLOVER 
Clover is the mainstay legume used in restoring nitrogen 
and humus to over-cropped farms of the Corn Belt. It is 
well adapted to the black prairie soils of the Corn Belt. It 
not only adds one more year to the rotation, thus resting 
the land from corn that much longer, but it actually enriches 
the soil by adding nitrogen. What is just as important, it 
makes available large amounts of phosphorus and potash in 
the soil by the decay of its roots. (The supply of phos- 
phorus and potash in the soil is not increased by growing 
legumes, but that which is already there is rendered more 
available by the acidity of the clover.) 
In field tests extending over twenty-nine years on the 
black corn land of central Illinois the experiment station 
of this State found that at the end of that time corn grown 
continually on the same land yielded twenty-seven bushels 
per acre as an average for the last three years of the test. 
Corn grown in rotation with oats yielded forty-six bushels 
per acre, while corn grown in rotation with oats and clover 
yielded fifty-eight bushels per acre without the aid of either 
fertilizer or manure, (See Bulletin 125, Illinois Agricul- 
