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- 



