114 THE PRACTICAL SIDE OF 



manures, enables them to grow and to 

 produce a crop, 



Looking at the subject from this point of 

 view, we may regard the soil as a medium 

 for the production of crops rather than as 

 their source. Before the discovery of the 

 fact that bacteria were the means of assisting 

 leguminous plants to obtain atmospheric 

 nitrogen, many experiments were made in 

 order to determine how and from what source 

 nitrogen was obtained by growing plants in 

 field culture in those cases in which, like 

 clover, a larger quantity was removed in 

 the crop than was known to be present in the 

 soil. 



It is now well known that although clover 

 is rich in nitrogen, the roots which are 

 left in the soil after the removal of a crop 

 may contain more nitrogen than was present 

 in the soil before the seed was sown. Thus, 

 when barley was sown upon one portion of a 

 field at Rothamsted, which had grown cereal 

 crops in the preceding five years, barley with 

 clover being sown upon the other portion, 

 the quantity of nitrogen removed by the 

 barley crop grown alone was 37 lb. per acre, 

 while that removed in the clover crop reached 

 151 lb. per acre. In the third year barley 



