ORGANIC MATTER AND NITROGEN 223 



ing the composition of the tops and roots of the most important 

 field legumes. It summarizes a series of investigations by Penny 

 and Close, and confirms much other data relating to these crops 

 and bearing directly upon the problems of supplying the soil with 

 organic matter and nitrogen. 



As an average of all determinations, it is safe to say that about 

 one third of the nitrogen of the red-clover plant is contained in the 

 roots and stubble, and that the growth of clover above ground 

 contains, before rotting or leaching, about 40 pounds of nitrogen 

 to the ton of air-dry substance. 



Alfalfa contains a somewhat larger proportion of its nitrogen in 

 the roots, at least during the first year of its growth; and possibly 

 the total nitrogen of the alfalfa roots would average one half as 

 much as the total removed in the crops, even when the plants are 

 several years old, considering the entire root system, which com- 

 monly reaches a depth of 20 feet or more with old plants. Alfalfa 

 hay contains 50 pounds of nitrogen per ton. 



In the case of such annuals as cowpeas and soy beans, not more 

 than one tenth of the nitrogen is found in the roots and stubble, as 

 a rule. The crop above ground contains (when thoroughly air-dry) 

 about 43 pounds of nitrogen per ton for cowpeas and about 53 

 pounds per ton for soy beans. 



Extensive experiments are in progress in Illinois to determine, 

 under actual field conditions, what systems of grain farming (with 

 green manures and crop residues) and what systems of independent 

 live-stock farming will increase or maintain the organic matter 

 and nitrogen of the soil; but these are investigations that require 

 time, and but few results have as yet been published. 



A series of pot cultures has been reported (Illinois Bulletin 

 115) which illustrates the fact that legume green manures may 

 take the place of commercial nitrogen. 



The soil used in these experiments was the yellow silt loam from 

 the unglaciated area of southern Illinois (Pulaski County), which, 

 as will be seen from Table 15, is quite deficient in nitrogen. The 

 field from which this soil was collected had been under cultivation 

 for about 75 years, during which time the average yield of wheat 

 had decreased from about 25 bushels to 5 bushels per acre. 



In the pot-culture experiments, catch crops of cowpeas were 



