Availability in Various Substances 181 



The increased vigor, due to long-continued development 

 under favorable conditions, may, in a measure, become 

 fixed in the bacteria. There are facts, at least, that 

 point strongly in that direction. The significance of 

 this circumstance will be discussed under soil-inoculation. 

 Availability of nitrogenous materials. — The relation 

 must play an important part in determining the relative 

 availability of the various nitrogenous materials em- 

 ployed for manuring purposes. Agricultural chemists 

 and practical farmers know that substances like dried 

 blood, meat meal and ground fish yield their nitrogen 

 rather rapidly to the growing crop, while other substances 

 like leather-meal, wool and peat are a very unsatis- 

 factory source of nitrogen to plants. The first of these 

 are designated as available, while the last are called 

 unavailable, or difficultly available. Experience and 

 investigation have arranged such nitrogenous substances 

 in the order of their availability in somewhat the fol- 

 lowing fashion: 



Nitrate 100 



Ammonium sulfate 90 



Dried blood, horn meal, green clover 70 



Fine bone meal, ground fish, meat meal 60 



Manure 45 



Wool waste 30 



Ground leather 20 



This table brings out the existing relations in a 

 general way. It should not be forgotten, however, that 

 the absolute and relative availabilities are modified by 

 soil and climatic conditions. The differences in availa- 

 bility as brought out in the table a-re determined largely 



