174 BOAKD OF AGKICULTUKE. [Pub. Doc. 



Soil Nitrogen and its Availability. 



The examination of 49 samples of American soil showed 

 them to cany in the first 8 inches from 640 to 10,000 

 pounds of nitrogen per acre, and the subsoil carried from 

 1,800 to 6,200 pounds. This amount of nitrogen equals 

 that removed by 15 to 100 large annual crops of any farm 

 plant. Only a small percentage of this nitrogen is in such 

 form that it is available to plants. Can it be rendered 

 available ? 



Before the nature of the change which takes place in the 

 soil was understood, it was known that certain conditions 

 were favorable for changing soil nitrogen into the form of 

 nitrate. Samples of Manitoba soils which carried a))out 

 7,000 pounds of total nitrogen per acre were kept for 300 

 days under favorable conditions for nitrification, and from 

 these experiments it was estimated that not less than 800 

 pounds per acre were converted into solul)le nitrates which 

 would be availal)le for crop production. While the condi- 

 tions under which these samples were placed for nitrification 

 were perhaps more favorable to the ra[)id carrying forward 

 of the process than could be produced in the field, it is not 

 to be inferred that the amount so changed represents the 

 total nitrogen in these soils that could be rendered available. 

 There seems to be no reason whv, with time and favorable 

 conditions, practically all that which analysis shows a soil 

 to contain could not thus be converted into a soluble form. 



From the bacterial considerations which we have been 

 studying, it follows that one of the primary conditions for 

 the transformation of nitrogen is the presence of proper bac- 

 teria in the soil and proper cojidftions for their growth. It 

 is a practical question to learn how these bacteria being not 

 alread}^ present may be added to the soil, and how they may 

 be stinuilated in activity if they are present. Bacteriolo- 

 gists are strenuously applying themselves to the solutions 

 of these questions, and, although the answer is as yet iji- 

 comi)lete, some facts of high significance have already been 

 established. 



