THE LOSS OF KITROGEK. 107 



losses from the washing out of the nitric acid by the 

 winter rains. A high temperature is favorable to the 

 production of nitric acid in our soil, and the collecting 

 power of the wheat has ceased before the highest tem- 

 perature of the summer has been reached. We may 

 make an imaginary sum of the result as follows : 



Lbs. of nitrogen washed aicay per acre. 



From soil without vegetation 40 



From soil with wheat, 15 lbs. retained by crop 25 



From soil with wheat and seeds— retained by wheat, 15 lbs.; by seeds, 

 25 lbs . . . 5 



Green yegetation is the great agent by which nitric 

 acid is converted into insoluble forms; it is evident, 

 therefore, that before we can assign to any of our crops 

 their proper economic function in a rotation, we must 

 take into account both the length of time to which the 

 period of their growth extends, and also the range and 

 depth of their roots. The tendency of the Eothamsted 

 experiments is every year leading us more and more to 

 the conclusion, that the source of nitrogen in our crops 

 is to be found in the amount of that substance stored up 

 in our soils. If further investigation should establish 

 this to be absolutely true, the current irieas with regard 

 to the properties of several of our crops will require con- 

 siderable modification. 



