Nitrogen in Soils. 



85 



feet in one-foot sections on May 24 and again on Aug. 22, 

 and the results are given in the table below : 



Nitric acid in fallow ground in pounds per acre. 



These figures are a mean of the amounts found in nine 

 different sub-plots, the soil being a clay loam changing into 

 sand in the third foot. It will be seen that the total amount 

 of nitric acid at the close of May was 112.35 Ibs., contain- 

 ing 24.97 Ibs. of nitrogen, enough for only about 14.3 

 bushels of wheat. On the 22nd of August, however, there 

 had been an increase to 450.11 Ibs. per acre, containing 

 100.02 Ibs. of nitrogen, enough for nearly 60 bushels of 

 wheat per acre. 



101. Source of Soil Nitrogen. Until recently it was 

 maintained that the nitrogen for the growth of all plants 

 was derived from the humus of the soil and from the small 

 amount of ammonia and nitrous and nitric acids brought 

 down by the rains. It is now known that the free nitrogen 

 of the atmosphere is the ultimate source of soil-nitrogen, 

 and that the soil-nitrogen is being continually returned to 

 the air again just as was long ago recognized to be the case 

 with the carbon of living forms. 



1. The immediate source of humic nitrogen is the slow 

 decay of organic matter, whether this be the roots, stems or 

 leaves of plants or the tissues and waste products of ani- 

 mals, and a large part of the life processes r *f the world 

 take place between the conversion of humus into living tis- 

 sues and dead tissues back into humus again. 



2. The formation of nitrous and nitric acids through an 

 oxidation of the nitrogen of the air by electrical discharges 



6 



