Loss and Availability of Nitrogen 157 



comes proper to inquire whether the transformations 

 due to them may not, at times, be wasteful. 



Loss of nitrogen in the soil. — Many facts recorded in 

 agricultural science prove that under certain conditions 

 the nitrogen removed by crops forms but a small por- 

 tion of the total quantity lost from the soil. Investi- 

 gations show that in the continuous cultivation of wheat 

 the changes in the humus may be so wasteful as to con- 

 stitute a most serious drain on the nitrogen resources 

 of the soil. The losses thus occasioned bear a certain 

 relation to the physical character of the soil, to its water- 

 holding power, to its chemical composition, to the 

 methods of tillage to which it is subjected, and to the 

 crops grown upon it. The bacterial digestion of humus 

 proceeds quite rapidly in the open sandy soils. The de- 

 composition processes there may be so rapid as to pre- 

 clude the accumulation in them of any considerable 

 quantities of humus. Under such conditions, the organic 

 nitrogen applied is changed more or less wastefully. 



Availability of nitrogen. — In assigning a certain degree 

 of availability to nitrogenous substances from one 

 source or another, the significant part played by the 

 soil and its bacteria in the transformation of such sub- 

 stances is frequently overlooked. Barnyard manure, 

 green-manure, or tankage, that show a high rate of 

 ■availability in one soil may prove much less available 

 in another. For instance, out of every one hundred 

 pounds of nitrogen applied in barnyard manure, the 

 crops of one soil may recover thirty-five pounds in the 

 first year, ten pounds in the second year, and five pounds 

 in the third year. The same crops may recover from the 



