Chemical Nature of Soils. 



77 



amounts of it will meet the needs of niter- form nig germs 

 and thus allow large crops to be produced where, with a 

 poor form of humus, this would be impossible. 



The results of their studies in this line are stated in the 

 table below : 



In speaking of these results the^ say, "It thus appears 

 that, on the average, the humus of the arid soils contains 

 three times as much nitrogen as that of the' humid, that in 

 the extreme cases the nitrogen percentages in the arid hu- 

 mus actually exceeds that of the albuminoid group, the 

 flesh -forming substances." 



"It thus becomes intelligible that in the arid region a 

 humus percentage, which, under humid conditions, would 

 justly be considered entirely inadequate for the success of 

 normal crops, may, nevertheless, suffice even for the more 

 exacting crops. This is more clearly seen on inspection of 

 the figures in the third column, which represent the product 

 resulting from the multiplication of the humus percentages 

 of the soil into the nitrogen of tLe humus." 



90, Chemical Composition of Soils Compared With the 

 Rock from Which They Are Derived. When a soil accumu- 

 lates in place from slow decomposition of the underlying 

 rock there is sometimes a close resemblance in chemical 

 composition between the rock and the derived soil, but in 

 other cases there is little resemblance between them. If 

 the rock is made up of a large percentage of relatively solu- 

 ble materials, as is the case with most limestones, then the 

 solvent power of water, combined with the effects of leach- 

 ing, tend to cause a concentration of the relatively insoluble 



