286 DRY-FARMING 
in the soils of the Great Plains and from three to four 
times as much as is found in the soils of the Great 
Basin and the High Plateaus. It may be assumed, 
therefore, that the Indian Head soil was peculiarly 
liable to nitrogen losses. Headden, in an investi- 
gation of the nitrogen content of Colorado soils, 
has come to the conclusion that arid conditions, like 
those of Colorado, favor the direct accumulation 
of nitrogen in soils. All in all, the undiminished 
crop yield and the composition of the cultivated 
fields lead to the belief that soil-fertility problems 
under dry-farm conditions are widely different from 
the old well-known problems under humid conditions. 
Reasons for dry-farming fertility 
It is not really difficult to understand why the 
yields and, apparently, the fertility of dry-farms 
have continued to increase during the period of re- 
corded dry-farm history — nearly half a century. 
First, the intrinsic fertility of arid as compared with 
humid soils is very high. (See Chapter V.) The 
production and removal of many successive bountiful 
crops would not have as marked an effect on arid as 
on humid soils, for both yield and composition change 
more slowly on fertile soils. The natural extraordi- 
narily high fertility of dry-farm soils explains, there- 
fore, primarily and chiefly, the increasing yields on 
dry-farm soils that receive proper cultivation. 
