300 DRY-FARMING 
at least every third or fourth year is likely to be 
dangerous in years of deficient rainfall. 
This review of the question of dry-farm fertility 
is intended merely as a forecast of coming develop- 
ments. At the present time soil-fertility is not giving 
the dry-farmers great concern, but as in the countries 
of abundant rainfall the time will come when it will 
be equal to that of water conservation, unless indeed 
the dry-farmers heed the lessons of the past and adopt 
from the start proper practices for the maintenance 
of the plant-food stored in the soil. The principle 
explained in Chapter IX, that the amount of water 
required for the production of one pound of water 
diminishes as the fertility increases, shows the inti- 
mate relationship that exists between the soil-fer- 
tility and the soil-water and the importance of main- 
taining dry-farm soils at a high state of fertility. 
