186 DRY-FARMING 
ing a small amount of sodium nitrate it was reduced 
to 585 pounds. If so large a reduction could be 
secured in practice, it would seem to justify the use of 
commercial fertilizers in years when the dry-farm 
year opens with little water stored in the soil. 
Similar results, as will be shown below, were obtained 
by the use of various cultural methods. It may, 
therefore, be stated as a law, that any cultural treat- 
ment which enables the soil-water to acquire larger 
quantities of plant-food also enables the plant to 
produce dry matter with the use of a smaller amount 
of water. In dry-farming, where the limiting factor 
is water, this principle must be emphasized in every 
cultural operation. 
Methods of controlling transpiration 
It would appear that at present the only means 
possessed by the farmer for controlling transpiration 
and making possible maximum crops with the mini- 
mum amount of water in a properly tilled soil is to 
keep the soil as fertile as is possible. In the light 
of this principle the practices already recommended 
for the storing of water and for the prevention of the 
direct evaporation of water from the soil are again 
emphasized. Deep and frequent plowing, preferably 
in the fall so that the weathering of the winter may be 
felt deeply and strongly, is of first importance in 
liberating plant-food. Cultivation which has been 
