158 DRY-FARMING 
ducing evaporation. * Fortier, in the experiments in 
California to which allusion has already been made, 
showed the greater value of deep cultivation. Dur- 
ing a period of fifteen days, beginning immediately 
after an irrigation, the soil which had not been 
mulched lost by evaporation nearly one fourth of 
the total amount of water that had been added. A 
mulch 4 inches deep saved about 72 per cent of the 
evaporation; a mulch 8 inches deep saved about 88 
per cent, and a mulch 10 inches deep stopped evapo- 
ration almost wholly. It is a most serious mis- 
take for the dry-farmer, who attempts cultivation 
for soil-moisture conservation, to fail to get the best 
results simply to save a few cents per acre in added 
labor. 
When to cultivate or till 
It has already been shown that the rate of evap- 
oration is greater from a wet than from a dry surface. 
It follows, therefore, that the critical time for pre- 
venting evaporation is when the soil is wettest. 
After the soil is tolerably dry, a very large portion 
of the soil-moisture has been lost, which possibly 
might have been saved by earlier cultivation. The 
truth of this statement is well shown by experiments 
conducted by the Utah Station. In one case ona soil 
well filled with water, during a three weeks’ period, 
nearly one half of the total loss occurred the first, 
while only one fifth fell on the third week. Of the 
