220 STORRS AGRICULTURAL EXPERIMENT STATION. 
and with the same manuring, but without the irrigation, only 
ordinary crops could be obtained. 
A large and variable quantity of water is evaporated directly 
from the soil. The amount of this depends upon several con- 
ditions, the chief of which are the state of the weather, the 
kind of crop on the soil, the amount of cultivation, and whether 
or not the soil is mulched. In times when rainfall is insuffi- 
cient for the best growth of crops the atmospheric conditions are 
usually such as to favor the evaporation of moisture from the 
soil. The amount of evaporation that takes place depends upon 
the amount of wind that may be blowing over the soil, and the 
degree of saturation of the air. Meteorologic data showing the 
relative humidity of the air frequently indicate that on hot, 
dry days the air contains as low as from twenty to fifty per 
cent. of its water-holding capacity. Under such conditions, 
especially in connection with winds, the moisture evaporates 
from the soil very rapidly. ‘The shade afforded by crops like 
grass and small grains tends to lessen the amount of evapora- 
tion from the soil, while crops which do not shade the ground 
as much furnish conditions more favorable for the escape of 
moisture. It is a well-known fact that mulch in the form of 
coarse hay, straw, etc., tends to prevent the escape of moisture. 
This, together with the cleaner fruit that results, is one of the 
reasons for using such materials on strawberry fields. Frequent 
stirring of the surface soil by cultivation has much the same 
effect in preventing the escape of moisture as the direct use of 
mulch. In the experiments by the writer, on the evaporation 
of moisture from heavy loam and light loam soils, the soils in 
a part of each series were frequently stirred at the surface, 
while the others were not stirred. The average loss of mois- 
ture from the soil not stirred was equal to one and one-third 
inches, while the average loss from the stirred soil was three- 
quarters of an inch. This means that not far from twice as 
much water was evaporated from the soil left ina naturally 
compact condition over that lost where the surface was mulched 
by frequent stirring. | 
It is frequently the case that plants require a very large 
amount of water during a short period of time at certain sea- 
sons of the year. ‘This is especially true when they are 
developing fruit. An abundant supply of water just before 
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