The Storage and Use of Soil Moisture 
quires more water than can be supplied by capillarity. Plants 
will suffer and die under extreme conditions after having used 
the available water within reach of the roots, even tho there is 
additional water in the soil immediately below. Under a system 
of alternate cropping and summer tilling we have found an ac- 
cumulation of water just below the feeding zone of the crops. 
During dry seasons when the crops have been suffering for mois- 
ture this water did not move upward by capillarity in sufficient 
quantity to be of material benefit to the crop. There is no evi- 
dence that it will replace to any considerable extent during an 
interval of even several months the water removed from an upper 
soil zone. This is true on soils separated by a considerable dis- 
tance from a supply of free water, as sheet water. Where there 
is a constant supply of free water, there will be a rather rapid 
movement of water for a certain distance thru the soil, depend- 
ing upon the type and compactness of the soil. 
The frequent, rapid drying of several inches of soil at the sur- 
face has in some cases been accounted for thru the quick move- 
ment of water by capillarity. It seems to indicate a more rapid 
movement than is found in the lower soils. There is, doubtless, 
an increased movement due to higher temperature, but the greater 
circulation of air in the soil near the surface is a large factor In 
the rapid drying of surface soils. 
GRAVITATIONAL WATER. 
As a soil becomes more and more nearly saturated, it reaches 
the point where gravity exerts a stronger pull than surface ten- 
sion. Water then begins to move downward thru the soil and 
tends to connect with the ground water or sheet water below. 
When the ground water is at a great depth, as it is on most of 
the table-lands, it is decidedly doubtful if any surface water 
ever reaches it. When the surface soil becomes oversaturated 
with water, the downward movement of the water continues 
until, by distributing the water thru a larger body of soil, the 
force of gravity is finally equalized by the capillary power of the 
soil. 
MAXIMUM WATER-HOLDING CAPACITY OF A SOIL. 
The maximum water-holding capacity of a soil is the amount 
of water that soil will retain against the pull of gravity. When 
water is added to a soil in sufficient amount, the films of water 
around each soil particle become thickened, and the small spaces 
between the soil particles filled with water. In the addition of 
