Irrigation and Drainage 131 
distributed evenly through the furrows. On light soil 
difficulty is likely to be experienced with the banks’ 
cutting, causing more water to run down one furrow than 
another. When this difficulty occurs, some form of 
permanent outlet may be provided to advantage. This 
insures fairly even streams. In many places small lath 
or galvanized iron tubes are put through the bank at the 
head of each row. These are long enough to protrude a 
little on both sides of the bank. Though these tubes are 
often helpful, they are not without objections. In a 
heavy soil devices of this kind usually are not required. 
To run water the entire length of a long field is a mis- 
take even where the slope of the land permits. On flat 
fields, cross ditches usually should be not more than two 
or three hundred feet apart; even on sloping ground the 
distance should rarely exceed five hundred feet. Waste 
ditches at the bottom of the land should always be pro- 
vided, in order that use may be made of all the water that 
does not soak into the land. Allowing water to go to 
waste where it does no one good, but causes injury, cannot 
be condemned too strongly. 
When sub-irrigation is practiced, water is allowed to stand 
in deep ditches from which it soaks laterally till all the land 
is moistened. This method can be used only where a rather 
open surface soil covers a layer that prevents the water 
from percolating rapidly. Where these conditions prevail, 
sub-irrigation offers an ideal method of applying water. 
Water requirements of beets. (Plate XII) 
The amount of irrigation water required to produce a 
maximum crop of beets varies with the sunshine, wind, 
