52 
BULLETIN 1026, U. S. DEPARTMENT OF AGRICULTURE. 
and other row crops are irrigated by furrows between the rows. The 
method of flooding from field laterals, used on nearly two-thirds of 
the total irrigated area of the valley, does not vary essentially from 
the general practice. Supply ditches are located at the margin of the 
field; small laterals from these extend into the field; and through 
openings in these field laterals the water flows out over the land. In 
general, the effort is so to fit the layout of the supply ditches and 
field laterals to conditions of soil and topography that with a head 
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IRRIGATED PER 24-HOUR DAV 
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Fig. 4. — Relation between the head, used and the area irrigated per 24-hour day 
for flood and furrow irrigation. 
of from 2 to 3 second-feet a thorough irrigation may be secured 
with a minimum expenditure of time and work. For this reason the 
details of practice vary almost with the number of fields. 
Supply ditches are carried along the margin of the field or follow 
ridges, the former location being preferred if conditions are at all 
suitable as less space is required and cultivating and harvesting may 
be carried on with less difficulty. Practically all these ditches are 
