IRRIGATION IK NORTHERN COLORADO. 
53 
equipped with concrete or wooden turnouts to supply the field laterals. 
For alfalfa the field laterals are permanent, but for annual crops 
they are made each spring with a ditching plow, and after irrigation 
is completed they are plowed flat again so that harvesting machinery 
JULY 
20 
AUGUST SEPTEMBER 
10 20 10 20 
2 

Fig. 
-Irrigation of alfalfa. Water requirements of 988 acres in 1916 and 
of 686 acres in 1917. 
may pass over them without difficulty. If the field to be irrigated is 
smooth and has a uniform slope, the field laterals are made parallel, 
75 to 200 feet apart, and oblique to the main slope of the land. In 
this case the water from one lateral irrigates the field down to the 
