14 BULLETIN 913, U. S. DEPARTMENT OF AGRICULTURE. 
used economically. On light soils a small stream can not be dis- 
tributed evenly over the fields, and, whatever the type of soil, irri- 
gating with a small stream takes much more time than should be 
used for that purpose. When a farmer has a large enough acreage 
to give him a stream of 2 or more cubic feet per second he can use 
a continuous flow to better advantage, since it is a large enough 
stream to work with, and he can rotate the water among his own 
fields. 
Under rotation systems the various farmers under a canal receive 
water in turn, and in this way each gets a larger stream than if he 
received a continuous stream, and he can use the water to good ad- 
vantage and get through with it. leaving him more time for other 
work. The quantity of water received is regulated by the length of 
time a stream is used by each farmer, rather than by the size of the 
stream. This system has the disadvantage that the farmer can not 
always get water just when he thinks he needs it, but usually rota- 
tion schedules are arranged to fit, as nearly as possible, the needs 
of the crops grown, and the advantages of having large streams and 
doing the watering quickly more than offset any disadvantage of 
* waiting for turns. 
The ideal system is to get water on demand. In such cases a 
water supply is like a bank account. The farmer has a credit of his 
season's supply and can draw as he needs it. This system can be 
adopted only where storage facilities are available for holding the 
water until it is called for. 
Usually the farmer will have no choice as to which system he 
will work under, except that he may choose where he will settle, 
and keep this point in mind in making his choice. If a farmer is 
acquiring land under an established irrigation system, local inquiry 
as to results under the system will be the best means of determining 
the satisfactory character of a distributing system, as well as the 
value of the water supply. 
WASHINGTON : GOVERNMENT PRINTING OFFICE : 1920 
