194 IRRIGATION FARMING. 



is augmented by the run-off from the upper check. The 

 irrigating ditches frequently replace cross levees, so 

 that water can be admitted to a check from both sides 

 at once. When the average time required to fill 

 checks on sandy soils exceeds three hours, it may 

 generally be assumed that water is wasted. Either 

 the checks are too large or there is not enough water 

 turned in. Heavy soils, however, do not take up 

 water rapidly, and, aside from requiring more time to 

 absorb water, they do not permit its flow to subsoils so 

 readily as do sandy soils, consequently more time may 

 be allowed to fill a check in clayey soil without undue 

 waste. Twenty-four hours should be regarded as the 

 permissible limit. 



Checks are occasionally very large. One was seen 

 in service having an area of sixty acres, but in this 

 instance the land was exceptionally level. The water 

 supplied to it was reported to have been as great as 

 250 second-feet. Such areas in one check are never 

 advisable and are merely temporary features of a grow- 

 ing system. Eight to ten acre checks are large, and 

 those of two to five acres are generally preferred. 



Embankments around the checks may be either 

 permanent or temporary. The latter are rare. Per- 

 manent check levees are made of two types, either with 

 very steep sides and narrow tops, so as to occupy as 

 little space as possible, or very broad and flat, so as not 

 to interfere with farming operations. The flat embank- 

 ment becomes a part of the cultivated area and gen- 

 erally is the most produ<5live part of the irrigated field. 

 It is constru(5led by scraping up material from a broad 

 area on both sides if the ground is nearly level, or from 



