246 IRRIGATION PRACTICE 



The furrows are usually made after seeding but before 

 the plants come up, by the use of special implements 

 described in Chapter XX. Shallow furrows, usually 5 

 inches deep and from 6 inches to 3 feet apart, are ordi- 

 narily employed. Their length varies from 150 to 600 feet, 

 depending on the slope, the nature of the soil and various 

 other conditions. Long furrows are of doubtful value, 

 for the upper end of the furrow receives water for a longer 

 time than does the lower end, and, consequently, in long 

 furrows the upper end may be over-irrigated when the 

 lower end has received just enough. Shorter furrows 

 obviate this danger, at least in part. (Figs. 58, 59.) 



156. Time of irrigating wheat. The time of irriga- 

 tion, one of the most important factors in the economical 

 use of water, depends in part upon the distribution of the 

 rainfall throughout the year. Land for spring grain is 

 especially suitable for fall and winter irrigation. Such 

 lands, when plowed in the early fall and given a good 

 soaking in the fall, will contain much stored water in the 

 spring to germinate the seed and to maintain the young 

 plants far into the early summer. However, fall and win- 

 ter irrigation is to be considered only when the natural 

 winter precipitation is insufficient to saturate the soil to 

 a depth of 8 to 10 feet. It is especially in districts where 

 the precipitation comes largely in spring and the growing 

 season, and where the winter and fall are dry, that irri- 

 gation during the dormant season is of much value. 



When the soil enters the spring in a somewhat dry con- 

 dition, it becomes necessary to provide by irrigation the 

 water needed for germinating the seed. This may be 

 accomplished by applying a thorough irrigation to the 

 soil before seeding, after which the land is plowed, 

 then sown to the crop. The objection to this method is 



