270 



IRRIGATION PRACTICE 



the land, immediately after seeding, is "laid off," ''marked" 

 or furrowed. The furrows thus made become permanent, 

 and last usually as long as the field is used. They may 

 become partly filled from year to year with the sediment 

 carried by irrigation water, but this is removed by the 

 annual cleaning. The method of applying water by fur- 

 rows is the same for alfalfa as for other crops. (Fig. 67.) 



i 



FIG. 67. Plan of irrigating an alfalfa field in Colorado. 



Perhaps 5 per cent of the total irrigated area of alfalfa 

 is sub-irrigated by natural means, as already explained. 



168. Time to irrigate alfalfa. If the fall and winter 

 rainfall is insufficient to saturate the soil, fall or winter 

 irrigation of alfalfa, especially if the winters are mild and 

 open, has been found quite satisfactory. It is imperative, 

 however, that water applied to alfalfa in the fall or winter 

 be made to soak into the soil, for if water stands on the 

 soil, in winter, the crop will probably be injured. Water 

 should not be applied in the fall until some time after 



