322 FORAGE PLANTS AND THEIR CULTURE 



suited to alfalfa, though fair success can be secured where 

 an impermeable layer occurs a foot or so beneath the sur- 

 face. While alfalfa roots will penetrate a firm subsoil, 

 they apparently possess no greater ability in this respect 

 than most trees and shrubs. 



The growth of the root on young plants is very rapid. 

 Hays at the Minnesota Experiment Station found them 

 to be 3 feet long in plants when 2 months old, and 

 6J feet when 3 months old. Headden in Colorado 

 reports roots 9 feet long on plants 9 months old. 



Alfalfa roots have sometimes been reported as being 

 destructive to drain tiling. Cook in Ohio records a case 

 where the roots in a field seven years old had filled up 

 thirty-two feet of three-inch drain tile placed three feet 

 beneath the surface. It is very doubtful, however, 

 whether alfalfa left only three years will in any way affect 

 the tiles. 



384. Relations to soil moisture. Alfalfa roots will 

 penetrate but a few inches deeper than the permanent 

 water table. Further downward growth is probably 

 mainly due to lack of air. It is on account of this moisture 

 relation that alfalfa should be planted only on deep, well- 

 drained soil, as other crops thrive better where the water 

 table is shallow. 



According to Fortier, alfalfa on irrigated land does not 

 do well after the third year. He thinks this is due to the 

 fact that the water table is kept too high during the spring 

 and summer. 



Alfalfa does not endure being covered by flood waters. 

 During the growing season it may be destroyed if covered 

 by water for twenty-four hours. When dormant, how- 

 ever, it will withstand a similar flooding for a week or 

 more. 



