320 FORAGE PLANTS AND THEIR CULTURE 



382. Life period. The life period of the alfalfa plant 

 varies according to conditions and variety. In the semi- 

 arid regions of America, authenticated cases of fields 

 twenty-five years old are recorded, and much longer ages 

 are asserted. In the more humid East, fields rarely per- 

 sist more than five years, largely owing to the ingress of 

 weeds. 



In Europe fields under ordinary conditions are reputed 

 to last four to six years ; under favorable conditions, nine 

 to twelve years ; and in exceptional cases, fifteen to 

 twenty years, or very rarely thirty years. 



Arabian alfalfa is a short-lived variety, few individuals 

 persisting as much as four or five years even under favor- 

 able conditions. 



Yellow or sickle alfalfa lives, according to Werner, 

 six or eight years. 



Variegated alfalfa is perhaps as long-lived as ordinary 

 alfalfa, but records are lacking. 



Alfalfa yields are heaviest from plots three years or 

 more old, and tend to decline by the seventh year. Crud 

 in France secured the heaviest yields in the third and 

 fourth years followed by. a gradual decline to the seventh 

 year. Walz in Germany obtained maximum yields in 

 the third, fourth, fifth and sixth years, a gradual dimi- 

 nution of the yield following in the next three years. 



383. Roots. The roots of alfalfa are remarkable for 

 their length and the depth to which they penetrate the 

 soil. Under ordinary conditions they will descend to a 

 depth of 6 feet, and authentic instances are recorded 

 where they have reached a depth of 15 feet. Less 

 well-authenticated reports of roots 25 to 45 feet in length 

 have been made, while Stebler. and Schroter cite Bonnet's 

 record of a tap root 66 feet long. In ordinary alfalfa the 



