840 FORAGE PLANTS AND THEIR CULTURE 



(Quantities of water used are expressed in acre-inches, 

 of alfalfa are expressed in pounds to the acre.) 



Yields 



404. Care of an alfalfa field. After a good stand of 

 alfalfa has been secured, its subsequent treatment apart 

 from harvesting, and in dry regions, irrigating should 

 be mainly to hold weeds in check. The worst weeds that 

 invade alfalfa fields are blue-grass in the north, and Ber- 

 muda-grass and crab-grass southward. Other weeds are 

 held largely in check by the regular mowings, but the weedy 

 grasses can be eradicated only by careful harrowing. 



Blue-grass and Bermuda are both perennials, and grad- 

 ually kill out the alfalfa as the grass sod extends. Usually 

 this requires three or four years. Crab-grass grows most 

 luxuriantly in moist hot weather, under which condi- 

 tions alfalfa languishes, so that crab-grass often com- 

 pletely destroys an alfalfa field in the Southern States in 

 a single season. 



The best implement to destroy grass in alfalfa is the 

 spike-tooth harrow, especially the form with broad chisel- 

 shaped teeth. Where the ground is very hard, it is neces- 

 sary first to use a disk harrow. This implement often 

 splits up the crowns of the alfalfa plants, but this injury 



