54 BuLivETiN 78 



acre we would obtain 3,000,000 plants if all germinated. Estimating 

 that under field conditions only two-thirds of the seeds produce 

 plants, we would have 2,000,000 seedlings, or about 45 plants to 

 the square foot. This number would be considered a good stand. 

 As the plants grow older they crowd each other and some die. 

 With an original stand of 45 plants to the square foot, more than 

 half usually succumb during the first year. At two years 11 plants 

 to the square foot is an abundant stand, and this will be normally 

 reduced to an average stand of 5 to 6 plants by the end of 4 or 5 

 years. 



In dr}' farming, the stand must necessarily be thinner on the 

 ground (2 or 3 plants to the square foot) in order that each plant 

 may secure an ample supply of water. For this reason many 

 growers of alfalfa in f-^miarid sections find it best to sow not more 

 than 8 to 10 pounds of seed to the acre. On the other hand, in 

 humid sections where the danger of weeds is great, 20 pounds to 

 the acre is not too much. 



When it is intended that the field be devoted largely to the 

 production of seed, not more than 10 to 12 pounds should be sown. 



Varieties . — The natural adaptability of alfalfa and the wide range 

 of soil and climatic conditions within which it has been grown, have 

 resulted in many distinct types and races. Whenever alfalfa is 

 grown for a long series of years in a given region from seed pro- 

 duced locally, it slowly becomes acclimatized. Those mixtures or 

 variations which are best suited to the conditions prevailing flourish 

 and crowd out the less favored individuals. Strains acclimatized 

 to a given regioti are called regional varieties. In transferring seed 

 from one country to another the measure of its success is usually 

 proportional to the degree of similarity between the climatic factors 

 of its old and new homes. However, unless we have definite infor- 

 mation as to the exact origin of an imported strain, the length of 

 time that it had been planted in that given region, and the local 

 conditions under which it was grown, we must be very uncertain 

 as to the likelihood of its value in Arizona. Not all strains of alfalfa 

 from Turkestan, for example, have an equal value or climatic 

 adaptation. Local conditions and the number of years they had 

 been grown in that region will largely govern their quality. 



As an example of an imported strain which has proven valuable, 

 Peruvian alfalfa may be mentioned. The seed of this strain is now 

 being produced in large quantities by the Yuma alfalfa seed 

 growers. It is an upright, vigorous and very productive sort with 

 narrow leaves and light purple flowers. Peruvian alfalfa is inclined 



