310 FORAGE PLANTS AND THEIR CULTURE 



373. Humidity relations. Alfalfa is especially adapted 

 to regions possessing a semi-arid climate, and in such areas 

 succeeds well in nearly all types of soil, and through a 

 wide range of normal annual temperatures. In moister 

 climates, such as much of Europe and the eastern United 

 States, success is rarely secured excepting where soil 

 conditions are unusually favorable. In arid regions the 

 plant will withstand great heat without injury, but a 

 combination of heat and humidity is decidedly harmful. 

 On this account, success with the crop in tropical or sub- 

 tropical regions can be secured only where the climatic 

 conditions are such as to render artificial irrigation 

 necessary. 



Even in temperate climates, wet weather is more 

 injurious than drought. According to Stebler, little 

 success is secured in Europe where the annual rainfall 

 exceeds 32 to 36 inches. In the United States, however, 

 marked success is obtained on certain soils in Mississippi 

 and Alabama, where the annual rainfall exceeds 50 inches, 

 but in general an excess of annual rainfall over 40 inches 

 is decidedly unfavorable to the plant. 



374. Soil relations. Under semi-arid conditions of 

 climate, alfalfa succeeds in most types of soil excepting 

 those heavily charged with alkali. On account of its 

 great root development, deep soils are especially suitable 

 to alfalfa. Good drainage is also essential, as alfalfa 

 roots will not grow in water-logged soils. 



Under humid climatic conditions, alfalfa is especially 

 intolerant of adverse soil conditions. In such climates, 

 its culture is rarely successful, except on deep, fairly fer- 

 tile, well-drained soils rich in lime. A few types of soil 

 rich in potash, but poor in lime, have also been found suit- 

 able, but liming increases the crop even in such soils. 



