2 BULLETIN 1087, U. S. DE]?ARTMENT OF AGRICULTURE. 



gions because of the protection afforded to dormant or resting buds. 

 However, artificial i^rotection by means of straw has been found to 

 reduce the mortality of nonhardy plants only slightly under severe 

 winter conditions. This would seem to indicate that cold resistance 

 is an inherent characteristic and is dependent only to a slight degree 

 on the soil protection that is afforded the resting buds. It is the 

 purpose of this bulletin to present data showing more definitely the 

 root characteristics assumed by representative varieties of alfalfa 

 under stated field conditions for the relation they may have in the 

 adaptation to environmental conditions. The descriptions of root sys- 

 tems contained herein are of the well-known varieties of alfalfa 

 grown at the Redfield Field Station in South Dakota, under conditions 

 which are j)robably quite representative of a considerable area of 

 the northern Great Plains. It is recognized that with a different soil, 

 climate, and method of culture, variations may occur, but it is be- 

 lieved that the general conclusions reached in this bulletin would be 

 unchanged. A statement of the conditions under which the plants 

 were grown is deemed desirable and is included with the other data 

 jDresented. 



FACTORS TENDING TO PRODUCE MODIFICATIONS OF ROOT 



GROWTH. 



Hoot growth is influenced principally by soil, climate, cultural 

 treatment, and injuries, and to a lesser degree by many other factors. 

 Alfalfa is found growing under conditions of moisture from heavy 

 to light precipitation; on soil types ranging from stiff, heavy clay 

 to almost pure sand ; and at altitudes from below sea level to 13,000 

 feet or more above sea level. Many of the alfalfas that have been 

 introduced into the United States have been grown in different coun- 

 tries hundreds and possibly thousands of years within compara- 

 tively small areas and under peculiar soil and climatic conditions. 

 It is hardly -to be expected, therefore, that any one location can be 

 found that will provide optimum conditions for the development 

 of the root systems of all the different alfalfas. 



SOIL CONDITIONS. 



Hoot development is influenced by distribution of plant food, soil 

 moisture, soil texture, water table, and hardpan or other hard mate- 

 rial. Unusual soil formations in which there is a peculiar distri- 

 bution of plant food may cause modifications in root growth, be- 

 cause roots have a tendency to remain and develop in the areas of 

 the most favorable conditions of plant food. A number of experi- 

 ments have been reported showing the influence of such plant-food 

 distribution on root development. 



