88 DRY-FARMING 



no determinations were made of the depth of the 

 roots in later years, though it had undoubtedly 

 increased. Alfalfa was the deepest rooted of all 

 the crops studied by the American stations. Potato 

 roots filled the soil fully to a depth of three feet; 

 sugar beets to a depth of nearly four feet. 



In every case, under conditions prevailing in the 

 experiments, and which did not have in mind the 

 forcing of the roots down to extraordinary depths, 

 it seemed that the normal depth of the roots of ordi- 

 nary field crops was from three to eight feet. Sub- 

 soiling and deep plowing enable the roots to go 

 deeper into the soil. This work has been confirmed 

 in ordinary experience until there can be little ques- 

 tion about the accuracy of the results. 



Almost all of these results were obtained in humid 

 climates on humid soils, somewhat shallow, and 

 underlaid by a moiv or less infertile subsoil. In 

 fact, they were ol^tained under conditions really 

 unfavorable to plant growth. It has been explained 

 in Chapter V that soils formed under arid or semi- 

 arid conditions are uniform^ deep and ])(jrous and 

 that the fertility of the subsoil is, in most cases, 

 practically as great as of the topsoil. There is, 

 therefore, in arid soils, an excellent opportunity 

 for a comparatively easy penetration of the roots 

 to great depths and, l^ecause of the available fertility, 

 a chance throughout the whole of the subsoil for 

 ample root development. ^loreover, the porous 



