Although these results are not concordant, they show that the weight of the roots is considerable, in many cases far beyond the belief of those who have given the subject little or no attention.  It may be noted that on the basis of the figures above obtained, it is very probable that the roots in one acre of an average wheat crop would weigh in the neighborhood of a thousand pounds—­possibly considerably more.  It should be remembered that the investigations which yielded the preceding results were all conducted in humid climates and at a time when the methods for the study of the root systems were poorly developed.  The data obtained, therefore, represent, in all probability, minimum results which would be materially increased should the work be repeated now.

The relative weights of the roots and the stems and the leaves do not alone show the large quantity of roots; the total lengths of the roots are even more striking.  The German investigator, Nobbe, in a laborious experiment conducted about 1867, added the lengths of all the fine roots from each of various plants.  He found that the total length of roots, that is, the sum of the lengths of all the roots, of one wheat plant was about 268 feet, and that the total length of the roots of one plant of rye was about 385 feet.  King, of Wisconsin, estimates that in one of his experiments, one corn plant produced in the upper 3 feet of soil 1452 feet of roots.  These surprisingly large numbers indicate with emphasis the thoroughness with which the roots invade the soil.

Depth of root penetration

The earlier root studies did not pretend to determine the depth to which roots actually penetrate the earth.  In recent years, however, a number of carefully conducted experiments were made by the New York, Wisconsin, Minnesota, Kansas, Colorado, and especially the North Dakota stations to obtain accurate information concerning the depth to which agricultural plants penetrate soils.  It is somewhat regrettable, for the purpose of dry-farming, that these states, with the exception of Colorado, are all in the humid or sub-humid area of the United States.  Nevertheless, the conclusions drawn from the work are such that they may be safely applied in the development of the principles of dry-farming.

There is a general belief among farmers that the roots of all cultivated crops are very near the surface and that few reach a greater depth than one or two feet.  The first striking result of the American investigations was that every crop, without exception, penetrates the soil deeper than was thought possible in earlier days.  For example, it was found that corn roots penetrated fully four feet into the ground and that they fully occupied all of the soil to that depth.

On deeper and somewhat drier soils, corn roots went down as far as eight feet.  The roots of the small grains,—­wheat, oats, barley,—­penetrated the soil from four to eight or ten feet.  Various perennial grasses rooted to a depth of four feet the first year; the next year, five and one half feet; 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.