Dry-Farming : A System of Agriculture for Countries under a Low Rainfall

by John Andreas Widtsoe

Kinds of roots

The root is the part of the plant that is found underground. It has numerous branches, twigs, and filaments. The root which first forms when the seed bursts is known as the primary root. From this primary root other roots develop, which are known as secondary roots. When the primary root grows more rapidly than the secondary roots, the so-called taproot, characteristic of lucerne, clover, and similar plants, is formed. When, on the other hand, the taproot grows slowly or ceases its growth, and the numerous secondary roots grow long, a fibrous root system results, which is characteristic of the cereals, grasses, corn, and other similar plants. With any type of root, the tendency of growth is downward; though under conditions that are not favorable for the downward penetration of the roots the lateral extensions may be very large and near the surface

Extent of roots

A number of investigators have attempted to determine the weight of the roots as compared with the weight of the plant above ground, hut the subject, because of its great experimental difficulties, has not been very accurately explained. Schumacher, experimenting about 1867, found that the roots of a well-established field of clover weighed as much as the total weight of the stems and leaves of the year's crop, and that the weight of roots of an oat crop was 43 per cent of the total weight of seed and straw. Nobbe, a few years later, found in one of his experiments that the roots of timothy weighed 31 per cent of the weight of the hay. Hosaeus, investigating the same subject about the same time, found that the weight of roots of one of the brome grasses was as great as the weight of the part above ground; of serradella, 77 per cent; of flax, 34 per cent; of oats, 14 per cent; of barley, 13 per cent, and of peas, 9 per cent. Sanborn, working at the Utah Station in 1893, found results very much the same

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.