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CHAPTER XI

ROOT HABITS OF VARIOUS MEADOW
AND PASTURE GRASSES

   The use of grasses for forage is scarcely less important than their use for the production of human food. Experiments in reseeding and improving depleted range lands have shown that a knowledge of the root habits of the seedlings, as well as those of the mature plants, is of very great importance. Large amounts of forage cannot be grown nor flower stalks and seeds produced except by plants with well-developed root systems which not only absorb sufficient water and nutrients but accumulate an abundant food supply which is again used at the end of the season of dormancy.

BROME GRASS

   Brome grass (Bromus inermis) is a perennial with creeping rootstocks or rhizomes and fine fibrous roots. It is an excellent pasture grass in the semiarid regions from Kansas to Canada and westward to Washington, in which regions many eastern grasses will not thrive.

   Root Growth during the First Year.--Plants grown at Lincoln were 14 inches tall when only 11 weeks old. The roots were abundant to a depth of 2.3 feet; a few penetrated beyond 3 feet in both lowland and upland silt loam soils. When 4 months old (Aug. 20), and the flowering stalks were beginning to appear, the grass had spread by rhizomes and produced a dense sod. The roots had formed a close network, quite filling the soil to a depth of about 2 feet. They were dark brown in color and densely clothed with root hairs, and had a great network of fine, wellbranched rootlets. The latter were several inches in length, and the tertiary branches were 1 to 2 inches long and very numerous. Some light-colored roots were intermixed with the brown ones. These were younger, shorter, and often less branched but took on the darker color and other typical root characters when more mature. Below 2 feet, roots were much less abundant. In fact, at a depth of 1.5 feet, they began to thin out considerably but were fairly numerous to the working level at 2.7 feet. Some extended 1 to 2 feet deeper. In the upland, the stand of plants was thinner and the roots were not quite so long.

   Root Habits of Older Plants.--Three-year-old plants at Manhattan, Kan., were excavated from a fine, compact loam underlaid at a depth of about 12 inches with a somewhat gravelly and sandy subsoil. 204 This gave way at 4.2 feet to solid limestone rock. Many roots extended to the rock layer where some continued growth along its upper surface. Although the root growth was densest in the first 12 inches, the soil was filled with great masses of roots and their network of branches to the rock layer. It appears that full depth of penetration was not attained, because. at Fargo, N. D., roots of this species were found to penetrate to a depth of over 4 feet when only 1 year old and to a depth of 5.5 to 6.5 feet when 2 years old. 203 Thus, brome grass rapidly produces a wonderfully efficient and deeply penetrating root system, numerous rootlets occupying every cubic inch of the soil to a depth of several feet. Because of its deeply rooting habit, it is very drought resistant and well adapted for growing in light soils and in dry climates but does well also on good moist soils. Its excellent root system doubtless goes far towards making brome grass "the best pasture grass yet found for the prairie states of the Northwest and the Pacific Northwest." 194

ORCHARD GRASS

   Orchard grass (Dactylis glomerata) is an excellent pasture grass, especially when combined with other grasses. Its habit of growing in bunches or tussocks makes it less desirable for meadows. Plots of orchard grass were grown on both lowland and upland soils at Lincoln for purposes of root examination.

   Root Growth during the First Year.--When 11 weeks old, an excellent stand of good growth, 1 foot high, characterized the grass in the lower area; that of the upland was much thinner and only 5 inches tall but of healthy appearance. Notwithstanding the great difference in aboveground development, the working depth of roots was approximately the same, 2.3 feet. Maximum penetration was about 3 feet in both areas. By August 26, the tufts or bunches of grass were provided with roots which literally filled the surface soil with great masses of tan-colored fibrous roots to a depth of nearly 2 feet, below which level they became fewer in number but were abundant to a depth of 3.2 feet. The roots were tough and rather coarse. They were well furnished with laterals 1 to 3 inches or more in length, which were branched to the second order. The ultimate rootlets were very fine. In the deeper soil, the branching was rather largely confined to one plane in the soil crevices. Some of the delicate roots reached a maximum depth of 4.4 feet. The plants in the upland plots had developed so poorly that they were not further examined.

   At Geneva, N. Y., where heavy clay loam was underlaid at a depth of 6 to 10 inches with a tenacious gravelly clay, orchard grass roots were examined during their first year of growth. 14 Fine fibrous roots filled the soil to a depth of 1 foot, a large number reached the 21-inch level, and a few were traced to a depth of 3 feet. Some of the fine roots spread horizontally more than 21 inches from the plant.

   Root Habits of Mature Plants.--Plants 2 or 3 years old at Manhattan, Kan., reached a depth practically the same as the extreme height of the grass, which was 3.5 feet. 204 The surface 6 inches of fine, compact, sandy loam was so filled with the thick fibrous mass of roots that it was very difficult to wash out all of the soil. Below 10 inches in depth, the roots were fewer, the largest part of the root growth lying within the surface foot of soil, The deeper subsoil was quite sandy. The root system bore a close resemblance to that of wheat and oats but had an even greater fibrous growth in the surface soil. The roots were tough and woody and nearly white in color.

   From these data, it may be seen that the roots of orchard grass develop rapidly, reaching depths of 2 to 3 feet by midsummer of the first season's growth. Later, as the plants continue to tiller and form the uneven sod, many new roots develop. Meanwhile, the older ones have extended well into the third and fourth foot of soil. All of the roots are well branched and furnish such an excellent absorbing system that, when pastured, this grass remains green even during a long, hot summer and late into fall.

MEADOW FESCUE

   Meadow fescue (Festuca elatior) is a common European forage grass. Like the preceding grasses it has been introduced from that country into the United States, but although well adapted to the same region as timothy and bluegrass it has never been extensively grown and holds a rank of minor importance among forage grasses in America.

   Root Growth during the First Year.--The root development of this grass was examined on lowland silt loam soil at Lincoln on June 13, when the plants were 8 inches tall but only 7 weeks old. The fine fibrous roots already had a working depth of 18 inches, and some roots extended to a maximum depth of over 2 feet.

   A second examination was made when the grass was nearly 4 months old and 8 to 10 inches tall. No flower stalks had appeared. The roots had a working depth of 3 feet, although some penetrated 8 to 12 inches deeper. The soil was quite well filled to a depth of 1.5 feet with great masses of brown roots, which were only slightly less abundant to 2 feet. The roots were very fine, the largest scarcely a millimeter in diameter and many were only one-fourth as thick. They originated in great numbers from the base of the plant, 6 to 24 or even more from a single stem. Although most of the roots pursued a course somewhat obliquely to almost vertically downward, others spread laterally more or less parallel with the soil surface or obliquely outward 3 to 6 inches before turning downward. They were exceedingly well furnished with thread-like laterals ranging from a few millimeters to several inches in length, all of which were branched and profusely rebranched, ending in hair-like termini. Many of the roots did not reach the general, working level; others penetrated far beyond. The 6 to 8 inches of root ends were not so well branched and were hairlike.

   Plants of meadow fescue at Geneva, N. Y., during their first season of growth, had roots which filled the soil to a depth of I foot and several were traced to the 32- inch level. 14 A horizontal spread of 9 inches was ascertained. It seems clear that the excellent growth made by this species during the first summer is augmented, like that of most perennials, during subsequent years. Three-year-old plants at Manhattan, Kan., reached a depth of about 4 feet. 204

BLUEGRASS

   Kentucky bluegrass (Poa pratensis) has escaped from cultivation in the prairie region, and has become an important species in the less arid parts of the grassland area. Its great economic importance as a lawn and pasture grass is well known.

   General Root Habits.--This grass propagates by means of rhizomes which lie near the soil surface. They are 1 to 2 millimeters in diameter and well branched. The dark-colored, fine, fibrous, minutely branched roots occur in such abundance that, with the creeping rootstocks, they form a dense, tough sod. Some of the roots have a wide lateral spread, often running nearly parallel with the soil surface at depths of only 2 to 3 inches for distances of 1 to 1.5 feet. Usually, they run more obliquely or even vertically downward. Root depth appears to vary considerably with soil conditions. Undoubtedly, in and climates where frequent light sprinkling is practiced, the roots are very superficial, but in deep moist subsoils, they have been found at depths of 5 to 7 feet.

   Root Growth during the First Season.--At Geneva, N. Y., in heavy clay loam, bluegrass, during its first year, made an excellent growth. 14 The dark-colored, very fibrous roots filled the soil to a depth of 12 inches, many reached a depth of 18 inches, and some very fine roots were traced to a depth of over 3 feet. The roots extended laterally about 12 inches from the base of the plant.

   Variation of Mature Roots under Different Soils and Climates.--In a light sandy soil in eastern Nebraska, bluegrass roots completely filled the soil to a depth of 2.5 feet. They were numerous to the 5-foot level, and a few reached a depth of 7 feet. The fine roots were abundantly supplied with hairlike laterals, usually less than an inch in length, but branched and rebranched to the third order. Even the root tips were well branched with rootlets 1 to 3 inches long.

   In upland clay loam soil at Lincoln, the roots were somewhat less extensive, although bluegrass sod had been in possession of the area for 2 or 3 years. The greatest root development was in the surface 2 feet of soil, but roots were fairly abundant to a depth of 3.3 feet and the longest extended to nearly 6 feet. The wide lateral spread of surface rootlets, so highly developed in the sand, was much less in clay loam.

   At the same station, in silt loam alluvial soil, the working depth was determined at 2.8 feet, although many roots penetrated deeper. A maximum penetration of 5 feet was found. A root depth of nearly 4 feet was determined for this species at Manhattan, Kan. 204 At a depth of 2 feet, however, the roots were few in number, and comparatively few extended below 18 inches. These data are scarcely in agreement with those from Wisconsin where "blue grass is eminently a surface feeder whose roots so fully occupy the soil that there is no room for the roots of other plants to associate with them." 123

   Summary and Discussion.--Summarizing, bluegrass has very fine, dark-colored, profusely and minutely branched roots, which develop so rapidly that, at the end of the first season, 12 to 18 inches of surface soil are filled with an absorbing network, and deeper portions of the root system absorb in the third foot. Lateral spread and the occupation of a few inches of surface soil are both pronounced. Mature plants extend their roots below the surface sod to depths varying from 5 to 7 feet. The root habit is greatly modified by edaphic conditions.

   The successful competition of bluegrass with native grasses in portions of the tall- grass prairie and its invasion into fields of cultivated crops, like alfalfa, are largely due to its methods of propagation, its massive root system, and its dense sod-forming habit. Bluegrass is also tolerant of light shade. It requires a rather moist climate to thrive and becomes especially dominant during seasons with an excess of rainfall, but it is not easily destroyed by drought.

   During a dry period, bluegrass ceases growth and, as a result of protracted dry periods, may even become brown and apparently dead, but upon the advent of rain, it quickly revives. Its ability to withstand trampling and its early growth in the spring as well as late in the fall make it an excellent pasture grass over wide areas. The cessation of growth during dry midsummers is very disadvantageous to the stock raiser. A study of its root development affords a clear understanding of its growth habits. It is a species exceptionally well adapted for absorption in the surface soil, though in times of drought, it must rely to a large extent upon absorption by the deeply penetrating roots.

ROOT DEVELOPMENT OF OTHER CULTIVATED GRASSES

   The preceding descriptions of four rather common meadow and pasture grasses illustrate in a striking manner the rapid growth and excellent development of the roots of cultivated grasses. In this respect, they are similar to the native species. Although the general plan of the fibrous root systems of all grasses is somewhat similar, exact study will reveal marked differences in rate of development, fineness of branching, depth of penetration, lateral spread, effici ency as absorbing organs, etc., all of which data are imperative for a thorough understanding of scientific crop production.

   In this connection, the following measurements obtained at Geneva, N. Y., are of interest. 14 The plants were grown in a rich, heavy clay loam underlaid at 6 to 10 inches in depth with a tenacious gravelly clay. They were excavated during late July or August of their first season of growth.

                       Depth to   Depth to   Depth to
                         which     which       which    Lateral
   Species               roots      many       a few     spread
                       were very    roots      roots    of roots,
                        abundant,  extended,  extended,  inches
                         inches     inches     inches

Bent grass
 (Agrostis canina)         20         25                   24
Meadow foxtail
 (Alopecurus pratensis)    18                    31        18
Red top
 (Agrostis vulgaris)       22                    40         9
Reed canarygrass 
 (Phalaris arundiiiacea)   15         25         33        15
Sheep's fescue
 (Festuca ovina)           12                    27         9
Timothy
 (Phleum pratense)         15                    34        12
Tall meadow oat grass 
 (Avena elatior)           12         21         30        24

 

GRASS ROOTS IN RELATION TO SOIL STRUCTURE
AND PRODUCTIVITY

   When the virgin prairie sod is first broken, the soil is mellow, moist, and rich and produces abundant crops. But after a few years of continuous cropping and cultivation, there occurs a great change in its physical condition. It becomes more compact and harder to till, dries more quickly than formerly, bakes more readily, and when plowed, often turns over in hard lumps and clods. After a clayey soil has been cropped for a long time, it tends to run together. It is very sticky when wet, but when dry, the adhesive characteristic almost entirely disappears. The grass roots and humus which formerly held it together are decayed and gone. When loosened by the plow, it is often easily drifted and blown away. But when sowed to grass, marked improvement occurs, for grass is a soil builder, a soil renewer, and a soil protector. Covering the land with grass is nature's way of restoring to old, worn-out soils the productivity and good tilth of virgin ones. The perfect tilth and freedom from clods, so characteristic of virgin soils, are always more or less completely restored wherever the land has supported a cover of grass for a number of years. The covering of sod prevents the puddling action of rain. As the roots develop, the soil particles are wedged apart in some places and crowded together in others. The small soil grains become aggregated into larger ones. Each year, many of the old roots die and are constantly replaced by new ones. The soil is filled with pores of the old root channels; the humus from the decaying roots helps cement soil particles into aggregates and thus lightens and enriches it. In this way, the mellow texture of the virgin soil is restored, and the accumulation of organic debris, largely from the decayed masses of old roots, adds greatly to its fertility.* (* Rewritten from Ten Eyck, Kan. Agr. Exp. Sta., Bull. 175.)


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