J. E. Weaver

Effects of Excessive Natural Mulch on Development, Yield, and Structure of Native Grassland

1. An upland prairie, undisturbed by mowing, grazing, or burning for 15 years, was studied. About 80% was covered with a nearly pure stand of Andropogon gerardi. Similar stands of Panicum virgatum and Sporobolus heterolepis each occupied about 9%. 2. A dense natural mulch, 4.5-8 inches deep and weighing 6-9 tons per acre, covered the deep loam soil. The mulch intercepted much precipitation but promoted more rapid infiltration of water which reached the soil and greatly retarded evaporation. It increased the organic matter of the surface soil 1.5-2% and nitrogen content 0.1% of its oven-dry weight. 3. Roots and rhizomes grew thickly below the mulch and mellowed the surface soil. Pore space was 61.7%, and volume-weight was 0.97. 4. Soil temperatures 22⚬-28⚬ F. lower under the mulch in May delayed growth about 3 weeks compared with plants where the mulch had been removed. Production of flower stalks was considerably later in all mulched grasses and also less in Andropogon. Flower stalks were abundant on all unmulched grasses. 5. Yields in June, July, and August were 53, 26, and 29% less from mulched stands of Andropogon, and 57, 55, and 26% less in Panicum than those from unmulched stands. 6. Consequences of the effects of the mulch upon the environment were the production of a nearly pure, but some-what thinner than normal, stand of Andropogon. The understory characteristic of upland prairie had all but disappeared. The usual mid grasses of upland were few or none. Only a few of the taller forbs remained. 7. Dense stands of Panicum with forbs characteristic of very moist sites were typical. Between the large bunches of prairie dropseed the deeply mulched soil was usually free of vegetation.

Prairie Plants and Their Environment: A Fifty-Year Study in the Midwest

Some of the problems presented by natural vegetation are discussed, and the importance of grassland utilization is emphasized. Subjects considered included changes wrought by soil types, shrub and tree growth, moisture amounts, grazing practices, erosion and temperature. 2 bibliographies and a subject index are included. [From Abstr. 49: 74730]-M.R.H. Other CABI sites 

Classification of Root Systems of Forbs of Grassland and a Consideration of Their Significance

Plants other than grasses constitute an important part of the native grasslands of North America. M\4ost of these are forbs, a few are shrubs and half-shrubs. Probably 85 to 90 percent of the forbs are perennial and most are as deeply rooted and many far more deeply rooted than the grasses. Their number varies considerably from place to place. In the prairie of the central part of the North American Lowland and on the hard lands and sandy soils of the Great Plains they compose, perhaps, between 5 and 15 percent of the vegetation. They are least abundant in the drier habitats. A recent summary of the community root habits of grasses and an interpretation of the findings included a discussion of soils and climate of each of these extensive areas (Weaver 1958). Hence this ileed not be repeated here. Suffice it to say that in mixed prairie westward the drier air and decreased water content of soil become limiting factors for growth. Forbs decrease gradually in number, size of individuals, and in the extent of their groupings in societies. This condition prevails despite the fact that the more mesic species of prairie are largely replaced by more xerophytic ones of the Great Plains. Forbs accommodate themselves not only to the climate but also to the environment imposed upon them by the grasses. On lowland prairie most forbs are tall. They grow even more rapidly than the grasses and may for a long time or continuously overtop them. Many other species flourish oni upland true prairie where they form extensive societies. Much competition occurs between grasses and forbs, not only for light but also for water and nutrients. Roots of most grasses occupy only the first 4 to 6 feet of soil. Usually forbs are more deeply rooted. Their roots have rates of growth not unlike those of grasses and depths of 3 to more than 4 feet may be attained during the first growing season and 8 to 15 feet at maturity. Hence, they may absorb partly below the root zone of grasses and thus lessen root competition. Perhaps 90 percent of the abundant forbs, like most prairie grasses, are not only perennial but have a life span extending over a long period of years. The root habits of a large number of species of forbs have been examined during a period of several years throughout a wide territory from western Iowa, through Nebraska and Kansas, to the mountains of Colorado. Nearly all of the root systems studied were those of mature perennial plants, undisturbed by grazing. Nearly always 3 to 8 plants of a species were examined. Drawings were made simultaneously with the excavating of the roots and always to exact measurements. In the drawings the roots were arranged as nearly as possible in their natural position in a vertical plane. At each examination the work extended over a field sufficiently large, sometimes several square miles in extent, so that the effects of any local differences in soil texture or structure were largely eliminated.

Soil‐Root Relationships of Certain Native Grasses in Various Soil Types

INTRODUCTION Knowledge of the soil as a medium for the growth of roots has increased very greatly in the past three decades. Earlier studies on the root depth and distribution of native Midwestern range and pasture grasses were made with only minor consideration of specifie soil types or soil horizons The objectives of these early studies were to ascertain the general relationships of roots to soil and to each other as regards spread, depth, and degree of development in the same community and in different and widely separated units of vegetation. Some attention was given to the response of root systems to the great drought (Weaver & Albertson 1943). These studies formed a background for similar studies of crop plants With the rapid development of soil science and much emphasis on the role of vegetation, especially grasses, in soil formation, a distinct need has arisen for a better understanding of the intimate relations of roots and soil. A beginning was made by Hanson & Whitman (1938) in their study of the characteristics of major grassland types in western North Dakota. They observed the abundance and depth of roots in the several soil types. Study has been made of the quantities of organic materials provided to the soil by the mass of grass roots, and the rate at which they are formed (Weaver & Zink 1946; Weaver, Hougen, & Weldon 1935). The quantity of living underground materials, especially in the upper portion of the soil, has been ascertained (Weaver & Harmon 1935; Shively & Weaver 1939). Some information on the length of life of individual roots has been obtained (Weaver & Zink 1946a) as well as the length of time required in grassland for roots to decompose and return to the soil (Weaver 1947). The effects of grazing on the root systems of several range grasses have also been ascertained (Weaver & Darland 1947). A new method has been devised which consists of obtaining representative samples of entire root systems , of studying the intimate relations of roots and soils, and of measuring root production quantitatively at various soil levels. This, together with more exact mapping of soils, a better understanding of the relationships of one soil type to another, and especially the greater accuracy and detail with which soil profiles are now described, makes it possible to ascertain more definite relationships between the roots of grasses and the soil in …

Flood plain vegetation of the central Missouri valley and contacts of woodland with prairie.

So profoundly has this river modified the effects of the general grassland climate that in many places prairie has given way to woodland and forest. Several distinct forest communities along the river in southeastern Nebraska and adjacent parts of Kansas, Missouri, and Iowa extend for short distances over the uplands, but farther along the major streams. Most of the trees and shrubs of this forest are near the extreme western limit of their range. The extreme outposts of the forest are represented by relatively few species of trees and shrubs along the creeks and sheltered ravines which more or less dissect the hillv and rolling portions of the prairie.

Relation of Root Distribution to Organic Matter in Prairie Soil

1. A typical square meter of vegetation was selected in the upland, Andropogon scoparius prairie on Lancaster loam soil, near Lincoln, Nebraska, and another in the lowland, A. furcatus prairie on the Wabash clay loam soil of the floodplain of the Missouri River. 2. The surface soil was removed in 6-inch layers and the deeper soil in foot sections to the depth of root penetration; the roots and rhizomes were carefully removed by washing, and their dry weights, nitrogen contents, and organic contents determined. 3. Water content of soil and atmospheric factors affecting plant development were measured and rate of growth of the vegetation was determined. Root habits of the plants excavated were noted. 4. The soils varied so uniformly in texture, structure, and fertility with depth, that (except in buried surface layers) root distribution was of the usual type found for these species over a wide range of prairie soils. 5. In the Lancaster loam 60 per cent of the underground parts of the dominant grass was found in the surface 6 inches; the remainder of the root system was distributed to a depth of 4 feet. In the Wabash clay loam 68 per cent of the underground parts (60 per cent excluding rhizomes) was found in the surface 6 inches; the remainder of the root system extended to the depth of 7 feet and nearly to the water table. 6. The hygroscopic coefficient and moisture equivalent of each section of the soil profile were determined as indexes of the texture. The volume-weight of the soil in the undisturbed field condition was determined. From the volume-weight, specific gravity, and field moisture content at the time of sampling, it was possible to calculate the pore space, space occupied by water, and air space in each section of the soil. 7. Volume-weight in the Lancaster loam increased gradually from 1.12 in the surface 6 inches, where an abundance of roots, rhizomes, and dead organic matter filled the soil, to 1.64 in the fourth foot, where both living roots and dead organic matter were relatively sparse. 8. Volume-weight in the Wabash clay loam increased gradually (except in buried surface soils) from 1.05 in the first 6 inches to 1.33 in the seventh foot. This was accompanied by a gradual decrease in both living root materials and dead organic matter. 9. Pore space in the surface 6 inches of Lancaster loam constituted 57 per cent of the volume of the soil. On an average 25 per cent was occupied by water and 32 per cent by air. It decreased with depth to 39 per cent at 4 feet, where 19 per cent was occupied by water and 20 per cent by air. 10. Pore space in the surface 6 inches of Wabash clay loam occupied 60 per cent of the soil volume. On an average 32 per cent was filled with water and 28 per cent with air. It decreased regularly with depth (except for buried surface layers) to about 51 per cent in the seventh foot, where water occupied 41 per cent and air only 10 per cent. 11. The organic matter and nitrogen content of the roots in the upland soil were somewhat higher than in the lowland, especially in the surface 6 inches. 12. The composition of the rhizomes in the lowland was determined separately; their organic matter and nitrogen content were greater than in the roots, owing to the storage of food reserves. 13. The percentage of organic matter and nitrogen in each layer of the soil was determined, and the weight of each per square meter of soil calculated. 14. The ratio of soil organic matter to nitrogen varied in the Lancaster loam from 20 in the surface soil to 8.3 in the fourth foot, a variation typical of upland prairie soils. 15. The ratio of organic matter to nitrogen in the Wabash clay loam showed variations corresponding to the variations in the organic content at different depths. This indicates that the strata of high organic content had accumulated a surface type of organic matter during intervals in the silting process by which the present soil has been built up. 16. Except in the surface 6 inches of soil, there is an approximately linear relation between the amount of root material and the amount of soil organic matter in the various soil horizons. 17. In the surface soil the presence of a large amount of living rhizome and root material and the favorable conditions for the decomposition of dead organic matter increase the proportion of roots and rhizomes to soil organic matter. 18. Roots and rhizomes constitute about one-tenth of the total organic matter in the surface 6 inches of soil; in the deeper sections the proportion decreases gradually from 3 to 4 per cent in the second 6 inches to 1 per cent in the fourth foot of the Lancaster soil, and 0.25 per cent in the seventh foot of the Wabash soil.

Range and Pasture Management

Range and pasture management , Range and pasture management , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Effects of Different Intensities of Grazing on Depth and Quantity of Roots of Grasses

T HE writer has been interested in prairies, pastures, and root depth and distribution over a period of many years. He had the privilege of examining these relationships in the Palouse prairie of Washington long ago while numerous representative areas still remained in a virgin condition (5, 6). Extensive studies have been made in the hardlands of Colorado, Kansas, and Nebraska many years before, during, and following the great drought of 1933-40 (7, 8, 1, 11). Vegetation and root habits have been studied in sand hills (7, 8, 4), in bluffs of wind-blown loess (12), and wet soils of lowland. The trench and hand pick method was employed throughout and roots in prairie and pasture were measured, compared, and sketched in the field. Their depth, spread, and chief characteristics were recorded. Only general consideration was given to soil type. At that time there was no method of quantitatively comparing one root system with another or the roots from one soil with those of the same species from a different soil. The need for such a method has been felt for a long time and lack of one that could be put intlo general use has probably greatly retarded root studies. This paper is concerned with a new quantitative method of studying root-soil relations and particularly its application to the effects on the underground plant parts brought about by grazing. The

Root System of Quercus macrocarpa in Relation to the Invasion of Prairie

1. An ecotone between the grassland and the deciduous forest along the Missouri River occurs in southeastern Nebraska. The mean annual precipitation is 28-32 inches; humidity is relatively low, evaporation and wind movement are relatively high; the silt loam soils are deep but during drought contain only a small amount of water available for growth. Thus competition for water between the grasses and the invading shrubs and trees is great. 2. Quercus macrocarpa is the most xeric forest tree. Since the cessation of prairie fires it is invading the grassland either directly or in the wake of the Rhus-Symphoricarpos-Corylus chaparral. 3. The shrubs advance largely by means of rhizomes into the grassland. Their roots often extend outward and then upward under the grasses. Those of Symphoricarpos especially are so finely branched and abundant as to compete successfully with the excellently developed and extensive root systems of the plants of the prairie. 4. The oak seedling develops a deep taproot before the leaves are unfolded. The strong, finely branched taproot extends into moist soil 3-5 feet the first summer. 5. Mature trees 50-65 years old were 35-40 feet tall. 12-18 inches in basal diameter, and grew 10-40 feet apart in a pure stand. 6. The taproot gave rise to thirty or more large main branches, most of which arose in the first 2 feet of soil. It tapered rapidly and extended to a depth of 14 feet. 7. Most of the main branches, which varied from 1 to 7 inches in diameter, extended widely (20-60 feet) before turning downward. Some grew even deeper than the taproot. All branched repeatedly, and together they occupied a very large volume of soil. 8. Many branches of the main roots grew vertically downward 8-15 feet, each more or less resembling the taproot system of an oak sapling. Others extended obliquely or vertically upward and filled the surface soil with a mat of absorbing rootlets. 9. Ropelike roots, 0.5 inch or less in diameter, extended many feet without much change in thickness. A cordlike type, 3-5 mm. thick, was also abundant. A third type consisting of fine, much branched rootlets clothed the widely extending skeletal framework and furnished the bulk of the absorbing surface. Mycorrhizal mats were abundant. 10. The weight of the roots equaled that of the tops; the volume of the roots was about one-tenth less than that of the parts above ground. 11. Low water content of soil is compensated by a widely spreading, well branched root system. This may account for the wide spacing of the oak trees and the open forest canopy.

Annual Increase of Underground Materials in Three Range Grasses

Any thoughtful student who has seen the mellow, granular, fiber-filled soil of virgin midwestern prairie and the same soil that has been cropped with maize or wheat for only a decade has cause for deep concern. For the cropped soil has lost its mellowness, the granular structure of discrete crumbs has largely disappeared as has also the binding root fiber. The soil when dry is often like dust, dust that pours between the fingers and is dispersed by the wind before it reaches the ground. Throughout the Midwest soil drifting has greatly increased, and erosion by water has become accelerated with length of time of cultivation and the cropping of more arid lands. Such soils have lost much of their fertility. They are greatly reduced in water-absorbing and waterholding capacity, and because of their small percentage of aggregates or their single-grain condition they may readily drift. Grasses not only provide the soil with a protective cover against the forces of erosion but they also bring about a recovery of soil fertility which has been partly exhausted by continuous cropping. Under a cover of grass, a favorable crumb structure (the amount of which is a rough measure of the fertility of a given soil) is produced. These aggregates, a high percentage of which are large, are much more resistant to movement by wind and water than are the particles of dust. They promote rapid absorption of water and permit freer movement of both water and gases within the soil. Soil aggregation under grassland as brought about biologically is partly through the accumula-