Master's Theses

Document Type

Thesis - campus only access

Date of Award

Summer 1961

Degree Name

Master of Science (MS)

Department

Biology

Advisor

G. W. Tomanek

Abstract

The study area, having a total of 434 acres, was placed in the "Soil Bank" in 1958. A sorghum cover crop was seeded in spring of 1959 and the area was seeded to grass on November 25, 1959. Rate and mixture of seeded grasses were as follows: three pounds of blue grama per acre; three pounds of bluestem mix per acre which includes big bluestem, little bluestem, Indian grass, and side-oats grama; and three pounds of switch grass per acre. An upland site was selected for detailed study and was divided equally into an unmowed and mowed area. On July 14, 1960, the area surrounding the unmowed area was mowed at a height of seven inches. Mulch was clipped at four different dates to determine amount of sorghum mulch and rate of decomposition. The microclimate was sampled with appropriate instruments. Factors measured were air and soil temperature, relative humidity, evaporation, light intensity, and wind velocity on both the mowed and unmowed areas. A soil profile description was written and soil moistures were determined weekly for the growing season. Density, frequency, and composition were determined for both weedy species and seeded grass. In addition, percent flowering was determined for the latter on both the mowed and unmowed areas. A series of three list quadrats were established and charted at the beginning and end of the growing season in both areas to determine how each seeded species responded to weedy competition. Responses to competition were also studied by growth measurements and root bisects. Results were as follows: (1) The amount of mulch left after one year of decomposition was 1.22 tons per acre, a loss of 2.31 tons from the original of 3.53 tons. (2) Mechanical analysis indicated high clay content from 0.6 to 5.0 feet. (3) The mowed area had a higher percentage of soil moisture than the unmowed area with exception of September when sorghum regrowth on the mowed area required more moisture than matured weedy species in the unmowed area. (4) Weekly average maximum and minimum air temperatures and maximum soil temperatures of the mowed area were several degrees cooler than on the unmowed area. (5) Relative humidity did not vary greatly between the unmowed and mowed areas. (6) Evaporation, wind velocity, and light intensity were greater in the mowed area than in the unmowed area throughout the growing season. (7) Grass seedlings in the unmowed area showed signs of environmental stress earlier and more completely than grass seedlings of the mowed area. (8) Switch grass and blue grama usually were a little more advanced vegetatively in the mowed area than in the unmowed area. (9) An average of 2.210 weedy plants occurred per square-foot. (10) Data indicated grasses in the unmowed area and mowed areas were very similar in vegetative distribution with the unmowed area having a frequency of 74.45 percent and a density of 1.156 percent while the mowed area had a frequency of 75.55 percent and a density of 1.057 percent. (11) Mowing greatly increased flower production of switch grass, blue grama, side-oats grama, Indian grass, little bluestem, crested wheatgrass, and sand dropseed which had a flowering percentage of 11.67, 17.56, 60 .07, 20.57, 66.67, 100.00, and 14.29 percent, respectively, in the mowed area while the same species on the unmowed area had a flowering percentage of 4.94, 12.09, 24.24, 0.0, 0.0, 53.33, and 0.0 percent, respectively. (12) Switch grass, blue grama, and side-oats grama plants of the mowed area had a much darker green healthy color, larger inflorescences, increased seed production, and shoot height was greater than those from the unmowed area. (13) Crown area of switch grass and blue grama increased more on the mowed than on the unmowed area. (14) Mortality of switch grass and blue grama was greater in the unmowed area than in the mowed area. (15) Data indicates that broad-leaved herbaceous species hinder normal shoot development of seeded grasses by competing for light and soil moisture. (16) Root bisects indicated that switch grass and side-oats grama of the mowed area had a greater maximum root penetration and lateral spread than the same plants of the unmowed area. Little difference occurred in development of blue grama roots on either area. (17) Switch grass and blue grama of the open areas of the unmowed area had a greater maximum root penetration and lateral spread than the same plants under a Russian thistle. (18) Bisects of four weedy species showed that mare's-tail and lambs-quarter goosefoot had reached approximately the same maximum root penetration as the seeded grasses while roots of tumbleweed pigweed and tickle grass were in the upper two feet of soil. Results of the various studies were also illustrated by photographs, figures, and tables.

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© 1961 Sheldon Saxton

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