Mark W. Dott

Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Biology and Microbiology


Much of the food production in the world today depends on the presence of an adequate supply of nitrogen in the soil. Whether farming methods are simple or intense, nitrogen in usually the primary limiting factor in this production. In order to relieve this limitation, much of the world's agriculture has turned to the commercial manufacture and application of nitrogen fertilizers to increase crop output and to bring new lands into production. The manufacture of nitrogen fertilizer is an energy intensive process requiring large amounts of petroleum. The increasing price of fossil fuels is then passed on in the form of higher food prices, making it increasingly difficult to meet the growing world-wide demand for food. On a global scale, the Haber-Basch method of producing chemical fertilizer consumes more than 2 million barrels of oil daily. As an alternative to this type of fertilization, the process of nitrogen fixation has come under close study. Significant contributions of nitrogen to crop production have been well documented in the cases of the legume Rhizobium symbioses, and in the contribution of nitrogen to paddy rice by bluegreen bacteria. One aspect of nitrogen fixation that has not been as clearly defined, however, is that of chemoheterotrophic associative nitrogen-fixing bacteria. There have been many encouraging, but also some contradictory reports of plant growth increases caused by bacteria growing in the rhizosphere. Any advancements made in this area could have significant effects on the production of non-legume crops such as corn and wheat. Also, since new discoveries involving nitrogen fixation by root-associated bacteria could potentially be used in nearly any type of farming, it represents an important area of study. This study was conducted with the following objectives: 1) to determine if the roots of spring wheat display a ''rhizosphere effect" on nitrogen-fixing bacteria. 2) to determine if the stage of growth of the plant affected the activity of these bacteria, and 3) to determine the effect of inoculation of known nitrogen-fixing bacterial species onto the wheat plant. That is, do the applied bacteria survive in high numbers in the rhizosphere and do they promote nitrogen increases in the plant.

Library of Congress Subject Headings

Bacteria, Nitrifying
South Dakota State University Theses



Number of Pages



South Dakota State University