The use of herbicides in cropping systems is routine in western Canada as is the practice of rotating crops between cereals, oilseeds and pulse crops. Often, herbicides that are appropriate one year in the crop rotation are not compatible with the following crop. Additionally, certain herbicides are designed to target certain enzyme pathways that can interfere with amino acid synthesis. These pathways also exist in the microbial community, including Rhizobium species. Rhizobia have a unique symbiotic relationship with legumes. In return for a carbon source, rhizobia not only fix atmospheric dinitrogen (N2) for the plant, but also can increase soil N reserves for the following year. With herbicides targeting amino acid synthesis in both plants and microbes, there is a possibility that N2 fixation may be inhibited by the application of certain herbicides.<p>
This project was designed to examine possible negative effects of herbicide application on N2 fixation in field pea (Pisum sativum L.) and chickpea (Cicer arietinum L.). The study included field, growth chamber and laboratory experiments in which the effects of pre- and post-emergent herbicides, as well as herbicide residues in soil were examined.<p>
In the field experiments, some early season measurements suggested that herbicide application had a negative impact on various growth and N2 fixation parameters. However, as the season progressed, plants recovered from early herbicide damage and N2 fixation ultimately was relatively unaffected. Growth chamber experiments similarly revealed that N2 fixation was largely unaffected by herbicide application when the application rates were relatively low (i.e., at rates intended to simulate partial herbicide breakdown, and thus lower than the recommended field rate). Although, N2 fixation was suppressed where high rates of herbicide (i.e., greater than recommended field rate) were applied, the efficiency of the rhizobia to fix N2, (i.e., the amount of N2 fixed per unit nodule mass), was unaffected. This along with a laboratory experiment which monitored growth of rhizobia in vitro, confirmed that rhizobia were not directly affected by the herbicides used in this study and that overall N2 fixation was not inhibited directly by the application of these herbicides. It was concluded that any negative impact on N2 fixation caused by herbicides used in this study, was related to the impact of the herbicide on crop growth, and was not due to any direct effects of the herbicide on the rhizobia.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-02092009-090503 |
| Date | 25 February 2009 |
| Creators | Taylor, Angela D. |
| Contributors | Nelson, Louise M., Knight, J. Diane, Holm, F. A. (Rick), Walley, Frances L. |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-02092009-090503/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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