Date of Award


Document Type


Degree Name

Master of Science



First Advisor

Dr. Lisa K. Muehlstein

Second Advisor

Dr. Bradley W. Goodner

Third Advisor

Dr. Christopher L. Stevenson


This study measures the effects of 2,4- dichlorophenoxyacetic acid (2,4-D) on growth and nitrogen fixation capabilities of the native microbial soil community during eight field trials conducted over an eight month period. After application of 2,4-D, soil samples were analyzed for enumeration of diazotrophic and general microbial communities, and for nitrogenase activity as measured by the acetylene reduction assay (ARA). Statistical analyses were conducted using Minitab. Results show that 2,4-D significantly stimulated growth of diazotrophic microbes in 87.5% of the trials and was found to have a stimulatory growth effect on the general microbes in 62.5% of the trials. A significant stimulatory effect on nitrogenase activity was found in 28.6% of the analyzed trials. Results indicate that our current lawn care practice of applying a mixture of fertilizer/herbicide needs further study. Application of the herbicide 2,4-D prior to fertilizer application may be more nitrogen efficient.

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