Submitted to: World Congress of Soil Science
Publication Type: Abstract Only
Publication Acceptance Date: 7/27/2006
Publication Date: 8/1/2006
Citation: Kim, S., Kremer, R.J. 2006. AUXIN-PRODUCING BACTERIA AND UREASE ACTIVITY IN THE RHIZOSPHERE OF GLYPHOSATE-RESISTANT SOYBEAN [abstract]. 18th World Congress of Soil Science, July 9-15, 2006, Philadelphia, PA. 2006 CD-ROM.
Technical Abstract: Repeated use of glyphosate on glyphosate-resistant crops has raised concerns regarding the potential environmental impacts of this herbicide. Glyphosate may affect microbial production of plant-growth-regulating compounds including hydrogen cyanide, phytohormones including auxins, and other unidentified phytotoxins. Certain foliar-applied products may offset potential adverse impacts of herbicides on soil microbial ecology. For example, biostimulants (products containing plant hormones) and liquid fertilizers affect soil microorganisms by providing additional nutrients or growth factors that alter metabolic activity and improve crop growth and productivity. The objectives of this study were to describe changes in bacterial populations which synthesize a common auxin (indole-3-acetic acid; IAA) and urease activity in the rhizosphere of glyphosate-resistant soybean (Glycine max, 'Roundup Ready'). This study was conducted on a Mexico silt loam (fine, smectitic, mesic, Aeric Vertic Epiaqualf) in central Missouri, U.S.A. Glyphosate was applied to main plots at the V4 developmental growth stage (pre-bloom) of soybean at the label rate (0.84 kg a.e. ha minus 1 ). Foliar amendments [biostimulant and urea (21% N) solution] were applied to split-plots 10 d post-glyphosate application. Soybean roots and associated soil were collected from the outer rows of each plot immediately prior to and 10, 20, and 30 days after glyphosate application. Populations of IAA-producing bacteria were lower in all glyphosate treatments compared with non-glyphosate treatments regardless of foliar amendment. Urease activity 30 d post-glyphosate application was significantly lower in glyphosate treated plots. These results indicate that glyphosate altered rhizosphere bacterial populations that synthesize IAA and altered microbial urease activity; foliar amendments with or without glyphosate had little effect.