Monday, 7 November 2005
16

Interactions of Glyphosate and Foliar Amendments with Iaa Synthesis and Urease Activity by Rhizosphere Bacteria of Glyphosate-Resistant Soybean.

Su-Jung Kim, University of Missouri, Department of Soil, Environmental & Atmospheric Sciences, 302 Natural Resources Bldg, Columbia, MO 65211 and Robert J. Kremer, USDA-ARS, Cropping Systems and Water Quality Research Unit, 302 Natural Resources Building, Columbia, MO 65211.

Increased use of glyphosate-resistant crops has raised concerns regarding the potential environmental impact of glyphosate. Furthermore, other foliar-applied chemicals may impact soil microbial ecology. 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. Grozyme® and PT-21® are foliar amendments used to increase crop yield. Metabolites implicated in growth-suppressive activity include hydrogen cyanide, phytohormones such as indole-3-acetic acid (IAA), and unidentified phytotoxins. The objectives of this study were to describe changes in IAA synthesis and urease activity of rhizosphere bacteria of glyphosate-resistant soybean (Glycine max, ‘Roundup Ready'). This study was conducted at Bradford Agronomy Center of the University of Missouri-Columbia. Roundup (RU) herbicide was applied to main plots at the recommended growth stage (pre-bloom) following the suggested label rate. Split-plots were treated with foliar amendments of biostimulant or urea (21%) solution 10 days after the RU application. Soybean roots and associated soil were collected from the outer rows of each plot immediately prior to RU application and at 10, 20, and 30 days after RU application. The populations of IAA-producing bacteria decreased in overall RU treatments. Urease activity 30 DAT significantly decreased in RU only treatments compared to treatments containing urea. These results indicate that glyphosate in association with certain foliar amendments may influence the rhizosphere bacterial populations which synthesize IAA and also may alter microbial enzyme activity.

Handout (.pdf format, 1957.0 kb)

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