Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2005
Publication Date: 10/28/2005
Citation: Kim, S., Kremer, R.J. 2005. Interactions of glyphosate and foliar amendments with IAA synthesis and urease activity by rhizosphere bacteria of glyphosate-resistant soybean [abstract] [CD-ROM]. ASA-CSSA-SSSA Annual Meeting Abstracts. ASA-CSSA-SSSA Annual Meeting. Nov. 6-10, 2005, Salt Lake City, UT. Interpretive Summary:
Technical Abstract: Increased use of glyphosate-resistant crops has raised concerns regarding the potential environmental impacts of glyphosate. Biostimulants (products containing micronutrients, selected microorganisms, and plant growth regulators) and liquid fertilizers applied with glyphosate may affect metabolic activity of soil microorganisms and affect crop growth and productivity. Metabolites of soil microorganisms implicated in plant growth-suppressive activity include phytohormones such as indole-3-acetic acid (IAA) and other potentially phytotoxic compounds. The objectives of this study were to describe changes in IAA synthesis and urease activity of rhizosphere bacteria of glyphosate-resistant (‘Roundup Ready’) soybean. A field experiment arranged in randomized complete block with a split-block arrangement for Roundup® application was conducted in 2003 using soybean cv. DeKalb DKB38-52 grown in a Mexico silt loam (fine, montmorillonitic, mesic Mollic Endoaqualf) chisel-plowed prior to planting. Roundup Ultra Max® (RU) was applied in a strip block design to soybean (V4 - V5) at 0.84 kg a.e. ha-1 and main plots not receiving RU were sprayed with a conventional herbicide mix. Split-plots were treated with foliar amendments of biostimulant or 21% urea 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 (DAR). The populations of IAA-producing bacteria decreased in RU treatments regardless of additional foliar treatments. Urease activity 30 DAR significantly decreased in RU-alone treatments compared to RU+ urea. The results indicate that glyphosate in association with certain foliar amendments may influence the rhizosphere bacterial populations which synthesize IAA and alter microbial enzyme activity, which may affect overall nutrient transformations, nutrient uptake and plant-microbe interactions.