Submitted to: Agronomy Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 10/24/2003
Publication Date: 11/2/2003
Citation: MEANS, N., KREMER, R.J., RAMSIER, C. EFFECTS OF GLYPHOSATE AND FOLIAR AMENDMENTS ON SOIL MICROORGANISMS IN ROUNDUP READY SOYBEAN. AGRONOMY ABSTRACTS. 2003. Interpretive Summary:
Technical Abstract: In 2002 75% of soybeans (Glycine max) produced in the United States were genetically modified for glyphosate resistance or Roundup Ready (RR) varieties. Glyphosate is systemic and translocates and accumulates in plant roots and other meristematic regions. Glyphosate may affect soil microorganisms directly or indirectly by accumulating in the rhizosphere. Biostimulants and supplemental nutrient solutions may remediate the potential adverse effects of glyphosate on soil microorganisms. Research objectives were to determine effects of glyphosate on microbial activity in the rhizosphere of RR soybean and assess if foliar amendments might offset those effects. A field experiment arranged in randomized complete block with a split-block arrangement for Roundup application was conducted in 2002 and 2003 using RR soybean (DeKalb DKB38-52) grown in a Mexico silt loam (fine, montmorillonitic, mesic Mollic Endoaqualf) under light tillage. Roundup Ultra Max was applied in a strip block design to soybean (V4 - V5) at 0.84 kg a.e. ha**-1 and main plots not receiving Roundup were sprayed with a conventional herbicide mix. At 10-days post-herbicide application, biostimulants PT-21 (9.2 kg ha**-1; 21.0% N) and Grozyme (33.5 mL ha**-1) were applied. Soil and plant samples taken 0, 5, 10, 15, 20, and 25 days after herbicide application were assayed for enzyme activity, respiration, and total culturable fungi. Surface sterilized roots were cultured for Fusarium spp. on Komada agar. Glyphosate stimulated Fusarium root colonization of RR soybean. Foliar amendments appeared to suppress Fusarium root colonization by 20 d post Roundup application. Changes in soil microbial diversity and activity in the rhizosphere may affect nutrient transformations, nutrient uptake, and plant-microbe interactions.