By:     Alix C. Hakala¹, George F. Vance¹, Andrew R. Kniss², and Jay B. Norton¹

Departments of Renewable Resources¹ and Plant Sciences²; University of Wyoming, Laramie, Wyoming 82071-2000

Abstract:

The conversion of weed control methods from conventional herbicide applications to the use of a single herbicide (glyphosate) to control weeds has created a paradigm shift in both soil and crop science.  Concerns have arisen with respect to the soil bioavailability of Manganese (Mn) and the effects of Mn deficiency in glyphosate-resistant crops.  A greenhouse study was conducted in the spring of 2011 to investigate whether glyphosate reduced soybean uptake of Mn, which could result in crop damage among other physiological detriments.  A three-factor factorial arrangement of 5 Manganese (as MnCl₂) rates, 3 glyphosate rates, and three soybean varieties were grown in a Mollisol collected from the Sustainable Agriculture and Research Extension Center (SAREC) near Lingle, Wyoming.  During the growth process, laboratory experiments were performed to examine the soil solution sorption chemistry of the Mn, glyphosate, and Mn-glyphosate complex.  In separate experiments, total soil Mn concentration, bioavailable fraction, and water-soluble concentrations of Mn were determined to evaluate soil dynamics both separately and in conjunction with the herbicide.  After a 12 week growth period, the Mn concentrations were then analyzed in the roots and above-ground biomass in combination with chlorophyll and soybean injury.  The greenhouse experiment was also duplicated in field trials at SAREC during the summer of 2011 to confirm correlation.