Manganese Management Effects on Glyphosate-resistant Soybean Response to Glyphosate Applications.

Glyphosate-resistant (GR) soybean is widely accepted in the United States. Recent research in Indiana and elsewhere has confirmed that manganese (Mn) deficiency following foliar applications of glyphosate may be limiting yield in GR soybeans on certain soils. The objectives of this study are to 1) better understand the soil and glyphosate application factors that reduce the uptake and translocation of Mn in GR soybean plants and 2) determine the optimum mode for Mn supplementation in GR soybean production systems. A field study was initiated at 3 Indiana locations in 2007. Main treatments were 4 levels of glyphosate application frequency (zero, pre only, pre plus single post, and pre plus double post), and sub-treatments were 3 levels of banded manganese application (0, 2.5 and 5.0 kg/ha).. Full weed control was achieved on all plots by pre-emerge residual herbicide application. Leaf tissue and seed samples were taken at 4 different growth stages and analyzed for various nutrients. Soil samples were taken to determine soil micronutrient availability and soil pH on an individual plot basis. In 2007, the application of glyphosate didn’t cause major yield reductions; and Mn supplementation didn’t increase soybean yield substantially. At one location, both leaf Mn and seed Mn concentrations increased following the high manganese application rate.. Our first year results indicated little yield response to fertilizer Mn and glyphosate treatments for the particular soil pH conditions at these 3 sites. We will continue our study on the relationship among yield, micronutrient uptake, and glyphosate applications in 2008. Our results may be useful for the improvement of micro-nutrient management in GR soybean production systems..