I liked the quote “an authoritative new study” for an article in Better Crops. Better Crops operates as a magazine for the Potash and Phosphate Industry. It carries a range of articles, commentaries and reports on conferences, etc. The articles are not peer reviewed and come in a variety of formats.
This particular paper
Manganese Nutrition of Glyphosate Resistant and Conventional Soybeans is more like the sort of article that would be dashed off for a farmer newspaper rather than an authoritative study. The methods are a bit weak, were any herbicides used? If not why not? The statistical analysis is lacking. Is the 7 Bu/ac difference statistically significant? Years were pooled. Were yields identical in the two years or not? If these questions were answered we might know more.
Despite this paper, you won’t find farmers rushing to ditch RR soybeans. Weed problems can lead to much bigger reductions in yields. In addition, RR soybeans allow farmers to no-till and plant earlier resulting in higher yields.