Excellent question! I've heard it's the ones with "purple flowers". However, I had those in the 500+ acres of soybeans 20 feet from my hives and got nothing last year. There was an article in either ABJ or BC a few months back about soybeans and thier fickleness. I was hoping the article would give a laymans answer to that question. I reread that article less than a week ago and found nothing more detailed than "certain varieties".I have never found anything on how to ID what variety of soybeans actually provide nectar. I live in the heart of soybean country and I'm not seeing it. Is there a way to visually ID the correct nectar providing soybean plants? Or, is it up to the bee's to tell me?