I am actually growing a tomato and 3 soy plants along with two cloves of garlic on a seven gallon container. It has been about a month and the tomato is HUGE. Not sure if the soybeans are going to suffer yet.

Last season I grew a variety of tomatoes, basil and soy in the same 5x8 raised bed and everything seemed to do just fine. I had a bumper crop of tomatoes, they certainly weren't harmed. It was my first time growing soy, and it was a late variety, so I'm told. I assume growing any legume is beneficial for the soil as they fix nitrogen...