What dirt do you recommend? I'm doing a science project,about what will start if you put a...

I'm doing a science project,about what will start if you put a lot of brackish water contained by one plant,a little contained by one plant,and none in the other plant.The single problem is I don't know the best kind of dirt for a Radish plant would be.
Answers:    use potting soil--you can take it at lowes or home depot or even walmart in the garden box
Why do Americans refer to earth, soil or compost as dirt ? When they try to describe concrete dirt how can you really know what they mean?