By all means test it. However it is a bit late to make any big changes. By the time the results are back your plants should already be growing!
But there are some generic things you can do.
1) Incorporate some good composted organic material in the transplant holes and the squash hills before you seed.
2) Inoculate the beans as you plant the seeds to fix nitrogen.
3) Use a good compost tea (AACT) or seaweed/emulsified fish extract as foliar spray.
4) Paper and mulch the whole 20X20 area.
5) Observe closely when you work the area. Look for signs of anything that might be a problem later. For example: How many worms are in the soil? Is the soil rich and loamy? Drainage? Insects, spiders, etc... good or bad? Try to pay attention to everything.
6) Talk to the other gardeners in the community plot. They know the particular conditions there better than anyone.
7) Good luck!
