I've planted, managed, and maintained 18 acres of my own plots in 3 states with an ATV, a hand spreader, and an ATV sprayer. That's it. I've also managed about the same with a 48hp Kubota, cab, 4x4, 6' tiller, cultipacker...etc.
The difference? MUCH quicker with the ATV. Seriously. Today, I am down to about 6 acres but I plant by spraying to expose the soil, 3xs during the summer...and then spreading different bases of blends the end of July, and around Labor Day.
I happily sold my tractor...and I had over 500 hours on her. Anyways, there is a LOT that you can do to have some very high quality plots w/o a tractor. If I was going to plant corn...I would go the tractor route, but even beans I can plant without tillling in anyway, no drilling either.