Fred,
I think I have a site here that might help you in the future. This company makes tractor mounted planters for the large gardener and small farmer. I grew up using a Covington Planter, and they are very effective planting/cultivating machines. This coming winter I will be replacing an old single row planter that is as old as dirt itself. I'm going with the 1 Row Planting Unit which is pictured on the TP 707 cultivator frame. As Indy was describing, the cultivator is the device that works the ground on both sides of the planter. With this unit, you would take off the planter once your planting is completed. That which is left, TP 707, which is also pictured independently, is the cultivator. Then you go back over the row of corn, beans, etc. Yes, this planter can plant just about anything. You will notice that the feet on this cultivator are bolted on. They can also be removed and feet called sweeps added in their place. these have essentially wings that extend out on either side to cut up the weeds. These weeps come in just about every size imaginable. You simple go to a local tractor supply store and select ones that will work. You know, experiment. It sounds like you have the ability to make your garden even larger than 50x100. With a planter/cultivator like this, you could easily work several acres if you choose or a rather small garden. The big box out in front of the planting unit is what fertilizer, 5-10-15, is added too when planting. The seeds go into the small box shown on the rear. It is a very simple design that has been around since nearly the turn of the century and it works great. The one I have now is so old the sheet metal is rusting through everywhere.
I called the company and they told me to order about 2 months before needing. So keep this in mind for next planting season if you develop an interest in it. I've talked to a couple of dealers and they have quoted me prices from $850 to about $1200 for the entire setup: planter and cultivator. So like everything, you'll have to call around for the best price. Also, removing the planter is very simple. Loosen four bolts and it's off.
They also manufacture what is called a side dresser. This is a device that looks like the planter, but it is only used to apply nitrogen, etc. to your corn as you cultivate it. Indy could help us out here. I usually apply granulated nitrogen when the corn gets up around a foot tall. At this point, you are cultivating it for the last time, because soon it will be too tall, and your tractor would damage it. Once nitorgen is down, pray for rain. With a little water your corn will literally take off. This side dresser I've described looks like the planter but it runs along just on the side of your row. It will fit on the same single row cultivator that the planter takes. Just make sure you get the mounting brackets. Call the company. They are very helpful and will send info.
Now let me really confuse you. If you wanted to save a little money at first and just go with the planter and cultivator, maybe decide on the side dresser later, you can also apply nitrogen with the planter unit. Remember, it has a box up front that holds and applies fertilizer when planting. The way you do this is by removing the opening foot that tears up the ground just in front of the planter unit. Drive between the rows while hugging the edge of any given row. This will offset the planter just enough so that it is not running over your corn, and neither is your tractor. The dispenser will apply the nitrogen right down beside your corn. I know this sounds involved, but like anything, it is quite easy once you've done it once. We've actually applied nitrogen to our small corn patches like this for years. However, I do have my eyes on that side dresser. I'm hopping to pick it up next year as well. One cultivator frame is all that you need. However, if you know where they hold auctions for farm equipment, you can pick up frames like those shown in the picture for just a little.
I hope this helps. Even if you aren't interested in a planter/cultivator now, I promise you that you will if you get into gardening. Its like any hobby. Your toys for it never stop growing.
Enjoy /forums/images/graemlins/cool.gif Almost forgot
http://www.covingtonplanter.com