**EDIT**
I'm finding other sources that say that sterile "terminator seeds" are a patented technique, but that Monsanto has promised not to use it. Straight from the horse's mouth:
http://www.monsanto.com/newsviews/pages/terminator-seeds.aspx

So it appears that my info below is wrong. I will try to talk with my family and get the full story. That being said, I'll leave my original comment and the followup below unaltered.
*********


My firsthand knowledge of this stuff was from more than 10 years ago, and also when I was pretty young (early 20's). So I did some web searching to try to get updated since your question is a very interesting one:

http://web.mit.edu/demoscience/Monsanto/about.html

According to that, Monsanto is the company behind "Roundup Ready", and their corn (and other crops in the line) do use sterile "terminator seeds". It also mentions that farmers "must purchase the most recent strain of seed from Monsanto" each year.

I was never in the decision-making structure of my family farm, but I did remember that we couldn't just buy the Roundup Ready seed *once* and then hold a small amount back as seed for the next year and continue to get the benefits.

I'm not 100% sure exactly how the modification for sterility works -- I don't know if the plant will sprout if you plant the sterile seeds and just fail to produce any ears / fruit, or if it just won't germinate at all. I do remember that we had to be quite careful to fully clean out the corn grown from the GM seeds from our storage bins, and better yet to store our non-GM corn to be used for future seed in entirely different bins. That was done to make sure that we didn't end up planting any of the sterile stuff.

I'm sure that the seed dealers that sell the GM stuff really push farmers to buy and plant it every year, as hinted to in that link. But you certainly don't *have* to. On the other hand, if you go back to non-GM seed for a year or two or more, you can't use a strong herbicide like Roundup if you have an unexpected outbreak of weeds or other pest plants -- the Roundup would kill the non-GM crop along with everything else.

Basically, I don't specifically begrudge companies like Monsanto for their practices concerning these GM crops. The "terminator seeds" are controversial, but don't seem like a big deal to me. If you could buy GM seeds once and then just hold back some of your harvest for next season's seed, they'd only get your money once AND we'd probably lose the original strains. So I see that as kinda win-win, especially if you don't 100% buy into their sales department urging you to use GM seed every single year.

I don't want to sound like a shill for Monsanto -- some of their other practices are pretty shady, particularly political lobbying. But from the perspective of my family farm, the GM corn that we use was/is a real beneficial thing. Significantly less pesticide/herbicide use over time, and it allows for expanded low/no till farming. Before herbicides, tilling was one of the only ways to kill off pest plants. But, it also makes the fields lose some moisture and nutrients. Expanded farming and ubiquitous tilling was largely the cause of the "dust bowl" dirty 30's. Anyway, I'd say that a lot of good has come out of modernized techniques and technology like GM crops.