Well, when I write about our farmers and our farms, I always talk about the obvious reason to keep our farmland, i.e. "No Farms, No Food," as the American Farmland Trust always says.
However, there are many other reasons that farmland is so important that most people often aren't aware of. One of the biggest is the fact that our farms are green space and can contribute to a healthy environment. Sadly, we don't hear about all of the work they do in this regard, all we hear about are the big bad, corporations, which I don't really consider "real" farms and which are degrading our environment.
Here's the story I wrote covering all of this, I would love to hear your feedback! http://www.care2.com/greenliving/why-saving-farmland-is-so-important.html