Cleev, the ballast in the tires provides two benefits; counterweight for a front end loader and better traction. You say you aren't getting a front end loader, so do you think you'll need more traction? If not, I wouldn't fill the tires. However, I have a front end loader and have water and antifreeze in my rear tires (maybe not environmentally friendly if you have a leak, but not as corrosive as calcium chloride). Calcium chloride is popular up north, and I don't know of anyone in my part of the country who would even consider putting it in their tires, plus the fact that I don't where you could get it if you wanted it. It may be more environmentally friendly; I don't know, but I do know that if you get a leak, it'll kill the grass and it'll be a long time coming back because a neighbor bought a used tractor from Minnesota and the first leak he had was right in front of my house so he pulled in to air it up in my shop and killed the grass where he stopped. That was when he found out he had that stuff in his tires. Since then he's also had to replace both rear wheels that rusted out.
Bird