Land use is a hotbutton issue in many areas. Trying to protect farmland and rural areas from becoming cities while not stifling development is a tough needle to thread.
I am not a lawyer, nor am I familiar with the laws up in your area. However, I was involved in a farmland preservation campaign around here and know a little about what's going on.
You might want to contact American Farmland Trust, if I remembered the name correctly. If you can show that the land in question has historically been in agriculture and especially if it has been in the same family for several generations, your desire to modify the type of agricultural use to suit a different market might be something they would help you out with. It sounds like it has been lying fallow since '96, so what you want to do is resurrect an older farm and bring it back into farm use.
Basically, AFT works to purchase the development rights to a piece of ground and to assure that it stays in agriculture for all time.
If your equine establishment can be viewed as a horse farm, especially if you raise a lot of your own feed and stock, that will help. Just setting up a bridle path network without growing some crops or raising some critters may not be agricultural enough. It's more of a yuppy thing than a farm thing. Make it as farmy as you can.
Be aware, though, that selling your development rights will limit your choices as to how the land gets used, even to the extent of preventing you from building houses for your kids on a piece of it. Investigate thoroughly before you commit to anything.
Also, check into the township zoning regulations and whether or not they have the strength of law in your area. Most people want zoning to protect their ideas about how things should be from being ruined by the way their neighbors want things to be. Then when they find out that they have limited their own options they apply for exemptions or variances. If you can show that your equine adventure will be good for the community (perhaps by bringing in dollars from outside the area and stimulating the local economy) you might find some friends on the zoning board.
Good luck.