"I love this house because it backs up to farmland."

"The views from this house are great because there aren't any other houses behind it."

"This home offers such great privacy without any neighbors behind it - just wide open farmland."

All of these are reasonable sentiments, but remember...

If you own (or are buying) a house in a residential area that currently backs up to farmland...

1.  That farmland might remain farmland for as long as you own the house.

2.  That farmland might become housing some day.

Most farmland is zoned for agricultural use -- so if the farmland behind your house is zoned as such, a potential builder or developer will have to apply to have the land rezoned.  Thus, you'll likely get some sort of notice that someone intends to turn that farmland into housing.

Buying a home that backs up to farmland is a great idea - you'll likely love having only a farm as a back neighbor - but remember that the farmland might not always remain as farmland.