Transition of 2 materials in 2 adjacent polygons

In old versions of Blender I remember it was possible to make soft transitions between two materials in the same mesh if they were assigned to contiguous polygons. This was a very simple and effective way of blending limits instead of using complicated mask between for instance rocks and ground materials. Just a setting in material editor... Perhaps-forgive me- I am not in the right place to ask ? But would it be possible to "recover" this kind of features by such a simple way ?