Sculpt your terrain in Blender. Then use Blender's vertex paint feature to paint the textures onto the terrain. You need a variety of seamless terrain textures (Hobobo has several at ShareCG), you put those in your brush and paint away. Blend and layer the textures together so that you avoid the tiling effect.

Poser 11 Pro, Windows 10

Auxiliary Apps: Blender 2.79, Vue Complete 2016, Genetica 4 Pro, Gliftex 11 Pro, CorelDraw Suite X6, Comic Life 2, Project Dogwaffle Howler 8, Stitch Witch