Hi,
I know of two ways to get what you want.
1. Manually blend the edges of the photoreal textures to match the underlying ground textures. This is done in a paint program after importing the image using a program like DXTBmp (because these textures are usually in a format most paint programs don't understand). Specify your paint program in DXTBmp, load the image into DXTBmp, Image/Send to Editor, edit the image in your paint program and save it, then back in DXTBmp Image/Reload After Edit, and save it. You may need to save it with MipMaps, I don't know - that' a checkbox at the right side of DXTBmp.
2. Use a ground polygon to blend the two, using the alpha channel to make the polygon partially transparent in spots. ModelConverterX can make ground polygons out of polygons created as an MDL or other object types in GMAX, Sketchup, Blender, or other such program. If this is near an airport, ADE can also create ground polygons from scratch (but you have to create the texture in both cases).