smooth texture seams with terrains

[Freetimecoder]

Hi,

first I thought, this is a nice Terrain:
http://b2cs.delcorp.org/examples/terrain.blend
(well I'm still thinking it)

And I nearly got it, but just nearly. I tried anything "I know" about Blender to get these smooth textureseams. But I didn't succeed. So I searched with google and with the search function but I found nothing which solved my problem.
I still have these ugly hard seams.

Does anybody know how I can do that?
Greetings