A 128x128 ground texture is about the same as 256x256 or 512x512.

The only difference is that 256x256 is higher quality of picture. 512x512 is the highest quality picture.

128x128 is lowest, but there is no difference beside the quality of picture.

do you have a screenshot to i see the differences?

I dont have a picture of ground textures directly. But it is similar to head textures like this:

http://img823.imageshack.us/img823/5639/ground512.png

Above is 512 ground


Below is 128 ground



http://img249.imageshack.us/img249/4033/ground128.png