You need to use a texture variation macro. Look in the grass material in the Starter content. You will see one there. For my landscape i have 2 diffrant grass textures to make it not like like you are tiling it.
For the landscape blend maps. you sould get splat maps for that saves a lot of work realy i does. if you use world machine it has a macro for that if you google it a bit more you will fine some great tutorials. the preview weight is used for showing witch texture you want to see, in the preview window ontop of the details. increase the mapping scale. And a other tip you can use upto 128 textures of you set in the texture sample node(I forgot witch one exactly) the second setting to sheard:warp.