Hi.
Specifically talking about grass using textures (and not the geometry grass from CineRender), there are a couple of things that you could do:
1. The texture you are using may be tileable, but it is not equalized; in other words, it is showing a darker corner that reveals the tiling and needs to be fixed. Here's a tutorial for that:
https://tolas.wordpress.com/2009/05/26/tutorial-how-to-equalize-textures-in-photoshop/
If it doesn't tile, well, you'll need to fix that too.
2. If you don't have any, look for some in cgtextures.com, under nature->grass. The selection is pretty good.
3. You can use one of the most common tricks to avoid or reduce repetition: combine a couple of textures. In the surface options, with the CineRender settings, for the color setting use texture:fusion or texture:layer. It will allow you to combine two or more textures to achieve the effect. The missing part, at least here, is that you only get a single size value. The attached is from a 3D software where you can apply different mapping coordinates to each texture, so you have more control. The effect will improve even with this limitation.
Hope that helps.
Best regards.