I have a very large plane that I am using for grass. The grass texture is seamless and has to be tiled like 200 times .
It looks fine, (no visable tiling) But… it’s too clean. I want to add some dirt bare spot patches here and there, more like real grass. If I do it directly on the texture in PS than it is going to be immediately apparent that it is tiled.
What would be the best way in Cycles, to accomplish what I am trying to do?
Use a noise texture as mix factor in between your grass and something else.
Here, I used 2 textures and a Color Mix but it can as well be 2 materials and a Mix Shader.
The size of the noise textures set how tightly or loosely packed the spots are. The Color Ramp on the line defines how smooth or sharp you want the transition in between the 2 as well as the balance in between the grass and the dirt, depending on where you set the markers.
The most common way I think is to add a second material and create a mask layer to hide portions of the grass and let through a dirt texture or something. You can also add a clouds texture to vary the color of the grass. Grass is usually patchy with some patches dark green and others light green/yellow. Rocks and stuff like that also help to break up the scene and they are very easy to add. I’ll post this and see if I can figure out how to do a mask layer in cycles.
Thanks Kalurra and Brent for your ideas. I’m going to experiment and see what I can come up with.
I’m still getting my arms around how to use those mask layers in the render layer tab. I probably should have mentioned
this project is going to be animated… don’t know if that makes any difference or not.
If you want to take a look at the type of landscaping I am trying to work with on this project go here…
Animation isn’t a problem for my method… as long as you don’t grow a volcano in the middle of the lawn. 
Any way… I looked at your video and I thought about something a little more subtle for your lawns.
Use the noise texture as factor to mix your grass texture with a color. Your lawns really need to stay clean and artificial for such a presentation. The less you do, the better.
