It's weird that it didn't work for you. Let's try again.
First you need three bitmaps (jpeg or better, targa). The first is you grass texture (say Grass.jpg), the second is a photoshopped version of the first, very desaturated and almost white (Chalk.tga), the third is your white lines/text/whatever on a black background (Mask.tga). For that last, you can use one the filters in Photoshop to make irregular edges.
Then you need three materials:
- Grass Mtl: Use a Standard material with Grass.jpg in the Diffuse slot. Apply it to a plane and adjust the tiling as you see fit. When you're done, drag from the Diffuse to the Bump slot. That way you keep the same tiling values.
- Chalk Mtl: Drag the Grass Mtl to an empty slot in the materials window to make a copy and - again - keep the tiling, rename it and, in the Diffuse slot, replace Grass.jpg by Chalk.tga. You might need to lower the bump value or else it will look to sharp.
- Blend Mtl: this time create a Blend material. Drag the Grass Mtl to its Material 1 slot, then the Chalk Mtl to its Material 2, click on the Mask slot and browse to your Mask.tga file. Finally apply that material to the plane.
Render, adjust your lights, render again, etc... and that's it.
Extra: For the indentation of the chalk lines, in the Chalk Mtl, add Mask.tga in the Displacement slot with a small negative amount.
This is what I got (with a bad grass texture, you can see the repetion of patterns):
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