I was cycling through maps right now, and many of the maps have the same "error", you use the "turf" texture to make grassland, but turf is turf and not grassland.
The main difference is, grass spawns on grassland (the small 2d thingies props,it only spawns after you reopen the scene, though), not on turf. Looks quite nice on high grafic settings. Also, grassland gets slight varieties in its colour by itself, making the map look "fresher".
How to get grassland? Just delete textures (middle mouse while in texture paint mode).
Turf is nice where you want turf, but big areas of it in the wildernes just look wrong.
Example of the difference:
Picture 1 is pure grassland, Picture 2 nearly pure "turf", with a small stripe of grassland to the left