Looking several articles I found this, apparently is very popular and a simple method.
The technique consists of do planes vertically to a very short distance (about 0.5 cm) repeated 10 times so that the height of the grass will be 5 cm. The texture of the drawings is a texture with alpha channel for do that transparent and It simulate the branches of the herb. This gives a realistic effect to the scenery with only 10x2 Triangles.
Besides, it has another advantage, as the texture of the drawings are saved with mipmaps, the grass will only appear in a radius of about 20 meters, this is very positive because with this way we do not force the graphics engine to load these textures at very long distances.
I've done some testing and I have to look at some details of the transparencies because in some areas not seen as seen as it should be, Here are some of pictures.
