Using Photoshop I made a grass texture map by taking samples from my source photograph. This map was applied to a plane geometry for color or as the diffuse map. To this texture map a bump map (MR Noise) and a displacement map (MR dent) was also incorporated. Certain vertices of this plane were either deleted or re- positioned. The opacity level of the "Shadow Plane" was set at .7 in order to let the existing grass from the background photo to show through while still allowing the shadow to show.
One omni (shadows off) light and the IES Sun were used to illuminate the scene. Camera helpers and cam points were set up and a camera generated. The image was rendered with Mental Ray.

Using Mental Ray photographic exposure controls my camera settings are:
shutter speed 1/ 700. sec.
f/9.0
film ISO 200

The ambient light is a gray color and the global light tint is pale yellow @ 1.2

IES sun color is set to a blue hue @ 13000 lx with ray traced shadow

Wire frame view of the model with the camera match B/G. The blue line from right showing the position/path of the daylight system.