If he was in the leichte artillerie, then that would explain the riding breeches and boots he's wearing, as he was probably in a horse-drawn unit. I also notice he wears some sort of cufftitle on his sleeve, but cannot read it. He appears to be SS, though I only say this due to what appears to be a deaths head on his cap, and the apparent lack of a breast eagle. Also, he looks to be wearing a pistol under his left arm. Note, however, that this picture isn't terribly plain to me, and my aging eyes give me trouble at times. Hope this was some help to you.
"Lay it close and keep it coming!" Erwin Rommel, 1916