I think it's a horse drawn harrow/cultivator. If it works like the one I saw my grandfather using in his garden, the levers adjust both the depth of the shanks' ground penetration and the height of the wheel in front. The wheel when completly lowered would raise the height of the harrow for transport and when maximaly lowered would allow maximum shank penetration. The fact that the shanks are adjustable too allows for a wide range of cultivation depths for various applications and soil conditions.
PH