A pilot reported his Zenith Zodiac CH-601 HDS lost power at 150 FT after takeoff and required an immediate landing in a frozen field beyond the runway's end with no damage to the aircraft.

Narrative

Aircraft lost at least 50% of power after take-off; between 50 FT and 150 FT AGL. Engine was still running but aircraft would not climb. Switching tanks and running fuel boost pump did not solve problem. [I] was too high to land on remaining runway; too low for safe go-around. Field immediately beyond runway was clear (no obstacles or people; etc.) so I cut the power and descended to land. Field was a harvested cornfield. Short roll-out on frozen ground surface; no damage to aircraft or anything on ground; no injuries whatsoever. We recovered the airplane with pick-up trucks and towed back to airport via county roads. No damage to aircraft or property and no injuries during aircraft recovery. Upon reaching airport we ran the engine for many minutes on each tank and could not duplicate problem. Subsequent tests days later revealed that running the engine from the left tank would duplicate the problem; while switching to the right tank would smooth it out. We do not suspect carburetor ice from the problem last month; but believe that either the fuel in the left tank is contaminated (water or other debris) or perhaps the fuel tank vent line was clogged.