The pilot was attempting to take off from a wet, muddy, 2600-ft long sod runway (elevation 3300 feet MSL) with full fuel and 70 gallons of 2-4-D. The airplane was computed to be below its maximum certificated gross weight. The pilot selected 5 degrees flaps. Optimum takeoff performance is achieved using 20 degrees flaps. Temperature was approximately 88 degrees and the wind was reported to be from the west-northwest at 2-3 mph. Performance figures indicate the airplane should have been able to takeoff. The pilot told an FAA inspector the airplane lifted off momentarily then settled back to the runway. The pilot's accident report said the airplane did not become airborne and this discrepancy could not be resolved. The pilot said the airplane went off the left side of the runway, went through a small pond, struck the shoulder of a road, slid across the road, and came to rest on its nose in a large pond.