On October 18, 2017, at 1045 central daylight time, a Cessna 150J airplane, N50609, nosed over during a forced landing in Willmar, Minnesota. The flight instructor received minor injuries and the private pilot was not injured. The airplane received substantial damage to the wings and fuselage. The airplane was registered to an individual and was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. Visual flight rules conditions existed near the accident site at the time of the accident, and a flight plan had not been filed. The local flight had departed from the Willmar Municipal Airport (BDH), at the time of the accident.The purpose of the flight was a flight review for the private pilot. The flight instructor stated they checked the magnetos and carburetor heat during the engine runup, at 1,500 rpm, and both functioned normally. They initiated the takeoff on runway 21 (2,980 ft long, turf) which they stated was damp and soft from recent rain. The private pilot initiated the takeoff and stated that the airplane seemed slow to accelerate. The flight instructor reported he felt the nose "dive" a couple times, so he instructed the private pilot to increase back pressure and get the airplane in ground effect because of the soft runway. The private pilot stated the flight instructor took control of the airplane and lifted it off the runway. The airplane became airborne about 2,000 ft down the 3,000 ft long runway. The flight instructor stated he lowered the nose in ground effect to gain airspeed, but the airplane did not accelerate, and it was nearing an aerodynamic stall. The flight instructor stated there was a road and a field on which to land. He turned the airplane, but had to level off because he was concerned the airplane was going to stall. He stated that during the forced landing in a plowed field, he flared too high, and the airplane contacted the terrain hard on the main gear. The nose gear dug into the soft terrain, collapsed and the airplane then nosed over. The flight instructor did not notice the tachometer, but he reported that the private pilot stated the rpm never increased above 1,900. A postaccident examination and test run of the engine was conducted. The engine started without hesitation on the first attempt. The engine ran smoothly at various power settings and ultimately at full throttle which produced 2,764 rpm.