The pilot of the amateur-built, amphibious, light-sport airplane reported that the airplane accelerated and lifted off from the asphalt runway without incident; however, during the initial climb it encountered "severe turbulence." The pilot was not able to control the airplane and was attempting to return to the airport when it landed hard in a soy bean field, resulting in substantial damage to the fuselage. Postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation; nor did the pilot report any. The pilot reported that winds at the time of the accident were light and variable, with gusts up to 8 knots.