The helicopter pilot was flying between six and seven feet above the ground, at an airspeed of 20 knots, over a field of rice to cross-pollinate the crop. The pilot stated that he encountered a low rotor rpm situation and the helicopter started to settle. As soon as the helicopter descended, the landing skid became tangled in the rice plants, the helicopter impacted the rice field, and came to rest on its side. During the collision with terrain, the tail boom and main rotor separated from the fuselage. An examination of the helicopter and its systems, conducted by a Federal Aviation Administration inspector, revealed no preimpact mechanical failures or malfunctions.