The pilot reported that he was spraying a drainage ditch when he encountered a railroad track embankment. He increased altitude to clear the tracks, but as he descended back into the ditch on the opposite side of the tracks to continue spraying, he observed a set of power lines in his flight path. He attempted to maneuver to avoid the lines, but the left landing skid of the helicopter struck the lines. The helicopter subsequently impacted an adjacent corn field about 250 feet from the power lines. The pilot was seriously injured, and the helicopter sustained substantial damage to the fuselage and tailboom. The pilot reported that there were no failures or malfunctions related to the helicopter prior to the accident.