THE PLT RPRTD THAT DRG FLT AT 1500 FT, HE REACHED FOR THE ELEVATOR TRIM & INADVERTENTLY ROTATED THE FUEL SELECTOR TO ONE OF THE OFF POSITIONS. THE ENG THEN LOST POWER FROM FUEL STARVATION. THE PLT ESTABLISHED A GLIDE TO A NEARBY FIELD & ATTEMPTED TO RESTART THE ENG. HOWEVER, HE HAD DIFFICULTY MAINTAINING SPEED DRG THE EMERGENCY APCH & ELECTED TO CONCENTRATE ON FLYING THE ACFT. WHEN HE LANDED IN A BARLEY FIELD, THE WHEELS CONTACTED THE CROP & THE ACFT NOSED OVER. THE PLT RPRTD HE HAD A TOTAL OF 3 HRS OF FLT TIME IN THIS MAKE & MODEL OF ACFT.