While climbing out, I noticed the left fuel tank was indicating less than one-quarter full. I (very unwisely while climbing out) decided to switch to the right tank. The tank selector valve on the Cessna 120 is between the seats. Without looking down, I moved the tank selector handle from the left past the center detents to the right, intending to feed from the right tank. There at 300 feet, still climbing over a muddy, plowed Illinois corn field, my engine quit. Too low to turn back, I set up to land in the black field.