At 1400 central time, an American Champion 8GCBC struck a ditch and nosed over while landing on a gravel road near Sunburg. The pilot was not injured. The pilot said the purpose of the flight was to take aerial photographs of some Minnesota farms. While in cruise, he got the sudden urge to use the bathroom and selected a gravel road to land on. The pilot stated that during landing rollout he noticed a sign on the left side of the road and he maneuvered to the right to avoid it, causing the right wheel to go into the ditch.