Stain Buster Mud
The best ways to remove mud stains

Fabric
Let the mud dry, and then brush off as much as possible. Pretreat with a prewash stain remover and wash as usual.
Upholstery
Let the mud dry, and then vacuum up as much as possible. Mix one tablespoon of washing up liquid with two cups of cool water. Using a clean white cloth, sponge the stain with the detergent solution and blot until the liquid is absorbed. Keep sponging and blotting until the stain disappears. Sponge with cold water and blot dry.
Carpet
Let the mud dry, and then vacuum up as much as possible. Mix one tablespoon of washing up liquid with two cups of warm water. Using a clean white cloth, sponge the stain with the detergent solution and blot until the liquid is absorbed. Keep sponging and blotting until the stain disappears. Sponge with cold water and blot dry.
Worth a try
If the mud stains persist, it's possible that they were caused by an iron-based clay. In that case, treat them as rust stains.