the diffuse color is wrong. make it dark brown, and make the spec color shift to a pale yellow. mud also has tight spec values... to play with that use a gloss map if you have that option. You also need to make the mud look soft like the reference.
Also make the diffuse a darker brown. All the colors melt together too much as it is now and you can't really tell what those pools are. On a sidenote: you should do something about your grass alpha planes. I never make grass on a single non-subdived plane unless I -KNOW- that they will always face the camera (be a…