GA SMA TAXIED ONTO GRASS AREA AND PROPELLER WAS DAMAGED WHEN NOSE WHEEL SUNK IN THE SOFT TURF.

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I TAXIED THE SMA OUT FOR TKOF AFTER ITS 100 HR INSPECTION. DURING THE RUNUP I REALIZED THE VACUUM PRESSURE WAS TOO HIGH; I GOT THE WARNING LIGHT. I DECIDED TO TAXI BACK TO HAVE THE MECHS LOOK AT IT. I DECIDED TO TURN THE AIRPLANE AROUND ON THE TXWY. THE TXWY WAS REASONABLY NARROW AND I REALIZED THE ACFT WOULD NEED TO GO ONTO THE GRASS MOMENTARILY TO COMPLETE THE TURN. AS I TAXIED SLOWLY ONTO THE GRASS; THE NOSEWHEEL SUNK IN; CAUSING THE PROP TO CONTACT THE GRASS; THROWING DIRT ALL OVER THE PLACE. THE PROP DIDN'T STOP; IN FACT I THOUGHT INITIALLY THAT I HAD JUST BLOWN DIRT BACK; BUT WHEN I STOPPED THE ENG I REALIZED THAT IT HAD HIT. THE PROP WAS RUINED; THE LAST 2' OR SO OF EACH TIP WAS MANGLED. A CONTRIBUTING FACTOR WAS THE PROB WITH THE VACUUM SYS. THE FBO SHOULD HAVE TESTED THE AIRPLANE BEFORE PUTTING IT BACK ON LINE. I COULD HAVE AVOIDED THE WHOLE PROB BY TAXIING OUT ONTO THE RWY AND THEN BACK TO THE TXWY INSTEAD OF TURNING IN A NARROW SPACE; BUT I DIDN'T WANT TO TIE UP THE RWY AS AIRPLANES WERE IN THE PATTERN. (SEE WHAT HAPPENS TO NICE GUYS?) BESIDES; IN PROBABLY 90% OF THE ARPTS IN AMERICA; AIRPLANES ARE TIED DOWN ON THE GRASS. I'VE OPERATED ON GRASS MANY TIMES. THE FAA REQUIRES THE DEMONSTRATION OF SOFT FIELD LNDG SKILLS; IMPLYING THAT IT'S A STANDARD PROC TO OPERATE ON A SOFT SURFACE. IT JUST DIDN'T OCCUR TO ME THAT THE GND WOULD GIVE WAY LIKE IT DID.