RWY CONDITION QUITE POOR; NOSEWHEEL SINKS AND COLLAPSES ON BEGINNING OF TKOF ROLL.

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ON THE SECOND LEG OF FLT XXX; I HAD 1 PAX ON BOARD; NO FREIGHT. PREVIOUSLY I LANDED RWY 30 AND BACK-TAXIED RWY 30 TO THE RAMP. ON THE LNDG AND BACK-TAXI THE RWY SEEMED FINE. I DIDN'T FEEL ANY OR SEE ANY SOFT SPOTS OTHER THAN ON THE MIDDLE OF THE TXWY; OF WHICH I AVOIDED. FOR THE DEP I TAXIED TO RWY 30. AT THE END OF THE TAXI I BEGAN TO ADD PWR FOR THE TKOF. I WAS USING SOFT FIELD TKOF PROC. WITH PWR LEVERS 1/2 WAY TO FULL; THE NOSEWHEEL DUG IN AND FOLDED. I SHUT DOWN THE ACFT AND EVACED MY PAX (SHE INDICATED SHE WAS UNHURT). THIS SOFT SPOT WAS HARD TO SEE FROM WHAT APPEARED TO BE A RECENT PLOWING. AFTER THIS INCIDENT I LEARNED OF AS MANY AS 3 PLTS OF TWIN ENG PLANES WHO HAD TROUBLE IN THE SAME SPOT. AFTER OUR PLANE WAS REMOVED THE ARPT MGMNT DUMPED IN GRAVEL AND BLADED IT OVER; AS HE PROBABLY DID FOR THE OTHERS. THIS LEFT A HIDDEN SOFT SPOT. HE NEVER RPTED IT TO FLT SVC. I BELIEVE THIS SHOULD HAVE BEEN NOTAMED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HIS COMPANY HAS BEEN WORKING WITH THE ARPT MGR AND THE FAA TO DETERMINE WHAT WAS GOING ON AND TO IMPROVE THE SIT. RWY CONDITION HAD BEEN NOTAMED PREVIOUSLY AND THEN NOTAM REMOVED. RPTR QUITE SURPRISED WHEN NOSEWHEEL SUNK AND BROKE.