THE PILOT'S ATTENTION WAS DIVERTED TO INSIDE THE COCKPIT FROM A LOW OIL PRESSURE CONDITION AFTER HE MANEUVERED FROM AN AGRICULTURAL SWATH RUN. AS HE ATTEMPTED TO ADJUST THE ENGINE CONTROLS FOR THE CONDITION, THE AIRPLANE STALLED AND DESCENDED UNCONTROLLED INTO A COTTON FIELD. THE PILOT STATED THE AIRPLANE HAD REACHED 300 FEET AGL WHEN THE STALL OCCURRED AND HE DID NOT HAVE ENOUGH ALTITUDE TO RECOVER BEFORE IMPACT. THE USABLE OIL QUANTITY FOR THE ENGINE IS 16 QUARTS. FOUR QUARTS OF OIL WERE DRAINED FROM THE ENGINE BY THE FAA INSPECTOR AND RECOVERY PERSONNEL AT THE ACCIDENT SITE.