THE ACFT SETTLED BACK TO GROUND CONTACT AFTER REACHING AN ALT (EST BY THE PLT) OF 60 FT AGL DURING TAKEOFF INITIAL CLIMB. THE PLT STATED THAT HE RECOGNIZED THE ACFT WAS SETTLING TOWARD THE GROUND & NOTICED A DISSIPATION OF AIRSPEED. THE PLT SAID THAT HE THEN 'ELECTED TO HOLD LOAD AS LONG AS POSSIBLE BEFORE DUMPING. I DUMPED THE LOAD 20 FT ABOVE THE POINT WHERE I KNEW I WAS GOING TO IMPACT THE GROUND.' THE DENSITY ALT WAS COMPUTED TO BE 4700 FT (ARPT FLE 3800 FT) BY THE IIC. IN THE AREA OF THE PLTS REPORT RESERVED FOR RECCOMMENDATIONS FOR PREVENTION (OF THIS ACCIDENT TYPE) THE PLT WROTE 'I BELIEVE THAT I GOT INTO A SITUATION KNOWN AS'REGION OF REVERSE COMMAND.'' THE DEFINITION OF THIS PHENOMENONDESCRIBES AN AERODYNAMIC SITUATION IN WHICH THE TOTAL DRAG OF THE ACFT INCREASES AS THE AIRSPEED DECREASES. THIS DRAG INCREASES TO A POINT WHERE INSUFFICIENT POWER IS AVAILABLE TO MAINTAIN ALTITUDE. THE PLT ALSO REPORTED THAT THE ACFT LOAD CONSISTED OF 200 GALLONS OF 2,4,D & ROUNDUP, IN ADDITION TO 55 GALLONS OF AVIATION FUEL ON BOARD.