ACFT was observed departing on RWY 35 of a 4,250' PVT AG strip after having been loaded to near capacity with 46% nitrogen fertilizer. ACFT lifted off, crossed a fence parallel to the RWY and struck a fence that was perpendicular to the north end of the RWY. After striking the fence, ACFT settled to the GRND in an adjacent pasture. The ACFT's RT wing struck and rode up over a land plane. The ACFT subsequently struck a series of rice harrows that were supported by a barrel, flipped over and slid to a stop inverted. PLT received serious head and neck injuries. His shoulder harness support mount separated and exhibited extensive corrosion. Evidence indicated that corrosion had been previously treated. Data indicated that the ACFT departed with a 11 knot tail wind on grass strip which increased the T/O roll by 65% or approx 1,000 to 2,235'. PLT initiated dumping after lift off at mid-field.