The pilot had conducted a brief pleasure flight. He intended to land to the west on a 330 m grass airstip on his own property. The strip ran east west with a 12.5 degree upslope to the west. He estimated the wind components to be 5 kt headwind and 15 kt crosswind. However, on short final, the aircraft encountered moderate turbulence and windshear. The pilot elected to overshoot, but because of the steep upslope, this required a turn north or south. He advised that from past experience in PNG, having landed on many bush strips, he would normally have turned into wind during an overshoot into a one way uphill airstrip. However, on this occasion he inadvertently turned downwind and encountered more windshear and loss of airspeed. With the aircraft facing downwind and very low in airspeed, he elected to land straight ahead in the paddock. During the latter part of the landing roll the aircraft nosewheel collided with a rock and the aircraft overturned. The pilot subsequently advised that the aircraft had recently undergone a complete overhaul and that had not contributed to the accident.