Pilot reported that the aircraft encountered sink soon after take-off. The main wheels contacted the crop (tea) and the aircraft nosed over. The pilot indicated that there were no mechanical problems with the aircraft of which he was aware. The aircraft had been operating with similar loads throughout the day. The wind was gusting at the time of the accident, and there was a possibility of windshear being present. In addition, the pilot had conducted more than 80 flights on the day of the accident, for about 6 hours flying time. It is possible, therefore, that he was suffering some fatigue at the time of the accident.
