The aircraft was engaged to spray pasture with insecticide. After a ground inspection of the treatment area, the aircraft was loaded, prior to its first take-off from the strip. Another company aircraft was also operating from the 800 metre long strip. Take-off direction was to the west, with a 2 uphill slope, and a 2 to 3 knot tailwind component. The first aircraft departed without problem. The pilot of VH-KNL, departing some three minutes later, reported that the aircraft's tail was slow to lift off the ground. Some 700 metres from the start of the take-off run, the aircraft encountered soft ground. The pilot selected 20 degrees of flap but this had little effect. The aircraft became airborne and he commenced to dump his load. The aircraft struck a ridge 30 metres from the end of the airstrip, bounced and came to rest on a second ridge 200 metres further on. The pilot reported that the engine had been operating normally, but that he had been late dumping his load, when the aircraft failed to perform. There had been insufficient strip remaining to abandon the take-off. This accident was not the subject of a formal on-site investigation.