Archives of psychiatry and psychotherapy

The effects were studied of potassium sulfate and potassium chloride applied at rates up to 640 kg/ha K on tuber specific gravity, size and susceptibility to internal bruising. The field experiments from which these data were obtained were conducted during the 1982-83 and 1983-84 seasons throughout the main potato-growing areas of South Australia. For the deficient and marginal site groupings, there was a consistent positive trend in specific gravity as potassium sulfate rates increased up to 640 kg/ha K. There was a slight negative trend when potassium chloride was used. Potassium fertiliser had no consistent effect on specific gravity at sites in the non-responsive grouping. Petiole or tuber potassium concentrations were poorly correlated with specific gravity. In the deficient and marginal groups increasing rates of potassium increased the yield of 80-350, 350-450, 450-680 and greater than 680-g tubers. The percentage increase in yield was greatest for the larger size grades (350-450 g or larger). At sites in the non-responsive group potassium had no effect on tuber size. At 2 out of 9 sites the effect of potassium chloride on tuber size was significantly different from that of potassium sulfate. Potassium chloride at rates of 160 and 320 kg/ha K reduced the susceptibility of tubers to internal bruising at 3 out of 4 sites. Potassium sulfate was effective at 3 out of 6 sites but only at the highest rate tested (640 kg/ ha K). Susceptibility to internal bruising was significantly (P t 0.01) negatively correlated with both petiole and tuber potassium concentrations. Prognostic critical potassium concentrations above which internal bruising was minimised were 8.30% in petioles or 1.84% in tubers. These values were calculated using the Cate-Nelson separation