The response of potato (Solanum tuberosum L.) cultivars Russet Burbank and Kennebec to soil and fertiliser potassium (K) was studied on basaltic krasnozems of north-west Tasmania. Yield increases in response to fertiliser K were recorded at sites with up to 300-400 mg/kg of bicarbonate extractable soil K. The close correlation between relative yield and soil K indicated that soil K can reliably predict fertiliser requirements. Petiole K concentrations at early tuber set increased with fertiliser K at responsive sites; maximum yields were achieved with 12-14% petiole K for Kennebec and 11-13% for Russet Burbank. Petiole K concentrations provide an excellent indication of the K status of a growing crop. Tuber K concentrations increased with both soil and fertiliser K, and yields of 50-80 t/ha removed 180-380 kg K/ha in the tubers. At severely deficient sites specific gravity and crisp colour increased with low rates of fertiliser K, but the general trend was for fertiliser K to reduce specific gravity and crisp colour. Bruising susceptibility decreased with fertiliser K at some sites but the physiological disorder, 'hollow heart', was not influenced by fertiliser K. There were consistent differences between the 2 cultivars. Russet Burbank required higher soil K, had lower petiole and tuber K concentrations and removed less K in the marketable tubers.

Four field experiments were conducted to examine the yield response and cadmium (Cd) concentration of potatoes (Solanum tuberosum L. cv. Russet Burbank) grown with banded or broadcast phosphorus (P) fertiliser at rates up to 240 kg P/ha. The Cd content of the triple superphosphate (TSP) was 151 mg/kg. All 4 sites were on intensively cropped, high P-fixing krasnozem soils in north-western Tasmania, with concentrations of Colwell-extractable P ranging from 112 to 210 mg/kg. All sites showed economic yield responses to banded P, but broadcast P was much less effective except at the site where the response to banded P was least. Yield responses came mostly through increased tuber number, but at 1 site the tubers were also bigger. There was no effect of P on tuber size distribution or specific gravity. Increasing rates of banded TSP increased tuber Cd concentrations by 50-300% at the 3 sites where they were measured; broadcast TSP had little effect. Tubers from the site with pH 6.0 had much higher Cd concentrations than those from the sites with pH 6.5 and 6.6. Petiole Cd concentrations were about 5 times greater than tuber concentrations.