Yield and phosphorus nutrition of potatoes (Solanum tuberosum L.) cv. ‘Delaware’ grown on a yellow Karrakatta sand containing freshly- and previously-applied Alkaloam–gypsum

Abstract

Summary. Potatoes (Solanum tuberosum L.) cv. ‘Delaware’ were grown over winter on a yellow Karrakatta sand amended with Alkaloam–gypsum (AG; previously referred to as red mud–gypsum) at up to 240 t/ha, both freshly-applied (2 experiments) and applied 2.5 years earlier (1 experiment). Several levels of phosphorus fertiliser (0–600 kg P/ha) were applied to the freshly-applied AG and a single level (600 kg P/ha) was applied to the previously-applied AG. Amendment of the soil with 60 t AG/ha (freshly-applied) doubled the amount of fertiliser phosphorus retained in the top 30 cm of soil when 100 kg P/ha was applied. On freshly-applied AG, bicarbonate-extractable phosphorus showed an upward trend with level of AG, being 16 mg/kg (0–15 cm) at 0 t AG/ha and 34 mg/kg at 90 t AG/ha. This will decrease phosphorus fertiliser requirements in the following potato crop by 49% relative to unamended soil based on previously published soil test standards. Amendment with freshly-applied AG increased the level of applied phosphorus required for 99% of maximum petiole phosphorus concentration by 46 and 139% in the 2 experiments compared with unamended soil. Maximum yield was significantly reduced by 7–10% at 60 t/ha of freshly-applied AG compared with unamended soil while on residual AG it was only reduced at 240 t/ha (12%) (trend only). Yield reductions were not correlated with a reduced availability of phosphorus, however, they may have been due to a reduced availability of potassium. The concentrations in the tubers of antimony, arsenic, cadmium, chromium, cobalt, lead, mercury and nickel did not exceed legal limits on soil amended with AG.