Effects of soilless media, nutrition, and pH on tuber russeting in Sandersonia aurantiaca

Abstract

The effects of two soilless media (peat/pumice and bark), three nitrogen (N) rates (25, 100, and 500 g N/m²), three potassium (K) rates (12.5, 50, and 200 g K/m²), and media pH (4.4, 4.8, 5.5, and 5.9) on tuber russeting in Sandersonia aurantiaca were assessed in two experiments. Russeting scores were less in the bark medium and increased with N rate and with increasing pH. Tuber weight and secondary tuber numbers were less in the bark medium than in the peat/pumice medium and increased with increasing N rate and pH, but declined at the highest rates. Tuber numbers were greater in the peat/ pumice medium and with increasing N rate. Tuber N concentrations increased markedly with increasing N rate. There was no effect of K rate on tuber quality. To maximise production of export quality tubers with low secondary tuber numbers and an acceptable level of russeting, N rates of up to 33 g N/m² in a peat/pumice medium are recommended at pH levels of less than 5.0. Using a bark medium will reduce tuber russeting, secondary tuber numbers, and weight.

Keywords:

• Sandersonia aurantiaca
• sandersonia
• tuber
• soilless medium
• nitrogen
• potassium
• pH
• russeting
• tuber quality