Effect of plant density and depth of harvest on the production and quality of licorice (Glycyrrhiza glabra) root harvested over 3 years

Abstract

Licorice (Glycyrrhiza glabra) root production was investigated in Central Otago, Canterbury, and Waikato regions of New Zealand over 4 years. Increasing plant populations at establishment had a large effect on production. Maximum root and rhizome production was achieved with plant populations above 24 000 plants/ha. Low plant densities favoured rhizome production and high densities favoured root production. Sampling roots and rhizomes to 900 mm showed that the majority of production was in the top 300 mm. Roots harvested from below 300 mm contained less glycyrrhizin than surface roots. Glycyrrhizin concentration increased each year and surpassed the minimum international standard of 4% in the first harvest in the Waikato but not until the third harvest at South Island sites. By the third harvest both Waikato and Canterbury grown licorice contained similar amounts of glycyrrhizin but with 90% of the glycyrrhizin content in roots in the 0–300 mm soil layer in the Waikato and in the 0–600 mm soil layer in Canterbury. These trials show that licorice can be grown in New Zealand with fresh root and rhizome yields of 17–28 t/ha in the second and third years of production and with a glycyrrhizin content above the minimum international standard.