New Zealand Journal of Crop and Horticultural Science abstracts

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Effect of environment and time of planting on the production and quality of yacon (Smallanthus sonchifolius) storage roots

J. A. Douglas
J. M. Follett*

New Zealand Institute for Crop and Food Research Limited
Private Bag 3123
Hamilton, New Zealand
email: douglasj@crop.cri.nz

M. H. Douglas

New Zealand Institute for Crop and Food Research Limited
Private Bag 50 034
Mosgiel, New Zealand

B. Deo

New Zealand Institute for Crop and Food Research Limited
Private Bag 4704
Christchurch, New Zealand

J. J. C. Scheffer

New Zealand Institute for Crop and Food Research Limited
Cronin Rd., RD1
Pukekohe, New Zealand

R. A. Littler

Department of Statistics
The University of Waikato
Private Bag 3105
Hamilton, New Zealand

M. Manley-Harris

Department of Chemistry
The University of Waikato
Private Bag 3105
Hamilton, New Zealand

Abstract The tuberous root yields of yacon (Smallanthus sonchifolius) were compared from field trials planted in September, October, and November at four sites (Pukekohe, Hamilton, Lincoln, Mosgiel) across New Zealand. The September plantings gave the highest yields at all sites, with the October plantings giving 17% less yield and the November plantings 61% less. The September planting at Hamilton produced the highest yield of 90 t/ha, Pukekohe 64 t/ha, Lincoln 22 t/ha, and Mosgiel 15 t/ha. Regression analysis established a strong positive relationship between dry root yield and accumulated growing degree days (GDD) below 10°C calculated for base temperatures 0, 6, and 8°C (R2 = 0.87–0.88). Regression analysis R2 values declined above 10°C. Dry root yields were high where heat accumulation was at least 1800 GDD8 for the growing season with c. 1 t/ha of dried roots being produced for every additional 100 GDD8 above 1200 degree days. This relationship helps to identify suitable production environments for yacon. Best root production also needs an undefined level of cool temperatures as at the warmest site crown production was favoured. Total fructo-oligosaccharide (FOS) content of the yacon roots varied from 48.2% to 67.5%. November yacon had the lowest FOS content and conversely the highest content of non-FOS carbohydrates.

Keywords yacon; Smallanthus sonchifolius; time of planting; root yield; fructo-oligosaccharides; growing degree days

New Zealand Journal of Crop and Horticultural Science, 2007, Vol. 35: 107–116
0014–0671/07/3501–0107      © The Royal Society of New Zealand 2007
*Deceased.
H06086; Online publication date 20 March 2007. Received 12 September 2006; accepted 9 February 2007

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