Tuberous roots of yacon (Polymnia sonchifolia) contain a large amount of oligofructans. So, they draw great attention as a healthful diet, and powder of the tuberous roots and tea of the leaves of yacon are sold already. But reports concerning the cultivation of yacon are few, and the injuries to the yield by continuous cropping has not been tested yet.
So, we compared the growth and yield of yacon in two fields; in one field yacon was replanted for four years (continuous cropping field) and in the other field yacon was replanted for three years followed by no cultivation for one year (no-cultivation field).
Three experimental plots were made on each field; soil disinfection plot, plowing plot replacing surface soil with subsoil and usual cultivation plot.
Results as follows:
1) Main stems grew more vigorously in the continuous cropping field than in the no-cultivation field.
2) Number of stems per plant was higher in the no-cultivation field.
3) Top weight of yacon from each plots in the continuous cropping field had a tendency to be heavier than that from the plots in the no-cultivation field. But, in the no-cultivation field, top weight in the soil disinfection plot was heavier than the other two plots.
4) In the no-cultivation field, total weight of tuberous roots 100g exceeding were low in the plowing plot replacing surface soil with subsoil and the usual cultivation plot.
5) Thickening of tuberous roots were inferior in the no-cultivation field.
6) Correlation between the fresh weight of tuberous roots and the top fresh weight was r=0.94.
7) We concluded that yacon is not subject to injury by continuous cropping.

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Tuberous roots of yacon (Polymnia sonchifolia) contain a large amount of oligofructans. They have a growing interested as a food for health and as a raw material of oligofructans. Then it is necessary to establish yacon culivation technique.
We tested on the effect of the weight of seed tuber on the growth and yield of yacon.
Three experimental plots were made; 10g plot, 30g plot and 50g plot. Three replications were made on each plot.
The results were as follows:
1) Growth of yacon in all stage tended to the best in 50g seed tubers planting and slow in 10g seed tubers planting.
2) The number of stemes per a plant on November 2 were 4.3 in 10g plot, 5.1 in 30g plot and 5.9 in 50g plot, and it was significance in each plot.
3) The top fresh weight was produced 967g/plant in 10g plot, 960g/plant in 30g plot and 1005g/plant in 50g plot, but it was nonsignificance in each plot.
4) The yield of yacon tuberous roots in the weight was produced 1545g/plant in 10g plot, 1706g/plant in 30g plot and 1712g/plant in 50g plot, and the weight in 50g plot was closed to 30g plot, but it was nonsignificane in each plot.
5) From the yield of yacon tuberous roots in each plot, it was suggested that the weight of seed tuber in planting would be desirable to 30-50g.

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We have been cultivation tests of Yacon (Polymnia sonchiforia) since 1987, and their results were reported. But it is not yet tested that the influence of ridging on the growth and yield of yacon.
We tested on the influence of the methods of ridging on the growth and yield of yacon in Light-colored Andosol.
Three experimental plots were made; level row plot, level row→high ridge (by earthing up) plot and high ridge plot. Three replications were made on each plot.
The results were as follows:
1) Growth of yacon of main stem in all stage was nonsignificant difference in each plot.
2) The top was produced 748g/plant in level row plot, 900g/plant in level row→high ridge plot and 904g/plant in high ridge plot, but nonsignificant difference in each plot.
3) The tuberous roots was produced 1268g/plant in level row plot, 1280g/plant in level row→high ridge plot and 1584g/plant in high ridge plot, but nonsignificant difference in each plot.
4) From yield of yacon tuberous roots in each plot, it was suggestted that the earthing up at August 4, it would have little influence on yacon yield.
5) From yield of yacon tuberous roots in each plot, it was judged that high ridge culture would be useful for the harvest of the tuberous roots of yacon with a potato digger.

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Tuberous roots of yacon (Polymnia sonchifolia) contain a large amount of oligofructans. They have a growing interested as a physiologically functional food and a raw material of oligofructans. Then it is necessary to establish yacon cultivation technique.
We tested on the influence of the number of times of weeding on the growth and yield of yacon on a Light-colored Andosol field.
Three experimental plots were made: four times of weeding plot (4 times plot), two times of weeding plot (2 times plot) and non-weeding plot. There replications were made on each plot.
The results were as follows:
1) The main stem length at harvest time was 112.2cm/plant in 4 times plot, 104.6cm/plant in 2 times plot and 91.1cm/plant in non-weeding plot.
2) The top dry weight was produced 89.7g/plant in 4 times plot, 80.4g/plant in 2 times plot and 26.4g/plant in non-weeding plot.
3) The largest leaf on the main stem on September 1 and after that was always the largest in 4 times plot, and the smallest in non-weeding plot.
4) In each plot, the relative illuminance at the base of the plants were the lowest on August 4, but at the top of the plants in non-weeding plot, it was the lowest on September 2.
5) The yield of yacon tuberous roots in the weight was produced 1772.2g/plant in 4 times plot, 1522.9g/plant in 2 times plot and 175g/plant in non-weeding plot.
6) The correlation of the top dry weight with the yield of the tuberous roots in the weight or numbers were very high and the correlation coefficient were over 0.99.
7) These results suggested that the weeding in yacon cultivation would be valuable work espcially early growing stage, and it must do three or four times by the beginning in September.

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Tuberous roots of yacon (Polymnia sonchifolia) contain large amount of oligofructans. They drew great attention as raw materials for the extraction of oligofructans. So, it is necessary to the establish yacon cultivation techniques.
We have done an experiment on the date of planting for the growth and yield of yacon.
Planting were done on April 10, April 20, April 30 and May 10. Four replication were done at each planting.
The results were as follows:
1) The average soil temperature (10cm in depth) of the last ten days of April was 15.8°C.
2) Growth of yacon in all stages of April 10 planting was slow but the best in April 20 planting.
3) The top fresh weight was the lowest in April 10 planting but the highest in April 20 planting.
4) The yield of yacon tuberous roots in the weight and numbers were the lowest in April 10 planting but the highest in April 20 planting.
From the yield of yacon tuberous roots in each planting, it was suggested that the last ten days of April would be the most suitable planting time of yacon in this region. And it would be desirable to plant earlier, if the soil temperature rises about 15°C.

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Tuberous roots of yacon (Polymnia sonchifolia) contain a large amount of oligofructans. So, they draw great attention as a healthful diet. Powder of tuberous roots and tea of leaves are commercially sold.
Establishment of yacon cultivation technique is now a necessity. But the effect of topdressing on growth and yield of yacon has not yet been tested.
Effects of topdressing were tested in 1993 and 1994.
Results as follows:
1) Tops of yacon grew vigorously and stem numbers increased by topdressing.
2) Total yield of tuberous roots did not increase by topdressing.
3) Yield of tuberous roots exceeding 300-400g decreased by topdressing.
4) Topdressing has little effect on yield of tuberous roots in the tested.

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Cultivation of yacon (Polymnia sonchifolia) has gradually been spreading in Japan. We experimented on the effect of planting methods on the growth and yield of yacon by using a Light-colored Andosol. Two experimental plots were made: plot A in which seed tubers were placed directly into the field soil and plot B in which seedlings were transplanted after raising them.
The results were as follows.
1) Growth of yacon in plot A was faster than that in plot B in the initial stage. But, at harvest, the difference of top fresh weights and dry weights were not significant in both plots.
2) Since the yield of yacon tuber in plot A (46.8t/ha) was much higher than that in plot B (27.8/ha), the method placing seed tubers directly into the field soil will be more suitable to obtain maximum yield.
3) Since more time was used for weed control in plot A than in plot B, investigation of the weeding system will be necessary.

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