Abstract
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.
