Study design

Study 1

Data on plant height, leaf number and leaf area were collected every month for four months from the four innermost plants in the plots. These data were averaged to calculate mean plant height, number of leaves per plant and total leaf area per plant. Leaf area was determined according to Modi (2007). When one or more of the four central plants did not emerge any four plants were selected from the plot. Should fewer than four plants emerge in the whole plot then the average of those that had emerged was recorded.

Yield at maturity was determined by harvesting all corms from the four innermost plants, weighing the total fresh weight, counting the total number of corms and calculating the average to determine the total number of corms and total fresh weight per plant. Fresh corms were also weighed individually, classified into different weight classes and their mean specific gravity and dry corm weight recorded. Corms were freeze-dried at harvest for starch content, sugar content, alpha amylase activity and mineral content determination.

The crop planted first (in October) was considered mature when all above ground biomass had died off for the first planting; maturity was subsequently defined at four week intervals for the subsequent plantings.