The middle four rows in each plot were harvested by hand on 14 June and 9 June in 2000
and 2002, respectively. The number of tubers per plant, tuber yield per plant, and mean
tuber weight (g) were determined from 10 randomly selected plants in each subplot prior to
harvest. After harvesting, tubers of each plot were graded into three size categories (>45,
28–45 and