These interactions were
significantly different on tuber yield per plant, yield of >45 mm tuber and total tuber yield
per hectare in 2002 (Table 6). Un-irrigated treatment gave the lowest values for yield
parameters except smaller size (28–45 mm) total tuber yield, and yield reductions were 32
and 37% compared to the most yielding treatment in the 2000 and 2002, respectively. In
2000, tuber yield, bigger size and total tuber yield per ha increased with more water amount
under both irrigation method, although no significant differences were found between I66
and I100 treatments under SD and in overall mean of irrigation levels (Table 6). In 2002, the
irrigation at 66% level resulted in the highest tuber yield values except 28–45 mm size
tuber yield under both irrigation method, and there were significant reductions on total
yield when applying more water (Table 6). Yield depletion at the 100% irrigation level in
2002 can be attributed to rainfall that more and expanded during the growing period.