RESULTS
Tuber yield was higher in 1999 early season planting
than in 2000 late season planting by 28 percent. Late planted cassava tuber yields were reduced by 44% in NR
8082, 45% in TMS 000447 and 15 % TMS 00033. It was,
however, increased in the lowest yielding variety TMS
91/453 by 17%. Tuber yield differ significantly between
varieties (Table 2). Yields were highest from NR 8082
and TMS 00033 planted early or late. The yield reduced
from 44 t/ha to 25 t/ha in NR 8082 due to late planting
but TMS 00033 was stable and varied from 36 to 31 t/ha.
Varietal differences in number of tubers per plant was
significant for early planting with TMS 91/453 having the
lowest number of tubers and yield during this period. For
late planting, the numbers of tubers were similar among
the varieties and ranged between 5 and 6 per plant. The
incidence of tuber rot in 1999 early plating was 17 and
20% in TMS 00447 and TMS 91/453, respectively. For
the 2001 late planting, TMS 00447 had the highest
incidence of rot (17.60%) but in both periods of planting,
NR 8082 and TMS 00033 had the lowest tuber rot of 8 -
11%.
The addition of fertilizer did not improve the tuber yield
of early-planted cassava varieties but the late cultivation
showed negative yield response to fertilizer. Reduction in
tuber yield was significant with the addition of 400 and
800 kg NPK per hectare. Fertilizer application did not
have influence on the number of tubers per plant and the
incidence of tuber rot (Tables 2 and 3). Across the
fertilizer rates, number of tubers per plant was between 5
and 6 and the incidence of rot varied from 12-17% and
11-15% of tuber harvested in early and late planted
cassava, respectively. Severity of rot was mild for variety and fertilizer in both early and late planting despite the
significant interaction observed during late planting. At
this period, NR8082 showed higher resistance to rot than
other varieties except TMS 00033 at 800 kg/ha fertilizer
rate.