| dc.description.abstract | Three sweet potato varieties namely, Kemb-30, Kemb-9 and Kemb-
8 were evaluated in two trials conducted at the Field station of
the Faculty of Agriculture, University of Nairobi in the first
cropping (1991 May planted crop) and second cropping (1991 October
planted crop) seasons, respectively. The main objective of the two
trials was to evaluate the effect of cutting fixtures and stubble
height on dry matter yield of both tubers and vines, nutri tive
quality, regrowth and varietal response. The trials of both
seasons were laid out in a split-split plot randomized block design
replicated three times. The three varieties of sweet potatoes
constituted the main plots and two stubble heights (i.e. 25cm and
50cm) constituted the sub-plots. Four levels of cutting fixtures
(i.e. 4-weekly, 6-weekly, 8-weekly and control) superimposed on
stubble heights constituted sub- sub plots. In both seasons Kemb-8
tuber yields were significantly lower (P .:5 0.05) than those of
Kemb-30 and Kemb-9. However, no significant differences in tuber
yield was observed in the latter two. The tuber yields of the 25cm
stubble were significantly lower (P .:5 0.05) than the less cut
stubble of 50cm for Kemb-30 and Kemb-9. However, Kemb-8 was least
affected by either stubble height. Cutting fixtures of 4-weekly,
6-weekly and 8-weekly were not significantly different in their
tuber yields. However, the tuber yields of the control were
significantly higher than the latter three. In the first cropping
season Kemb-9 yielded a significantly better grade quality
(marketable yield) (P ~ 0.05) than Kemb-30 and Kemb-8. However, in
the second cropping season no significant differences were observed
between Kemb-9 and Kemb-30. The stubble height and cutting
treatments did not elicite any significant differences in grade
quality (marketable yield) amongst the cultivars. In the first
cropping season the 50cm stubble yielded significantly higher (P ~
0.05) tuber number per plant than the 25cm stubble. In the second
cropping season no significant difference in tuber number per plant
occurred. Results have however, suggested that less cutting of
vines (i.e. at 50cm stubble and at 8-weekly or control) generally
tended to increase tuber yield, tuber grade and tuber number per
plant. Kemb-8 vine yields were significantly higher (P ~ 0.05)
than Kemb-30, but no significant differences (P ~ 0.05) were
observed between Kernb-8 and Kemb-9; and also between Kemb-9 and
Kemb-30 in both seasons. The response of Kemb-30 was however,
consistently low across the cutting fixtures. The cuts at 8-weekly
and the control, on the other hand, produced higher vine yields.
In both seasons, highly significant positive association with tuber
yield was exhibited by higher average number of tubers per plant,
a better marketable yield (grade quality) and a less severe stubble
height for the three varieties of sweet potatoes. Leaf area did
not show as much association as there was a lot of variation among
varieties and the association of the latter with tuber yield across
all varieties and cuts in terms of leaf area in both seasons was
actually negative. vines across all varieties had significantly (P
~ 0.05) a higher content of CP than napier grass and appropriate
for complimenting napier grass in Zero grazing. The tuber fraction
in terms of its possible utility value as a feed appears to rest in
its inherently high hemicellulose content (53%) compared to napier
grass (30%) and vines (9%). | en |
