| dc.description.abstract | Sugarcane has been grow~ at the Coast of
Kenya for a long time. The Ramisi factory is one
of the cildest in the country. It produces a millwhite
sugar and has an annual. production potential
of 30,000 tons. The factory has the largest nucleus
estate in the country that has an area of 45,000 acres
with 12,000 acres actually under cane. The estate
supplies about 75% of the cane to the factory, the
rest is provided by the out-growers. At the Coast
normally, three harvests in a three year period are
obtained .. After that second ratoon the fields are
ploughed and replanted.
Very few trials on the effects & weeds on the
production of sugarcane have b89n done in Kenya. In
this thesis, work on the effect of weeding and row
spacing in sugarcane is reported. The objects of the
experiment were to determine: . I
(i) the effects of weed competition on t~a
yields of cane and sugar,
(ii) the influence of row spacing on weed growth
and cane yields, ,
(iii) the period of growth the cane crop is likely
to suffer most fro~ neglected weed control.
A factorial experiment was laid out in May, 1976
in plant cane of the cultivar C0421 at Famoni estate
of the Associated Sugar Company, Ramisi. The soil is
sandy clay loam that was deficient in phosphorus and
nitrogen and was acidic.
The field was ploughed and harrowed during the
major rainfall season. The rains were favourable for
germination of cane. Three noded setts were planted
end to end in the base of the furrow, after dipping
into a bath containing Aretan (an organo-mercurial
chemical) to protect the seedcane against soil-inhabiting
fungi. Double superphosphate at the rate of 250 kg
per hectare was applied before planting in the base
nf furrows and covered with a little soil. Half the
nitrogenous fertilizer (250 kg/ha of C.A.N.) was applied
four weeks after planting and the rest half dose was
top dressed four weeks later. Rainfall in 1976 was
over 100 cm. Toe only crop grown at the site~ which
...has been cropped for several years. is sugarcane. On
the experimental plots there were both perennial and
annual grass and broad-leaved weeds.
the trial consisted the following treatments:-
Spacings: Sl - 100 em
S2 - 125 em
S3- 1'50'Cm
'-weeding:
A - Control = free from weeds up to time of harvest
8 - Free of weeds for the first 120 days and weed infested
,until harvest
C - Free of weeds for the first 90 days and weed infested
,until harvest,
o - Free of weeds for the first 60 days and weed infested
until harvest
E - Free of weeds for the first 30 days and weed infested
until harvest
F - Free of weeds for the first 15 days and weed infested
until harvest ,
G - Control = weed infested up to time of harvest
H - Geed infested fer the first 120 days and free up
to time of harvest
I - Weed infested for the first 90 days and free up
to time of harvest
J - Weed infested for the first 60 days and free up
to time of harvest
K - Weed infested for the first 30 days and free up
to time of harvest
L - Weed infested for the first 15 days and free up
to time of harvest.
The following data was collected at harvest
and during the experiment:
a) yields of cane
b) Sucrose coptent
c) Number of millable canes
d) Number of tillers per stool
e) Germination percentage
f) Height and diameter of the stalks
g) Number and fresh weight of weeds
h) Weed cover of the plots.
The results showed that cane yields were
substantially reduced due to the presence of weeds
particularly during the early stages of cane growth.
The percentage losses in yield due to unchecked weed
growth were about 70%.
The trial gave a definite indication that -
weeds adversely affect the development of crop at
early stage of growth but extent of damage decreases
at an advanced stage after the crop closes over and
shades the surrounding areas.
The presence of weeds for the first 60 days
depressed production by about- 50% and there was no
advantage in controlling after 90 and 120 days or only
for the first 15 days. The yields from these treatments
were the same as those obtained from the unweeded
control plots. But as the number of days in which the
crop was unweeded decreased, yields progressively
increased. Weed free conditions for the'first 120 days
after planting gave the same yields as the plots that
were free from weeds up to time of harvest. Considering
the number of weedings involved it becomes even
better in terms of net profit. It is suggested that
the unexpected drop in yields in the plots that
suffered weed-infestation for the first 15 and 30
days was due to the unavoidable delay in planting
after the land had been ploughed. It is obvious from
the results that weed competition between 30 and 90
days reduced the yield significantly.
The sucrose percentage in cane for the various
treatments was the same and Brix readings showed no
definite trend in the juice quality of the cane.
Reductions in yield due to weeds were brought
about mainly by the effect of weeds on the number or
millable canes and their height. Weeds had no effect
on the diameter of canes.
.The results clearly indicate that weed-free
conditions are necessary between 30 and 90 days for
optimum production of millable canes. Any weed
competition during this period adversely affects the
number of canes produced. Longer periods of weed-free
conditions produced larger number of canes and
resulted in high yields. Weed-free control produced an
average of 68,130 millable canes per hectare as
against 24,020 canes produced where there was no weed
control - a reduction of about 65%. As the number of
days when the crop was kept weed-free increased there
was a progressive increase in ~he production of millabIe
canes. Weed competition for the first 15 days only
gave the same yields as the plots kept weed free till
harvest. Similarly weed-infestation after 90 days
from planting did not reduce the number of millable
canes produced. As the number of days when the crop
experiences weed competition increases# a substantial
drop in the product ion of millable canes, is seen in
the results
Weeds did not affect the number of tillers per
stool produced and had no adverse effect on the
germination of cane under the conditions prevailing.
Stalk length is another important component of
cane yield and where canes were shorter the yields
were lower. The results clearly show that weed infestation
adversely'affects the height of cane. Weed
infestation throughout the cane growing period reduced
the height of cane by over 30% compared to the weed
free conditions. Similarly weed competition for 20
days and 90 days reduced the height of cane substantially
(25% and 22% respectively). Weeding the crop for only
15 days reduced the height by over 20% compared to
the weed-free control.
The results also show t hat weed'infestations
at the initial stages causes a setback that could not
be recouped even at later stages, resulting in
significant reduction in the final height.
From the results it appears that, in a normal
rainfall season, weed control measures should be taken
immediately after planting and to continue for the
first 120 days, or when the canopy closes. With a
clean seedbed at planting initial weed control could be
delayed. until 15 days from planting or even 30 days
during a dry season. During the rains it is important
to plant the cane as quickly as possible to avoid
the growth of weeds and their subsequent competition
at early stages of cane growth.
Therefore the indications are that at Ramisi
sugarcane need only be kept weed free for the first
120 days. This is the time when the canopy of the
plants closes and weed competition ceases.
Weed management in sugarcane may involve
cultural operations and the use of herbicides. As there
is no single method which is effective under all
farming situations. a combined use of all the
available techniques is needed to tackle the weed
management problems of the complex weed flora in
sugarcane.
In this study. reduction of row spacing from
150 to 125 or 100 cm did not affect the yield of
sugarcane. Although the number of millable canes in
the closer spacing treatments was significantly higher
than in the standard 150 cm between rows. the differences
in cane and sugar yields were not significant. The
individual cane weight was lower at narrow row spacing.
It can thus be seen that by reducing spacing 150 cm
downwards. we are not going to inc~ease yield. Wide
spacing, however provide favourable conditions for
weeds to grow and compete with the crop in the unshaded
row intervals | en |
