Abstract:

Intercropping of sweetpotato with beans is common in highly
populated medium and high altitude areas of Uganda. Both sweetpotato
and bean are crops on which abundant research information is available.
However, knowledge is still lacking on how the two crops interact yvhen
grown in the proximity of each other. This problem was addressed by
conducting two sets of sweetpotato/bean intercropping experiments
Production Research Institute (NAARI), Kampala. The first experiment
aimed compatibility of different sweetpotato
morphotypes with bean of different growth types. It consisted of eight
sweetpotato genotypes (Wagabolige, Entry 20, Entry 21, Bitambi, Tororo
3, New Kawogo and Tanzania) and four bean genotypes (White Haricot,
MMS 224, A 197, and GLP 585) in the 1993/94 season with the
objective to study the compatibility of the mixtures.
In the 1 994/95 season, six sweetpotato genotypes (Wagabolige, Bitambi,
Tororo 3, New Kawogo and Tanzania) and two bean genotypes (White
Haricot and GLP 585) were used. In both seasons double rows of bean
were planted with double rows of sweetpotato at densities of about
440,000 and 33,333 plants/ha for bean and sweetpotato, respectively,
in a split plot design in four replications. The second experiment aimed
at determining the effects of spatial arrangements and plant population
density of sweetpotato on the productivity of the components.
between 1993 and 1995 at Namulonge Agricultural and Animal
at evaluating the
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It consisted of one bean genotype (White Haricot); three sweetpotato
genotypes (Wagabolige, Bwanjule and Tororo 3); two spatial
arrangements (single and double rows) and four sweetpotato plant
densities (1 6,666; 22,222; 33,333 and 66,666 plants/ha). Double rows
of bean were planted with either single or double rows of sweetpotato
in Growth and yield
measurements were done at 4 WAP and continued at two weeks
interval. Beans and sweetpotato were harvested at three and six MAP,
respectively.
Light interception efficiency increased by an average of 8.1% of
intercropping in all plant types except the spreading type. Bean plant
height and leaf area indices of both species were also reduced by
intercropping. Sweetpotato LAI increased with an increase in
sweetpotato population while bean LAI increased with an increase in
plant height and number of primary branches.
Storage root yield was increased by intercropping in the first
experiment by an average of 23.1%,of the sole crop yield, but was
reduced by an average of 22% in the second experiment. Bean yield
was reduced by an average of 40.7% and 54% in the first and second
experiments, respectively. The most compatible sweetpotato and bean
morphotypes for intercropping relative to their respective sole crop yield
was the erect and the determinate types, respectively.
I
a split-split plot design in. three replications.
the sole crop. Sweetpotato vine growth rate was reduced by
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In the first experiment the highest productivity of 30.1 t/ha and 28.4 t/ha
were produced in mixtures with genotype Wagabolige in 1993/94 and
1994/95 season, respectively.
In 1994/95 and 1995/96 cropping seasons (experiment II), the
highest productivity of 15.7 t/ha and 20.1 t/ha, respectively -were
achieved at 66,666 plants/ha. Bean yields were low accounting for only
2.4% and 1.5% of the productivity in 1994/95 and 1995/96,
respectively. Generally bean yields were highest with a sweetpotato
population of 22,222 plants/ha.
The competitive ability of bean was higher in single row than
but declined with increase in sweetpotato density.
Sweetpotato had lower competitive ability in single row than double
rows.
Mean land equivalent ratios (LER) were 1.60 and 1.32 and mean
LER + ATER (area time equivalent ratio) were 1.33 and 1.53 for
1 993/94 and 1 994/95, respectively. In 1 994/95 and 1 995/96 the mean
LER were 1.38 and 1.22 with average LER + ATER of 1.38 and 1.21,
respectively. These values indicate that sweetpotato/bean association
is biologically sound.
In monetary terms, sweetpotato/bean association is economically
sound because mean monetary equivalent ratios (MER) were 1.60 and
1.15 for experiment one and two, respectively.
I
double rows
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Mixtures of sweetpotato and bean have higher nutrient demand than
when they were grown in pure stands, with sweetpotato demand
exceeding that of bean.