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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
ESTIMATING YIELDS AND YIELD GAPS:
Experiences from East Africa
Godfrey Taulya, Lydia Wairegi, Piet van Asten
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
PRESENTATION OUTLINE
1. General approach
2. Yield estimation in banana/plantain systems
3. On-farm monitoring study vs. one-time farm visit survey
4. Non-destructive bunch weight estimation
5. Yield-determining factors and yield gaps
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
GENERAL APPROACH
1. What is happening in
farmer fields ?
2. Study single factors in
controlled environments
3. Field validation and testing
for interactions
4. Modeling to understand
interactions and extrapolate
5. Proposing technologies for
on-farm testing
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
Understanding existing spatial variability
at regional scale
0 125 250 km
L. Kivu
L. Edward
L. Tanganyika
L. Victoria
Rwanda
Uganda
TanzaniaBurundi
DRCongo
Kenya
30°E 35°E
0°
5°S
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
Understanding existing spatial variability
diagnostics at farm scale
Michael Okumu, Severine Delstanche
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
YIELDS IN BANANA/PLANTAIN SYSTEMS
Integrative index for
impacts of:
• constraints
• cultural practices
Yield bunch weight
• Harvests are year-round
• Temporal variations in
fresh bunch weight
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
YIELD DATA COLLECTION BY FARMERS
One-time farm visits during surveys patchy data
o Mature bunches may be weighed
o Immature bunches: visual ‘guestimates’ + extrapolation
Farm monitoring studies comprehensive data
o Challenge: Synchronizing farm visit with harvest operations
Yield data collection by farmers in monitoring studies
o Extra demands on the farmer (time and labour)
o Literacy/numeracy skills; accuracy and consistency in data
o Restricting studies to literate farmers can bias datasets
• Greater resource endowment, higher standard of management
are correlated with higher literacy levels
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
ESTIMATION OF FRESH BUNCH WEIGHT
General allometric function for estimation of fresh bunch weight (FBW, kg)
at harvest was established through linear regression:
Where:
H is number of hands per bunch
F is number of fingers on second-last hand
V is the pseudostem volume at 1-m above ground (cm3)
k is linear regression intercept while a, b and c are coefficients
Where:
G0 is girth at base of pseudostem (cm)
G1is girth at 100 cm above ground level (cm)
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
Across regions in Uganda
APPLICATION OF ALLOMETRIC FUNCTION
Across cultivars in Uganda
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
LIMITING FACTORS AND YIELD GAPS
Each farm was visited once in 4
to 6 weeks
Input data for the allometric
function were collected on
flowered plants
Agronomic management/crop
environment, pest damage data
were also collected
Boundary line analysis
identify the limiting factor/s
and to quantify the yield gap
due to each factor
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
LIMITING FACTORS AND YIELD GAPS
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
LIMITING FACTORS AND YIELD GAPS
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International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org
Evaluation of yield-determining factors during plant growth,
and
Non-destructive estimation of bunch weights based on
allometry permit:
Identification of limiting factors
Quantification of yield-gap
CONCLUSIONS