Contents• What is yield gap?• Why is yield gap study important?• Review for previous studies in Africa• Tentative protocol• Conclusions
What is yield gap?YGM, model-based yield gap (potential yield is simulated with a model)YGE, experiment-based yield gap (potential yield is estimated with a field experiment)YGF, farmer-based yield gap (potential yield is estimated with maximum of farmers’ yields) (Lobell et al., 2009)
Why is yield gap study important?• Identify areas with potential to increase food supply• Identify causes of yield gap• Provide research prioritization• Identify measures to increase crop production
The causes of yield gaps (FAO, 2004)• Biophysical• Technical management• Socio-economic: farmers’ knowledge, household income/expenses/investment• Institutional/policy: government policy, rice price, credit, input supply, land tenure, market• Technology transfer and linkages: competence and facilities of extension staff; farmers’ resistance to new technology
Previous studies on yield gaps in Africa• 4 agroecological zones in West Africa• Irrigated lowland, rainfed lowland and rainfed upland• Assessment of on-farm yield variation and its causes
Yield gaps in West Africa: 40% of potential yield 12 100% potential yield 80% potential yield On-farm yield (t/ha) 8 4 y = 0.4337x 0 0 4 8 12 Potential yield (t/ha)Model-based yield gap was used for irrigated lowland, whereas experiment-based yield gap or farmer-based yield gap was used for rainfed systems.
Irrigated lowland in Sahel, Sudan savanna, and Guinea savanna (Wopereis et al. 1999)• Timing and amount of N fertilizer• P and K deficiency• Unreliable irrigation• Delayed planting in the wet season• Weed control• Late harvestingIrrigated lowland in Equatorial forest (Becker and Johnson, 1999)• Water control• Seedling age• Time of weeding• Number of N splits• P application
Rainfed lowland rice (Becker and Johnson, 2001)• Bunding• N rate• Fertilizer N split• P fertilizer• Timing of weed controlRainfed upland rice (Becker and Johnson, 2001)• Fallow length• N availability• Weed management• Unidentified constraints may be drought, P, soil physical properties, or pests
Limitations in previous studies in Africa• West Africa only >>> More than 10 countries including East Africa• Unexplained yield gaps; unidentified factors >>> field monitoring using simple score (weed incidence, pest damage, field water condition, salinity and etc.) >>> soil nutrients & physical properties
Tentative protocol• Survey plan• Field survey and data collection• Follow-up interview (after harvest)
Survey plan 1• Selection of target community and fields by socio- economic unit, based on diagnostic survey• 50-100 fields per hub• Farmers often have several parcels in the community for rice cultivation, and one parcel is to be selected for this survey• Weather station
Survey plan 2• In the first visit, area to be surveyed is determined (at least 200 m2)• Field survey is to be made at least every 15-20 days from around 10 days after transplanting or direct seeding until harvest• Field observers should not give advice on crop management practices to farmers
Field survey and data collection 1Data collection at first visit Data collection at 2nd visit to visit before harvestCode number for each surveyed area & sketching mapLatitude/longitude, and elevation (m)Rice ecologyApproximate area of the parcel (include surveyed area)Previous crops or length of fallowVarietyIrrigation / drainage systemLand preparation methodCrop establishment method and intercroppingCrop densitySoil samplingEstablishment of plots where rice is harvestedGrowth stages of rice plants Growth stages of rice plantsRice canopy cover Rice canopy coverWater status Water statusIron toxicity (irrigated or rainfed lowland) Iron toxicity (irrigated or rainfed lowland only)Alkali Injury & salt injury (irrigated or rainfed lowland) Alkali injury & salt injury (irrigated or rainfed lowland only)Weed infestation Weed infestationCanopy cover of crops intercropped with rice Canopy cover of crops intercropped with rice Diseases Insect pests
Field survey and data collection 2Data collection on crop management practices (‘rate-and- date’), through interview and providing sheets in which farmers can fulfill their activities in the surveyed plot.• Soil fertility management• Weed management• Pesticide use• Water management
Field survey and data collection 3Data collection at harvestRice canopy coverWater statusIron toxicity (irrigated or rainfed lowland)Alkali Injury & salt injury (irrigated or rainfed lowland)Weed infestationCanopy cover of crops intercropped with riceHarvest dateYieldLodging incidenceRice samples for nutrient analysisSpikelet fertilityRat/bird damage
Follow-up survey• Constraints and farmers’ poor crop management practices are identified Follow-up interview• Identify causes of poor crop management practices• Get an idea about a level of farmers’ knowledge of rice cultivation and technologies use
Conclusions• Multidisciplinary approach• Intensive field observation + interview• Training
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