D. Mukasa

tCoffee is Uganda’s biggest export commodity, produced mainly by an estimated one million smallholderfarmers (<2.5 ha). Arabica (Coffea arabica L.) and Robusta (Coffea canephora Pierre ex Froehn.) are thetwo coffee species grown. Robusta is dominantly cultivated at lower elevations (<1400 m) such as inCentral and Northern Uganda and Arabica is dominant at higher elevations (>1400 m) such as Eastern,Southwest, and Northwest Uganda. Actual yields are far below (<30%) potential due to various biotic, abi-otic, and management constraints. Yet, there is no quantitative information on site-specific productionconstraints and the yield gaps attributed to those constraints. In this study, yields and diverse produc-tion factors were monitored in 254 plots of five major coffee growing regions (i.e., Central, North, East,Southwest, and Northwest). Boundary line analysis was applied to evaluate the relative importance ofthe individual production factors in limiting coffee production and to quantify the associated yield gapsat regional level. The impacts of rainfall variation on coffee yield were evaluated separately by regressionanalysis. The results of boundary line analysis indicated that biotic constraints (coffee twig borer) andpoor management practices (unproductive coffee trees and low coffee plant density) restricted Robustaproduction in the Central region; poor soil nutrient status (especially potassium) and lack of mulchingwere the causes of yield loss of Robusta grown in the Northern region. For Arabica, unfavorable soilproperties (high soil pH and phosphorus concentration) and excessive number of shade trees were themost important constraints in the East; high soil magnesium concentration and poor mulching limitedcoffee yield in the Southwest; poor soil nutrient status (especially phosphorus and potassium) and lowcoffee plant density were the important yield limitations in the Northwest. Average explained yieldgaps of individual coffee plot due to the most important production constraints were 45%, 52%, 57%,49%, and 50% of attainable yield, respectively, in the Central, Northern, Eastern, Southwest, and North-west regions. Considerably less annual precipitation was received in 2009/2010 coffee growing seasoncompared with that in the previous three years (2006–2008). Seasonal rainfall shortage occurred in theSouthwest was a significant limitation to Arabica production, while excessive rainfall across the wholegrowing season was associated with yield reduction in the Eastern and Northwest regions. We concludethat there was a large yield gap for both Robusta and Arabica coffee grown in Uganda. Boundary lineanalysis allows the evaluation of relative importance of individual production constraint directly in theplot. The important production constraints varied strongly depending on the regions, which calls forsite-specific management implementations. Soil fertility can be improved by implementing integratedsoil fertility management (ISFM) that makes use of nutrients from the soil, recycled crop residues, mulchand chemical fertilizers. Attentions should also be given to other management practices such as coffeeplant density, unproductive coffee trees and shade trees etc.

tCoffee is Uganda’s biggest export commodity, produced mainly by an estimated one million smallholderfarmers (<2.5 ha). Arabica (Coffea arabica L.) and Robusta (Coffea canephora Pierre ex Froehn.) are thetwo coffee species grown. Robusta is dominantly cultivated at lower elevations (<1400 m) such as inCentral and Northern Uganda and Arabica is dominant at higher elevations (>1400 m) such as Eastern,Southwest, and Northwest Uganda. Actual yields are far below (<30%) potential due to various biotic, abi-otic, and management constraints. Yet, there is no quantitative information on site-specific productionconstraints and the yield gaps attributed to those constraints. In this study, yields and diverse produc-tion factors were monitored in 254 plots of five major coffee growing regions (i.e., Central, North, East,Southwest, and Northwest). Boundary line analysis was applied to evaluate the relative importance ofthe individual production factors in limiting coffee production and to quantify the associated yield gapsat regional level. The impacts of rainfall variation on coffee yield were evaluated separately by regressionanalysis. The results of boundary line analysis indicated that biotic constraints (coffee twig borer) andpoor management practices (unproductive coffee trees and low coffee plant density) restricted Robustaproduction in the Central region; poor soil nutrient status (especially potassium) and lack of mulchingwere the causes of yield loss of Robusta grown in the Northern region. For Arabica, unfavorable soilproperties (high soil pH and phosphorus concentration) and excessive number of shade trees were themost important constraints in the East; high soil magnesium concentration and poor mulching limitedcoffee yield in the Southwest; poor soil nutrient status (especially phosphorus and potassium) and lowcoffee plant density were the important yield limitations in the Northwest. Average explained yieldgaps of individual coffee plot due to the most important production constraints were 45%, 52%, 57%,49%, and 50% of attainable yield, respectively, in the Central, Northern, Eastern, Southwest, and North-west regions. Considerably less annual precipitation was received in 2009/2010 coffee growing seasoncompared with that in the previous three years (2006–2008). Seasonal rainfall shortage occurred in theSouthwest was a significant limitation to Arabica production, while excessive rainfall across the wholegrowing season was associated with yield reduction in the Eastern and Northwest regions. We concludethat there was a large yield gap for both Robusta and Arabica coffee grown in Uganda. Boundary lineanalysis allows the evaluation of relative importance of individual production constraint directly in theplot. The important production constraints varied strongly depending on the regions, which calls forsite-specific management implementations. Soil fertility can be improved by implementing integratedsoil fertility management (ISFM) that makes use of nutrients from the soil, recycled crop residues, mulchand chemical fertilizers. Attentions should also be given to other management practices such as coffeeplant density, unproductive coffee trees and shade trees etc.

Coffee and banana are major cash and food crops, respectively, for many smallholders in the East African highlands. Uganda is the largest banana producer and 2nd largest coffee producer in Africa. Both crops are predominantly grown as monocultures. However, coffee–banana intercropping is common in densely populated areas. This study assessed the profitability of intercropped coffee–banana systems compared to mono-cropped systems in regions growing Arabica (Mt. Elgon) and Robusta (south and west) coffee in Uganda. The study was carried out in 152 plots in 2006/2007. Data were collected through structured farmer interviews, field measurements and observations. Coffee yields did not differ significantly (P ⩽ 0.05) between mono-crops and intercrops. Arabica coffee yields were 1.23 and 1.18 t ha−1 year−1 of green beans in mono-cropped and intercropped plots, respectively. Robusta yields averaged 1.25 and 1.09 t ha−1 year−1 of green beans in mono-crops and intercrops, respectively. Banana yields were significantly higher (P ⩽ 0.05) in intercrops (20.19 t ha−1 year−1) compared with mono-crops (14.82 t ha−1 year−1) in Arabica growing region. In Robusta growing region, banana yields were significantly lower (P ⩽ 0.05) in intercrops (8.89 t ha−1 year−1) compared with mono-crops (15.04 t ha−1 year−1). Marginal rate of returns of adding banana to mono-cropped coffee was 911% and 200% in Arabica and Robusta growing regions, respectively. Fluctuations in coffee prices are not likely to affect the acceptability of intercrops when compared with coffee mono-crops in both regions, but an increase in wage rates by 100% can make intercropping unacceptable in Robusta growing region. This study showed that coffee–banana intercropping is much more beneficial than banana or coffee mono-cropping and that agricultural intensification of food and cash crops in African smallholder systems should not solely depend on the mono-crop pathway.► Yields did not differ between mono-crops and intercrops for both coffee types. ► Intercrops had higher banana yields than mono-crops in Arabica growing region. ► Intercrops had lower banana yields than mono-crops in Robusta growing region. ► Intercropping is agronomically and economically more beneficial than, mono-cropping.