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.

https://dx.doi.org/10.1016/j.eja.2014.11.003

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https://dx.doi.org/10.1016/j.eja.2014.11.003

Plant Density; Mulching; Soil Fertility

Africa South Of Sahara

Uganda

European Journal of Agronomy