Agronomic and environmental determinants of coffee yield, quality and cyclicity across Burundi
(2026)
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; Vanlauwe, Bernard- Abstract
- (en) Coffee is the most widely consumed cultural and social beverage in the world after water. It plays a major economic role in both producing and consuming countries. Despite favorable agroecological conditions, arabica coffee production in Burundi, its main export crop, faces critical challenges: a drastic drop in production, low and highly variable yields from one year to the next (alternation), and insufficiently competitive quality. Whereas the performance of coffee trees remains largely suboptimal, the interactions between agronomic, environmental, and nutritional factors and their combined impact on yield, cyclicity, and quality has never been studied in an integrated manner in Burundi. This thesis identifies and analyzes the factors determining the performance of Arabica coffee by integrating three dimensions: yield and yield variations, interannual production stability, and physical and sensory quality. The study combines field surveys, soil and leaf analyses, standardized sensory evaluations, and multivariate statistical methods, involving 155 farms spread across the country's three main coffee-growing areas. The results indicate that agronomic and soil fertility factors are important contributors to coffee performance in Burundi, although the relatively low proportion of explained variance suggests that other unmeasured factors may also play a significant role. Their influence nonetheless appears stronger than that of environmental factors such as climate or altitude. Burundian coffee plantations exhibit substantial yield gaps, averaging 59% below potential, with average yields ranging from 887 to 1,268 kg ha⁻¹ depending on the agroecological zone, while maximum observed yields reached 2,533 kg ha⁻¹. Random forest analysis identified soil organic carbon, mulch thickness, and soil magnesium content as the most important yield-driving variables, while the main limiting factors included inadequate weeding and mulching, aging plantations, soil acidity, and deficiencies in phosphorus, exchangeable bases, and low organic carbon. Regarding production stability, the study demonstrated that biennial bearing, which severely affects producer incomes, can be mitigated through improved soil fertility management, particularly by optimizing soil nitrogen and phosphorus content and balancing the cation ratio (Ca + Mg) / K, with plantation age also impacting stability. For coffee quality, results showed that altitude significantly increases bean size but has no direct effect on sensory quality. Instead, soil cation balance, particularly calcium availability and the avoidance of potassium and magnesium imbalances, emerged as the decisive determinant of sensory quality, with foliar analyses confirming the importance of N, P, and Ca for bean development while excess foliar Mg reduced quality. Disease and pest incidence (coffee leaf rust, coffee berry disease, insect damage) proved to be the most penalizing factors for sensory quality. The compositional nutritional diagnosis (CND) study established specific nutritional standards for three performance objectives (high yield, high quality, and combined performance), revealing that nutritional imbalances vary by objective: yield is mainly limited by relative deficiencies in calcium, magnesium, and manganese, while quality is more sensitive to imbalances in phosphorus, calcium, and manganese. Multivariate analyses revealed a clear structuring of nutritional indices reflecting lithological contrasts, separating soils derived from silica-rich acidic rocks from those developed on iron- and phosphorus-rich basic rocks. This thesis demonstrates that improving coffee cultivation in Burundi requires appropriate soil fertility management, nutritional balance, plantation renewal, and disease control. There is significant room for improvement, which can be achieved without expanding the area under cultivation. The major contributions of this thesis include: highlighting the central role of manageable agronomic factors, developing an approach that simultaneously integrates yield, stability, and quality, and identifying concrete levers to reduce cyclicity and stabilize producers' incomes. From a scientific standpoint, the results enrich our understanding of the interactions between soil, nutrition, and coffee tree performance on small tropical farms. On a practical level, they provide a basis for developing appropriate agronomic recommendations that can simultaneously improve productivity, quality, and stability. Integrating these approaches into agricultural advisory services and policies promoting high-quality coffee could contribute to a lasting improvement in producers' incomes and the resilience of Burundian coffee farming.
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Kagisye, A. (2026). Agronomic and environmental determinants of coffee yield, quality and cyclicity across Burundi. https://hdl.handle.net/2078.5/276559