Abstract

Coffee (Coffea robusta) is an important crop for Vietnam. Vietnam obtains the second highest yield of coffee in the world, just after Brazil, with around 1.2 million Mg per year. Exported coffee products contribute significant income to the Vietnamese economy, about US$3.62 billion in 2014 alone. Most coffee plantations in Vietnam are located in the Central Highland region on two main soil types: (i) Reddish brown soil derived from basic and intermediate magmatic rocks (basaltic soil); and (ii) Reddish yellow soil derived from acid magmatic rocks (granite soil). The poor nature of both soil types, but particularly that of the granite soils, poses significant challenges when considering plant nutrition strategies and practices. Therefore, special concern has been devoted to nutrient requirements and fertilization dosage and regime. In a previous study, an annual dose of 600 kg potassium chloride (KCl) was suggested as an optimum suitable for coffee plantations in the region, yielding 3.5-4 Mg ha^-1 coffee beans. However, this amount is twice the theoretical K required to obtain a similar yield range. The objectives of the present follow-up study were: 1) to elucidate whether the excess K quantities enriched the orchards’ soils, were absorbed and accumulated in the trees, or were lost to the environment; 2) to suggest ideas for testing and improving fertilization efficacy under these particular environmental conditions. The results demonstrate that the soils of the Central Highlands of Vietnam are rather poor, undergo active erosion processes and possess very low cation exchange capacity (CEC), with restricted ability to store and provide nutrients. Extensive nutrient leaching takes place during the rainy season. Nutrient uptake by trees is very limited to brief occasions, whereas large portions of the nutrients applied are leached away and lost. We suggest that a substantial reduction in fertilizer applications is considered during the rainy season. Most nutrition requirements should be supplied during the dry season, along with frequently scheduled irrigation. Such a regime, if implemented, may improve fertilization efficacy, reduce K inputs, and bring about a further increase in coffee yield.