Maro G.P.^1,, Mbwambo S.G.¹, Monyo H.E.¹, Mfaume D.P.², Urassa A.³

A pilot study was undertaken to establish the response of Arabica and Robusta coffee to liming in the acid coffee soils of Tanzania, and its applicability to smallholder coffee farmers. It involved three field trials at Lyamungu (Hai) and Mbimba (Mbozi) for Arabica coffee, and Maruku (Bukoba) for Robusta. In each site, two side-by-side trials were laid out under Randomized Complete Block Design (RCBD), six treatments replicated three times. Random soil samples were taken and pH-water measured at 1:2.5 soil-water ratio. Lime requirement was determined using the barium chloride-triethanolamine titration method and regressed against the pH values. The ensuing linear trendline equations were used to calculate the standard lime requirements (LR), and treatments were assigned in the order 0.0LR, 0.25LR, 0.5LR, 0.75LR, 1.0LR and 1.5LR. Methods were top-dressing and incorporation to at least 10cm depth. Change in soil pH, growth characteristics and 3-year yield data were collected, rearranged to fit a split-plot design where methods were considered as sub-factors, and exposed to ANOVA and mean separation by Tukey’s HSD method using CoStat software. The change in pH reflected the dosage of lime used. Dosages were highly significant in Mbimba, and very highly significant in Lyamungu and Maruku, showing an added advantage of liming. Mean yields increased in the order Robusta new (313-426 kg ha^-1) < Arabica new (988-1347 kg ha^-1) < Arabica superimposed (1252-1815 kg ha^-1). This study has unveiled the hitherto unrealized hurdles of lime application among smallholders; including complexities in lime requirement determination, availability and quality of liming materials, methods and uniformity of application. While research is underway to determine a simple but accurate LR determination method and explore the interaction between lime and phosphorus, mulch and manure/compost, smallholder coffee farmers should adopt a CAN/MRP regime rather than direct liming.

acid soils, coffee response, ecological zones, lime requirement, Tanzania