Amending the Acid Coffee Soils of Tanzania: Calibration of Lime Estimation Approaches

Three lime requirement algorithms were calibrated against the standard lime incubation in the acid coffee soils of Tanzania using three topsoil samples from Masama Sawe (Hai District), Mfiriga (Njombe Rural District) and Msia (Mbozi District), all of pH3 equivalent to 0, 0.5, 1.0, 2.0, 5.0 and 10.0 tons CaCO3 per ha. These were mixed with 100g of soil per dish and incubated for six weeks at room temperature and near field capacity. At the end of week 1, 2, 4 and 6, 10g of each was mixed with 25ml of distilled water, shaken for 30 minutes in an end-to-end shaker and the pH of the soil (1:2.5) was read. The amount of CaCO3 added was then plotted against pH, and a LR determined graphically. Three liming algorithms were suggested for sandy loam, loam and clay soils that use ΔpH (target pH – initial pH; the former set at 5.5) and percent organic matter. They were validated using a separate database and compared against similar algorithms developed in Brazil, Nigeria and China. The results suggest the Brazilian algorithm LR = 0.0699*(ΔpH*OM)0.9225, being closest to the incubation algorithms, to be tentatively adopted in Tanzania, pending further validation. The discussion touches the concerns about acidity and liming in Tanzania, alternatives available, and a potentially lucrative lime industry based on locally available lime deposits.