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Blueberry production is limited to acidic soils (pH < 5.5) for reasons that are not thoroughly understood. The objective of this study was to examine the effects of proportion of N-NH 4 + among the total applied inorganic N {N-NH 4 + /(N-NH 4 + +N-NO 3¯) } (RNH 4 +) on rabbiteye blueberry plant growth and mineral uptake under different CaCO 3 soil levels. Rabbiteye blueberry (Vaccinium virgatum Ait., cv. TitanTM) plants were grown in sandy soil mixed with four levels of applied CaCO 3 [0 (control, without any added CaCO 3), 1%, 5%, or 10% (w/w)] in full factorial combination with three levels of RNH 4 + (33%, 66%, or 100%), which were applied through a fertigation system. Leachate pH, biomass accumulation, the concentration of chlorophyll in the leaves, and the concentrations of minerals in leaves and stems were measured. Increased rates of RNH 4 + induced acidification of the leachate solution, which was diminished by the increasing rates of applied CaCO 3 in the soil. Biomass production decreased linearly as the leachate pH rose above 5.5. Biomass production was positively associated with increased Mn concentrations in the leaves and with decreased Ca concentrations in the stems. The current study demonstrates that the application of high levels of RNH 4 + can reduce the pH of neutral and alkaline soils with moderate level of CaCO 3 below the threshold (5.5), and enables the production of rabbiteye blueberry in unsuitable soils.

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