Calcium source and method of application evaluations demonstrated that applications of preplant strip CaS04 from several sources were the most consistent means, of those evaluated, for improving potato yield and quality on sandy, low exchangeable Ca soils. Calcium sulfate was superior to finely ground dolomitic lime in all years, although triple superphosphate performed as well as CaSO4 in 1 of the 2 yr that it was evaluated. Calcium chloride applications resulted in reduced plant emergence at the higher Ca rates used in these experiments. Calcium fertilizer concentrated in the hill prior to planting was generally superior to preplant broadcast and sidedress applications of the same material. These results are similar to those obtained with peanut where Ca applied to the zone of fruit formation was more beneficial than Ca placed in the zone of root formation, and dolomitic limestone was not effective in meeting the Ca requirement of the developing fruit (Colwell and Brady, 1945). It has also been demonstrated that high broadcast applications of gypsum (3090 kg ha~') to peanut at early bloom improve peanut yields and quality (Hallock and Garren, 1968). Therefore, it is possibble that broadcast applications at higher rates than those examined here may be as effective as strip applications in the hill for improving potato yield and quality. Soluble Ca sources applied preplant strip were the most effective for increasing periderm Ca concentration and tuber Ca uptake, which has been shown to reduce tuber susceptibility to bacterial soft rot, internal brown spot, and sub-apical necrosis (McGuire and Kelman, 1984;Tzeng et al., 1986). Since concentrating the material in the zone of tuber formation was the most effective means for increasing tuber Ca uptake and no increase in Ca uptake was observed in the plant tops, it is likely that tuber Ca is taken up directly from the soil or by specialized tuber or stolon roots, or both, rather than by root uptake and xylem transport of Ca.

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