Several recent studies, including from our laboratory, have provided evidence that by improving tuber calcium level, we can improve tuber quality such as low internal defects and better storability. The purpose of this study was to be determine the influence of supplemental calcium fertilization on tuber size and tuber number. For this purpose, plantlets of Solanum tuberosum cv. Russet Burbank raised in tissue culture were planted in 20-L pots filled with sandy loam soil with pH of 6.9 and soil calcium level of 350 ppm. All treatments received same total amount of nitrogen (at the rate of 280 kg·ha–1). Five treatments were evaluated: i) nonsplit nitrogen (from ammonium nitrate), ii) split nitrogen (from ammonium nitrate), iii) split nitrogen + gypsum, iv) split nitrogen (from liquid nitrogen) + calcium chloride, and v) split nitrogen (from calcium nitrate). The total calcium was applied at the rate of 168 kg·ha–1. Gypsum application was made at 4 weeks after planting, and other sources of calcium were applied on a split schedule (equally split at 4, 6, 8 weeks after planting). Four months after planting, tubers were harvested and evaluated. In general, all calcium treatments had lower tuber number and greater tuber size compared to the nonsplit nitrogen control. The percentage of total A-grade tubers as well as the percentage yield from A-grade tubers was increased by all calcium applications. These results suggest that calcium content I the soil can influence both potato tuber number and tuber size.
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