Potato tuber tissue is calcium-deficient. Consequently, increasing Ca concentration is desirable to improve tuber quality. The purpose of the present study was to determine the influence of supplemental Ca and N fertilization on internal quality of potato. Three products (calcium nitrate, calcium chloride, and gypsum) were used to increase tuber calcium concentration. We tested combinations of both soluble sources of calcium and gypsum. Each treatment had five replications and received same total amount of N, supplied either from ammonium nitrate, liquid N (UAN: 50% urea + 50% ammonium nitrate) and calcium nitrate or combination of these sources (at rate of 225 kg·ha–1). The total Ca was applied at the rate of 168 kg·ha–1. Application of N at emergence and hilling (nonsplit) was compared to split application of N and Ca at hilling, 2, 4, and 6 weeks after hilling. At harvest, ≈100 tubers from each replication were cut in half along longitudinal axis and visually inspected for internal defect in both years. Application of Ca, especially in split schedule and from soluble sources, significantly increased tuber tissue Ca concentration. In 1998, the incidences of hollow heart (HH) and internal brown spots (IBS) were very low. The treatment containing calcium nitrate and calcium chloride combination produced the lowest total defects, whereas application of gypsum was not effective at reducing defects. In 1999, application of all Ca sources including gypsum, reduced HH and IBS. Data from these studies suggest that tuber calcium level is increased by field applications of moderate amount of Ca and tuber quality is impacted by N and Ca application. Furthermore, seasonal climatic variations appear to have dramatic influence on the incidence of internal defects in potato tubers.
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