Impact of Source and Timing of Calcium and Nitrogen Applications on ‘Atlantic’ Potato Tuber Calcium Concentrations and Internal Quality

Three Ca sources and two application schedules were compared for their effectiveness for increasing tissue Ca concentrations in 170 to 284 g field-grown tubers of ‘Atlantic’ potato (Solanum tuberosum L.). Additional observations were made of internal physiological defects. Paired measures of tissue (periderm and nonperiderm) Ca concentration and internal quality (± hollow heart, ± internal brown spot) were made on individual tubers produced in plots fertilized with N at 224 kg·ha and Ca at either 0 or 168 kg·ha, supplied from either gypsum, calcium nitrate or NHIB (9N–0P–0K– 11Ca, a commercial formulation of urea and CaCl2). Application of N and Ca at emergence and hilling (nonsplit) was compared to application at emergence, hilling, and 4 and 8 weeks after hilling (split). Tuber yield and grade were unaffected by treatments. Split Ca application (from either calcium nitrate or NHIB) increased mean tuber nonperiderm tissue Ca concentrations and the percentage of tubers with an elevated Ca concentration in both years compared with non-Ca-supplemented controls. Split Ca application also resulted in greater increases in Ca in nonperiderm tissue than nonsplit Ca application in 1994. Although the correlation coefficient between Ca level in periderm and nonperiderm tissue of >400 individual tubers was highly significant in both study years, linear regression analyses suggested the Ca level in the two tissues were poorly related. Split application was associated with a 37% reduction in the incidence of internal tuber defects, relative to nonsplit application in 1994. Calcium application did not affect tuber internal quality based on means analysis, but chi-square analysis suggested that Ca concentration and internal quality of individual tubers may be related. The incidence of internal defects was 16.4% in tubers with nonperiderm tissue Ca ≤100 μg·g–1 dry weight compared to 10.6% in tubers with nonperiderm tissue Ca >100 μg·g–1 dry weight. These data suggest that 1) it is feasible to increase tuber Ca levels by field applications of moderate amounts of Ca, 2) tuber quality is impacted by N and Ca application schedule, and 3) Ca concentrations in tuber periderm and nonperiderm tissues may be controlled independently. developing tubers, but not main roots (Kratzke and Palta, 1986). These studies were instrumental in developing the hypothesis that tuber Ca concentrations are dictated primarily by the amount of Ca taken up by roots arising directly from stolons and tubers (Kratzke and Palta, 1986), in addition to direct tuber uptake from soil solution (Marschner, 1995). If true, the form, placement, and timing of Ca application would impact the efficacy of field-based Ca treatments intended to increase tuber Ca (Kratzke and Palta, 1986). The available evidence suggests the Ca concentration of the soil solution surrounding, but not beneath tubers, dictates primarily tuber Ca concentration (Kratzke and Palta, 1986). Seasonal applications of N in combination with adequate soil moisture availability probably optimizes tuber yields and quality of ‘Russet Burbank’ potato (McCann and Stark, 1989; Ojala et al., 1990; Stark et al., 1993), especially in years when leaching occurs. Water potential gradients between foliage and tubers also affect tuber Ca levels (Win et al., 1991). Because moisture and fertility requirements change during crop development, a goal of in-season management is to supply adequate soil moisture and fertility at each crop stage, thereby avoiding excessive inputs, which reduce profits and increase the likelihood of groundwater contamination (Ojala et al., 1990). Localized tissue Ca deficiencies are implicated as a mechanism initiating cell death and tissue necrosis (Bangerth, 1979; Collier et al., 1980; Levitt, 1942; Olsen et al., 1996). Necrotic lesions in potato tubers referred to as brown center, internal brown spot, internal heat necrosis, and internal rust spot may also Increases in plant tissue Ca concentration are more likely to result from altered flux of Ca in xylem sap than from increasing Ca supply to roots (Kirkby, 1979; Marschner, 1995). However, previous reports suggest that this hypothesis does not apply to Ca in potato (Solanum tuberosum) tubers (Kratzke and Palta, 1985, 1986; Simmons et al., 1988). For example, Kratzke and Palta (1985) demonstrated that water taken up by the main basal roots of the potato plant bypasses tubers and is delivered to aboveground tissue. The same authors then used a split-pot approach to fertigate zones containing either developing tubers or main roots of individual plants separately (Kratzke and Palta, 1986). Tuber Ca levels were affected by the Ca supply to the region containing