Yield and jonagold apple fruit quality as influenced by spring sprays with commercial Rosatop material containing calcium and boron

The aim of the experiment was to examine the efficiency of spring sprays with Rosatop material containing calcium (Ca) and boron (B) on apple (Malus domestica Borkh.) yield and quality. The experiment was carried out in 1998-2000 in the Experimental Orchards of the Research Institute of Pomology and Floriculture, Skierniewice, Poland on mature Jonagold apple trees/M.26 EMLA planted at a spacing of 4.0 x 2.0 m on a sandy loam soil with medium B concentration. Trees were sprayed [1] with commercial Rosatop material (16% Ca and 0.75% B) at the stages of pink bud, bloom beginning, petal fall, and 2 weeks after full bloom at a rate of 2-3 L ha(-1) per spray; [2] with Rosatop as in the previous combination and with calcium nitrate [Ca(NO3)(2)] 6, 4, and 2 weeks before harvest at a rate of 8k-ha(-1) per spray; and [3] with Ca(NO3)(2) from 5 weeks after full bloom to harvest at 2-wcek intervals (6 sprays per season) at 5-8 kg ha(-1). Trees sprayed with water served as control. Studied sprays had no effect on fruit yield, mean fruit weight, color, and fruit maturity status at harvest. Sprays with Rosatop, Rosatop plus Ca(NO3)(2), or only Ca(NO3)(2) increased Ca concentrations in fruit after 8 weeks of their development and at harvest with exception of sprays with Ca(NO3)(2) in 2000 that did not affect fruit Ca level at harvest. Status of nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and B in fruit tissues was not influenced by applied sprays. In 2 out of 3 years, fruit sprayed with Rosatop plus Ca(NO3)(2) or only Ca(NO3)(2) were firmer and less affected by internal breakdown after storage than control ones. In all years, foliar applications of Rosatop or Rosatop plus Ca(NO3)(2) decreased fruit sensitivity to bitter pit; in the case of sprays with Ca(NO3)(2) this effect was observed only in 2 growing seasons. Soluble solids concentrations in fruit after storage and fruit decay were not affected by studied spray treatments. These results indicate that spring sprays with Rosatop material can be recommended in apple orchards on coarse-textured soils with low B concentrations to increase fruit resistance to physiological disorders (mainly bitter pit). To improve tree cropping, foliar Ca fertilizers richer in B than Rosatop material should be used in spring spraying.