Under calcium spraying nutrients accumulation in the initial stages of fruits development is critical in “Rocha” pears

Abstract

Balanced supply of essential nutrients in fruit trees, such as “Rocha” pears, is an important tool to achieve maximum yield and fruit quality, yet under fertilization the interactions among nutrients accumulation may be positive (synergistic) or negative (antagonistic), being also possible to have no interactions. Through foliar spraying of “Rocha” pear trees with Ca, this study aimed to assess the interactions with other micro and macronutrients in the leaves, the related implications on the synthesis of photoassimilates and the subsequent kinetics of accumulation in the fruits at harvest. Between fruit set and 30 mm diameter, two times spraying, with fifteen days range, were carried out with Ca(NO₃)₂  or CaCl₂ (0.1, 0.3 and 0.6 kg ha^{− 1} or 0.4, 0.8 and 1.6 kg ha^{− 1}, respectively). Thereafter, with similar interval periods, for all treatments, trees were sprayed with CaCl₂ (firstly at a concentration of 4 kg ha^{− 1} – second phase, followed by four with 8 kg ha^{− 1} – third phase). During fruit development, through the three spraying phases with Ca, the accumulation of Ca, K, P, S, Mg and Zn showed substantial variations in leaf tissues, which at fruit maturity determined some special and quantitative variations in tissues accumulation of C, H, O, K, Mg, Cl, Cu, Zn, Mn, Fe. Nevertheless, the functioning of the photosynthetic apparatus and the morphological and colorimetric parameters were not impaired. Considering that during fruits development, although Ca translocation prevails in the xylem, being its redistribution through the phloem strongly limited, it was concluded that accumulation depends of the type of Ca fertilizer and concentration, prevailing an oscillating balance among Ca K, P, S, Mg and Zn deposition in the leaves and its slow removal from the mesophyll cells to the fruits until maturity. Besides, as at fruit maturity xylem functionality can be minimal, the major accumulation of Ca in the peripheral layers of the fruits, resulted from Ca spraying, whereas translocation through the xylem favored its accumulation in the core in the early stages of fruit development. Following this behavior, C, H, O, K, Mg, Cl, Cu, Zn, Mn and Fe further showed complex accumulation interactions in the fruits.

Keywords: Chlorophyll a fluorescence parameters; Foliar spray with calcium; Calcium accumulation in fruits; Kinetics of calcium accumulation in leaves; Nutrients interactions; Pyrus communis L.;