THE INTERACTION BETWEEN CALCIUM CHLORIDE AND AMMONIUM-NITROGEN ON GROWTH, NITROGEN UPTAKE AND TRANSLOCATION IN APPLE AND SOUR ORANGE

There are reports indicating that Ca enhances N uptake and the growth of plants when N is supplied in the form of ammonium ion or as urea. The purpose of the present studies was to elucidate the effect of Ca on foliar N absorption and growth of ‘Red Delicious’ (RD) apple seedlings (Malus x domestica Borkh.), which were foliar-sprayed with urea. Also, the effect of Ca: NH₄ ratio in the rhizosphere of hydroponically-grown sour orange seedlings (SO) (Citrus aurantium L.) was studied in relation to the plants’ vegetative growth and N uptake. Eight applications of 83 mM urea containing 0, 10.4, 20.8, or 41.5 mM CaCl₂ were applied as a foliar spray to RD seedlings at 10 d intervals. Control plants were sprayed with nanopure water. Although foliar treatments with urea resulted in increased total leaf area, and leaf, stem, and root dry weight, the addition of CaCl₂ did not increase the response. However, the presence of CaCl₂ in the spray solution significantly increased concentrations of N in stems and roots suggesting that CaCl₂ enhanced translocation of foliar-applied nitrogen to these tissues. The calculation of total N uptake by plants provided no evidence, however, of stimulated N uptake due to CaCl2 presence in the foliar spray solution. SO seedlings were grown for six weeks in nutrient solutions in which all N was exclusively provided as ammonium ion with CaCl2:NH₄ molar ratios of 1.0, 1.3, 1.6, 1.9, 2.2 and 2.5. The level of Ca: NH₄ ratio had no effect on SO vegetative growth as measured by total leaf area, as well as leaf, stem, and root dry weight. At the Ca: NH₄ ratio of 1.3, however, the plants tended to have higher N concentrations in lateral and tap roots compared to those exposed to Ca:NH4 ratios of 1:1, 1.6, 1.9, 2.2, or 2.5. Since the growth of these plants was equal to that in the other treatments, this result may also suggest the enhanced N uptake.