The Influence of Calcium and Nitrogen Fertilization on the Freezing and Salinity Tolerance of Two Urban Tree Species

"Two field trials were undertaken to determine the influence of fall fertilization using two commercially available, calcium-based fertilizers (calcium nitrate, calcium nitrate borate) and a high-nitrogen fertilizer (N:P:K = 24:7:7), at a range of concentrations, on the freezing and salinity tolerance of two urban tree species, evergreen oak (Quercus ilex) and holly (Ilex aquifolium). In both the 2001 and 2002 field trials, fertilization with calcium nitrate and calcium nitrate borate at a concentration of 40 g/m2 (0.12 oz/ft2) increased the freezing and salinity tolerance of both species as measured by leaf chlorophyll fluorescence, electrolyte leakage, and chlorophyll content. In addition, calcium fertilization at this concentration significantly increased total plant dry weight recorded at the cessation of the experiment. Application of both calcium fertilizers at concentrations of less than 40 g/m2 provided no significant protectant properties. Applications of more than 40 g/m2 proved phytotoxic to the two test species. Irrespective of concentration, applications of N:P:K (24:7:7) fertilizer did not enhance or increase susceptibility to freezing and salinity damage compared to nonfertilized controls. However, N:P:K (24:7:7) fertilization significantly increased leaf chlorophyll content and total plant dry weight. Results indicate that fall applications of calcium nitrate and calcium nitrate borate at 40 g/m2 can increase the freezing and salinity tolerance of evergreen oak and holly." [Abstract]