Effects of bicarbonate content of irrigation water on nutritional disorders of some apple varieties

Effects of varying concentrations of bicarbonate in the irrigation water on seedlings of 'Red Delicious,' 'Golden Delicious,' and 'Golab-e-Kohanz' apple cultivars, grown in a greenhouse, were studied. To conduct this experiment, ammonium bicarbonate was used in order to obtain bicarbonate concentrations at 5, 10, 15, and 30 meq/L, and sulfuric acid was used to obtain a 0 level of bicarbonate in water. The electrical conductivity (EC) of the leachate water was nearly the same for 0, 5, and 10 meq/L bicarbonate, but doubled with the increase from 10 to 30 meq/L. Also, the bicarbonate concentration in the leachate increased with increasing levels of irrigation water bicarbonate, even though it was much lower in the leachates. Different bicarbonate levels in the irrigation water significantly reduced chlorophyll development. The difference was significant only between 30 mg/L and other levels after 40 d, but after 120 d (except for 0 and 5 meq/L) treatments at all other levels showed reduced chlorophyll intensities. There were also significant differences in chlorophyll intensities between different apple varieties before and up to 40 d of bicarbonate treatment, with 'Golden Delicious' having the most chlorophyll among the three varieties. The different intensities, however, were not significant after 80 and 120 d of bicarbonate treatments. After 120 d, the 0, 5, 10, 15, and 30 meq/L of bicarbonate had reduced the chlorophyll intensities by 4%, 6.5%, 18.2%, 35.6%, and 59.4%, respectively. Increasing levels of bicarbonate increased the leaf concentrations of nitrogen (N), potassium (K), and phosphorus (P), but lowered the concentrations of iron (Fe), magnesium (Mg), and manganese (Mn) and did not affect calcium (Ca), copper (Cu), or zinc (Zn) levels. Considering the equilibrium level of 3.5-4 mmole bicarbonate per liter of soil solution in calcareous soils brought about by CO2 pressures and calcium carbonate (CaCO3) minerals in the solid phase, it would not seem necessary to neutralize the irrigation water bicarbonates for concentrations below 5 meq/L. Instead, improvements in root development by improved soil aeration and prevention of excessive irrigation is probably beneficial. However, when the concentration of bicarbonate exceeds 5 meq/L in irrigation water, it is probably necessary to neutralize the bicarbonates for long-term irrigation purposes.