Root Zone pH Changes and Ion Uptake Imbalances by Triticale, Wheat, and Rye

Differential pH induced in growth media and the ion uptake imbalances of different cultivars are important criteria of degrees of aluminum tolerance. The objective of this study was to determine if changes in pH of nutrient solutions and soil and anion-minus-cation (A—C) uptake frem solution can be used to rank cultivars of triticale (X Triticosecale Witt Mack) of differential Al tolerance. Changes in pH induced by 11 cultivars of triticale, wheat (Triticum aestivum L.), and rye (Secale cereale L.) were measured in 1/5-strength Steinberg solution with initial pH of 4.8 and in Al-toxic Tatum clay loam subsoil (clayey, mixed, thermic, Typic Hapludults) at different lime rates in a growth chamber. The A—C uptake, pH, and H⁺ changes were measured for 4 days in a solution containing 1 − 10⁻³ M KNO₃ plus 2 − 10⁻⁴ M Ca (NO₃)₂ initially adjusted to pH 4.65. Aluminumtolerant ‘Seneca’ and ‘Atlas 66’ wheats induced significantly higher pH in both solution and soil at low pH values of 3.84 and 4.39 than Al-sensitive ‘Arthur’ and ‘Morion’ wheats. However, at pH 5.88 Seneca produced significantly higher pH than Atlas 66 and Morion wheats. Aluminum-tolerant ‘6TA 298’ triticale induced the same pH in solution but higher pH in the soil than the more Al-sensitive ‘6TA 131’ ‘6TA 385’, ‘6TA 522’, and ‘6TA 203’ triticales except at pH 5.88, when 6TA 298 and 6TA 385 gave the same pH value. Abruzzi and Vitagraze ryes gave similar pH values to Atlas 66 in solution but were less effective in raising the pH of the soil. The A—C accounted for pH changrs (r = 0.731**) in solution containing KNO₃ and Ca(NO₃0₂ and there was an approximately stoichiometric relationship between A—C and H⁺ changes during each of the 4 days without clear separation of the cultivars according to their differential Al tolerances. The pH changes were consistently related to Al tolerance in the Steinberg solution for wheats and in the soil below pH 4.5 for triticales and wheats.