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Potassium/Magnesium Ratio Effects on Aluminum Tolerance and Mineral Composition of Wheat Forage

De . of Soil, Cro and Atmospheric Sci. (SCAS), Cornel1 Univ., Ithaca, NY 14853
U.S. Plant, Soil, and Nutr. Lab., Tower Rd., Ithaca, NY 14853.

^* Corresponding author.

Knowledge of cation amelioration of Al toxicity may improve our understanding of differential Al-tolerance mechanisms among winter wheat (Triticum aestivum L.) forage genotypes, and the causes of tetany in grazing cattle. A solution culture experiment was conducted using two winter wheat cultivars (Atlas 66 and Scout 66), two Al levels (0 and 50 µM), and three KMg ratios (0.1, 0.7 and 2.3, on a mol L^– basis). Root dry weights were decreased significantly by Al for Al-sensitive Scout 66, but not for Al-tolerant Atlas 66. Increasing the K/Mg ratio in the presence of AI significantly decreased root dry weight, root length, and the root tolerance index for Scout 66, but not for Atlas 66. Shoot and root Mg concentrations were always significantly lower for Scout 66 than for Atlas 66. Without Al, shoot K and Ca concentrations for the two cultivars were not significantly different. With Al, shoot K, Ca and Mg concentrations were depressed more for Scout 66 than for Atlas 66. The W(Ca + Mg) ratios increased significantly in Scout 66 with added Al, thereby causing an increased tetany hazard. Adding Al reduced shoot Cu and Zn concentrations in both cultivars, and Fe and Mn concentrations in Scout 66. Increasing the proportion of Mg in solution increased the Al tolerance for Scout 66, indicating that an appropriate K/Mg ratio is important in selecting for Al-tolerant wheat cultivars.

Received for publication April 22, 1991.