Alfalfa seedling growth in nutrient solutions as influenced by Aluminum, Calcium, and pH

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Abstract
Soil acidity is a major factor responsible for reduced alfalfa (Medicago sativa L.) yields in humid regions of the United States. The purpose of this study was to investigate the effect of Ca, Al, and pH interactions on alfalfa growth. Two experiments were conducted in modified plastic growth pouches. Experiment 1 studied the influence of pH (4.5 and 6.5) at varying levels of Al (0.00, 0.08, 0.15 mM) with 1 mM Ca, while experiment 2 studied the interaction between Ca (0.00, 0.30, 1.00, 3.00, 6.00 mM) and Al (0.00, 0.08, 0.15, 0.30 mM) at pH 4.5 on alfalfa shoot and root development. In the absence of Al, root and shoot growth were not affected by a pH of 4.5 as compared to a pH of 6.5. Increasing Al from 0.00 to 0.30 mM caused a reduction in both shoot and root growth at pH 4.5 when Ca was less than 3.00 mM. In the presence of 0.08 mM Al, additional Ca at 3.00 and 6.00 mM increased shoot growth equal to that of the 0.00 Al treatment. The optimum level of Ca for root development was at least 1.00 mM in the absence of Al; however, in the presence of 0.08 mM Al, additional Ca (≥3.00 mM) reduced Al toxic effects. Increasing levels of Ca (0.00 to 6.00 mM) decreased Al in roots from 9.4 to 4.7 g kg‐1 in treatments containing 0.30 mM Al. Additional Ca (≥3.00 mM) in the pH 4.5 nutrient solution was beneficial for shoot and root growth in the presence of 0.08 mM Al and a pH of 4.5 was not detrimental to alfalfa seedling growth unless at least 0.08 mM Al was present.