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Effect of Potassium on the Content of Amino Acids in Alfalfa and Orchardgrass Grown With NO^-₃ and NH⁺₄Nitrogen in Nutrient Solution Culture¹

Alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) were grown on nutrient solutions with N at 50 and 250 ppm having 25 or 75% of the N at each concentration supplied as NH⁺₄ and with K at 10, 50, and 250 ppm. Tissue was harvested at the late bud and pre-boot stages respectively, immediately frozen, and later analyzed for free and conjugated amino acids using a Beckman/Spinco amino acid analyzer.

NH⁺₄ nitrogen was more readily incorporated into the free amino acid pool than the NO^-₃ form. Aspartic acid plus asparagine was the predominant amino acid in both plant species, and the ratio of this fraction to glutamic acid plus glutamine reflected the effect of nutrition on nitrogen metabolism. In general this ratio decreased with an increasing K/N ratio in the nutrient solution, and the minimum ratio was found when the K/N ratio was 5/1. At this K/N ratio the alcohol-insoluble N fraction of total N was maximum. The highest amino acid content was found when the K/N ratio was 1/5.

² Head, Soils and Plant Nutrition Section and Plant Physiologist, respectively.

Received for publication May 29, 1967.