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Effect of Nutritional Stress on Plant Composition: I. The Interaction of Added Nitrogen with Varying Sulfur Supply¹

ABSTRACT

Greenhouse and laboratory experiments with alfalfa as the test plant were designed to test the hypothesis that minimum levels of certain plant metabolites may occur at an intermediate stage of nutritional stress. This possibility in the case of S was indicated by results which had been obtained for amide and free amino N in alfalfa hay and appeared to be at variance with reports in the literature that accumulation of these N fractions are symptoms of S deficiency.

Several levels of S both with and without applied N were used. Because of the sensitivity of Rhizobia activity to pH, CaCO₃ was added to keep the reaction of the medium in a favorable range at the varying nutritional levels. Plants were obtained by rooting cuttings from a single clone and were grown in both soil and liquid cultures. Physiological age at time of harvest was identified by flower development.

Since physiological studies indicate the importance of carbohydrate/nitrogen ratios, reducing and total sugars were determined as well as several N fractions. The implication of the findings in terms of nutritional stress effects are discussed.

¹ Contribution of the Department of Soils and Plant Nutrition, University of California, Davis. Presented before Div. IV, Soil Science Society of America, Aug. 7, 1958, at Lafayette, Ind.

² Associate Professor of Soils and Plant Nutrition and Laboratory Technician III, respectively.

Received for publication December 19, 1958. Accepted for publication June 15, 1959.