HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Barta, A. L. Search for Related Content PubMed Articles by Barta, A. L. Agricola Articles by Barta, A. L.

Response of Symbiotic N₂ Fixation and Assimilate Partitioning to K Supply of Alfalfa¹

Alfalfa (Medicago sativa L.) production requires ample K supply for maximum production of both herbage and protein. Since K appears to be a major nutritional factor affecting N accumulation and carbon assimilate movement in plants, its effect on symbiotic N₂ fixation in alfalfa may be critical. The objective of this study was to determine the effect of K supply on N₂ fixation (acetylene reduction) and carbon assimilate distribution during alfalfa regrowth. Alfalfa plants were established from seed using sand media in the glasshouse. Potassium was supplied at concentrations which resulted in shoot K concentration in the low (<2%), medium (2 to 3%), high (>3%) range. Plants supplied with a high level of K showed significantly increased shoot dry weight and a high rate of acetylene reduction 10 to 14 days after shoot removal when plants were in vegetative regrowth and were approximately 20 to 30 cm tall. No significant differences in acetylene reduction rate were observed when plants reached the bud and flowering stage of development. Root nodule dry weight, total non-structural carbohydrates, and concentration of starch and reducing sugars in nodules were not significantly affected by K supply. Twelve days after cutting shoots were labled with ¹⁴CO₂. Nodules from high K roots accumulated significantly greater label than low K nodules and also had significantly greater percent label in the amino acid fraction when sampled 1 hour after labeling. No significant differences were found in ¹⁴C distribution in nodules sampled 24 hours after labeling. The results suggest that the increased rate of N₂ fixation during alfalfa regrowth in adequately K supplied plants may be the result of greater assimilate transport to nodules and utilization for synthesis of amino acids.

Key Words: Medicago sativa L. • Acetylene reduction • Carbohydrate distribution • Nutrient deficiency

² Associate professor in agronomy.

Received for publication February 6, 1981.