Agronomic and Acetylene Reduction Evaluation of Three Annual Medics

Abstract

Little research has been reported on nitrogen fixation of annual medics such as black medic (Medicago lupulina), barrel medic (M. truncatula) var. Jemalong, and California burclover (M. polymorpha). A greenhouse study was initiated with these 3 medic species to estimate their nitrogen fixation potentials. Considerable variations existed for all indices used to evaluate nitrogen fixation. Barrel medic, var. Jemalong, produced moderate acetylene reduction rates and had the highest top growth weights. This variety also maintained the greatest plant vigor throughout the observation period. High top growth weight, root fresh weight, nodule count, and root score were all associated with high acetylene reduction rates. Plant vigor and color scores were less associated with acetylene reduction rates. Assuming acetylene reduction is a true measure of nitrogen fixation, this experiment indicates the annual medics fix significant amounts of nitrogen.