Nitrogen Fixation (Acetylene Reduction) Associated with Roots of Winter Wheat and Sorghum in Nebraska

Wayne L. Pedersen, University of Nebraska - Lincoln
K. Chakrabarty, University of Nebraska - Lincoln
R. V. Klucas, University of Nebraska - Lincoln
Anne M. Vidaver, University of Nebraska - Lincoln

Document Type Article

Published in APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Jan. 1978, p. 129-135. Copyright 1978 American Society for Microbiology. Used by permission.

Abstract

Root segments and root-soil cores (6.5-cm diameter) from fields and nurseries of winter wheat and sorghum were tested for N₂ fixation by using the acetylene reduction assay. Wheat samples (~1,200) from 109 sites generally had low or no activity (0 to 3.1 nmol of C₂H₄ produced per h per g [dry weight] of root segments), even after 24 h of incubation. However, a commercial field of Scout 66, located in western Nebraska, exhibited appreciable activity (290 nmol of C₂H₄ produced per h per g [dry weight] of root segments). Of 400 sorghum lines and crosses, grain sorghums (i.e., CK-60A, Wheatland A, B517, and NP-16) generally exhibited higher nitrogenase activity than forage sorghums or winter wheats. CK-60A, a male sterile grain sorghum, was sampled at four locations and had the most consistent activity of 24 to 1,100 nmol of C₂H₄ produced per h per core. The maximum rate extrapolated to 2.5 g of N per hectare per day. Numerous N₂-fixing bacterial isolates were obtained from wheat and sorghum roots that exhibited high nitrogenase activity. Most isolates were members of the Enterobacteriacae, i.e., Klebsiella pneumoniae, Enterobacter cloacae, and Erwinia herbicola.