Copper,nitrogen, and Rhizobium japonicum relationships in determinate soybean

A relationship among Cu, N, and Rhizobium japonicum was hypothesized because previous research had shown that (a) 35% or more legumes in the Atlantic Coastal Plain have Cu concentrations of 6 mg kg^‐1 or less, (b) Cu influences N fixation in some legumes, and (c) irrigated soybean (Glycine max L. Merr.) can accumulate most of its N through fixation. Soybean were grown on a Cu‐deficient Norfolk (fine‐loamy, siliceous, thermic Typic Paleudult) loamy sand with 3 fertilizer sources of Cu, 2 strains of R. japonicum, and with or without 336 kg ha^‐1 of N fertilizer. Application of Cu significantly increased the number of pods plant^‐1 suggesting pod abortion in determinate soybean may be caused by low Cu, but seed yield was not increased. Fertilization with N increased vegetative growth, but not total biomass or seed yield. Inoculation with R. japonicum strain 110 significantly increased seed yield by 0.3 Mg ha^‐1 compared to strain 587. The yield increase was similar with or without fertilizer N application indicating strain response was not totally caused by improved N efficiency. There was no relationship between seed yield and nodule occupancy as measured by the ELISA technique.