Soil amendment effects of rape (Brassica napus) residues on pea rhizosphere bacteria

Rhizosphere bacteria were isolated from pea (Pisum sativum) plants grown in soil amended with a green manure of high-glucosinolate rape (Brassica napu s 'Dwarf Essex'), and from pea plants grown in soil without amendment. Tota l viable counts of bacteria and fluorescent Psuedomonas spp., and proportio nate representation of actinomycetes and Gram-negative bacteria in the pea rhizosphere community were not significantly different for amended and non- amended pea. Carbon substrate utilization patterns obtained from Biolog GN microplates were compared. Rhizosphere isolates from the two treatments, th at differed by less than 50% in utilization of specific carbon substrates, were considered to use those substrates in a similar manner. Cluster analys is was used to evaluate relationships of strains according to their abiliti es to utilize the different carbon substrates. Non-amended pea and amended pea isolates used 88% of the carbon substrates in a similar manner, and clu ster patterns were similar for the amended and non-amended pea strains. The number of nodules formed on amended and non-amended pea roots by Rhizobium leguminosarum were not significantly different. Amendment of soil with rap e residues did not appear to significantly alter the pea rhizosphere popula tion and community attributes measured. (C) 1999 Published by Elsevier Scie nce Ltd. All rights reserved.