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 napus ‘Dwarf Essex’), and from pea plants grown in soil without amendment. Total viable counts of bacteria and fluorescent Psuedomonas spp., and proportionate 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, that differed by less than 50% in utilization of specific carbon substrates, were considered to use those substrates in a similar manner. Cluster analysis was used to evaluate relationships of strains according to their abilities to utilize the different carbon substrates. Non-amended pea and amended pea isolates used 88% of the carbon substrates in a similar manner, and cluster 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 rape residues did not appear to significantly alter the pea rhizosphere population and community attributes measured.