Effects of tillage and inorganic fertilizers on culturable soil actinomycete communities and inhibion of fungi by specific actinomycetes

This study examined the influence of reduced tillage and varying nitrogen regimes on culturable soil actinomycete communities in soils under barley and canola in northern Alberta. Residues of barley and canola were also sampled from experimental sites in central Alberta. The 10 most commonly cultured actinomycetes (all Streptomycetes) were tested in vitro for antagonism towards 10 plant pathogenic fungi. The actinomycetes Streptomyces halstedii and Streptomyces rochei were the most antagonistic, and two unidentified others displayed some antagonistic activity. Counts of S. halstedii and total culturable actinomycetes were made in spring and fall. Fall plowing reduced both total actinomycete and S. halstedii counts in both spring and fall, and zero tillage and minimum tillage reduced S. halstedii counts in the spring only. Nitrogen had no effect on total counts, and only the lowest rate of nitrogen (0 kg ha(-1)) slightly reduced S. halstedii counts in the spring. S. halstedii was present on canola residues. This research indicates that differing practices within agricultural fields may not be the main determinant of actinomycete community size and diversity. (C) 2003 Elsevier B.V. All rights reserved.