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Disease Control and Pest Management

Vertical Distribution of Soil Microorganisms Following Subsoiling in a Cotton Management System. R. S. Hussey, Assistant Professor, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens, GA 30602; R. W. Roncadori, Associate Professor, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens, GA 30602. Phytopathology 67:783-786. Accepted for publication 8 December 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-783.

Soil in cotton plots was sampled at four depths (0-18, 19-38, 39-53, and 54-70 cm) to determine the influence of continued subsoiling on the vertical distribution of selected soil microorganisms. Subsoiling under the planting row for three consecutive years had little influence on the vertical distribution of soil microorganisms as sampled during the 3rd yr. It increased the population density of Fusarium spp. at the 39-53 cm level, but had no effect on them at other levels nor on Rhizoctonia solani, Pythium spp., or plant-parasitic nematodes at any levels of the soil profile. Spores of vesicular-arbuscular mycorrhizal fungi decreased at the 54-70 cm level after subsoiling, but were not changed at the other levels. Populations of plant-parasitic nematodes, Pythium spp., Fusarium spp., Endogonaceae spores, and R. solani were greatest in the top 18 cm of soil. Significant changes in population densities occurred between soil samples collected before planting and at harvest. Population densities of Hoplolaimus columbus increased at all depths and Helicotylenchus spp. increased within the top 53 cm of soil during the growing season. The populations of Helicotylenchus spp. were uniformly distributed throughout the 70 cm of soil sampled. Populations of Pythium spp. and Fusarium spp. remained stable and mycorrhizal fungi spores increased within the surface 18 cm of soil.