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Rhizosphere Competition in Model Soil Systems. David M. Benson, Graduate Assistant, Colorado State University, Fort Collins; Ralph Baker, Professor of Botany and Plant Pathology, Colorado State University, Fort Collins. Phytopathology 60:1058-1061. Accepted for publication 15 February 1970. DOI: 10.1094/Phyto-60-1058.

Model soil systems were used to measure competition in conditions known to promote biological control of bean root rot. Glucose (5,000 ppm C) was added to the soil systems (to simulate addition of a carbon source in the rhizosphere) and its rate of utilization assayed. Rate of utilization of glucose in cellulose (4500 ppm C)-amended soils decreased in 6-8 days, correlating with N immobilization. The addition of KNO3 (1,225 ppm) nullified the effect. Lignin and chitin together increased rate of utilization of glucose in comparison with raw soil. In general, glutamic acid utilization with these amendments was similar to glucose utilization. This contributes further evidence that biological control with lignin-chitin amendments results from competition for carbon. There was no increase in total CO2 evolution from soil amended with NO3-N compared with raw soil. CO2 evolution from glucose-amended soil was rapid, and carbon became limiting after 12 days. With cellulose amendments, however, N was the limiting factor in its decomposition. Lignin and chitin amendments increased CO2 evolution as compared with raw soil. Addition of NO3-N to this system failed to alter significantly the increased CO2 evolution noted with these amendments.

Additional keywords: Biological control, soil microbiology.