Collection of soil samples. Isolation of groups of microorganisms from soil. Enumeration and observation of microorganisms in situ. Microorganisms in the rhizosphere. Isolation of plant pathogens from soil. Isolation of plant pathogens from roots. Control of soil environment. Extraction of soil solutions. Respiration and enzyme activity. Growth and survival. Root exudates. Screening soil microorganisms for antagonism. Testing for antibiotic activity. Production, stability, and activity of antibiotics in soil. Biological control. Culture media.