EFFECTS OF BIOCIDAL TREATMENTS ON BIOLOGICAL AND NUTRITIONAL PROPERTIES OF A MULL-STRUCTURED WOODLAND SOIL

The effect of microwave radiation (MIW), gamma irradiation (GIR), autoclaving (ACL), methyl bromide fumigations (0.01 mol/l; MBR-1 and 0.04 mol/l; MBR-2), chloroform fumigation (CHL) and propylene oxide fumigation (POX) on soil respiration, N- and P-mineralization and pH of a rendzina soil was measured in a laboratory experiment over a period of 120 days. Soil samples were taken from the Ah horizon of a beechwood mull rendzina on limestone (carbon content 8%, C/N ratio 14, pH 5.8). Control and treated soil samples were inoculated with a soil suspension (passed through a 45 mum sieve) and incubated in glass vessels at 20-degrees-C. CO2 release was recorded and N(min) content, P(min) content and soil pH were determined. Of the treatments, MIW, MBR-1 and CHL defaunated the soil but did not eliminate microbial populations, while soil sterilization was achieved by ACL, GIR, MBR-2 and POX. In comparison to the control, CO2 release of POX treated soil was increased strongly throughout the experiment. CO2 release of the other treatments reached the control level after about four weeks of incubation. In MBR fumigated soil CO2 production fell below the control level after 10 weeks indicating toxic effects of inorganic bromide residues in the soil. The content of NH4+-N was high and that of NO3--N was low in all treatments in comparison to the control. Nitrifying bacteria did not recover after being damaged by biocidal treatments. N(min) content of POX treated soil was lowest, indicating immobilization of N for microbial growth. The phosphate content of treated soil samples generally exceeded that of the control soil throughout the experiment. Treatments increased soil pH by 0.2 to 0.7 units. C-, N- and P-status of the soil was affected strongly by each of the treatments. For defaunation CHL and for sterilization GIR and ACL caused least side effects.