Effects of biocidal treatments on biological and nutritional properties of a mull-structured woodland soil

Abstract

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 μm sieve) and incubated in glass vessels at 20°C. CO 2 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, CO 2 release of POX treated soil was increased strongly throughout the experiment. CO 2 release of the other treatments reached the control level after about four weeks of incubation. In MBR fumigated soil CO 2 production fell below the control level after 10 weeks indicating toxic effects of inorganic bromide residues in the soil. The content of NH 4 +-N was high and that of NO 3 −-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.