At doses exceeding those used in agriculture, Carbyne and its constituents of formulation, barban and solvents, exert several effects on the activity of soil micro-organisms. Soil respiration was initially stimulated by addition of all the formulation components. In the case of solvent and Carbyne applications, the stimulated respiration was accompanied by a rise in the bacterial population in response to the additional carbon in the solvent. In contrast, there was no initial increase in microbial population in barban-treated soil. Carbyne, and to a less extent barban, inhibited respiration in soil during later stages of incubation (up to 220 days) although bacterial numbers present were considerably higher than in untreated soil. As barban and Carbyne treatment also depressed the rate of glucose utilization and increased phosphatase levels in soil, it is suggested that the active ingredient (barban) interferes with respiratory processes of soil micro-organisms. Nitrification in soil was inhibited for at least 18 weeks following treatment with barban and Carbyne, during which time neither Nitrosomonas nor Nitrobacter could be detected. Periodic introduction of fresh soil failed to re-establish nitrification. Solvent caused only a temporary inhibition of nitrification during the first two weeks. Using a multipoint inoculation technique, physiological tests revealed that treatments had a selective action on soil bacteria. This upset the balance of populations in soil, which failed to return to the control state for a considerable period. Carbyne treatment reduced numbers and types of fungi in soil. Some of the microbial effects of barban (nitrification inhibition and phosphatase stimulation) were shown to be partly attributable to 3-chloroaniline, a metabolite of barban detected in soil treated with barban and Carbyne. However, the metabolite did not cause the effects to persist nor did it inhibit glucose utilization. The presence of barban, either alone or in combination with solvent as Carbyne, appeared essential for the full and prolonged expression of all the observed effects.
|Date of Award