Effects of the Herbicide Barban and its Commercial Formulation Carbyne on Soil Micro‐organisms

Abstract

At high concentrations barban, its commercial formulation Carbyne or the formulating solvent, initially increased soil respiration. Increased respiration due to Carbyne or the solvent was accompanied by bacterial proliferation in response to the organic carbon of the solvent. There was no initial increase in bacterial population in barban‐treated soil. Soil respiration was inhibited after Carbyne treatment during the later stages of incubation (up to 220 days) despite a bacterial population larger than in untreated soil. Barban and Carbyne depressed the rate of glucose utilization and increased phosphatase activity in soil; it is suggested that barban interferes with the respiratory processes of soil micro‐organisms. Low concentrations (2 parts/106) of 3‐chloroaniline were detected in soil treated with either barban or Carbyne. Carbyne and its ingredients also affected the growth and physiological properties of soil bacteria and fungi.

Effects of the Herbicide Barban and its Commercial Formulation ‘Carbyne’ on Nitrification in Soil*

“…However, processes leading to ammonification appear to be unaffected. This agrees with an earlier observation (Quilt et al 1979) that treatment of soil with Carbyne increased the proportion of organisms capable of hydrolysing urea and reducing nitrate. In the present experiments, barban was established as the toxic agent since the solvent component of Carbyne had no lasting effect.…”

“…Although nitrification in soil was inhibited by 3-chloroaniline, a microbial metabolite of barban (Wright & Forey 1972), the inhibition was of short duration. Moreover, inhibition occurred at a concentration of 50 parts/106 3-chloroaniline, while addition of 200 parts/106 barban (either alone or as Carbyne) produced a maximum 3-chloroaniline concentration of only 2-3 parts/106 (Quilt 1972;Quilt et al 1979). Thus it seems reasonable to ascribe the permanent inhibition of nitrification to barban as such.…”

“…In the present experiments, barban was established as the toxic agent since the solvent component of Carbyne had no lasting effect. The temporary inhibition of N03--N accumulation observed in solventtreated soil occurred at a time when the bacterial population was increasing and metabolic activity was high (Quilt et al 1979), and may have been due to utilization of the available N by the expanding population. Alternatively, it may have been that the high level of 'noxious' components in the solvent was inhibitory to nitrifying organisms.…”

“…Alternatively, it may have been that the high level of 'noxious' components in the solvent was inhibitory to nitrifying organisms. As these may eventually be utilized by soil microbial heterotrophs (Quilt 1972;Quilt et a/. 1979) the inhibitory effect would be alleviated.…”

“…Details of the sandy loam soil, the herbicide and solvent and their application to the soil were given previously (Quilt et al 1979). Barban was applied to give a concentra-* The Editors' regret that this paper was lost in the post for several months.…”