S. Lehr et al., MINERALIZATION OF FREE AND CELL-WALL-BOUND ISOPROTURON IN SOILS IN RELATION TO SOIL MICROBIAL PARAMETERS, Soil biology & biochemistry, 28(1), 1996, pp. 1-8
Although microbial degradation into CO2 offers one of the principal me
ans for removing organic pesticides from soils, the influence of quant
itative and qualitative soil microbial properties on mineralization of
pesticides is poorly understood. In a laboratory study, we examined t
he relationship between soil microbial biomass and activity, estimated
by heat output and adenine nucleotide fractions, and the mineralizati
on rates of C-14-ring-labelled free and plant cell-wall-bound isoprotu
ron, a phenylurea herbicide, in four soils originating from different
cropping systems. (CO2)-C-14 production of free isoproturon ranged fro
m 14 to 23% of the initial activity over 67 d and differed significant
ly between soils. (CO2)-C-14 formation from cell-wall-bound isoproturo
n was about one-third of that of free isoproturon with only small diff
erences in the mineralization capacities of all four soils. For free i
soproturon, mineralization correlated significantly with soil microbia
l biomass (estimated by substrate-induced heat production) in three so
ils, while in a soil from a former hop plantation no correlation was f
ound. For cell-wall-bound isoproturon, no correlation between soil mic
robial biomass or activity and (CO2)-C-14 production was found. High C
u concentrations in one soil, resulting from fungicide treatments duri
ng former hop cultivation, are probably the reason for an increased me
tabolic status of the soil microorganisms characterized by the relativ
e quotient of heat production (rqheat) and for the higher mineralizati
on rate of free and cell-wall-bound isoproturon per unit biomass compa
red to the other sails. Our results suggest that non-specific soil mic
robial properties are not sensitive enough to describe the influence o
f soil microbial activities on the mineralization of free and plant ce
ll-wall-bound isoproturon.