The objective of this study was to quantify 2,4-
D (2,4-dichlorophenoxyacetic acid) mineralization in soil profiles characteristic of hummocky, calcareous-soil landscapes in western Canada. Twenty-five soil cores (8 cm inner diameter, 50 to 125 cm length) were collected along a 360 m transect running west to east in an agricultural field and then segmented by soil-landscape position (upper slopes, mid slopes, lower slopes and depressions) and soil horizon (A, B, and C horizons). In the A horizon, 2,4-
D mineralization commenced instantaneously and the mineralization rate followed first-order kinetics. In both the B and C horizons, 2,4-
D mineralization only commenced after a lag period of typically 5 to 7 days and the mineralization rate was biphasic. In the A horizon, 2,4-
D mineralization parameters including the first-order mineralization rate constant (
k 1), the growth-linked mineralization rate constant (
k 2) and total 2,4-
D mineralization at the end of the experiment at 56 days, were most strongly correlated to parameters describing 2,4-
D sorption by soil, but were also adequately correlated to soil organic carbon content, soil pH, and carbonate content. In both B and C horizons, there was no significant correlation between 2,4-
D mineralization and 2,4-
D sorption parameters, and the correlation between soil properties and 2,4-
D mineralization parameters was very poor. The
k 1 significantly decreased in sequence of A horizon (0.113% day
?1) > B horizon (0.024% day
?1) = C horizon (0.026% day
?1) and in each soil horizon was greater than
k 2. Total 2,4-
D mineralization at 56 days also significantly decreased in sequence of A horizon (42%) > B horizon (31%) = C horizon (27%). In the A horizon, slope position had little influence on
k 1 or
k 2, except that
k 1 was significantly greater in upper slopes (0.170% day
?1) than in lower slopes (0.080% day
?1). Neither
k 1 nor
k 2 was significantly influenced by slope position in the B or C horizons. Total 2,4-
D mineralization at 56 days was not influenced by slope positions in any horizon. Our results suggest that, when predicting 2,4-
D transport at the field scale, pesticide fate models should consider the strong differences in 2,4-
D mineralization between surface and subsurface horizons. This suggests that 2,4-
D mineralization is best predicted using a model that has the ability to describe a range of non-linear mineralization curves. We also conclude that the horizontal variations in 2,4-
D mineralization at the field scale will be difficult to consider in predictions of 2,4-
D transport at the field scale because, within each horizon, 2,4-
D mineralization was highly variable across the twenty-five soil cores, and this variability was poorly correlated to soil properties or soil-landscape position.
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