Spatial variability of soil properties and 2,4-D sorption in a hummocky field as affected by landscape position and soil depth

Abstract

Gaultier, J., Farenhorst, A. and Crow, G. 2006. Spatial variability of soil properties and 2,4-D sorption in a hummocky field as affected by landscape position and soil depth. Can. J. Soil Sci. 86: 89-95. Since pesticide fate and leaching models increasingly incorporate spatial variability, the objective of this study was to quantify the variability of soil properties and 2,4-D sorption within a hummocky field as affected by landscape position and soil depth. Seventy-two soil cores collected at 5-m intervals along a transect were segmented by soil horizon (A, B and C) and landscape position (upper, mid, lower and depression). As expected, soil organic carbon content significantly decreased, and soil pH and soil carbonate content significantly increased with soil depth, while clay content was significantly greater in the B horizon than the A and C horizon. Soils from the depressional area generally had higher soil organic carbon content, soil carbonate content, clay content and soil pH than soil samples from other slope positions. The sorption of 2,4-D by soil was positively correlated with soil organic matter content and negatively correlated with soil carbonate content. These soil properties and herbicide sorption varied along the transect and with soil depth. Regardless of whether or not the landscape was segmented by landscape position, for both the A and C horizon, predictions of 2,4-D sorption by soil were generally good using simple regression models that contained soil organic carbon content and carbonate content as the only parameters. However, for the B horizon, the prediction of 2,4-D sorption by soil was very poor when all sampling points along the transect were considered, but greatly improved for the mid-and depressional slope positions when soils were segmented by landscape position. We conclude that segmentation by slope position could be a useful additional tool when predicting pesticide fate and leaching at the large-scale. As well, the negative association between soil carbonate content and 2,4-D sorption warrants further attention as a large portion of Canadian agriculture encompasses calcareous soils. . Comme il fallait s'y attendre, la teneur en carbone organique diminue significativement alors que le pH et la concentration de carbonates augmentent significativement avec la profondeur; parallèlement, il y a sensiblement plus d'argile dans l'horizon B que dans les horizons A et C. Le sol des dépressions contient généralement plus de carbone organique, de carbonates et d'argile que le sol prélevé ailleurs sur la pente et son pH est plus élevé. La sorption du 2,4-D par le sol présente une corrélation positive avec la concentration de matière organique et une autre, négative, avec la concentration de carbonates. Ces propriétés du sol et la sorption de l'herbicide varient avec l'emplacement le long du transect et la profondeur. Les modèles à régression simple n'ayant pour seuls paramètres que la concentration de carbone organique et de carbonates prévoient généralement bien la sorption du 2,4-D p...

Variations in soil properties and herbicide sorption coefficients with depth in relation to PRZM (pesticide root zone model) calculations

“…There was a positive linear relation between SOC and 2,4-D Kd, as observed for other surface and subsurface soils in agricultural fields (Farenhorst et al, 2003;Gaultier et al, 2006;Farenhorst et al, 2008). This is not surprising because soil organic carbon content is the primary factor influencing 2,4-D sorption (Reddy and Gambrell, 1987;Mallawatantri and Mulla, 1992;Hermosin and Cornejo, 1993;Johnson et al, 1995).…”

“…In agreement with other studies (Hermosin and Cornejo, 1991), we also observed a negative linear relation between clay content and 2,4-D Kd. However, soil clay content had no significant influence on the sorption of 2,4-D in soil horizons of a conventional-tilled soil-landscape in Canada (Gaultier et al, 2006).…”

“…When using Koc in the simulations, PRZM was relatively sensitive to changes in either Koc or SOC because of the influence of these input parameters on calculating Kd values. As such, in addition to accurate SOC data for horizons within soil series, a better estimate of how Koc values vary among soil horizons (Gaultier et al, 2006) is important to reduce the error associated with current regional-scale assessments in policy analyses.…”

“…These results suggest that risk assessments of herbicide leaching to depth require data on herbicide sorption throughout the entire soil profile. However, herbicide sorption processes are more frequently studied in surface soils than subsurface soils (Gaultier et al, 2006). 6.…”

Predictivity Strength of the Spatial Variability of Phenanthrene Sorption Across Two Sandy Loam Fields

“…Besides sorption, OC content has also been found to play a role in pesticide mineralization and microbial activity (Vinther et al 2008). Gaultier et al (2006) found that for the A horizon, regression models including only soil OC and carbonate content were sufficient to successfully predict 2,4-D sorption.…”