The spatial variability of soil properties and 2,4-D sorption and desorption in two calcareous prairie landscapes

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Stephens, Kristian Dietrich
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Pesticides are widely used worldwide to increase agricultural crop yields, in which most of the applied pesticides are herbicides. Following application, herbicide sorption and desorption are the two most important processes controlling the herbicide's behaviour in the environment. This study examined the effects that soil properties and tillage have on the spatial variability of 2,4-Dichlorophenoxyacetic acid (2,4-D) sorption and desorption which may be useful for landscape based agricultural management and for pesticide fate modeling. The two agricultural sites were a heavily-tilled eroded hummocky landscape near Morris, Minnesota and a glacial till undulating landscape near Miniota, Manitoba. The herbicide sorption and desorption experiments were determined by the standard batch equilibrium method which used 14C labeled 2,4-D solutions. Both landscapes were delineated into landform element complexes (LECs) by a landform description model for describing the spatial distribution of the soil properties and herbicide behaviour within the landscapes. In the Morris site 100, 138, and 63 sampling points were allocated to upper, middle, and lower LECs, which encompassed 33%,46%, and 21% of the 301 points, respectively. At Miniota a total of 51, 72, 73, and 14 sampling points were allocated to the upper, middle, lower, and depressional LECs, which comprised 24%, 34%, 35%, and 7% of the 210 points, respectively. However, concerns were raised about microbial degradation of the herbicide during the sorption experiments, thus a preliminary study was first conducted to determine the effects of soil sterilization by mercuric chloride on the sorption of the 2,4-D by soil. Results indicated the mercuric chloride strongly decreased the capacity of the soil to retain herbicides and that the interference of the mercuric chloride with herbicide sorption increased with increasing soil organic carbon contents...