These slides shows that a solute can move preferentially along the walls of a soil column.
Note the dark red dye stain at the edge of the soil disc and the lack of dye in the middle of the disc, below. This effect can be minimized by wetting the inside of the soil column and adding an swelling clay (i.e., montmorillonite), allowing the excess clay to fall out of the column, and carefully packing the column. Use a funnel when adding the soil to the column so that it doesn't touch the clay lining.
This stainless-steel column system allows an integrated evaluation of emission potential and efficacy of pesticides. The system consists of a large, packed soil column and a sampling chamber for measuring the pesticide emissions at the soil surface. Leachate can be measured from a port at the bottom of the column. Soil pests can be inoculated into the column and their survival may be assayed after pesticide treatment. This laboratory equipment has been frequently used to evaluate the emission of fumigants from soil and to determine fumigant efficacy.
Gan, J., Hutchinson, C., Ernst F., Becker, J.O. and Yates, S.R. 2000. Column system for concurrent assessment of emission potential and pest control of soil fumigants. Journal of Environmental Quality 29:657-661.
Hytibar Emission Reduction
A field experiment was conducted to study the effectiveness of a high-barrier plastic film (Hytibar) and reduced methyl bromide (MeBr) application dosages in decreasing MeBr emission from soil fumigation. Comparison was made with a conventional polyethylene film (PE) and a regular application rate. MeBr emission from nine small field plots was continuously measured with two replicated active chambers. Replicated soil cores were taken to a depth of 3 m to determine MeBr degradation and obtain a mass balance. Results indicated that about 64% of applied MeBr was lost to atmospheric emission when covered with the PE tarp. The emission was reduced to 37.5% when covered with the Hytibar tarp for 5 days. MeBr emission was virtually eliminated when covering with the Hytibar tarp for more than 10 days (only 1.1-3.2% loss). The low emission rate was verified from the degradation measurements which, along with the flux measurements produced nearly 100% mass balance. Combined use of a high-barrier plastic film such as the Hytibar with reduced application rates can significantly reduce MeBr atmospheric emission in soil fumigation.
Wang, D., Yates, S.R., Ernst, F.F., Gan, J. and Jury, W.A. 1997. Reducing methyl bromide emission with a high barrier plastic film and reduced dosage. Environmental Science and Technology 31:3686-3691.
Wang, D., Yates, S.R., Ernst, F.F., Gan, J., Gao, F. and Becker, O.J. 1997. Methyl bromide emission reduction with field management practices. Environmental Science and Technology 31:3017-3022.