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DIVISION S-1 - SOIL PHYSICS

Numerical Analysis of Transport of Trifluralin From a Subsurface Dripper

^a Department of Environmental Physics and Irrigation, Institute of Soils, Water and Environmental Sciences Agricultural Research Organization The Volcani Center, Bet Dagan 50250, Israel
^b Department of Environmental Physics and Irrigation, AGRA Earth & Environmental Ltd., 160 Traders Blvd. East, Suite 110, Mississauga, ON, L4Z 3K7 Canada
^c Department of Soil Physical & Environmental Chemistry, Institute of Soils, Water and Environmental Sciences Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel

* Corresponding author (vwrosd{at}volcani.agri.gov.il)

The transport of a pulse of trifluralin (2,6-dinitro-N,N-dipropyl-4-[trifluoromethyl] benzenamime) applied via a subsurfacedripper was analyzed numerically. Results of the analyses suggest that the movement and spread of trifluralin in the soil is considerably retarded by its strong adsorption to the solid phase of the soil. This is particularly so in soils which contain aconsiderable fraction of organic C and in fine-textured (clayey) soils with low hydraulic conductivity and high water retentivity. Water uptake by plant roots and the resultant rapid decrease of water velocity with increasing distance from the dripper restricts further the downward movement of trifluralin and its potential to pollute the groundwater. The presence of dissolved organic matter (DOM) in the irrigation water may enhance both the movement and the spread of trifluralin in the soil, particularly in coarse-textured soils with a relatively small fraction of organic C. Because of the strong adsorption of trifluralin to the soil, its concentration in the aqueous phase of the soil is very low and it decreases further with increasing time because of degradation and nonequilibrium sorption. This is particularly so in coarse-textured soils with a relatively large fraction of organic C. Nevertheless, results of the analyses suggest that for soils of quite widely differing textures and organic C contents, a trifluralin concentration of c_t = 10^-6 kg m^-3 may persist in the vicinity of the dripper for a relatively long period of time (90 d) even with relatively small applied mass (3 x 10^-5 kg).

Abbreviations: 3-D, three-dimensional • CDE, convection dispersion equation • DOM, dissolved organic matter • HOC, hydrophobic organic compounds • PPCG, polynomial preconditioned conjugate gradient