Da. Ellerbroek et al., MODELING PESTICIDE TRANSPORT IN AN IRRIGATED FIELD WITH VARIABLE WATER APPLICATION AND HYDRAULIC CONDUCTIVITY, Journal of environmental quality, 27(3), 1998, pp. 495-504
The impact of spatially varying hydraulic properties on chemical trans
port in the unsaturated zone has been extensively studied. However, fe
w studies have investigated the impact of variable water application o
n chemical transport. This paper uses field data and a modeling study
to evaluate the relative importance of intrinsic and extrinsic sources
of variability on pesticide transport through a field soil. Saturated
hydraulic conductivity represented the source of intrinsic variabilit
y and water application was studied as a source of extrinsic variabili
ty. A conceptual model of water now and solute transport was developed
based on results from soil cores, shallow groundwater samples, and dy
e studies. One important result of the field study was the detection o
f low levels of the applied pesticide metolachlor 2-ethyl-6-methylphen
yl)-N-(2-methoxy-1-methyethyl) acetamide]) in groundwater samples coll
ected at 2.6 m below ground surface after an average application of on
ly 0.097 m of water. Dye studies indicated gravity-driven fingered now
occurred in the subsoil, which may explain the early detection of pes
ticide in the shallow groundwater. Monte Carlo simulations revealed th
at the variability of water application had a greater impact on pestic
ide transport than the variability of saturated hydraulic conductivity
at this site. Therefore, improving sprinkler uniformity represents an
important best management practice (BMP) for reducing groundwater con
tamination by agricultural chemicals under the conditions studied.