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Solute transport properties are required to evaluate the risk of contaminating ground water with agricultural chemicals under a wide variety of crop and soil management practices. Most solute transport measurement techniques are tedious and lead to extensive soil excavation. Two experiments were performed to evaluate whether surface transport properties determined by a non-destructive time domain reflectometry (TDR) technique could be used to accurately predict subsurface leaching. TDR probes installed in the surface 2-cm of soil were used to determine resident solute concentration from measured soil surface soil bulk electrical conductivity. Resident concentrations were analyzed with a onedimensional (1-D) solute transport model in order to determine the surface solute transport properties. The surface measurements technique was first tested in a greenhouse soil. Surface dispersivities (1.02 cm) determined by the TDR method were similar to the 30-cm subsurface dispersivities (1.28 cm). The surface solute transport properties were used to predict the chemical concentration distributions within the 30-cm soil layer, and it was found that the centers of mass from predicted and observed subsurface chemical distributions were similar. Further testing of the TDR technique was done in a strip-cropped tile-drained field. The plant-row and interrow zones significantly affected surface and soil profile (120-cm) dispersivities. The soil profile dispersivity (2.68 cm) was larger and more variable than the surface dispersivity (0.91 cm) indicating greater heterogeneity of flow within the soil profile than at the surface. The large soil profile dispersivity indicated that multidimensional flow and lateral spreading occurred in the soil profile. In order to evaluate solute transport in the soil profile, a 1-D convective lognormal transfer (CLT) function model and a 2-D model

Management of chemicals in soil is important, yet the complexity of field soils limits prediction of management effects on transport. To date, few methods have been available for field measurement of chemical transport properties, but a recently developed dripper-time domain reflectometry technique allows rapid collection of data for determining these properties. The objective of this work was to apply this technique for comparison of chemical transport properties for different soil management zones. Experiments were conducted comparing four interrow management zones: no-till nontrafficked, no-till trafficked, chisel plow nontrafficked, and chisel plow trafficked. Drip emitters were positioned at 12 locations in each zone and used to apply water followed by a step input of CaCl 2 tracer solution. Breakthrough curves were measured via electrical conductivity with time domain reflectometry probes. The mobile-immobile model was fit to the breakthrough curves to determine chemical transport properties. Mean chemical transport properties were 0.34, 0.1 h -1 , 10 cm h -1 , 164 cm 2 h -1 , and 5 cm, for the immobile water fraction, mass exchange coefficient, average pore-water velocity, mobile dispersion coefficient, and dispersivity, respectively. All five properties showed significant differences between management zones. Differences in mass exchange and mobile dispersion coefficients coincided with differences in tillage, while differences in mean pore water velocities coincided with differences in traffic. The immobile water fraction was largest for the no-till nontrafficked zone. These results represent one of very few reports for field measurement of chemical transport properties and the first application of this approach for comparison of chemical transport properties across management zones.

Most solute transport measurement techniques are tedious and require extensive soil excavation. A field experiment was conducted to evaluate whether surface transport properties determined by a nondestructive time domain reflectometry (TDR) technique could be used to accurately predict tile flux concentrations. A 14 by 14 m field plot selected above a 1.1-m deep tile drain was studied. Low electrical conductivity (EC) water was sprinkled on the plot surface, and after reaching a steady-state condition, a pulse of calcium chloride solution (16.3 cm) with an EC of 23 dS m -1 was applied through the same sprinklers. Time domain reflectometry equipment was used to record the change in EC of surface (∼ top 2 cm) soil at 45 locations. The EC of the tile drainage flow was measured continuously with an EC probe. The surface convective lognormal transfer (CLT) function parameters, log mean irrigation depth, μ I , and its standard deviation, σ I , were found to be 3.44 and 0.94 [ln(cm)], respectively, for a reference depth of 110 cm. These surface parameters were used in a one-dimensional (1-D) CLT model and in a two-dimensional (2-D) model (CLT vertical function combined with exponential horizontal transfer function) to predict the tile flux concentrations. The 1-D CLT model predicted an earlier arrival time of chemicals to the tile drain than observed values. The root mean square error, RMSE, of the 1-D CLT predictions was 0.123, and the coefficient of efficiency, E, was -0.47. The 2-D model predictions of tile flux concentrations were similar to the observed values. The root mean squared errors (RMSE) and E were 0.023 and 0.94, respectively. The findings suggest that in this field soil, the surface solute transport properties determined by TDR could be combined with a 2-D transport model to make reasonable predictions of tile flux concentrations.

Chemicals that leach through soil pose threats to surface and groundwater quality. It is difficult and expensive to measure subsurface chemical transport and the transport properties required for extrapolating predictions beyond limited observations. The objective of our study was to evaluate whether solute transport properties measured at the soil surface could be used to predict subsurface chemical movement. The study was conducted in a greenhouse soil pit. The solute transport properties of the surface 2-cm soil layer were determined by using time domain reflectometry (TDR) to measure the bulk electrical conductivity during a step application of CaCl2 solution. The movement of chemicals in the subsurface was measured within the top 30 cm of soil following a pulse input of CaCl2 solution. A comparison of the measured chemical transport properties in the surface and subsurface zones of the soil showed that the parameters were similar. Furthermore, the estimated parameters determined by the surface TDR method were used to predict the chemical concentration distributions within the 30-cm soil layer, and it was found that the centers of mass of predicted chemical distributions were not significantly different from the measured ones. Therefore, the surface TDR measurements could be used to successfully predict subsurface chemical transport within the upper 30 cm of the soil. This surface measurement technique is a promising tool for vadose zone chemical transport studies.