MEASURED AND PREDICTED SOLUTE TRANSPORT IN A TILE DRAINED FIELD

Authors: GAUR, ANJU - IOWA STATE UNIVERSITY; HORTON, ROBERT - IOWA STATE UNIVERSITY; Jaynes, Dan; BAKER, JAMES - IOWA STATE UNIVERSITY

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2006
Publication Date: 4/3/2006
Citation: Gaur, A., Horton, R., Jaynes, D.B., Baker, J.L. 2006. Measured and predicted solute transport in a tile drained field. Soil Science Society of America Journal. 70:872-881.

Interpretive Summary: Most methods for measuring the movement of agrichemicals in soil are difficult and require extensive soil excavation. We developed a new technique that uses easily measured changes in surface soil properties during irrigation to estimate chemical movement below the crop root zone of soil. The method involves applying a common chloride salt to the soil surface and leaching it through the soil with a single irrigation. Easily made measurements of changes in the electrical conductivity of the surface soil combined with a simple two-dimensional model of chemical transport in soil provide an estimate of the travel time of agrichemicals from the soil surface to below the root zone. We were able to show good agreement between the estimated rate of chloride movement and the measured appearance of the chloride in tile drainage. The findings suggest that solute transport properties of field soils can be determined from easily made surface measurements combined with a simple model. This finding will be useful to soil scientists and other environmental scientists interested in the movement of chemicals through soil and their possible contamination of water resources.

Technical Abstract: 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 non-destructive time domain reflectometry (TDR) technique could be used to accurately predict tile flux concentrations. A plot 14 by 14 m above a tile drain buried at a depth of 1.1 m was selected for the study. After reaching a steady-state condition, a pulse of calcium chloride solution (16.3 cm) with an electrical conductivity (EC) of 23 dS m-1 was applied through sprinklers. TDR 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, uI, and its standard deviation, oI, 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 1-D CLT model and in a 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 coefficient of efficiency, E, was -0.47. The 2-D model predictions of tile flux concentrations were similar to the observed values. The RMSE was 0.023, and the E was 0.94. The findings suggest than 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.