Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2006
Publication Date: 3/12/2007
Citation: Heitman, J.L., Gaur, A., Horton, R., Jaynes, D.B., Kaspar, T.C. 2007. Field Measurement of Soil Surface Chemical Transport Properties for Comparison of Management Zones. Soil Science Society of America Journal. 71(2):529-536. Interpretive Summary: Tillage, wheel-traffic, and other soil management practices can influence chemical movement in soils, but the lack of tools for field-measurement of transport properties has limited our ability to predict those effects. An irrigation dripper-soil moisture probe technique recently developed by ARS and Iowa State University (ISU) scientists was used to quantify chemical transport properties in soil management zones with different tillage (no-till and chisel plow) and tractor compaction (wheel-track and non-wheel-track) histories. Five chemical transport properties differed significantly among the four management zones. Differences in tillage influenced how chemicals diffused or spread through the soil, while differences in wheel-traffic influenced how fast water moved through the soil. These results provide one of very few reports for field measurement of chemical transport properties and are the first application of the new approach for comparing chemical transport properties across soil management zones. This technique and the ability to quantify differences in the chemical transport properties due to soil management will help solve water quality problems such as nutrient enrichment of surface waters and pesticide contamination of groundwater and will be of great benefit to soil scientists studying the fate and transport of chemicals in soil.
Technical Abstract: Soil management influences chemical movement through the profile, but due to soil resource complexity and the lack of field-measurement tools, our ability to predict how various practices will affect chemical transport has been limited. A recently developed dripper-time domain reflectometry technique that allows rapid data collection for several soil properties may solve this dilemma. Our objective was to quantify chemical transport properties for different soil management zones using this new technology. Experiments were conducted within four inter-row management zones: no-till non-trafficked, no-till trafficked, chisel plow non-trafficked, 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 calcium chloride tracer solution. Breakthrough curves were measured via electrical conductivity using time domain reflectometry probes. The mobile-immobile model was fit to the breakthrough curves to determine chemical transport properties. Mean chemical transport properties for the immobile water fraction, mass exchange coefficient, average pore-water velocity, mobile dispersion coefficient, and dispersivity, were 0.34, 0.11 hr**-1, 10 cm hr**-1, 164 cm**2 hr**-1, and 5 cm, 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 non-trafficked 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.