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SOIL & WATER MANAGEMENT & CONSERVATION

Field Measurement of Soil Surface Chemical Transport Properties for Comparison of Management Zones

^a Agronomy Dep., Iowa State Univ., Ames, IA 50011
^b International Water Management Inst., c/o ICRISAT, Patancheru, AP 502 324 India
^c Agronomy Dep., Iowa State Univ., Ames, IA 50011
^d National Soil Tilth Research Lab., Ames, IA 50011

^* Corresponding author (jheitman{at}iastate.edu).

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 CaCl₂ 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, 0.11 h^–1, 10 cm h^–1, 164 cm² 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.

Abbreviations: BTC, breakthrough curve • CPNT, chisel plow nontrafficked • CPT, chisel plow trafficked • EC, electrical conductivity • MIM, mobile–immobile model • NTNT, no-till nontrafficked • NTT, no-till trafficked • TDR, time domain reflectometry