Intermediate-Scale Tests of the Gas-Phase Partitioning Tracer Method for Measuring Soil-Water Content

Turfgrass Research. The lysimeter is 4.0 m deep, 2.5 m in diameter, and contains a homogeneous packing of Vinton fine Experiments were conducted in a well-instrumented weighing lysand (sandy, mixed, thermic Typic Torrifluvents) with a mean simeter (2.5 by 4 m) to evaluate the efficacy of the gas-phase-partibulk density of 1.38 Mg m 3 and porosity of 0.47. Details tioning tracer method for measuring soil-water content. The method regarding the lysimeter instrumentation and experiment setup is based on the use of conservative (nonpartitioning) and water-partimay be found in Nelson et al. (1999) and Carlson (2000). tioning tracers, wherein the partitioning tracer transfers into the water, The first two experiments (1 and 2) were conducted at a which retards its movement with respect to that of the nonpartitioning volumetric soil-water content of 0.06. Following an infiltration tracer. This retardation is a function of the soil-water content. The volumetric soil-water contents estimated from comparative moment event to increase the soil-water content to 0.15, two more analysis of the measured breakthrough curves were compared with experiments (3 and 4) were completed using flow rates similar values obtained using traditional methods, including gravimetric core to those used in the previous set. The lysimeter was then analysis, neutron thermalization, time domain reflectometry, and conallowed to drain and a fifth experiment was conducted at a version of soil tension. The values obtained from the tracer tests soil-water content of 0.07. Conditions for the five experiments compare favorably with the independently determined values. For are presented in Table 1. The flow rates were based on system the lower soil-water contents (6–7%), the tracer-estimated values were constraints and what would typically be found in the field 98% of the measured values. For the higher soil-water content during a full-scale tracer test. Sulfur hexafluoride (SF6) was (15%), the tracer estimated values were 77% of the measured values. used in all experiments as the conservative tracer while trichloThese results indicate that the gas-phase partitioning tracer method rofluoromethane (CFM) was used as the bulk-water partican provide representative estimates of soil-water content under the tioning tracer for Exp. 1 to 4 and difluoromethane (DFM) relatively ideal conditions employed herein. was used for Exp. 5. Pertinent properties of the tracers are