Breakthrough curves (BTCs) of the cation 45Ca2+, an anion 36Cl−, and 3H2O were measured during miscible displacement through water‐saturated soil columns packed with aggregates of an Oxisol. Two conceptual models were used to simulate the observed asymmetry and tailing in the BTCs caused by an apparent nonequilibrium situation in the porous medium. In both models the exchange process on one type of site was assumed to be instantaneous while the rate of isotopic exchange on another type of site was assumed to be either a diffusion‐controlled process (model 1) or a first‐order reversible kinetic process (model 2). Isotopic exchange in both models was described with a linear isotherm. It is shown that the two models are mathematically equivalent with respect to the derived BTCs.

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The study was conducted to determine the feasibility of using a tensiometer‐controlled irrigation system to reduce N leaching in turfgrass while maintaining acceptable growth. Bermudagrass (Cynodon dactylon × C. transvaalensis) was grown on a sand soil (Pomano fine sand, a siliceous, hyperthermic Typic Psammaquent) during a series of 2‐month (bimonthly) cycles. Irrigation was applied either daily (Daily irrigation), or when permitted by tensiometer soil moisture sensors (Sensor irrigation). Nitrogen at the rate of 5 g m−2 month−1 was applied bimonthly as NH4NO3, (AN) or sulfur‐coated urea (SCU), or as NH4NO3, through the irrigation system with each irrigation (Fertigation). The effect of these treatments on turfgrass color, clipping weights, and on tissue N content were measured. Nitrogen was determined in soil water samples obtained on a near daily basis from below the rootzone using ceramic cup suction lysimeters. Nitrogen leaching ranged from 56% to less than 1% of that applied, depending on treatment and cycle. The AN source combined with Daily irrigation produced the greatest N losses (22 to 56%), and Fertigation with Sensor irrigation produced the smallest losses (

Diffusion of nonadsorbed solutes (3H2O and 36Cl‐) out of two sizes of porous ceramic spheres (0.55‐ and 0.75‐cm radius) was measured. These data were analyzed to provide independent estimates of the input parameters required in two simulation models for describing solute transport in aggregated porous media with distinct mobile and stagnant pore‐water regions. Tracer‐saturated porous spheres were placed in tracer‐free 0.01N CaCl2 solution and the rate of tracer diffusion out of the porous spheres was measured by monitoring the increase in tracer concentration with time in the external electrolyte solution. Experimental results were analyzed using two mathematical models. Fick's second law, written in spherical coordinates, formed the basis for Model I. In Model II, the time‐rate of solute transfer into or out of the porous spheres was assumed to be proportional to the difference in tracer concentration inside and outside the porous spheres. The analytical solution to Model I for given initial and boundary conditions was substituted into Model II, to derive an explicit expression relating the empirical mass transfer rate coefficient (α) in Model II and known physical constants of the system. This theoretical analysis indicated that the α value is dependent upon the sphere radius, time of diffusion, volumetric water contents inside and outside the sphere, and the molecular diffusion coefficient. Over a range of experimental conditions, excellent agreement was found between measured α values and those calculated using the analytic expression developed here.

Breakthrough curves (BTC's) for 36Cl‐ and 3H2O displacement through water‐saturated columns of aggregated and nonaggregated porous media were measured at pore‐water velocities varying over an order of magnitude (2 to 96 cm/hour). These BTC's were used to verify two conceptual solute transport models in which the pore‐water was partitioned into inter‐ and intra‐aggregate regions. In both models, convective‐dispersive solute transport was assumed to be limited to the inter‐aggregate pore‐water region, while the intra‐aggregate pore‐water was assumed to behave as a diffusion sink/source for solute. The rate of solute transfer between the two pore‐water regions was described either by Fick's second law of diffusion written in spherical coordinates (Model I) or was assumed proportional to the concentraion difference between the two regions (Model II). Values of all input parameters in each model were measured in independent experiments rather than by curvefitting to the measured BTC's. Agreement between calculated and measured BTC's at all velocities was good for both models. The value of the mass transfer rate coefficient in Model II was found to vary with aggregate radius, time, and pore‐water velocity. This result was predicted based on theory and experimental results presented in an earlier paper. Conditions under which solute diffusion in aggregates leads to tailing or asymmetry in measured BTC's (during saturated water flow) were identified from a sensitivity analysis using Model I. For certain aggregate radii and pore‐water velocities, the diffusion sink/source effects of the aggregates could be incorporated into the dispersion coefficient, and this lumped‐parameter approach was used to successfully describe the measured BTC's.

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The release of sucrose and menthone from chewing gum was measured in-mouth and in-nose, respectively, during eating. Swabs of saliva were taken from the tongue and analyzed using a rapid, direct liquid-mass spectrometry procedure. Menthone concentration in-nose was monitored on a breath-by-breath basis using direct gas phase atmospheric pressure chemical ionization-mass spectrometry. Simultaneously with the volatile release, trained panelists followed the change in mint flavor by time-intensity (TI) analysis. Two types of commercial chewing gum were analyzed. Both showed that the panelists perception of mint flavor followed sucrose release rather than menthone release. The temporal analysis of the chemical stimuli, with simultaneous TI analysis, provided unequivocal evidence of the perceptual interaction between nonvolatile and volatile flavor compounds from chewing gum.

Miscible displacement techniques were used to study the movement of picloram (4‐amino‐3,5,6‐trichloropicolinic acid) through a water‐saturated Norge loam soil. The equilibrium adsorption and desorption isotherms for picloram and Norge loam soil were not single‐valued relations. Picloram mobility was reduced significantly when the average pore‐water velocity was decreased from 145 to 14.2 cm/day. Observed and predicted effluent concentration distributions were compared. Predictions were made with a S/360 CSMP simulation model, using two kinetic rate equations and an equilibrium Freundlich equation. The two kinetic models and the equilibrium model each satisfactorily described the observed effluent concentration distributions at low pore‐water velocities provided the nonsingle‐valued character of the adsorption‐desorption process was included in the calculations. At high pore‐water velocities, the kinetic adsorption models were found inadequate to predict the picloram movement. An empirical model was then developed, based on the assumption that equilibrium existed during displacement and that only a fraction of the soil participated in the adsorption process. This fraction was found to be a function of the average pore‐water velocity. With the empirical model, a reasonable fit between data and calculated effluent curves was obtained for all pore‐water velocities.