Download ANNUAL REPORT OF REGIONAL RESEARCH PROJECT

ANNUAL REPORT OF REGIONAL RESEARCH PROJECT W-188
January 1 to December 31, 2000
1. PROJECT:
W-188 CHARACTERIZATION OF FLOW AND TRANSPORT
PROCESSES IN SOILS AT DIFFERRENT SCALES
2. ACTIVE COOPERATING AGENCIES AND PRINCIPAL LEADERS:
Arizona
A.W. Warrick, Department of Soil, Water and Environmental Sciences, University of
Arizona, Tucson, AZ 85721
P.J. Wierenga, Department of Soil, Water and Environmental Sciences, University of
Arizona, Tucson, AZ 85721
W. Rasmussen, Department of Soil, Water and Environmental Sciences, University
of Arizona, Tucson, AZ 85721
California
M. Ghodrati, Dept. of Env. Sci. Pol. Mang., University of California, Berkeley, CA
94720-3110
J.W. Hopmans, Dept. of LAWR, Hydrologic Science, University of California Davis,
CA 95616
W.A. Jury, Dept. of Envir. Sciences, University of California, Riverside, CA 92521
F. Leij, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507
B. Mohanty, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507
D.R. Nielsen, Dept. of LAWR, Hydrologic Science, University of California Davis,
CA 95616
D.E. Rolston, Dept. of LAWR, Soil and BioGeochemistry, University of California
Davis, CA 95616
P.J. Shouse, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507J. Šimùnek, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507T. Skaggs, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507M.Th. van Genuchten, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside,
CA 92507
1
L.Wu, Dept. of Envir. Sciences, University of California, Riverside, CA 92521
Colorado
L.R. Ahuja, USDA-ARS, Great Plains System Research Unit Fort Collins, CO 80522
T. Green, USDA-ARS, Great Plains System Research Unit Fort Collins, CO 80522
G. Butters, Dept. of Agronomy, Colorado State University, Ft Collins, CO 80523
Delaware
Y. Jin, Dept. of Plant and Soil Sciences, University of Delaware, Newark, DE 107171303
Idaho
J.B. Sisson, EG&G, Idaho National Engin. Lab., Idaho Falls, ID 83415-2107
J. Hubbel, EG&G, Idaho National Engin. Lab., Idaho Falls, ID 83415-2107
Illinois
T.R. Ellsworth, University of Illinois, Urbana, IL 61801
Indiana
J. Cushman, Mathematics Dept., Purdue University, W. Lafayette, IN 47905
P.S.C. Rao, School of Civil Engineering, Purdue University, W. Lafayette, IN 47905
Iowa
R. Horton, Dept. of Agronomy, Iowa State University, Ames, IA 50011
D. Jaynes, National Soil Tilth Lab, USDA-ARS, Ames, IA 50011
Kansas
G. Kluitenberg, Dept. of Agronomy, Kansas State University, Manhattan, KS 66506
Kentucky
E. Perfect, Dep. of Agronomy, University of Kentucky, Lexington, KY 40546
Montana
J. M. Wraith, Land Resources and Environ. Sciences, Montana State University,
Bozeman, MT 59717-3120
Nevada
S.W. Tyler, Hydrologic Sciences Graduate Program, University of Nevada, Reno,
NV 89532
M. Young, Desert Research Institute, University of Nevada, Reno, NV 89512
New Mexico J.H.M. Hendrickx, New Mexico Tech, Dept. of Geoscience, Soccoro, NM 87801
North Dakota F. Casey, Dept. of Soil Science, North Dakota State University, Fargo, ND 581055638
2
Utah
D. Or, Dept. of Plants, Soils & Biomet., Utah State University, Logan, UT 84322
Washington
M. Flury, Dept. of Crop & Soil Sciences, Washington State University, Pullman, WA
99164
J. Wu, Dept. of Biological System Engineering, Washington State University,
Pullman, WA 99164
Wyoming
R. Zhang, Dept. of Renewable Resources, University of Wyoming, Laramie, WY
82071
CSREES
R. Knighton, USAD-CSREES, Washington, DC 20250-2200
Adm. Adv.
G.A. Mitchell, Palmer Research Center, 533 E. Fireweed, Palmer, AK 99645
3. PROGRESS OF WORK AND MAIN ACCOMPLISHMENTS:
OBJECTIVE 1: To study relationships between flow and transport properties or processes and
the spatial and temporal scales at which these are observed
Short-term consistency in solute transport processes in a field plot was studied by CaliforniaBerkeley. Although spatial variability in solute transport in field soils has been intensively
examined, there is far less information available on temporal changes in transport processes. If there
are changes in transport over time, then simply calibrating a model with a breakthrough curve for a
single time period may not be adequate. W-188 project members examined the consistency in solute
transport measurements in a field soil using two in situ nondestructive techniques, fiber optic
miniprobes (FOMPs) and time domain reflectrometry (TDR) probes. There was moderate
consistency in transport response measured by the TDR probes. Nonetheless, the FOMP data
suggested that solute transport converged into fewer flow pathways over time with repeated leaching.
The 5 cm long TDR probes also provided evidence of increased lateral flow in the first 5 cm of soil
with time. The temporal variability was surprisingly similar between the FOMPs and TDR probes,
even though their sampling volumes differ by more than four orders of magnitude. Relationships
between probe responses within the plot were examined using a Spearman’s rank test, confirming
that transport response pattern may not be temporally stable.
At California-Davis, soil spatial variability of hydraulic functions was described using
simultaneous scaling and a single set of scaling factors. The scaling approach has been extensively
used to characterize soil hydraulic spatial variability and to develop a standard methodology to assess
the variability of soil hydraulic functions and their parameters. The procedure consists of using
scaling factors to relate the hydraulic properties in a given location to the mean properties at an
arbitrary reference point. The conventional scaling approach is based on empirical curve fitting,
without paying much attention to the physical significance of the scaling factors. In this study, the
3
concept of simultaneous scaling of the soil water retention and unsaturated hydraulic conductivity
functions is applied to a physically based scaling theory. In this approach, it is assumed that soils are
characterized by a lognormal pore-size distribution, which leads directly to lognormally distributed
scaling factors.
Iowa investigated the influence of ionic strength and flow velocity on sorption and transport
of naphthalene in soil. The potential for soil and groundwater contamination by organic chemicals
such as polycyclic aromatic hydrocarbons (PAHs) is a national problem. Sorption and desorption
kinetics affect the fate and transport of PAHs. Reliable estimates of the sorption and desorption
kinetics are important for both risk assessment and efficient remediation of contaminated soils and
aquifers. W-188 project members conducted both batch and column studies to characterize fate and
transport of naphthalene in soil. In the column studies, the influence of ionic strength (0.01 to 0.5 M
of Calcium Chloride) and pore water velocity (2 to100 cm h-1) on sorption-desorption kinetics of
naphthalene was investigated. For the batch studies, the effect of ionic strength was examined. We
compared the rates of sorption and desorption in the column studies with those determined in batch
studies. The aqueous-phase ionic strength affected the sorption behavior and transport of naphthalene
by influencing the degree of aggregation. Greater aggregation at higher ionic strength resulted in
enhanced sorption affinity and capacity, and thus retarded the transport of naphthalene. The sorption
behavior from the batch and column studies was similar, having enhanced sorption at higher ionic
strength. However, a particular mechanism responsible for enhanced sorption of naphthalene at
higher ionic strength is unclear. Flow velocity also influenced sorption behavior.
Iowa also investigated temporal and spatial scale effects on diffusion in rock matrices. In
some pore spaces such as those in fracture networks (such as aggregate interiors and cracking clay
soils) and rock matrices (such as sand grains and gravel aquifer material), diffusion can display
anomalous, non-Fickian behavior. Such pore spaces are said to be at the percolation threshold,
meaning that the pores are very sparsely interconnected, and as a consequence much of the pore
volume is composed of dead-end pore complexes rather than flow pathways. Project members
conducted a simulation study of diffusion in both well- and sparsely-interconnected pore spaces over
a wide range of both times and distances, in order to assess long-term, long-distance behavior of
diffusing pollutants and to understand how macroscopic observations relate to the anomalous
diffusion. In well-connected porous media, diffusivity is unaffected by sample size and the mean
molecular travel time for diffusion through a sample scales with the square of the distance traveled
2
(e.g., the sample size, L ), but in sparsely-connected media diffusivity decreases with sample size,
and mean molecular travel time scales as approximately L3.8. In other words, applying diffusivity
measurements from a lab sample to a large rock formation can grossly over-estimate the diffusive
mass transfer. Additionally, in sparsely connected media, the effective porosity decreases with
sample size, and rather than being constant over the entire sample, it is greater in the center of the
sample than at the two ends. This means that, in order to see the linear concentration gradient inside
the sample, one has to adjust for the effective porosity. Simply examining solute concentrations
across the sample will not account for the difference between effective (connected to both ends) and
dead-end porosity. It requires more than a single measurement or a single sample to determine
whether a particular rock material displays anomalous diffusion.
Kansas studied the temporal stability of spatial yield patterns. Yield monitors have been used
to obtain yield data for three fields in Kansas cropped continuously to corn (center pivot irrigation).
4
Four years of data have been obtained from Fields A and C; seven years of data have been obtained
from Field B. Yield data from each field was block-averaged to 55-m square cells. Frequency
distributions for all fields and years exhibited strong negative skew. Therefore, relative differences in
yield for cell i in year j were computed using the expression
i, j 
Yi , j  Y j
Yj
where Yi, j is the yield for cell i in year j and Y j is the median yield for year j. Mean relative
difference for cell i was computed using
i 
1 n
 i , j
n j 1
where n is the number of years of yield data. All subsequent computations were made using mean
relative difference i and its associated standard deviation.
Temporal stability of spatial yield patterns was assessed by using Spearman rank correlation
to characterize the degree of association between yield maps from the same field. Ranges for
coefficients of determination were 0.34 < r2 < 0.44 for Field A, 0 < r2 < 0.56 for Field B, and 0.06 <
r2 < 0.29 for Field C. Temporal stability appears to be stronger for Field A than for the other fields.
Although these results suggest much stronger correlation than that found by Jaynes and Colvin
(1997, Agron. J. 89:30-37), temporal stability is still quite weak. This was confirmed by plotting
i as a function of rank. Only for Field A can we say with confidence that some locations have
systematically lower yield. An analysis of change in rank caused by the addition of each new year of
yield data showed that mean change in rank approached an asymptotic value of approximately 7 for
all fields. Furthermore, it appears that this asymptotic value is obtained after accumulating 4-5 years
of data. This suggests that long-term yield monitoring (> 5 years) may not prove useful in
establishing temporally-persistent spatial yield patterns.
North Dakota conducted field infiltration experiments that measured water transfer and
solute transport in a structured field soil. The objective was to examine correlations between water
transfer and solute transport properties of a soil that exhibits preferential flow. Time domain
reflectometry probes were placed horizontally 2 cm below an infiltrometer disk and water was
infiltrated until steady infiltration was reached. The water content continued to increase after the
steady flow rate was achieved, suggesting that was being transferred from, rapidly filling, highly
conductive pores to slowly filling, less conductive pores (i.e., immobile pores). Also, a suite of three
benzoic acid tracer were sequentially applied through the tension infiltrometer using the Jaynes et al.
(1995) method (W-188, Iowa). After the tracers were applied the soil was sampled to a depth of 4 cm
on one half of the infiltration area. After sampling the infiltrometer was placed back on the
infiltration area and tracer application continued. Steady infiltration was achieved quickly on the
unsampled area and there was little change in infiltration rate. The tracers were then sequentially
removed from the infiltration solution after which the soil was again sampled. The sequential
5
application and removal was done to observe the exchange of solute into and out of the immobile
domain, respectively.
California-USSL further improved the windows-based HYDRUS-1D and HYDRUS-2D
software packages by incorporating pedotransfer functions that enable users to rapidly estimate the
hydraulic input parameters for specific applications, and by coupling the codes with parameter
estimation subroutines. A three-dimensional version of HYDRUS is currently under development.
The HYDRUS codes have been applied to a large number of agricultural problems (infiltration, tile
drainage design, crop production, fate and transport of agricultural chemicals in the subsurface), as
well as to many problems in the general area of soil and groundwater pollution involving nonagricultural chemicals (such as radionuclides and contaminants released from industrial and
municipal waste disposal sites). The coupling of the HYDRUS codes with parameter estimation
subroutines enables the inverse estimation of a variety of hydraulic and solute transport parameters
from laboratory and/or field experiments. The parameter estimation options provide much more
effective methods for estimating the unsaturated soil hydraulic properties from relatively standard
infiltration, multistep outflow, and evaporation experiments.
California-USSL also conducted a study to determine if it is possible to predict particle-size
distribution (PSD) from limited soil texture data. A procedure was developed to predict PSD based
on measurements of the clay, silt, and fine plus very fine sand (particle diameters between .05 and
.25 mm) fractions. The procedure was shown to work well except in soils with very high silt
contents (> 70 percent silt).
Research continued at the California-USSL on random resister networks. Network models
of randomly sized capillary tubes are commonly used as surrogate media in theoretical investigations
of the transport properties of soils and rocks. The conductivity of network models can be calculated
by critical path analysis, a method based on the connectivity of highly conducting pathways and the
statistics of percolation theory. USSL used percolation cluster statistics and critical path analysis to
derive an analytical expression for the expected value of the hydraulic conductivity as a function of
system size, and have numerically verified the theory. They also derived a relationship between the
expected values of the hydraulic and electrical conductivities.
Soil moisture is an important state variable in the hydrologic cycle, and its spatio-temporal
distribution depends on many geophysical processes operating at different spatial and temporal
scales. To achieve a better accounting of the water and energy budgets at the land-atmosphere
boundary, it is necessary to understand the spatio-temporal variability of soil moisture under different
hydrologic and climatic conditions, and at a hierarchy of space and time scales. During the Southern
Great Plains 1997 (SGP97) Hydrology Experiment, W188 members at California-USSL and
California-Riverside measured the 0 to 6 cm soil water content on consecutive afternoons at four
hundred locations in a small, gently sloping range field. The soil moisture measurements were made
using portable impedance probes. Spatio-temporal data analyses of the two sampling events showed
a significant change in the field variance but a constant field mean, suggesting moisture was
redistributed by (differential) base flow, evapotranspiration, and condensation. Among the different
relative landscape positions (hill-top, slope, valley), the slope was the largest contributor to the
temporal variability of the soil moisture content. Using a sequential aggregation scheme it was
observed that the relative position influencing the field mean and variance changed between the two
sampling events, indicating time-instability in the spatial soil moisture data. Furthermore, high
6
resolution (impedance probe) sampling and limited (gravimetric) sampling gave different field means
and variances.
Kentucky investigated statistical relations between water retention parameters and solute
dispersivity for small, undisturbed soil cores. Differences in solute dispersion at any given flow rate
are controlled by pore characteristics under saturated conditions. Thus, if breakthrough curves and
pore characteristics are measured simultaneously, statistical relations can be developed to predict the
dispersivity () from independent measurements of the pore space geometry. We measured both  and
pore characteristics on short (6-cm long) undisturbed soil columns from six soil types, ranging in
texture from loamy sand to silty clay. Pore space geometry was characterized in terms of total
porosity (), the Campbell water retention parameters (a and b), and saturated hydraulic
conductivity (Ksat). Breakthrough curves were determined by monitoring changes in effluent
electrical conductivity in response a step decrease in influent CaCl2 concentration under steady state
flow conditions using a computerized data acquisition system. Dispersivities were computed from
the resulting breakthrough curves by the method of moments. Mean dispersivities ranged from < 0.5
cm for the loamy sand to > 20 cm for the silty clay. Stepwise multiple regression analyses indicated
that  increased as both a and b increased. All other factors being equal, the positive relationship
between  and a implies that fine textured soils are more dispersive than coarse textured soils.
Similarly, the positive relationship between  and b means that dispersion increases as the width of
the pore size distribution increases. Neither  nor Ksat contributed to the prediction of  once a and
b were included in the regression model. Using this statistical approach we were able to explain
47% of the observed variation in . Additional data for sands and clays may improve the
predictability of the regression model.
Kentucky also studied percolation thresholds in the pore space of 2-dimensional geometric
prefractals. Considerable effort has been directed towards developing fractal models of soil pore
space. Less has been done on applying percolation theory to soils. We combined these two areas of
research to investigate percolation behavior in prefractal porous media. Percolation thresholds in the
pore space of homogeneous random 2-dimensional prefractals were estimated as a function of the
scale invariance ratio (b) and iteration level (i) using the Hoshen-Kopelman algorithm and MonteCarlo simulation. The resulting percolation thresholds increased beyond the 0.593 porosity expected
in regular 2-dimensional site percolation networks. Percolation in prefractal networks occurs
through large pores connected by small pores. The thresholds increased with increasing b and i
values. Extrapolation to infinite iterations suggests there may be a critical fractal dimension (D) of
the solid phase at which the pore space percolates. The extrapolated value of D was approximately
1.89, which is close to the well-known fractal dimension of percolation clusters in regular 2dimensional site percolation networks. The percolation behavior of prefractal porous media has
important implications for analytical models of the soil water retention curve that are based on the
assumption of a power law distribution of pore sizes. Prefractal percolation models may also be
useful for simulating the transport of air, water and solutes in heterogeneous porous media.
Unstable flow was the subject of experiments conducted by California-Riverside. Two
fields comprised of sandy loam and loamy sand textures were chosen to represent a range of
conditions favorable to preferential flow during redistribution. The experiment consisted of the
uniform addition of infiltrating water under unsaturated flow conditions to the field surface by a
specialized low impact spray boom that adds the water to the surface at a spatially and temporally
7
uniform flow rate. Within the infiltrating water are a pulse of potassium bromide and ammonium
carbonate so that the pulse may be monitored in the soil by both analysis of soil samples and by
visible dye tracing both at the end of the infiltration phase and during four days of subsequent
redistribution. A series of preliminary studies were performed on the fields over a period of 4
months at a variety of input flow rates, until we were able both to induce and prevent preferential
flow in each field. Following these preliminary studies, a flow rate was chosen that maximized the
appearance of preferential flow and also contrasted its characteristics on the two fields.
The progress of the infiltrating and redistributing front was monitored on the two fields using
a combination of soil sampling and dye trace photography. The monitored region of the study area
was a soil cube 1.2 m on each side and 1 m deep that was photographed by shaving a trench face in
successive 10 cm increments to 50 cm from the end over several days following the end of
infiltration, spraying the face with a special solution to stain the regions that contained ammonium,
photographing the region with a precision digital camera over a prescribed grid, and then taking 120
soil samples on a 10 cm unit grid along the entire face. At the conclusion of the sampling, the
remaining undisturbed 50 cm half of the soil block was intensively sampled vertically by soil coring.
In all, some 3000 samples were taken and are now being analyzed for water content, nitrogen,
bromide, and select hydraulic properties. Until the samples are analyzed, it will not be possible to
assess fully the degree to which we were able to create preferential flow during the redistribution
phase. However, from the evidence obtained from the dye trace studies, we are optimistic that we
have detected preferential flow and can associate it with fluid and soil characteristics as indicated in
our proposal.
California-Riverside also studied atmospheric deposition and landscape controls on
watershed response. Large cities with high vehicle use and some agricultural operations such as
feedlots or dairy farms are areas of high emissions of ammonia or oxides of nitrogen (N). Terrestrial
and aquatic ecosystems located downwind of these N source areas are being “fertilized” by
atmospheric N deposition. In watersheds with chronic N deposition it is common to find elevated
nitrate (NO3-) concentrations in streamwater and groundwater. Few studies have addressed the
impacts of chronic N deposition on semiarid catchments. Semiarid catchments are particularly
sensitive to excessive NO3- loss because of alternating dry periods of N accumulation followed by
high precipitation inputs. Streamwater monitoring along a deposition gradient in the San Bernardino
Mountains in southern California suggest that NO3- export in streamwater is a function of N
deposition and N processing within the coupled terrestrial and aquatic ecosystems.
Large variations in NO3- concentrations among the streams within Devil Canyon (near San
Bernardino), located on the western, high-deposition end of a pollution gradient, provide an
opportunity to evaluate the factors that control NO3- loss from forested and chaparral semiarid
watersheds. Our research project will determine the relative influence of N deposition, nitrate
production rates in soils, stream source waters, in-stream processes, and catchment properties on
stream NO3- concentrations. This project will determine the biogeochemical and hydrologic controls
on stream nitrate concentration in five steps. We have begun monitoring deposition throughout the
Devil Canyon watershed using throughfall collectors. We are measuring stream, soil, and ground
water chemical composition and will use these measurements to determine the variable contributions
of different catchment source waters to stream chemical composition and particularly the impact of
changes in hydrologic flowpath on stream NO3- concentration. We will compare geographic data sets
8
for these watersheds to determine if differences in land cover properties are capable of explaining the
observed variability of stream NO3-. We also plan on conducting tracer experiments in the stream to
determine effective rates of nutrient uptake and hydrologic exchange in the stream.
Utah conducted a theoretical study on using thermodielectric effects on radar backscattering
towards developing correction factors for remotely sensed water content information, and for remote
delineation of differences in surface soil texture at large scales.
In several projects, Washington studied the relationship between flow and transport
properties and their spatial and temporal scales. Experimental, theoretical and numerical analyses
were carried out to examine (1) remediation of uranium contaminated mine waste, (2) virus transport
and sorption/inactivation in unsaturated porous media, (3) erosion processes in agricultural field
under the unique climatic conditions of the Northwest Wheat and Range Region (NWRR), and (4)
characteristics of subsurface hydrological processes in forest watersheds.
Washington also used column experiments to determine reaction rate coefficients of
uranium sorption/precipitation and to determine the sorption capacity of apatite suggested as
leaching barrier. In column studies uranium was not detected in the column outflow during 270 days
of column throughflow. EDAX analyses demonstrated that uranium migrated to a depth of about 3 to
4 cm, showing that apatite is a very effective material to remove uranium from the liquid phase.
Washington and Delaware collaborated on a study of virus transport in unsaturated porous
media. Project members developed a model to describe virus movement under sorption/inactivation
to solid-liquid and solid-gas interfaces. The results suggest that in the presence of reactive solid
surfaces, increased reactions at the solid-water interface, rather than at the air-water interface,
dominates in virus removal and transport under unsaturated conditions (Chu et al., 2001).
In Nevada, research efforts have focused on the dynamics of nitrogen transport in desert
soils. Investigators drilled and analyzed deep vadose zone profiles in southern Nevada to determine
the nitrogen dynamics of these ecosystems. Soil water chemistry from the Nevada Test Site at depths
up to 50 meters below land surface show that deep percolation to the water table was limited to the
late Pleistocene, a period of higher precipitation in the area. High levels of soil water chloride and
chloride profiles were used to age date the period of recharge. Surprisingly, elevated levels of nitrate
(up to 5000 mg/L) were found in the soil waters below the zone of active rooting. The accumulation
of elevated nitrate was shown to be derived from atmospheric deposition combined with a small
percentage of nitrogen fixation from soil microbial crusts (Hartsough et al, submitted). Most
significantly, the elevated leached nitrogen levels below the active rooting zone suggest that desert
ecosystem response is not limited by nitrogen as has been previously postulated, but that nitrogen
availability is closely tied to water availability which may not coincide with periods of biotic activity.
The soil core data also suggest that nitrogen leaching from these desert profiles has been relatively
consistent throughout the Holocene (the last 10,000 years) in spite of significant changes in the
vegetation communities.
Also at Nevada, work is also beginning in the alpine regions of Nevada and California to
study the dynamics of nitrogen and phosphorous transport in watersheds during and following forest
management practices. Field plots have been laid out and sampling of soil nutrient and soil
hydraulic properties has just been initiated. During the upcoming year, forest management (clearing,
thinning and prescribed fire) will be initiated on these plots to develop relationships between nutrient
loading to watercourses and these management practices.
9
OBJECTIVE 2: To develop and evaluate instrumentation and methods of analysis for
characterization of flow and transport at different scales
California-Berkeley developed methods for in situ characterization of solute transport in a hillslope
soil. The natural heterogeneity in water and solute movement in hillslope soils makes it difficult to
accurately characterize the transport of surface applied pollutants without first gathering spatially
distributed hydrologic data. Currently the most common technique to measure solute transport on
hillslopes has been to cut trenches in the soil and monitor the effluent. As it is not possible to place
such infrastructure in every watershed, portable in situ measurement devices must be developed.
This year we have examined the application of time domain reflectometry (TDR) to measure solute
transport in hillslopes. Three different plot designs were used to examine the transport of a
conservative tracer in the sloping soil from various perspectives. The TDR system was shown to be
an effective means to characterize solute travel times in hillslope soils. In addition, a consistent
qualitative pattern of tracer transport was described which identifies dominant processes and soil
features relevant to solute transport. The data demonstrate the preferential flow of the tracers; where
in one instance rapid solute transport was estimated to occur in as little as 3% of the available pore
space. Lateral subsurface flow was measured in all plots, most significantly in the two sets designed
to gather information on lateral flow. Finally, it was demonstrated that the soil anisotropy, while
partially responsible for causing lateral subsurface transport, may also homogenize the transport
response across the hillslope by decreasing solute spreading.
The dependence of soil strength on water content, and its variations within the soil profile
and across the field, was investigated at California-Davis. Soil mechanical impedance affects root
growth and water flow, and controls nutrient and contaminant transport below the rooting zone.
Among the soil parameters affecting soil strength, soil water content and bulk density are the most
significant. However, field water content changes both spatially and temporally, limiting the
application of cone penetrometers as an indicator of soil strength. A combined coiled penetrometermoisture probe was developed to study the influence of water content on soil strength. The coiled
TDR moisture probe consists of a 2 parallel copper wires, each 0.8 mm diameter and 30 cm long,
coiled around a 5 cm long PVC core with a 3 mm separation between wires. The performance of the
combined probe was compared with a conventional 2 parallel TDR probe for a Columbia fine sand
loam, a Yolo silt clay loam and washed sand. Calibration curves relating the soil bulk dielectric
constant measured by the coiled probe with water content were obtained in the laboratory and data.
In a followup study, the coiled TDR is integrated into the porous cup of a tensiometer, so that in situ
soil water retention and/or simultaneous soil water content and water potential is measured within
identical soil bulk volumes.
California-Davis and California-USSL jointly developed inverse modeling methods to
estimate soil hydraulic properties from transient experiments, giving much more flexibility in
experimental boundary conditions than required for steady state methods. As an additional advantage,
inverse modeling allows the simultaneous estimation of both the soil water retention and unsaturated
hydraulic conductivity function from a single transient experiment. In other ways, inverse modeling of
transient water flow is not much different than methods applied to steady flow. In either case, inversion
of the governing equation is required to estimate the unsaturated hydraulic conductivity function from
10
experimental data. Whereas the steady state methods invert Darcy’s equation, the governing equation
for a transient flow regime is Richards’ equation. Its inversion requires repeated numerical simulation
of the governing transient flow problem. Successful application of the inverse modeling technique
improves both speed and accuracy, as there is no specific need to attain steady state flow. Various
experiments were designed to estimated flow and transport parameters using the inverse modeling
approach.
In order to better understand diffusive and advective transport of volatile contaminants in
soil, the density of gas-phase contaminants responsible for several important transport phenomena in
natural soil systems were studied in the laboratory at California-Davis. One-dimensional laboratory
experiments were conducted to explore the transport of a dense gas (Freon-113) through air-dry sand.
Gas densities and fluxes were measured during transport through a column filled with Oso-Flaco
sand. Significant differences in fluxes and density profiles were observed for the three primary flow
directions (horizontal, vertically upward, vertically downward) at high source densities. Pressure
gradients due to the non-equimolar diffusion of freon and air were measured in the first 2.5 cm of the
soil column, but only for the horizontal and vertically downward experiments. Numerical models
based on the standard Darcy-Fickian transport equation did not fit the measured fluxes. Slip flow was
found to be significant relative to Darcy advective flow, but did not account for the discrepancy
between model simulations and data. Further research and theory development will be necessary in
order to ascertain why the standard equations do not adequately describe the diffusive and advective
transport processes for dense gases.
Iowa studied soil thermal properties as a function of soil volume fractions. The soil thermal
properties—heat capacity (C), thermal diffusivity (), and thermal conductivity ()—are important
in many agricultural, engineering, and meteorological applications. Soil thermal properties are
largely dependent on the volume fraction of water (), volume fraction of solids (vs), and volume
fraction of air (na) in the soil. In many natural settings , vs, and na vary greatly over time and space,
but data showing the effects of these variations on thermal properties is not readily available. In the
laboratory, we used a heat pulse method to measure the thermal properties of 62 packed columns of
four medium textured soils covering large ranges of , vs, and na. The resulting data revealed that
soil thermal properties are more strongly correlated with na (r2 = 0.86, 0.71, and 0.93 for C, , and
, respectively) than with  (r2 = 0.90, 0.32, and 0.63) and that vs has the weakest correlation to soil
thermal properties (r2 = 0.23, 0.69, and 0.57). The strong correlations of thermal properties with
air-filled porosity have not been previously reported, and may be useful for improved modeling of
soil thermal properties.
Iowa also measured soil thermal properties using the heat pulse method in the field in two
separate experiments. In the first experiment, they measured thermal properties of surface soil with
and without organic amendments. These measurements were made as one component in a larger
study on the ecological effects of incorporating organic materials, such as compost and red clover,
into the soil. In the second experiment, they measured surface thermal properties at 120 locations
along two 20-m transects in a soybean field. One transect was in the row and one transect was in the
trafficked inter-row. In both field experiments, they collected soil samples from all the measurement
sites and determined the water content and bulk density gravimetrically. Data processing from these
11
two experiments has not yet been completed.
Iowa also developed and evaluated methods for rapid field measurement of soil hydraulic
and transport properties. The procedure of Lee et al. (2000) was extended to study solute transport
properties at multiple field locations over a short time period. Solute transport properties included
the immobile water content (im), the mass transfer rate coefficient (), and the dispersion
coefficient (Dm). These parameters are required in predicting solute transport using the
mobile/immobile model (MIM). The setup of Al-Jabri et al. (2001) was utilized to conduct
measurements at field scale. A total of 38 field locations were rapidly evaluated for chemical
transport properties. TDR probes were installed at an angle from the soil surface, and measurements
were assumed to take place over the top 20 mm. Background and long step solutions were applied
from point sources at each location using a dripper line. The bulk electrical conductivity of the
applied solution was measured using the TDR. Automated measurements were facilitated by using
the TACQ package (Evett, 1998). Breakthrough curves (BTCs) for all field sites were constructed.
The solute transport parameters were estimated from on the observed (measured) BTCs using the
CXTFIT package. The estimated parameters were found to be comparable with values reported by
previous studies for nearby field locations. The setup and procedure allowed rapid estimation of all
transport parameters (im, , and Dm) with minimal time and labor requirements.
In a related study, hydraulic and solute transport parameters were measured in soils treated to
different cropping, tillage, and compaction levels. Hydraulic properties included the saturated
hydraulic conductivity (Ks) and the macroscopic capillary length (). The field experiments were
conducted on corn and soybean field locations (same soil type). The chemical transport properties
are as mentioned above. The corn and soybean fields were under no-till and chisel plow
management. Hydraulic and chemical transport properties were estimated in both the trafficked
(compacted) and untrafficked interrows. Thus, a combination of crop, tillage, and compaction levels
were evaluated for such properties. Data and chemical analyses are under way.
Kansas investigated methods for measuring soil water flux. Ren et al. (2000, SSSAJ 64:552560) proposed a new method for measuring soil water flux density in which a heat tracer was used to
quantify the magnitude of convective heat transfer resulting from soil water movement. Their
method utilized analytical solutions of the heat equation to describe temperature changes that occur
upstream and downstream of a line heat source following the emission of a heat pulse.
Unfortunately, these solutions contain integrals that must be evaluated using numerical integration
techniques. Insofar as one of the integrals is improper, specialized numerical integration procedures
are required. Collaborative work between Kansas and Arizona during the past year has focused on
reducing the integrals in the aforementioned solutions to the integral




W (u, )   z 1 exp  z   2 4 z dz
u
known in the groundwater hydrology literature as the well function for leaky aquifers. Furthermore,
an efficient method for evaluating W(u,) has been developed. The method, which involves
summing the first few terms of an infinite series, also provides a simple means of determining the
approximation error. Approximations can be made with
12
(1) m
W (u, )  
m!
m 0
n
m
 2 
  E m 1 (u )
 4u 
[1]
which converges rapidly for u > /2, or with
n
W (u, )  2 K 0 ()  
m 0
 2 
(1) m
(u ) m Em1  
m!
 4u 
[2]
which converges rapidly for u < /2. The series in Eq. [1] and [2] converge at the same rate along
the line u = /2. The magnitude of the error incurred by using the truncated series in Eq. [1] and [2]
is no greater than the absolute value of the first truncated term. Thus, W(u,) can be approximated
with known accuracy. We have investigated the number of terms required in Eq. [4] or [5] to
approximate W(u,) with error  104 in absolute value. W(u,) can be approximated with excellent
accuracy by using only 0, 1, or 2 terms throughout much of the u- domain. More than 2 terms are
required only near the line u = /2 for large values of .
Also at Kansas, the effect of forced convection on  measurements was studied. The dualprobe heat-pulse (DPHP) method is useful for measuring soil volumetric water content (). Previous
work has shown that, because of their small size, DPHP sensors are useful for measuring water
content near heterogeneities. One such heterogeneity is the soil surface. The performance of DPHP
sensors in obtaining near-surface measurements of  is of considerable interest and practical
importance.
Heterogeneity imposed by the soil surface is only one of several issues that must be addressed
in order to evaluate DPHP sensors for this application. Another issue of importance is the possibility
of heat convection due to the movement of soil water (forced convection). The usual heat transfer
theory for the DPHP method assumes only conductive heat transfer and thus implicitly neglects
forced convection. Inasmuch as water infiltration rates are often greatest near the soil surface, it
seems desirable to determine whether forced convection due to infiltrating water will cause error in
near-surface  measurements obtained with DPHP sensors.
The effect of forced convection on  measurement error has been estimated by developing
models that explicitly account for forced convection. Three DPHP sensor configurations have been
examined. Configuration I has the heater and temperature sensor probes in a plane parallel to the soil
surface. Configuration II has the probes in a plane normal to the surface with the heater probe nearer
the surface. Configuration III in similar to Configuration II, but has the sensor probe nearer the
surface. Water (saturated or unsaturated) flows downward at a constant rate for all configurations.
Water-saturated Hanlon sand (Ren et al., 2000, SSSAJ 64:552-560) with volumetric heat capacity C
= 3.07 MJ m3 K1 and thermal diffusivity  = 6.33 x 107 m2 s1 was used for calculations. Probe
spacing and heat duration were set to r = 0.006 m and t0 = 8 s.
The effect of forced convection on absolute error in water content () is predicted to be
substantially smaller for Configuration I than it is for Configuration II or III. And, for all practical all
purposes, it appears that the effect of forced convection will be insignificant for DPHP sensors
13
positioned in Configuration I ( < 0.002 if J < 5.58 cm h1). Experimental work to examine the
effect of forced convection in Configuration I is underway.
Montana and Utah introduced and verified the concept of using calibrated reference soils or
other porous media having known and reproducible water retention characteristics as a means to
estimate the unknown retention properties of soils in situ. Pockets of the reference soil/media may be
buried at experimental soil locations, with embedded time domain reflectometry (TDR) probes in
both the target and adjacent reference media. Monitoring changes in water content (θ) by TDR
allows inference of the retention properties of surrounding soil in hydraulic equilibrium via the
reference media retention curve(s). The method may be used to obtain both wetting and drying
relationships in contrast to many conventional techniques which generally provide only the
desorption (retention) response. Use of calibrated reference soils has several important advantages
over alternative approaches. Among these are in situ characterization of undisturbed intact soils,
ability to measure over the entire soil wetness range, measurement economy in using only paired
TDR sensors, and ability to maximize hydraulic continuity between the sensor and target soil through
selection of reference media properties. Seven different soils were used in experiments conducted in
a laboratory pressure plate apparatus, greenhouse, and a remote field site. Results indicate that the
ability to capture continuous paired θ over the entire wetness range (using automated systems) may
provide more accurate θ(h) than using pressure steps only, as ‘intervening’ information concerning
sorption and/or desorption behavior is not lost. Potential concerns include realizing consistent bulk
densities for the buried reference soil pockets, and obtaining measurements at the very wet end (near
effective saturation) for field applications. Imposed irrigation can address the latter issue, but may be
inconvenient or impractical in some cases. Routine application of the proposed paired sensor method
might be enhanced by fabrication of well-characterized, cylindrical soil or other porous media
packets enclosed in water-permeable liner material. This would address the related issues of
reference media sensor stability and reproducibility.
Montana continues to work towards development of improved methods to intensively and
nondestructively measure transport of ionic solutes in soils. The concentration (Ci) of ionic solutes in
soils is directly proportional to soil solution electrical conductivity (σw). Time domain reflectometry
(TDR) measures both soil water content (θ) and bulk soil electrical conductivity (σa) using the same
probes. However, physical/conceptual models are required along with TDR measurements in order to
use TDR for in situ estimates of Ci. We addressed a modeling approach [Mualem and Friedman,
1991] based on assumed analogy between tortuosity of electrical and hydraulic flow paths in variably
saturated soils. We derived a general expression for a pore geometry factor (FG) considering flow of
electrical current through randomly distributed capillary soil pores. Two FG were derived based on
two conceptual considerations of tortuous capillary length. Four water retention models (WRM)
were used to describe soil hydraulic properties in the FGs. When fitted to the same measured water
retention data, the four WRMs provided substantially different magnitudes for FG. The model using
the two new FG was then compared with field-measured θ and σa. One of the new FGs produced
smaller estimated σw than did that proposed in the original (1991) model. This is desirable based on
our own and several other published comparisons that indicated the original model may overestimate
σw in comparison with independent measurements.
Montana also assisted Department of Energy contractors in evaluating potential efficacy of a
proposed unsaturated flow encapsulation system. A portion of the sandy unsaturated zone beneath
14
the Brookhaven LINAC Isotope Producer (BLIP) located at the DOE Brookhaven National
Laboratory (BNL) on Long Island, New York was impacted through activation of soil immediately
around the proton beam target assembly. The block of activated soil is about 7 m below grade and 8
m above the water table. High energy neutrons and protons created by the proton beam hitting the
target are absorbed by the soil creating radioactive isotopes of natural-occurring elements in the soil.
The two principle isotopes of concern are tritium and sodium 22, which are easily transported to
groundwater. To minimize transport of contaminants to the aquifer, unsaturated flow through the
impacted soil needs to be reduced. A viscous liquid barrier (VLB) has been proposed as the
preferred method for preventing groundwater contamination. Formation of a VLB involves injecting
a low viscosity colloidal silica (CS) grout into the soil to fill the void space where it sets into a gel.
The grout will be injected to encapsulate the activation-zone soils. This creates a monolithic region
forming a barrier of reduced permeability and significantly altered soil water retention
characteristics. Results of unsaturated flow simulations, using VLB hydraulic properties measured in
the laboratory, demonstrated that the performance goal of the barrier constructed using CS grout,
variant MSE-6, would be met.
North Dakota, in collaboration with Iowa, developed and evaluated a miscible-displacement
system with an on-line HPLC for hydrophobic volatile organic chemicals. The system is capable of
measuring multiple solutes present in the column effluent and there is minimal chemical loss from
volatilization and sorption because the system is completely enclosed and constructed of nonsorbing
materials. A complete description and evaluation of this miscible-displacement system was
published recently (Casey et al., 2000 Soil Sci. 165:841-847).
North Dakota and California-USSL collaborated on the development of inverse methods
for the transport of chlorinated hydrocarbons subject to sequential transformation reactions. To
improve the parameter estimates from the simultaneous TCE and ethylene breakthrough curves an
inverse modeling method was added to HYDRUS-1D. The HYDRUS-1D was modified to include
parameters from both the TCE and ethylene breakthrough curves in the objective function for the
inverse model solutions. We evaluated the modified HYDRUS-1D with breakthrough curves of TCE
undergoing reduction through columns of zero-valent metals. The TCE and ethylene breakthrough
curves were successfully fitted with an equilibrium and nonequilibrium sorption model. The
simultaneous inverse model solution improved the reliability of the parameter estimates by adding
constraints to the optimized parameters. Analysis with modified HYDRUS-1D model also showed
that the nonequilibrium model provided better description of the fate and transport of TCE and its
degradation product ethylene.
California-USSL continued research on the estimation of soil hydraulic properties. Reliable
estimates of unsaturated soil hydraulic properties (water retention, hydraulic conductivity) are needed
in many hydrologic, subsurface pollution and crop production studies; unfortunately, these properties
are very difficult to measure rapidly and accurately in the field. As an alternative, they can be
estimated indirectly using pedotransfer functions (PTFs) from more easily measured soil survey type
data such as soil texture and bulk density. USSL developed a hierarchical neural network-based PTF
approach that is both flexibility (by providing better estimates when additional information is
available) and accurate (neural networks provide the best possible models). The approach also leads
to uncertainty estimates, and hence gives insight into the reliability of the predictions. This research
resulted in a computer software package, called Rosetta, that may be used to estimate the unsaturated
15
soil hydraulic properties from more easily measured or more readily available soil survey type data.
Users are able to download the software from the hope page (www.ussl.ars.usda.gov) of the Salinity
Laboratory. The information should help users to obtain better estimates for infiltration, drainage,
leaching, and surface runoff or related flow processes, for specific soil types.
California-USSL and California-Riverside developed a new methodology to directly
measure the porosity and its microscopic characteristics. The methodology is based on the analysis of
binary images collected with a backscattered electron detector from thin sections of soils. Pore
surface area, perimeter, roughness, circularity, and maximum and average diameter were quantified
in 36 thin sections prepared from undisturbed soils. Saturated hydraulic conductivity (Ks), particle
size distribution, particle density, bulk density and chemical properties were determined on the same
cores. We used the Kozeny-Carman equation and a combined neural network and bootstrap analysis
to predict the formation factor from microscopic, macroscopic, and chemical data. The predicted Ks
was in excellent agreement with the measured value (R2=0.91) when a hydraulic radius defined as rH
=pore area/pore perimeter and the formation factor were included in the Kozeny-Carman equation.
California-Riverside evaluated methods for measuring Oxygen Diffusion Rate (ODR). In
this research, a 100-kPa ceramic plate was attached and sealed to the bottom of each undisturbed soil
column. Two pressure-transducer equipped tensiometers and two TDR probes were used to monitor
water potential and content during the experiment. The ODR was measured by platinum electrode.
After the column was saturated, a vacuum pump was used to apply suction to drain water from the
bottom. The experiment was conducted in the soil matric potential ranged from 0 to 40 kPa. Results
showed that the threshold ODR value of 0.2 g cm-2 min-1 occurs at 4.5 kPa for the sandy soil and at
10 kPa for the loamy soil, which indicates that at field capacity (10 or 33 kPa), none of the soil will
have aeration problem. Indeed, maximum ODR values were achieved at water suctions that are
lower than considered as field capacity.
The threshold ODR value occurred at air-filled porosity close to 8% for the sandy loam and
17% for the loamy sand. Although the air-filled porosity at field capacity can provide a comparison
among different soils in consideration, it does not provide any information on how it will affect plant
growth. This research showed that different textured soils could reach to the same ODR level at
different air-filled porosities, implying that comparison of air-filled porosity among different soils has
little meaning relative to root growth. The diffusion coefficients of the two soils are substantially
different at the same threshold ODR value of 0.2 g cm-2 min-1. It indicates that ODR is affected by
water contents, not just by gas diffusion through the gas phase. This again implies that comparison of
diffusion coefficients among soils offer little information relative to soil aeration capability and
influence on root growth.
California-Riverside also investigated the effects of imposing differing water-pressure heads
on infiltration into water-repellent soils. Water repellent soils exhibit a positive water entry pressure
head, hp, in contrast to wettable soils that have a negative hp. A sand of particulate size between 0.05
and 2.0 mm was treated with two concentrations of octadecylamine to create a sand with hp values of
8.4 and 3.5 cm. The hydraulic conductivity (K) of the water repellent sands increased with
increasing values of h0. The K of the treated sand was equal to K of untreated sand when the ratio
h0/hp was approximately 3.1 for each treated sand. The infiltration rate increased with increased time
for lower h0 values, but decreased with increased time for higher h0 values. The transition from
increasing to decreasing infiltration rates with time occurred when h0/hp was approximately equal to
16
2.6. A positive hydraulic head was created at the interface of an overlying wettable and underlying
water which affected the infiltration rate consistent with the effects of h0 on a non-layered water
repellent sand. The following mechanism is proposed to explain the increase in infiltration rate with
time. In water repellent materials, positive hydraulic heads can be created within the profile during
infiltration which can increase as the depth to the wetting front increases. The higher hydraulic head
induces an increase in hydraulic conductivity that contributes to increased infiltration rate.
Alternatively, if the depth of ponded water is sufficient to cause a hydraulic conductivity equal to
that of the wettable material, the infiltration rate behavior is the same as traditionally observed for
wettable soils.
Utah developed a method for predicting unsaturated hydraulic conductivity functions based
on pore scale hydrodynamics of flowing films and flow in corners bounded by a liquid vapor
interfaces. The pore scale results were upscaled to represent sample scale hydraulic functions using
measurements of soil porosity, pore size distribution (inferred from retention curve), surface area,
and possibly, the saturated hydraulic conductivity. This modeling approach could be extended to
represent unsaturated properties of unsaturated fractured rock and macroporous soils.
Washington developed an experimental and theoretical methodology to determine the
moisture characteristics from freezing experiments. The instrumental methodology has been
improved considerably during the past year. A new TDR transmission line has been constructed and
improved insulating material has been tested. Systematic instrument tests have been, and are
currently being, performed to assess the effects of ionic strengths, the spatial sensitivity of
measurements, and the hysteresis of the freezing phenomenon. Soils and porous media of different
composition have been tested and measurement results compared with results obtained with classical
methods.
Washington is also testing dyes as vadose zone tracers to visualize flow pathways in soils.
Systematic laboratory tests have been conducted with Brilliant Blue FCF, a frequently used dye
tracer (German-Heins and Flury, 2000). The pH and ionic strength effect on sorption of the dye to
soil media has been investigated. Substantial sorption was found for the soil sample with the highest
clay content and the lowest pH. Increasing ionic strength led to increased sorption of Brilliant Blue
FCF. In aqueous solution, the absorption spectrum of Brilliant Blue FCF is not sensitive to pH nor
ionic strength.
Arizona conducted a flow and transport experiment at the Apache Leap Research Site, near
Superior, Arizona. Water was ponded on 9x9 meter area, subdivided into nine 3x3 meter square
subplots. The movement of water and tracer through the initially unsaturated, fractured tuff was
monitored using a neutron probe, tensiometers, and suction lysimeters. Each subplot had one
neutron probe access tube ( 5m deep), 5 tensiometers, and 5 suction lysimeters. Tensiometers and
suction lysimeters were installed at depths of 0.5, 1, 2, 3, and 5 meters. Ponding of water on each
plot started November, 1999. After 200 days of ponding, increases in water content and decreases in
tension were measured at all observation points down to 3m, but no significant changes in water
content and tension were noted at the 5 meter depth. Among the nine subplots, great variations in
infiltration rates were found. The infiltration rates varied from 0.036 cm/day to 0.75 cm/day. No
clear evidence of fracture flow was observed from our water monitoring devices, except infiltration
rates were higher for two subplots with apparent surface fractures. Plots with apparent surface
fractures maintained similar infiltration rate throughout the experiment. The pressure transducer
17
equipped tensiometers successfully recorded the wetting front arrivals at different depths in various
locations but no clear early wetting front arrivals, indicative of fracture flow, were observed.
Bromide was added to the irrigation water and all plots on May 30, 2000. Bromide was first
observed in the subsurface at the 1.0 m depth of the north central plot and at the 0.5 m depth in the
central plot, 14 days and 25 days after the first bromide application, respectively. Forty-four days
after bromide was first applied it was detected at 3 and 5 meter in two of the nine plots only. At this
time bromide was found in only 7 of the forty-five suction lysimeters with concentration higher than
3 ppm. The transport of bromide to some deeper depths in a relatively short time and the bypass of
bromide at many shallower depths is clear evidence of fracture flow, which was not evidenced from
the water content and tension data.
Nevada, in collaboration with the California-USSL, investigated flow and transport
processes through highly heterogeneous mining wastes commonly found in Nevada. Specifically,
the project members have been studying the transport processes of arsenic though gold heap leach
sites and gold waste rock dumps. Arsenic is present in many of the ores found in Nevada and its
transport from these large, artificial vadose zones to the underlying ground water has significant
environmental consequences. The collaborative effort involved modifying the coupled flow and
reactive geochemical transport code UNSATCHEM to include the dominant transport mechanism of
arsenic (pH dependant non-linear sorption, arsenic dissolution/precipitation, oxygen diffusion and
pyrite dissolution). Simulation results, using laboratory data on mine rock, shows multiple reaction
fronts as arsenic migrates through waste rock. Specifically, pH changes due to pyrite dissolution
tend to reduce arsenic mobility, however redox shifts to anoxic conditions counterbalances this
reduce mobility through transformations to more mobile As(III). Results indicate that elevated levels
of arsenic in drainage water from these sites will continue for significant time (>100 years) periods.
OBJECTIVE 3: To apply scale-appropriate methodologies for the management of soil and water
resources
In a four-year study, Iowa is using a paired watershed approach to gauge the effect of an optimum
N-fertilizer program on water quality in tile drainage. The treated watershed is 1000 ac and has 16
fields managed by 8 farmers. The late spring nitrate test, LSNT, as developed for Iowa, is being used
in conjunction with starter and a side-dress application of liquid N to manage N within a
corn/soybean rotations. Anhydrous ammonia is not being used due the inherent variability in its
application. In addition to surface water quality, yield, soil N, chlorophyll meter values, crop growth
is being collected. LSNT recommended N-fertilizer rates were slightly higher in 1997 and about 50
kg/ha less in 1998, and slightly lower in 1999 than farmer program rates. Since the project was
initiated in 1997, there has been a 3.5 mg/L reduction in the nitrate-N concentration leaving the
LSNT watershed compared to the control watershed (Fig. 3), while corn yields have been
comparable in two out of three years. Overall, the LSNT sub-basin has shown a 41.5% (7.3 mg L-1)
reduction in NO3 concentration by early fall of the fourth year (2000). This is the first study to
document the impact of an LSNT program on water quality at a spatial scale that is environmentally
meaningful.
Since 1996, NO3 loss from a subsurface drained field in central Iowa has been measured at
three N-fertilizer rates; a low (L) rate of 57 - 67 kg ha-1, a medium (M) rate of 114 - 135 kg ha-1, and
18
a high (H) rate of 172 - 202 kg ha-1. Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] were
grown in rotation with N-fertilizer applied in the spring to corn only. For the L treatment, NO3
concentrations in the drainage water exceeded the 10 mg-N L-1 maximum contaminant level (MCL)
established by the USEPA for drinking water only during the years that corn was grown. For the M
and H treatments, NO3 concentrations exceeded the MCL in all years, regardless of crop grown. For
all years, the NO3 mass loss in tile drainage water from the H treatment (48 kg-N ha-1) was
significantly greater than the mass losses from the M (35 kg-N ha-1-) and L (29 kg-N ha-1) treatments,
which were not significantly different.
Economic optimum N-fertilizer rates for corn grain production were between the L and M
treatments (67 to 135 kg ha-1) in 1996 and between the M and H treatments (114 and 172 kg ha-1) in
1998. Soybean grain production was unaffected by N-fertilizer treatments during the corn year of the
rotation. To balance the inputs and outputs of N to the system for the 2-yr rotation, N-fertilizer rates
needed to be at least at the H rate (202 kg-N ha-1 in 1996 and 172 kg-N ha-1 in 1998) given the
current tile drainage losses experienced by this system. However, NO3 concentrations in tile
drainage consistently exceeded the MCL for drinking water in the years corn was grown for all
N-fertilizer treatments and also during the years soybean was grown on the M and H treatments.
Thus, it appears that economic corn production cannot be sustained within this field under the
current rotation and management scheme without producing tile drainage water that exceeds the
MCL for NO3. The problem is not simply one of N-fertilizer use, but of a corn-soybean production
system created by artificial soil drainage and intensive tillage. Thus, NO3 concentrations exceeding
the MCL appears endemic to artificially drained soils cropped to corn within the Midwest.
Montana designed, constructed and field-tested a heavy-duty time domain reflectometry
(TDR) probe that fits hydraulic soil sampling machines. Mapping soil water content for site-specific
management of farm fields is commonly achieved through grid soil sampling. This effort frequently
requires intensive soil coring, which is destructive and time consuming. Precision farming and
research can be facilitated if soil sampling techniques are improved and made cost effective. The
new heavy-duty probe is simple enough to be adapted to the TDR equipment and hydraulic sampler
that a researcher or practitioner may already possess. The probe consists of a housing and adapter
that can be fabricated in a local machine shop from materials that are easily obtainable. Utility of the
probe to help in developing kriged field-scale soil water maps was demonstrated in several
production agricultural fields.
Montana established two 70-acre on-farm study locations in cooperation with agricultural
producers in northern Montana. Eighty neutron access tubes were installed at each study location,
and soil water content was measured at two-week intervals during the growing season. Phenology
and surface cover of the spring wheat crop was also monitored. An automated climate station was
located at each site, to provide real-time weather information including precipitation and potential
evapotranspiration. These are used in our combined computer simulation modeling and remote
sensing approach to provide continuously updated and spatially-distributed estimates of soil water
status and crop yield forecasts. Substantial progress was made in converting the computer model to
MS Access/Visual Basic format to facilitate interface with GIS programs currently used by
producers. Two Landsat 7 ETM+ images were acquired for each location, though one of these
images may be of limited utility due to presence of clouds. The MODIS remote sensing data for
planned use in regional modeling for the project was not available this year. Preparations are
19
currently underway to evaluate potential utility of hyperspectral remote sensing to infer progression
of crop water deficit.
Invasive plants such as spotted knapweed have been repeatedly implicated in potential
degradation of soil and water resources. Altered soil conditions might result from several factors
including increased erosion due to lower canopy and basal cover, reduced soil organic matter
contribution from tap-roots, and modified seasonal water and nutrient cycles. Degradation of soil
resources resulting in increased runoff and sedimentation might impact quality of surface waters.
However, evidence for invasive plant impacts on soil and water resources is mainly anecdotal, as
very little related research has been completed. Montana completed a study to evaluate impacts of
spotted knapweed on selected soil physical properties, soil hydraulic properties, soil water status, and
near-surface soil thermal properties. Six field study sites containing both spotted knapweed and
native grass plots were used. Basic near-surface soil measurements included particle size
distribution, bulk density, and total organic carbon content. Disk permeameters were used to obtain
soil hydraulic properties. Steady state infiltration was measured at four supply pressures at the same
location in each plot, and these were fitted to Wooding’s equation to obtain the hydraulic
conductivity function. Soil water content was monitored using neutron moisture meter and TDR.
Near-surface soil thermal regime was monitored using thermocouples. We found that the
relationships between vegetation effects and measured soil properties were variable and inconsistent
among blocks and study sites. Saturated hydraulic conductivity, estimated time to ponding, and a
parameter related to range in water conducting pore sizes were not significantly different between
infested and noninfested areas. Thermal properties including damping depth and apparent thermal
diffusivity were similarly not different between vegetative types. Infested areas had lower soil water
storage than noninfested areas from 60 to 100 cm depth during early to mid-growing season, and in
the upper 40 cm late in the growing season. This is likely due to differences in root architecture and
phenology. The results do not support a hypothesis of altered soil physical, soil hydraulic, or soil
thermal properties in response to spotted knapweed infestation. Degradation of soils by spotted
knapweed therefore remains mainly anecdotal.
North Dakota studied degradation and transformation of trichloroethylene in miscibledisplacement experiments through zero-valent metals. Miscible-displacement experiments were used
to study the fate and transport of trichloroethylene (TCE) in the presence of zero-valent metals.
Zero-valent metals (e.g., iron filings) are now being used in the development of new technology to
remediate groundwater contaminated with organic pollutants such as TCE. Previous research has
used batch experiments to study the degradation of TCE and design permeable reactive barriers,
which are permeable subsurface walls made of zero-valent metals through which polluted
groundwater passes. It is difficult to measure sorption with batch experiments while TCE
degradation is also occurring; furthermore, other dynamic processes (e.g., advection) are not
simulated with batch experiments. Miscible-displacement experiments were used to study the
transport and transformation processes that occur when TCE passed through three columns made of
1) sand, 2) iron filings, and 3) iron filings with copper coating. Results indicate that sorption is an
important process to be considered when TCE is flowing through zero-valent metal systems. Both
the equilibrium and non-equilibrium models did good jobs describing the breakthrough curves;
however, the confidence in the estimated parameters were low due to a wide range in the confidence
intervals. Nonetheless the normalized degradation rate coefficients were similar to earlier reported
20
rates, although at the lower end. This study was published recently in Environmental Science and
Technology (Casey, Ong, and Horton, 2000; ES&T 34:5023-5029).
Although solutions of multidimensional transient water flow can be obtained by numerical
modeling, their application may be limited in part as root water uptake is generally considered to be
one-dimensional only. California-Davis developed a two-dimensional root water uptake model
which was incorporated in a numerical multidimensional flow model. Root water uptake parameters
were optimized, minimizing the residuals between measured and simulated water content data. To
calibrate the flow and root water uptake model, a genetic algorithm was used to find the approximate
global minimum of the optimized parameter space. The final fitting parameters were determined
using the Simplex optimization algorithm. With the optimized root water uptake parameters,
simulated and measured water contents values were in excellent agreement, with R2 values ranging
between 0.94 and 0.99 and a root mean squared error of 0.013 m3 m-3. The developed root water
uptake model is extremely flexible and allows spatial variations of water uptake as influenced by
non-uniform (drip irrigation) and uniform water application patterns.
California-Riverside initiated a project that deals with agricultural operations (including
nursery operations) in the Newport/San Diego Creek, CA. The main objective is to evaluate the
effectiveness of implementing Management Measures (MMs) with the long-term goal of meeting
nutrient total maximum daily load (TMDL) established by the Regional Water Quality Control
Board. Two sampling stations were established with each station monitoring a separate plot. Upon
completion of baseline monitoring in 2001, the plots will be designated untreated and treated.
Management Measures and Management Practices will be initiated on treated plots with surface
runoff sampling continuing to determine the effectiveness of MM and MP implementation. Four of
the five sites were established in agricultural fields under strawberry production for the majority of
the year. The final site was established at a nursery operation. Flow is monitored continuously at all
ten sampling sites with water samples taken weekly over a 24-h sampling period. In addition, storm
sampling is initiated when precipitation is expected to be more than 6.35 mm (0.25”). In 2000, flow
from agricultural fields was minimal or non-existent since drip irrigation was utilized by the majority
of the operators in the watershed. Overhead irrigation events for establishing crops and protecting
against frost and wind produced the most significant flow rates. In contrast, surface runoff from the
nursery site occurred daily due to a combination of overhead irrigation and leaching requirements of
container-grown plants. A vegetative filter strip, installed in the main runoff channel, seeks to
reduce the flow rate allowing settling of sediment and the uptake of nitrate by the vegetation. The
vegetation filter strip provides a demonstration of a Management Practice that can be utilized to
minimize off-site movement of nutrients and possibly other contaminants.
California-Riverside also developed and tested a sensitive and rapid method for determining
the concentration of PAM. Application of polyacrylamide (PAM) to reduce soil erosion in irrigated
land has increased rapidly in recent years. A simple and reliable method to measure PAM in soil
extracts is of great need. The new rapid method is based on a combination of determining the total
amide-group concentration by the N-bromination method (NBM) and determining the dissolved
organic matter (DOM) content by spectrophotometry. The total amide-group concentration of both
PAM and DOM was determined by NBM at 570 nm. The DOM moiety, as proportional to DOM
concentration, was determined by spectrophotometry using an UV 254-nm wavelength. The actual
PAM concentration of a sample was obtained through NBM readings after subtracting the
21
interferential DOM contribution by a correction curve. The correction was based on the highly linear
relationship between NBM readings and readings of DOM at 254 nm. Since the composition of the
organic matter of each soil may differ, individual DOM correction curves should be used for each
soil. Analysis of PAM in extracts from two soils showed that recoveries ranged from 94% to 100.3%
for the 2 mg/L PAM, and from 98.4% to 101.4% for the 10 mg/L PAM with various DOM
concentrations. The coefficients of variation were less than 6% in all cases. Thus the proposed
method is efficacious for measuring PAM concentrations in soil extracts.
Knowing the adsorptive behavior of anionic polyacrylamide (PAM) by soils is useful in
predicting appropriate dose of application, depth of effective treatment, and its mobility in soil.
Adsorption isotherms of PAM by soil materials, six natural soils and their subsamples with partial
organic matter (OM) removed by H2O2 oxidization under different dissolved salt concentrations were
examined. The PAM adsorption isotherms fitted Langmuir equation well. Results showed that soil
texture, organic matter content, and dissolved salts (a combinative contribution of soil salinity and
irrigation water quality) influenced the extent of PAM adsorption. Soils with high clay or silt content
and low organic matter content had a high adsorptive affinity to anionic polyacrylamide. The amount
of PAM saturation adsorption increased significantly as the total dissolved salts (TDS) increased.
Divalent cations such as Ca2+ and Mg2+ were about 28 times more effective in enhancing PAM
adsorption than monovalent cations like Na+ and K+, mainly due to their stronger charge screening
ability. Soil samples after OM oxidization adsorbed more PAM than natural soils. The negative
effect of OM on PAM adsorption was attributed to the reduction of accessible adsorption sites by
cementing inorganic soil components to form aggregates and to the enhancement of electrostatic
repulsion between PAM and soil surface by its negatively charged functional groups.
California-Riverside also began work on a long-term program that will test the structure of
GLEAMS, RZWQM and similar models for appropriateness of model structure. The steps in this
process include: conducting a sensitivity analysis on “ideal data” sets, conducting a multi-criteria
calibration on “ideal sets”, utilize results to design tests of model weakness, test model with field
data. Preliminary results indicate that of the hydrologic parameters in the GLEAMS model only
CONA, CN2, and porosity are important in determining model output. Field measurements should
therefore focus on measurements of porosity and soil texture (used to calculate the CONA
parameter), while calibration exercises should focus on CN2 since this parameter cannot be readily
measured in the field. Further sensitivity analysis and calibration exercises are planned with field
data from field research sites. Testing is also planned for other agronomic water quality models.
Utah continued its collaboration with California-USSL, Dr. Snyder (UPR), and Dr. Hadas
(Volcani, Israel) in modeling soil pore space dynamics in aggregated soil subjected to wetting-drying
cycles and rapid loading by passage of farm implements. W-188 members extended an analytical
model for the rate of deformation soil aggregates as a function of capillary forces to represent the
behavior of an aggregate bed. Moreover, the model was extended to calculate strains (compaction)
and pore size evolution under rapid loading. We compiled a review paper on rheological properties
of wet soils and their relevance to modeling structural and resultant changes in soil pore space and
hydraulic properties. The aggregate deformation models were implemented in a stochastic
framework for modeling post-tillage soil pore size evolution.
Washington completed its research project on using Chitosan as an antitranspirant in
agricultural applications (Bittelli et al., 2001). Chitosan was applied foliarly to pepper plants and
22
water use was monitored. Peppers were grown in pots in a growth-chamber and a green-house, where
transpiration was measured by weighing pots. In an accompanying field study, water use was
determined by soil moisture measurement with TDR and an automated irrigation system. Foliar
application of chitosan reduced water use of pepper plants by 13, 26 and 43% for green-house,
growth-chamber and field conditions, respectively. Yields were only marginally affected by chitosan
treatment.
In an effort to evaluate the adequacy of the improved USDA WEPP (Water Erosion
Prediction Project) model for better modeling hydraulic structure functions and forest road erosion,
Washington (Wu et al., 2000) applied the model to a small conceptual forest watershed. A segment
of an insloping forest road with an impoundment or surface cross drain structure, together with the
roadside ditch channel and a waterway channel below the drainage structure, formed the main
components of a watershed. Different road system configurations with respect to the density of the
drainage structures along a road and downslope road gradient were examined under climate and soil
conditions for a representative forest watershed in Idaho State. Soil erosion and delivery ratios
resulting from the two road drainage system designs were compared. Results from this study show
that WEPP is a useful tool in predicting water erosion from insloping forest roads with impoundment
or cross drain structures as well as in helping establish optimum road drainage system designs.
Another effort devoted to improve the WEPP model involves adapting the model's
hydrologic subroutines for forest watershed applications. WEPP was originally developed to evaluate
the erosion effects of agricultural management practices, spatial and temporal variability in
topography, soil properties, and land use conditions within small agricultural watersheds.
Forestlands, typified by steep slopes, and shallow, young, and coarse-grained soils, are highly
different from common croplands. As a result, hydrologic processes in forest settings exhibit
significantly different characteristics (e.g., extremely low soil evaporation and surface runoff, and
predominant subsurface runoff) than in agricultural land uses. In refining the WEPP model,
modifications were primarily made in the approach to, and algorithms for modeling deep percolation
of soil water and subsurface lateral flow (Wu et al., 2000). The modified model was applied to a
conceptual Pacific Northwest forest watershed using local data. Results indicate that, compared to
the original model, the modified model can represent the hydrologic processes in forest settings in a
more realistic and adequate manner.
Water eroding cropland soil in the Northwestern Wheat and Range Region (NWRR) creates
major agricultural, economic, and environmental problems. Past studies show that most water
erosion in the NWRR is related to rain on high water content thawing soils. This process is often
exacerbated by warm, moist Pacific air masses that bring precipitation and rapid soil surface thaw.
Although water erosion is recognized as a serious problem, the effects of freezing and thawing on
soil detachment and transport remains one of the least understood aspects of the physical erosion
process. A comprehensive water erosion study began in the summer of 2000 with two main
objectives: to elucidate the mechanisms by which soil freezing and thawing affects runoff and
erosion through laboratory experimentation, and to mathematically formulate the mechanisms for
potential incorporation into erosion prediction models. The research has been divided into three
phases: experimental design and facility construction, experimentation and analysis of results, and
incorporation of results into a process-based erosion model. To date, phase one is near completion
(Place et al., 2000; Wu et al., 2001; Cuhaciyan et al., 2000). A full-scale tilting flume has been
23
designed and its construction is soon to be finished. The model allows for the testing of different
drainage designs. Laboratory tests of major soil hydraulic properties have been conducted on the
Palouse silt loam soil. Results obtained are comparable to those from previous studies. Through the
model tests, it was concluded that different porous materials should be used under different soil, flow
and tension conditions. In addition, one saturation cycle is sufficient to consolidate the soil to field
conditions.
Arizona examined the effect of gravity on flow from spheroids. This work came about from
collaborative research with Utah looking at relationships useful for describing subsurface, tension
permeameter. Known analytical relationships include: a. Steady-state absorption for all spheroids
and all hydraulic properties; b. Steady-state solution with gravity included for Gardner function (K
exponential with h); and c. Time-dependent case for absorption from spheres with and without
gravity but only for small times. The following illustrates relationships derived from Philip (1985
SSSAJ, p. 828 and 1986 WRR, p. 1874). In review, a prolate spheroid (sort of like a football) has a
small axis (ro) in the r direction and a longer axis  ro about which the ellipse is rotated. An oblate
spheroid (sort of like a grapefruit) has a longer axis ro and the shorter axis of rotation is  ro with 
now less than one. A sphere is simply in between with  = 1. For all spheroids steady sorption is
Qsorp = 4 (Kwet - Kdry)  c r0
where  is related to  and c is the capillary length. Pressure distributions were calculated and
compared with results obtained with HYDRUS. Results for both the Vinton fine sand and for the
Millville silt loam showed that for sperical sources (ro = 2.5 and 5.0 cm) the calculated flow rates
using the van Genuchten function were within about 5% of that using the analytical Gardner function
solution (the same Ks and c are used).
Ground water recharge in arid and semi arid regions is extremely difficult to quantify at
spatial scales relevant for most contaminated sites and for water resource evaluation. However, the
development and subsequent closure of mining sites has offered a unique opportunity to monitor
deep infiltration and recharge in disturbed land areas. Nevada has assembled data from long term
drainage rates from closed or inactive heap leach mining operations across Nevada to estimate deep
infiltration. These heap leach facilities are large (> 100 hectares) and are situated completely on
impermeable liners. As a result, they represent enormous lysimeters capable of measuring deep
infiltration at scales appropriate for model development. All deep infiltration through the tops of
these mine sites travels through the vadose zone, intersects the impermeable liner and exists through
a single collection pipe. Data from drainage rates from 9 mine sites have been collected to date and
indicate that significant deep infiltration occurs. Recharge rates (as a function of annual
precipitation) at these sites range from less than 1% to as high as 60%. Table 1 shows the
distribution of annual precipitation as a function of mean annual precipitation at each site. Mine
sites located in the most arid regions (<150 mm/year) show recharge rates as high as 50% or 75
mm/year. Such high recharge rates are consistent with previous work at PNNL that showed that
significant deep infiltration occurs in arid regions if the soil surfaces are coarse textured and
vegetation is limited. We are currently expanding this data base to several new mine sites and are
assembling data from active mine sites. Data from this study will be used to assess the long-term
drainage rates and potential for ground water degradation from closed mining sites and will be
extended to prediction of drainage fluxes through the adjacent waste rock dumpsites, where no
measurements of integrated deep infiltration can be made.
24
4. IMPACT STATEMENT:
Research conducted by the W-188 in 2000 made significant contributions to our current
understanding of water, heat and solute transfer in soils and porous media. Major impacts of the W188 research include:
Instrument development and improvement: A variety of soil physical instruments have been
developed, evaluated, and improved. Among these instruments are sensors to measure water
contents, bulk densities, porosities, soil moisture retention, heat and solute fluxes, and tracer
concentrations. The development of such instruments and the corresponding measurement theories is
an essential prerequisite for measurement of soil physical parameters at laboratory and field scales.
Soil physical parameters, such as water content or soil moisture retention, are being used by many
agricultural and environmental disciplines other than soil physics. New and improved instruments
will therefore have a broad and important impact on any basic and applied research and extension
dealing with soils and porous media in general.
Model development and improvement: Mathematical models are being used more and more
frequently to predict and estimate water flow and solute transport. Many models are difficult to use
and therefore often susceptible to operator errors. W-188 members have put emphasis on developing
user-friendly interfaces to ease the use and application of complicated models. A variety of new
models have been developed that will help to make more realistic predictions of kinetic reactions and
of root water uptake and evaporation, thus ultimately leading to an improvement of environmental
fate predictions and irrigation scheduling in agriculture. W-188 members have also successfully
implemented new algorithms to estimate soil hydraulic properties from readily available data, such
as soil texture and bulk densities. These algorithms will help to make better use of existing soil data
and improve site-specific management practices through more realistic predictions of water flow and
solute transport. Many of the models developed by W-188 members are readily available on-line.
Theoretical Advances of Water Flow and Solute Transport: Theoretical advances have been
made in flow and transport processes. In 2000, temporal and spatial scale effects on diffusion were
investigated. The effects of ionic strength, kinetic sorption, and physical nonequilibrium were
studied. Various upscaling procedures were proposed and investigated. Methods for quantifying
model uncertainty were developed. Pore-scale models of soil hydraulic properties have been
proposed. These types of theoretical advances will serve as building blocks in future development of
sustainable agricultural and resource management.
Spatial and Temporal Variability: W-188 research has improved our understanding of spatial
and temporal variability of soil physical and agronomic parameters. In 2000, research demonstrated
that slope is one of the most important factors in determining the spatial and temporal variability of
soil moisture across a landscape. The temporal consistency in solute transport measurements was
been evaluated. New physically based scaling techniques for heterogeneous soils were developed.
The temporal stability of yield and soil moisture patterns were evaluated. The improved
understanding and descriptions of soil variability provided by this research is crucial to the
development of scale-appropriate theories, models, and management.
Experimental Findings: In 2000, the W-188 group conducted or initiated a number of
important experiments. W-188 members initiated the first study to document the impact of a Late
25
Spring Nitrate Test program on water quality at a spatial scale that is environmentally meaningful.
Data were collected on correlations between water transfer and solute transport properties of a soil
that exhibits preferential flow, and on correlations between soil thermal properties and other soil
physical properties. The influence of water content on soil strength was measured, as was the effect
of air filled porosity on oxygen diffusion rates. Long-term infiltration in fractured tuff was
measured. New experimental techniques for characterizing unstable flow and preferential transport
have been developed. These types of experiments and data are needed to validate and improve
theories, models, and resource management.
The W-188 group is prolific in publishing its scientific results in technical journals. The long
list of publications shows the productivity of the group and emphasizes its impact on the scientific
literature.
5. ACTIVITIES PLANNED FOR 2001:
This is the second progress report for the W-188 5-year research project (1999-2004). Research in
2001 will continue on the objectives as described in Section 3. Some specific plans are:









Kansas will conduct field experiment will be conducted in which near-surface water content
variations are characterized over a range of spatial and temporal scales. This will provide a
data set that can be used to evaluate upscaling techniques.
Kansas will extend the above-described work on the temporal stability of yield patterns
using spectral analysis to characterize the spatial scales at which temporal stability or
instability occurs.
Kansas will continue experimental work on the effects of forced convection on 
measurements.
Montana and Utah will further pursue measurement of soil specific surface area using TDR,
through analysis of measurement responses to thermal perturbation.
Montana and Utah will evaluate potential importance of the Maxwell-Wagner effect for
measured TDR travel times in soils and porous media.
The data base obtained for the Maricopa field site (Arizona) will be used to test a variety of
1D, 2D and 3D models. The infiltration and redistribution data will be used in conjunction
with a variety of methods to determine unsaturated hydraulic properties at this site.
The effect of gravity on steady-state infiltration will be further pursued at Arizona. New
cases to be considered include generalization of the numerical results by scaling out the
saturated hydraulic conductivity and capillary length. Also, other boundary conditions will
be completed using HYDRUS, including unsaturated-saturated regimes with partially filled
sources.
North Dakota will collaborate with California-USSL on inverse analyses of infiltration
experiments using HYDRUS-1D.
Collaborative work (Montana, Minnesota, South Dakota, and North Dakota) will begin
on a four-year precision agriculture project. The project is funded by REEUSDA’s Initiative
for Future Agriculture & Food Sources (IFAFS).
26
6. PUBLICATIONS DURING 2000:
Abbaspour, K. C., A. Kohler, J. Šimùnek, M. Fritsch, and R. Schulin, Application of a twodimensional model to simulate flow and transport in a macroporous agricultural field with tile drains,
European J. of Soil Sci. (in press).
Ahmed, S.I., D.B. Jaynes, R.S. Kanwar, and S.J. Kung. 1999. Herbicide and tracer movement to
subsurface drains under simulated rainfall conditions. ASAE Paper No. 99-2200.
Ayars, J.E., R.A. Schoneman, F. Dale, B. Meso, and P.J. Shouse. 2000. Managing subsurface drip
irrigation in the presence of shallow groundwater. Agric. Water Management (in press).
Bachmann, J., R. Horton, R. R. van der Ploeg, and S. Woche. 2000. Modified sessile drop method
for assessing initial soil-water contact angle of sandy soil. Soil Sci. Soc. Am. J. 64:564-567.
Bakhsh, A., Colvin, T. S., Jaynes, D. B., Kanwar, R. S., and Tim, U. S. 1999. Applying GIS for
interpretation of spatial variability in yield: A case study. ASAE Paper No.MC99-125.
Bakhsh, A., D.B. Jaynes, T.S. Colvin, and R.S. Kanwar. 2000. Spatio-temporal analysis of yield
variability for a corn-soybean field in Iowa. Trans. ASAE. 43:31-38.
Bakhsh, A., R.S. Kanwar, D.B. Jaynes, T.S. Colvin, and L.R. Ahuja. 2000. Predicting effects of
variable nitrogen application rates on corn yields and NO3-N losses with subsurface drain water.
Trans. ASAE. (In press)
Bakhsh, A., R.S. Kanwar, D.B. Jaynes, T.S. Colvin, and L.R. Ahuja. 2000. Prediction of NO3-N
losses with subsurface drainage from manured and UAN-fertilized plots using GLEAMS. Trans.
ASAE. 43:69-77.
Barger, B., J.B. Swan, and D.B. Jaynes. 1999. Soil water recharge under uncropped ridges and
furrows. Soil Sci. Soc. Am. J. 63:1290-1299.
Bejat, L., E. Perfect, V.L. Quisenberry, M.S. Coyne, and G.R. Haszler. 2000. Solute transport as
related to soil structure in unsaturated intact soil blocks. Soil Science Society of America Journal
64:818-826
Bingham, G.E., S.B. Jones, D. Or., D., I.G. Podolski, M.A. Levinskikh, V.N. Sytchov, T. Ivanova, P.
Kostov, S. Sapunova, I. Dandolov, D.B. Bubenheim, G. Jahns. 2000. Microgravity effects on water
supply and substrate properties in porous matrix root support systems. Acta Astronautica 47:1-10.
Bittelli, M., Flury, M., Campbell, G.S. and Nichols, E.J., 2001. Reduction of transpiration through
foliar application of Chitosan. Agric. For. Meteorol., (in press).
Bristow, K. L., G. J. Kluitenberg, C. J. Goding, and T. S. Fitzgerald. 2001. A small multi-needle
27
probe for measuring soil thermal properties, water content and electrical conductivity. Comput.
Electron. Agric. (in press).
Brown, P.W., C.F. Mancino, M.H. Young, T.L. Thompson, P.J. Wierenga and D.M. Kopec. 2001.
Penman Monteith crop coefficients for use with desert turf systems. Crop Science (accepted).
Casey, F.X.M., R.P. Ewing, and R. Horton. 2000. Automated apparatus for miscible displacement
through soil of multiple volatile organic compounds. Soil Sci.165:841-847.
Casey, F.X.M., S. K. Ong, and R. Horton. 2000. Degradation and transformation of
trichloroethylene in miscible-displacement experiments through zero-valent metals. Environ. Sci.
Technol. 34:5023-5029.
Chu, Y., Jin, Y., Flury, M. and Yates, M.V., 2001. Mechanisms of virus removal during transport in
unsaturated porous media. Water Resour. Res., (in press).
Colvin, T.S., Jaynes, D.B., Kaspar, T.C., James, D.E., and Meek, D.W. 2000. Yield certainty with
plots or fields. Fifth International Conf. Precision Agriculture, July 16-19, 2000. Bloomington, MN
(in press)
Cooper, C., R.J. Glass and S.W. Tyler. 2001. Assessment of mass fluxes under double diffusive
convection in porous media. Water Resources Research. (In Press)
Costanza, M.S., T.D. Carlson, M.L. Brusseau and P.J. Wierenga. 2001. Trichloroethene vapor
transport in an intermediate-scale vadose zone system: Retention processes and partitioning tracer
based prediction. J. Cont. Hydrol. (in press).
Cuhaciyan, C.O., Wu, J.Q., Place, M.K., McCool, D.K. and Palmer, C.R., 2000. Design of a tilting
flume for testing frozen soil erosion. ASAE Pap. 200009, Am. Soc. of Agric. Eng., St. Joseph, MI.
Das, B. S., R. S. Govindaraju, G. J. Kluitenberg, A. J. Valocchi, and J. M. Wraith. 2001. Theory
and applications of time moment analysis to study the fate of reactive solutes in soil. In R. S.
Govindaraju (ed.) Stochastic methods in subsurface contaminant hydrology. American Society of
Civil Engineering (in press).
Das, B.S., and J.M. Wraith. 2000. New geometry factors for hydraulic property-based soil solution
electrical conductivity models. Water Resour. Res. 36:3383-3387.
Dinnes, D. L., Jaynes, D. B., Cambardella, C. A., Colvin, T. S., Hatfield, J. L., and Karlen, D. L.
Split application nitrogen fertilizer management effects on corn yield and water quality. Farm Bureau
Spokesman Press (Autumn Harvest). 1999.
Dinnes, D.L., Jaynes, D.B., Meek, D.W., Cambardella, C.A., Colvin, T.S., Hatfield, J.L., and Karlen,
D.L. 2000. Intensive N fertilizer management effects on water quality at the watershed scale. March
28-30, 2000. La Crosse, WI.
28
Ewing, R.P. and B. Berkowitz. 2001. Stochastic Pore-Scale Growth Models of DNAPL Migration
in Porous Media, Adv. Water Resour. 24 (3-4) 309-323.
Feng, G.L., J. Letey and L. Wu. 2001. Water Ponding Depths Affect Temporal Infiltration Rates in
a Water Repellent Sand. Soil Sci. Soc. Am. J. (Accepted).
Fennemore, G. G., Andy Davis, L. Goss and A. W. Warrick. 2000. A rapid screening-level method
to optimize location of infiltration pond. Ground Water (Accepted)
Gan, J., S.R. Yates, F. F. Ernst, and W.A. Jury, 2000. Degradation and volatilization of the fumigant
Chloropicrin after soil treatment. J. environ. Qual. 29: 1391-1397.
Gangloff, W. J., M. Ghodrati, J. T. Sims and B. L. Vasilas. 2000. Impact of fly ash amendment and
tillage method on water status of a sandy soil. Water Air Soil Pollut. 119: 231-245.
Garrido, F. M. Ghodrati, CG Campbell, M. Chendorain. 2001. Detailed characterization of solute
transport in a heterogeneous field soil. J. of Environ Qual. In Press.
Garrido. F., M. Ghodrati, CG Campbell. 2000. A method for In Situ field calibration of fiber optic
miniprobes. Soil Sci. Soc. Am. J. 64(1): 836-843.
German-Heins, J. and Flury, M., 2000. Sorption of Brilliant Blue FCF in soils as affected by pH and
ionic strength. Geoderma, 97:87-101.
Ghezzehei, T.A., and D. Or. 2000. Dynamics of soil aggregate coalescence governed by capillary and
rheological processes. Water Resour. Res. 36:367-379.
Ghezzehei, T.A., and D. Or. 2000. Rheological properties of wet soils and clays under steady and
oscillatory stresses. Soil Sci. Soc. Am. J. (in press).
Ghodrati, M. F. Garrido, CG Campbell, M. Chendorain. 2000. A multiplexed fiber optic mini-probe
system for measuring convective dispersive solute transport in soil. J. of Environ Qual. 29(2): 540550.
Green, R. L., L. Wu, and G. Klin. 2001. Summer cultivation treatment effects on field infiltration rates
and soil salinity on an annual bluegrass putting green. HortScience. (Accepted, August 2000. 20
manuscript pages).
Guo, L., Jury, W., Wagenet, R.J. and Flury, M., 2000. Dependence of pesticide degradation on
sorption: nonequilibrium model and application to soil reactors. J. Contam. Hydrol., 43:45-62.
Guo, L., W. Frankenberger, and W. Jury 2000 Characterizing kinetics of sequential selenium
transformations in soil. J. Environ. Qual. (in press).
Guo, L., W. Frankenberger, and W. Jury 2000. Measurement of Henry's law constant of dimethyl
selenide as a function of temperature. J. Environ. Qual. (in press).
29
Guo, Lei, W. Jury, R. Wagenet, and M. Flury 2000 Dependence of pesticide degradation on sorption:
nonequilibrium model and application to batch reactors. J. contaminent Hydrol. 43:45-62.
Henry, E. J., J. E. Smith and A. W. Warrick. 2000. Surfactant effects on unsaturated flow in porous
media with hysteresis: Horizontal column experiments and numerical modeling. J. Hydrology
(Accepted).
Holland, D. F., M. Yitayew and A. W. Warrick. 2000. Measurement of subsurface unsaturated
hydraulic conductivity. J. Irrig. Dr. Engr. 126:21-27.
Hollenbeck, K. J., J. Šimùnek, and M. Th. van Genuchten. 2000. RETCML: Incorporating
maximum-likelihood estimation principles in the RETC soil hydraulic parameter estimation code.
Computers and Geosciences 26(3):319-327.
Hopmans, J. W. and J. Šimùnek. 2001. Review of inverse estimation of soil hydraulic properties. In:
Characterization and Measurement of the Hydraulic Properties of Unsaturated Porous Media, eds.
M. Th. van Genuchten, F. J. Leij and L. Wu, University of California, Riverside, CA, 643-659,
1999.
Hopmans, J. W., J. Šimùnek, N. Romano, and W. Durner, Inverse Modeling of Transient Water Flow,
In: Methods of Soil Analysis, Part 1, Physical Methods, Chapter 3.6.2, Eds. J. H. Dane and G. C.
Topp, Third edition, SSSA, Madison, WI (in press).
Inoue, M., J. Šimùnek, S. Shiozawa, and J. W. Hopmans, Estimation of soil hydraulic and solute
transport parameters from transient infiltration experiments, Advances in Water Resources, 23, 677688, 2000.
Kaspar, T.C., Colvin, T.S., Jaynes, D.B., Karlen, D.L., James, D.E., Meek, D.W., Pulido,D., and
Butler,H.C. 2000. Estimating corn yield using temporal yield data and terrain attributes. Fifth
International Conf. Precision Agriculture. July 16-19, 2000. Bloomington, MN (in press)
Kluitenberg, G. J., and A. W. Warrick. 2001. Improved evaluation procedure for heat-pulse soil
water flux density method. Soil Sci. Soc. Am. J. (in press).
Lee, J., D.B. Jaynes, and R.L. Horton. 2000. Evaluation of a simple method for estimating solute
transport parameters: Laboratory studies. Soil Sci. Soc. Am. J. 64:492-498.
Lee, J.H., R. Horton, and D.B. Jaynes. 2000. A time domain reflectometry method to measure
immobile water content and mass exchange coefficient. Soil Sci. Soc. Am. J. 64:1911-1917.
Leij, F. J., and J. H. Dane. 2000. Comment on "A moment method for analyzing breakthrough
curves of step inputs" by C. Yu et al. Water Resour. Res. (in press).
Leij, F. J., and M. Th. van Genuchten. 2000. Analytical modeling of nonaqueous phase liquid
dissolution with Green’s functions. Transport in Porous Media 38:141-166.
30
Leij, F. J., and M. Th. van Genuchten. 2000. Analytical modeling of nonaqueous phase liquid
dissolution with Green's functions. Transport in Porous Media 38:141-166.
Leij, F. J., E. Priesack, and M. G. Schaap. 2000. Solute transport modeled with Green's functions
with application to persistent solute sources. J. Contam. Hydrol. 41:155-173.
Leij, F.J. 2000. Book review of "Analytical solutions of geohydrological problems" by G.A.
Bruggeman. J. Contam. Hydrol. 43:187-189.
Leung, S., L. Wu, B. Sanden, and J. Mitchell. 2000. Effect irrigation uniformity on nitrogen use and
nitrate leaching. Agri. Water Management. 1599:1-14.
Macur R.E., H.M. Gaber, J.M. Wraith, and W.P. Inskeep. 2000. Predicting solute transport using
mapping-unit data: Model simulations versus observed data at four field sites. J. Environ. Qual.
29:1939-1946.
Mitchell, J. B. Sanden, S. Allaire-Lueng, L. Wu. 2000. Sprinkler spacing does not affect carrot yield
and quality. HortTechnology 10:370-373.
Mmolawa, K. B., and D. Or, 2000. Root zone solute dynamics under drip irrigation: A review. Plant
and Soil 222:161-189.
Mmolawa, K. B., and D. Or, 2000. Water and solute dynamics under a drip irrigated crop:
Experiments and analytical model. Transactions of the ASAE (in press).
Mohanty, B.P., and T.H. Skaggs, 2000. Spatio-temporal evolution and time-stable characteristics of
soil moisture within remote sensing footprints with varying soil, slope, and vegetation. Adv. Water
Resour. (in press).
Mohanty, B.P., J.S. Famigletti, and T.H. Skaggs, 2000. Evolution of soil moisture spatial structure in
a mixed-vegetation pixel during the SGP97 hydrology experiment, Water Resour. Res.,
36(12):3675--3686.
Mohanty, B.P., T.H. Skaggs, and J.S. Famigletti, 2000. Analysis and mapping of field-scale soil
moisture variability using high resolution, ground-based data during the Southern Great Plains 1997
(SGP97) Hydrology Experiment, Water Resour. Res., 36(4):1023-1031.
Nassar, I. N., R. Horton, and G.N. Flerchinger. 2000. Simultaneous heat and mass transfer in soil
columns exposed to freezing/thawing conditions. Soil Sci. 165-208-216.
Novák, V., and J. Šimùnek. 2000. Modeling of water infiltration into soils with cracks, Acta
Hydrologica Slovaca, 1, 119-125 (in Slovak, with English summary).
Novák, V., J. Šimùnek, and M. Th. van Genuchten. 2000. Infiltration of water into soil with cracks.
J. Irrig. and Drain. Engrg. 126(1):41-47.
31
Or, D., 2001. Who invented the tensiometer? Soil Sci. Soc. Am. J. 65:000-000.
Or, D. and T.A. Ghezzehei. 2000. Dripping into cavities from unsaturated fractures under
evaporative conditions. Water Resour. Res. 36:381-393.
Or, D., F. J. Leij, V. Snyder, and T. A. Ghezzehei. 2000. Stochastic model for posttillage soil pore
size evolution. Water Resour. Res. 36(7):1641-1652.
Or, D., U. Shani, and A.W. Warrick. 2000. Subsurface tension permeametry. Water Resour. Res.
36:2043-2053.
Or, D., and J.M. Wraith. 2000. Comment on “On water vapor transport in field soils” by Anthony T.
Cahill and Marc B. Parlange (Water Resour. Res. 34: 731-739, 1998). Water Resour. Res. 36:31033105.
Perfect, E. 2000. Estimating soil mass fractal dimensions from water retention curves. In: Pachepsky,
Ya. A., J.W. Crawford, and W.J. Rawls (eds.), Fractals in Soil Science, Developments in Soil
Science 27, Elsevier, Amsterdam, the Netherlands, p.131-141
Perfect, E., and M.C. Sukop. 2000. Models relating solute dispersion to pore space geometry in
saturated media: A review. In: Physical and Chemical Processes of Water and Solute
Transport/Retention in Soil, Soil Science Society of America Special Publication, Soil Science
Society of America, Madison WI (in press)
Place, M.K., Wu, J.Q., Cuhaciyan, C.O. and McCool, D.K., 2000. The big freeze and thaw.
Resource, 11/12, Am. Soc. of Agric. Eng., St. Joseph, MI.
Qualls, R. J., B.L. Haines, W.T. Swank and S.W. Tyler. 2000. Soluble organic and inorganic nutrient
fluxes in clearcut and mature deciduous forests. Soil Science Society of America Journ. 64: 10681077
Ren, T., G. J. Kluitenberg, and R. Horton. 2000. Determining soil water flux and pore water
velocity by a heat pulse technique. Soil Sci. Soc. Am. J. 64:552-560.
Ressler, D. E., R. Horton, J. L. Baker, and T. C. Kaspar. 2000. Improved fertilizer applicator to
reduce nitrate fertilizer leaching from crop lands. In J. M. Laflen, J. Tian, and C. H. Huang (eds.)
Soil Erosion and Dryland Farming. p. 177-189. CRC Press, Boca Raton, Florida.
Rupp, D. E., J. S. Selker, and J. Šimùnek, A modification to the Bouwer and Rice method of slug-test
analysis for large-diameter, hand-dug wells, Groundwater, in press.
Schaap, M. G., and F. J. Leij. 2000. Improved prediction of unsaturated hydraulic conductivity with
the Mualem-van Genuchten model. Soil Sci. Soc. Am. J. 64(3):843-851.
Schaap, M. G., F. J. Leij and M. Th. van Genuchten. 2000. Estimation of the soil hydraulic
32
properties. In: B. B. Looney and R. W. Falta (eds), Vadose Zone Science and Technology Solutions,
Vol. 2, pp. 501-509, Battelle Press, Columbus, OH.
Scott, R. L., W. J. Shuttleworth, T. O. Keefer and A. W. Warrick. 2000. Modeling multiyear
observations of soil moisture recharge in the semiarid American Southwest. Water Resour. Res.
36:2233-2247.
Serbin G, Or D., and D. Blumberg. 2000. Thermodielectric effects on radar backscattering from wet
soils. IEEE TGARS (in press).
Seuntjens, P., K. Tirez, J. Šimùnek, M. Th. van Genuchten, C. Cornelis, and P. Geuzens. 2001. Aging
effects on cadmium transport in undisturbed contaminated sandy soil columns. J. Environ. Quality
(in press).
Shao, M., and R. Horton. 2000. Exact solution for horizontal water redistribution by general
similarity. Soil Sci. Soc. Am. J. 64:561-564.
Šimùnek, J., and J. W. Hopmans. 2000. Parameter optimization and nonlinear fitting. In: Methods
of Soil Analysis, Part 1, Physical Methods, Chapter 1.7, Eds. J. H. Dane and G. C. Topp, Third
edition, SSSA, Madison, WI (in press).
Šimùnek, J., J. W. Hopmans, D. R. Nielsen, and M. Th. van Genuchten. 2000. Horizontal
infiltration revisited using parameter estimation. Soil Sci. 165(9):708-717.
Šimùnek, J., D. Jacques, J. W. Hopmans, M. Inoue, M. Flury, and M. Th. van Genuchten, Solute
Transport During Variably-Saturated Flow - Inverse Methods, In: Methods of Soil Analysis, Part 1,
Physical Methods, Chapter 6.6, Eds. J. H. Dane and G. C. Topp, Third edition, SSSA, Madison, WI,
in press.
Šimùnek, J. and A. J. Valocchi, Geochemical Transport, In: Methods of Soil Analysis, Part 1,
Physical Methods, Chapter 6.9, Eds. J. H. Dane and G. C. Topp, Third edition, SSSA, Madison, WI (
in press)
Šimùnek, J. and M. Th. van Genuchten. 2000. Inverse estimation of unsaturated soil hydraulic and
solute transport parameters using the Hydrus-1D code. In: B. B. Looney and R. W. Falta (eds),
Vadose Zone Science and Technology Solutions, Vol. 2, pp. 815-827, Battelle Press, Columbus, OH.
Šimùnek, J., and M. Th. van Genuchten. 2000. The DISC computer software for analyzing tension
disc infiltrometer data by parameter estimation. Versions 1.0, Research Report No. 145, U.S. Salinity
Laboratory, USDA, ARS, Riverside, California, 34 p.
Šimùnek, J., M. Th. van Genuchten, M. Šejna, N. Toride, and F. J. Leij. 2000. The STANMOD
computer software for evaluating solute transport in porous media using analytical solutions of
convection-dispersion equation. Version 2.0, IGWMC - TPS - 71, International Ground Water
Modeling Center, Colorado School of Mines, Golden, Colorado, 32 p.
33
Sivamani, E., A. Bahieldin, J.M. Wraith, T. Al-Niemi, W.E. Dyer, T.-H.D. Ho, and R. Qu. 2000.
Improved biomass productivity and water use efficiency under drought conditions in transgenic
wheat constitutively expressing the Barley HVA1 gene. Plant Sci. 155:1-9.
Skaggs, T.H., L.M. Arya, P.J. Shouse, and B.P. Mohanty. 2001. Estimating particle-size distribution
from limited soil texture data. Soil Sci. Soc. Am. J. (in press).
Skaggs, T.H., D.B. Jaynes, R.G. Kachanoski, P.J. Shouse, and A.L. Ward, 2001. Solute Transport:
Data Analysis and Parameter Estimation, In Methods of Soil Analysis, Part I---Physical Methods, 3rd
Edition, Edited by J. Dane and C. Topp, ASA and SSSA (in press).
Skaggs, T.H., and F.J. Leij, 2001. Solute Transport: Theoretical Background, In Methods of Soil
Analysis, Part I---Physical Methods, 3rd Edition, Edited by J. Dane and C. Topp, ASA and SSSA (in
press).
Skaggs, T.H., G.V. Wilson, P.J. Shouse, and F.J. Leij, 2001. Solute Transport: Experimental
Methods, In Methods of Soil Analysis, Part I---Physical Methods, 3rd Edition, Edited by J. Dane and
C. Topp, ASA and SSSA (in press).
Song, Y., M. B. Kirkham, J. M. Ham, and G. J. Kluitenberg. 2000. Rootzone hydraulic lift
evaluated with the dual-probe heat-pulse technique. Aust. J. Soil Res. 38:927-935.
Stothoff, S., and D. Or. 2000. A Discrete-Fracture Boundary Integral Approach to Simulating
Coupled Energy and Moisture Transport in a Fractured Porous Medium. In: Dynamics of Fluids in
Fractured Rocks: Concepts and Recent Advances, pp. Geophysical Monograph Series, American
Geophysical Union, Washington, DC
Taguas, J.F., M.A. Martín, and E. Perfect. 2000. Simulation and testing of self-similar structures for
soil particle-size distributions using iterated function systems. In: Pachepsky, Ya. A., J.W. Crawford,
and W.J. Rawls (eds.), Fractals in Soil Science, Developments in Soil Science 27, Elsevier,
Amsterdam, the Netherlands, p.101-113
Taylor, R. K., N. Zhang, M. D. Schrock, J. P. Schmidt, and G. J. Kluitenberg. 2000. Classification
of yield monitor data to determine yield potential. ASAE Paper No. 001087. Annual International
Meeting, Milwaukee, WI. American Society of Agricultural Engineers.
Tuli, A., K. Kosugi and J.W. Hopmans. 2001. Simultaneous scaling of soil water retention and
unsaturated hydraulic conductivity functions assuming lognormal pore-size distribution. Adv. Water
Resour. In Press.
Tuller, M. and D. Or, 2000. Hydraulic conductivity of variably saturated porous media: Film and
corner flow in angular pore space, Water Resour. Res. (in press)
Ulery, A.L., S. Stewart, D.A. Reid, and P.J. Shouse. 2000. Vacuum method for field installation of
pipes and casings in sandy soils. Soil Sci. 165:269-273.
34
Vargas-Guzman, J. A., A. W. Warrick and D. E. Myers. 2000. Derivatives of spatial variances of
growing windows and the variogram. Math. Geol. 32:851-871.
Vaz, C.M., and J.W. Hopmans. 2001. Simultaneous measurements of soil penetration resistance and
water content with a combined penetrometer-TDR moisture probe. In Press. Soil Sci. Soc. Amer. J.
Ventrella, D., B. P. Mohanty, J. Šim_nek, N. Losavio, and M. Th. van Genuchten. 2000. Water and
chloride transport in a fine-textured soil: Field experiments and modeling. Soil Sci. 165(8):624-631.
Vogel T., M. Th. van Genuchten, M. Th., and M. Cislerova. 2000. Effect of the shape of the soil
hydraulic functions near saturation on variably-saturated flow predictions. Adv. Water Resour.
24(2): 133-144.
Vrugt, J. A., J. W. Hopmans, and J. Šimùnek, Calibration of a two-dimensional root water uptake
model for a sprinkler-irrigated almond tree, Soil Sci. Soc. Am. J. (in press).
Vrugt, J.A., J.W. Hopmans and J. Šimùnek. 2001. Calibration of a two-dimensional root water
uptake. Soil Sci. Soc. Amer. J. In Press.
Wang, Z., Wu, J.Q., Wu, L., Ritsema, C.J., Dekker, L.W. and Feyen, J., 2000a. Effects of soil water
repellency on infiltration rate and flow instability. J. Hydrol. (Amsterdam), 231/232:265-276.
Wang, Z., Wu, L. and Wu, J.Q., 2000b. Water-entry value as an indicator of soil water repellency
and wettability. J. Hydrol. (Amsterdam), 231/232:76-83.
Wildenschild, D., J. W. Hopmans, and J. Šimùnek, Parameter estimation for variable-rate outflow
experiments: Direct and inverse estimation approaches, Soil Sci. Soc. Am. J. ( in press).
Wildenschild, D., J.W. Hopmans and J. Šimùnek. 2001. Flow Rate Dependence of Soil Hydraulic
Characteristics. In Press. Soil Sci. Soc. Amer. J.
Wu, J., M. D. Ransom, G. J. Kluitenberg, N. D. Nellis, and H. L. Seyler. 2001. Land use
management using a soil survey geographic database for Finney County, Kansas. Soil Sci. Soc. Am.
J. (in press).
Wu, J.Q., Place, M.K. and Elliot, W.J., 2000a. Modeling soil erosion from insloping forest roads
with impoundment or surface cross drain structures. Proc. Impacts of Roads on Watershed
Hydrology, ASCE Watershed Management Conference, Logan, UT.
Wu, J.Q., Place, M.K., McCool, D.K. and Cuhaciyan, C.O., 2001. Effects of freeze/thaw conditions
on soil strength. Proc. Soil Erosion Research for the 21st Century, January 3-5, Honolulu, HI.
Wu, J.Q., Xu, A. and Elliot, W.J., 2000b. Adapting WEPP (Water Erosion Prediction Project) forest
watershed erosion modeling. ASAE Pap. 002069, Am. Soc. of Agric. Eng., St. Joseph, MI.
Zhang, N., R. Taylor, M. Schrock, S. Runquist, E. Runquist, G. Kluitenberg, J. Schmidt, and S.
35
Staggenborg. 2001. Evaluation of a field-level geographic information system (FIS) in precision
agriculture. In Proc. 5th International Conference on Precision Agriculture, Minneapolis, MN. July
16-19, 2000. ASA, CSSA, and SSSA, Madison, WI. (in press).
Zou, Ze-Yuan, Michael H. Young, Zhen Li and Peter J. Wierenga. 2001. Estimation of depth
averaged unsaturated soil hydraulic properties from infiltration experiments. J. of Hydrology (in
press).
7. SIGNATURES
_______________________________________________
T.H. Skaggs, Chair
Technical Committee, W-188
____________
Date
________________________________________________
G.A. Mitchell
Administrative Advisor, W-188
___________
Date
36