Set Loving Relationships as Your Highest Priority

I am honored to be invited to provide some advice to early career members. Many years have passed since I was an early career member. I am now completing 35 years as a soil science faculty member. During this time, I served as major professor for several Ph.D. students and post-docs who now have established careers in soil science. In fact, the favorite part of my job has been mentoring graduate students and post-docs. My goal is to help each student grow as a person and as a scientist in preparation to successfully move to the next stage of life. I count it a blessing to have had the opportunity to mentor many outstanding persons. Before I offer specific advice to early career members, I will provide some background information on myself to share how I discovered soil science and how I came to view an emphasis on loving relationships as my highest priority

The stream function of potential theory for a dual-pipe subirrigation-drainage system

An exact mathematical solution to Laplace\u27s equation is presented for appropriate boundary conditions associated with the problem of dual-pipe subirrigation and drainage. The solution can be used to determine a flow net within the groundwater flow region and the associated water table shape. The solution is general. The effects of several hydraulic and geometrical parameters on the groundwater system, such as thickness of saturated zone, position of subirrigation and drainage pipes, heads in the subirrigation and drainage pipes, crop evapotranspiration, fraction of inflowing subirrigation water that exits through the drains, and the aquifer hydraulic conductivity system are evaluated. Calculations are presented showing how pipe spacing affects the shape of the water table. For example, with hydraulic conductivity of 10 m/d, evapotranspiration of 0.01 m/d, drainpipe radius of 0.05 m, and subirrigation pipe radius of 0.0375 m, calculations show that the maximum water table elevation for a pipe spacing of 40 m is 0.64 m greater than for a pipe spacing of 16 m when 40% of the input subirrigation water volume is being removed from the system by drainage. Finally, the general mathematical solution can be used to predict chemical movement as well as water flow through the system

An Empirical Function to Describe Measured Water Distributions From Horizontal Infiltration Experiments

To determine the soil water diffusivity, D(θ), by the horizontal infiltration method of R. R. Bruce and A. Klute (1956) the slope of the water distribution curve and the area under the curve must be evaluated. Experimental data often exhibit scatter, thus making the evaluation of the slope difficult. In this paper a rapid, simple method is described that introduces an empirical function that by linear least squares regression yields a curve that fits water distribution data for a wide range of soil textures. The function is differentiable, and its integral is easily calculated with a numerical technique available on programmable scientific calculators. The proposed method produces estimates of D(θ) that reach expected large values near water saturation. This result offers a clear advantage over other simple methods that assume an exponential relation between D and θ and thus describe D(θ) adequately only over the middle range of water contents

Soil heat and water flow with a partial surface mulch

A computer model using the alternating direction implicit (ADI) finite difference method to study two-dimensional coupled soil heat and water flow with a partial surface mulch cover is developed. A new, simplified computational procedure, which has only tridiagonal matrix problems, for the ADI method is introduced. The model uses a soil surface energy balance equation to determine soil surface boundary conditions for both heat and water flow. The inputs required for the computer simulations are weather data, soil thermal and hydraulic properties, and mulch data. Numerical experiments are performed to examine the effects of soil type, mulch width, and weather conditions on soil heat and water movement. For continuous evaporation and drainage, 10-day simulations were performed for each combination of clay, loam, and sand soil and fractions of mulch cover of 0, 0.5, 0.8, and 1.0 of the row interval width. For repetitive evaporation and infiltration, 15-day simulations were performed. The mulch cover greatly reduces evaporation loss and the amplitude of daily soil temperature, water content, and pressure head variations. Large spatial variations in temperature and soil water content are predicted near the interface of mulch and bare soil surface. The soil hydraulic properties have important roles in controlling soil surface water content. The present model reasonably describes the soil thermal and hydrologic environments and thus can be applied successfully in soil science and groundwater hydrology and can be extended to related disciplines

Field Method for Measuring Mobile/Immobile Water Content and Solute Transfer Rate Coefficient

Numerous field and laboratory studies have documented the occurrence of preferential transport of solutes due to a fraction of the soil water being immobile and not taking part in the transport process. Domain models have been developed that describe these processes, but before we can apply them routinely, we need methods for measuring the required model parameters, particularly the fraction of immobile water to total water θlm/θ and the exchange coefficient between the mobile and immobile domains, α. We developed a field method for measuring both θlm/θ and α. The method uses a sequence of conservative anionic tracers consisting of Br−, pentafluorobenzoate, o-trifluoromethylbenzoate, and 2,6-difluorobenzoate infiltrated with time through a tension infiltrometer. Previous studies have confirmed that these tracers have very similar transport properties in a wide range of soils. The method was applied to an undisturbed loam and a greenhouse soil as an initial test of the approach. Calculated θim/θ fractions averaged 0.69 and ranged from 0.25 to 0.98, while calculated α values averaged 0.0081 h−1 and ranged from 0.0030 to 0.021 h−1. These values compare well with values reported earlier by other investigators. The method is simple and allows routine measurement of transport properties of field soils. The method can also be used to validate the applicability of domain models to specific soils

Conversion to perennial vegetation: Quantifying soil water regime, aeration, and implications for enhancing soil resilience to climate change

Iowa was once awash with native prairie vegetation, and now it is covered with annual crops. This project looked at the different effects these two systems have on Iowa\u27s landscape and natural resource base

Determination of effective porosity of soil materials

The performance of a compacted soil liner is partly a function of the porosity, which is important because the transport of materials through the liner occurs via the pore space. This project studies the pore spaces of compacted soil materials to estimate the effective porosity, which is the portion of the pore space where the most rapid transport of leachate occurs. Pore space of three soil materials, till, loess. and paleosol, was studied by using mercury intrusion porosimetry, water absorption, and image analysis. These analyses provided cumulative porosity curves from which the pore size distribution of soil samples were estimated. Theory was developed to estimate the effective porosity of a compacted soil material based upon a model of its pore size distribution and pore continuity. The effective porosities of compacted till. loess. and paleosol materials are estimated-to be 0.04. 0.08. and 0.09. respectively. These values are 10 to 20% of the total porosities. Comparisons between measured and predicted C1 travel times through compacted soil samples were made in order to verify the estimated effective porosities. The estimated effective porosities are reasonable because predicted C1~ first breakthrough times are similar to the measured first breakthrough times in the,soils studied. For these three soils predicted first breakthrough times are 5 to 10 times earlier when effective porosity is used.in the Darcy-equation based calculations as compared to Darcy-equation-based calculations that utilize total porosity

Estimating transit times of noninteracting pollutants through compacted soil materials

Pollutant travel times through compacted soil materials cannot be accurately predicted from the permeability (saturated hydraulic conductivity) alone, Travel time is also dependent on the effective porosity of the material; i.e., the portion of the total porosity that contributes significantly to fluid flow. Once permeability and effective porosity are determined for a selected material, travel times for noninteracting pollutants through specified thicknesses of compacted material at specified hydraulic gradients can easily be predicted. This paper presents a straightforward method of determining the effective porosity of compacted soil materials and compares measured and predicted solute breakthrough times for three compacted soil materials, The determination of effective porosity is based upon the total porosity and the spread on a log scale in the pore sizes of a compacted sample, Once the total porosity and pore size distribution information are obtained for a particular sample, the effective porosity can be determined by using a graphical solution. Pollutant travel time, T, through a compacted soil (i.e., when pollutant first appears at the bottom of the liner) can be predicted by T=EL/KI; where E is effective porosity, L is thickness of compacted sample, K is sample permeability, and I is hydraulic gradient. Chloride travel times through compacted samples of glacial till, loess, and paleosol materials were measured as less than 208 minutes (min.), between 15 and 30 min., and between 250 and 380 min., respectively. Predictions of noninteracting solute breakthrough for the glacial till, loess, and paleosol materials were 227 min., 32 min., and 270 min., respectively. Thus, the predictions are reasonably close to measurements. Further experiments using thicker soil samples are under way

Effect of Polyacrylamide Applications on Soil Hydraulic Characteristics and Sediment Yield of Sloping Land

The objective of this study is to determine how PAM applications to a fraction of the surface affect hydraulic parameters of flow, soil water infiltration and soil sediment yield during rainfall on steep sloping land. Five PAM application rates (PAMR) 0, 0.4, 0.7, 1.0 and 1.3 g kg-1 were used for 5 sloping plots in this study. As PAMR increased from 0 to 1.3 g kg-1 at the rainfall intensity (RI) of 1.58 mm min-1, the Froude numbers decreased from 34.7 to 9.1, the Reynolds numbers (Re) decreased from 568 to 305, and the Darcy–Weisbach coefficients increased from 0.0028 to 0.041. The total runoff values were 33.8, 35.9, 31.6, 25.6 and 18.1 mm when the PAMR were 0, 0.4, 0.7, 1.0 and 1.3 g kg-1, respectively. The cumulative sediment increased rapidly with the rainfall time. In conclusion, PAM applications to a fraction of soil surface can be effective at reducing the erosion of steep sloping land

The Feasibility of Shallow Time Domain Reflectometry Probes to Describe Solute Transport Through Undisturbed Soil Cores

Rapid and nondestructive methods for determining solute transport properties are useful in many soil science applications. Recently, a series of field methods and a time domain reflectometry (TDR) method that could estimate some of the mobile-immobile model (MIM) parameters, immobile water content (θim) and mass exchange coefficient (α), have been reported. The first objective of this study was to determine an additional parameter, dispersion coefficient (D m), using the TDR method. The three MIM parameters were estimated from the TDR-measured data, and the estimated parameters were compared with the estimated parameters from the effluent data. The second objective was to determine whether the TDR-determined parameters from the surface 2-cm soil layer could be used to predict effluent breakthrough curves (BTC) at the 20-cm depth. The TDR-determined parameters were used to calculate effluent BTCs using the CXTFIT computer program. Parameters obtained by curve fitting of the three parameters simultaneously using TDR data were not similar to the parameters obtained from the effluent BTCs. The parameter estimations were improved by fixing one or two independently determined parameter(s) before curve fitting for the remaining unknown parameter(s). The calculated BTCs were similar to the observed BTCs with coefficient of determination (r 2) being 0.99 and root mean square error (RMSE) being 0.036. The TDR data obtained from shallow soil layers were successfully used to describe solute transport through undisturbed soil cores