bluuebunny/crossref_metadata_2025 huggingface dataset:
Unified Solution for Infiltration and Drainage with Hysteresis Theory and Field Test
Authors: Si B. C. , Kachanoski R. G.
Published: July 2010

Hysteresis has been found in both the hydraulic conductivity, K, vs. pressure head, ψ, relationship, and the soil water content, θ, vs. ψ relationship. This limits the application of a unified solution for infiltration and drainage. A Haines' Jump model of hysteresis is proposed and combined with the Broadbridge and White form of K(θ) and the diffusivity, D, relationship, D(θ). This allows a unified analytical solution for infiltration and drainage. This solution accounts for hysteresis by allowing the inverse macroscopic capillary length scale, α, to be hysteretic. A method of a priori estimating the hysteretic nature of α is proposed and tested. The hysteretic change in α can be estimated from other θ(ψ) hysteresis models and then used in combination with the Broadbridge and White hydraulic functions. The predicted hysteresis in α was similar to that obtained from inverse procedures. The unified solution was applied to field‐measured soil water storage during infiltration and drainage. Neglecting hysteresis resulted in poor prediction of water storage during drainage based on hydraulic parameters estimated from infiltration. This was especially true for drainage with high initial water content. Incorporating the proposed hysteresis model resulted in prediction error less than measurement error. In addition, a single unified inverse procedure for estimating hydraulic parameters from combined infiltration and drainage measurements can now be developed.
Soil Quality Assessment after Weed‐Control Tillage in a No‐Till Wheat–Fallow Cropping System
Authors: Kettler T. A. , Lyon D. J. , Doran J. W. , Powers W. L. , Stroup W. W.
Published: July 2010

Adoption of reduced‐tillage fallow systems in the western USA is limited by winter annual grass weeds such as downy brome (Bromus tectorum L.). Moldboard plowing is an effective means of controlling downy brome in winter wheat (Tritcum aestivum L.)–fallow systems. The purpose of this study was to assess the influence of plowing and secondary tillage operations, for the purpose of weed control, on soil quality attributes of a silt loam soil that had been cropped in a sub‐till or no‐till (NT) winter wheat–fallow system for more than 20 yr. Compared with undisturbed NT, downy brome populations in plowed NT decreased 97 and 41% in the first and third crops following tillage, respectively. Wheat yields in plowed NT treatments were 30 and 9% greater in the first and third crops following tillage, respectively, compared with undisturbed NT. Soil quality indicators assessed were organic C (OC), total N, inorganic N, pH, electrical conductivity, bulk density, water infiltration rate, and pore‐size distribution. Five years after tillage, soil OC decline in the 0‐ to 7.5‐cm depth was 20% in plowed compared with undisturbed NT; however, OC increased 15% in the 7.5‐ to 15‐cm depth and was not different in the 0‐ to 30‐cm depth. Total soil N followed similar trends. Soil inorganic N in plowed NT decreased 37%, and soil pH increased 9%, compared with undisturbed NT, at the 0‐ to 7.5‐cm depth. Occasional tillage with the moldboard plow in a reduced‐ or no‐tillage management system will help control winter annual grass weeds, while retaining many of the soil quality benefits of conservation‐tillage management.
Preferential Water Flow Through Corn Canopy and Soil Water Dynamics Across Rows
Authors: Paltineanu I. C. , Starr J. L.
Published: July 2010

Small‐scale and spatially dependent variation in real‐time soil water dynamics, caused largely by agricultural practices, is not well understood. Objectives of this study were (i) to quantify the preferential stemflow vs. throughfall of water under rainfall and sprinkler irrigation during the closed corn (Zea mays L.) canopy period and from senescence to harvest, and (ii) to quantify in real time the corresponding row and interrow soil water dynamics under multiple annual no‐tillage and plow‐tillage corn experiments. Water redistribution through the corn canopy was studied for a 2‐yr period, with stemflow measured by placing flexible polyethylene bags on plants, and throughfall by placing jars between corn rows. Soil water dynamics was studied for a 3‐yr period, with multisensor capacitance probes and a monitoring system at five‐row and interrow positions for each tillage. Highly significant (P < 0.001) linear positive relationships were found between both stemflow (SF) and average throughfall (TF) to rainfall. An inverse third‐order relationship was found between the ratio of SF/TF and rainfall. Real‐time soil water dynamics data showed that the smaller rainfall events (<15 mm) resulted in a significant (P < 0.05) water infiltration advantage for the no‐tillage in‐row position compared with the no‐tillage interrow positions and compared with the plow‐tillage in‐row position. These results were consistent with the stemflow vs. throughfall data obtained under the closed corn canopy. Real‐time soil water dynamics vs. rainfall intensity at different soil layers showed the importance of rainfall and sprinkler irrigation redistribution induced by the canopy, type of tillage, and position across corn rows.
Simulation of Nitrate‐Nitrogen Dynamics for Cropping Systems with Different Rooting Depths
Authors: Delgado Jorge A. , Follett Ronald F. , Shaffer Marvin J.
Published: July 2010

Most agricultural systems in the San Luis Valley of south‐central Colorado include rotations that have crops with different rooting depths. The previous version of Nitrate Leaching and Economic Analysis Package (NLEAP), 1.10, was only capable of simulating the effect of management practices on the rooting zone of each crop to the nearest 0.30‐m increment. Therefore, a new version of NLEAP was needed to simulate the effect of best management practices (BMPs) on residual soil NO−3–N (RSN) for the root zone of each crop grown in the region and for a similar soil depth for these systems (e.g., 0–0.91 m). The improved NLEAP version 1.20 simulates maximum rooting depth to the nearest 0.03 m and RSN in multiple soil depths. These new features allowed us to simulate the effect of BMPs on RSN for the root zones of shallower‐rooted crops such as lettuce (Lactuca sativa L.) (0–0.37 m), potato (Solanum tuberosum L.) (0–0.40 m), and deeper‐rooted crops such as small grains (0–0.61 to 0–0.84 m). NLEAP simulated RSN for a soil depth identical for all of these cropping systems (0–0.91 m) (P < 0.001). This new version can be used by extension agents, farmers, consultants, and others to evaluate the effect of BMPs on soil NO−3–N dynamics for different rooting zones and for similar soil depths in the agricultural system, a capability that was not available with the previous version of NLEAP.
Measuring Hydraulic Properties Using a Line Source I. Analytical Expressions
Authors: Zhang Z.Fred , Kachanoski R.Gary , Parkin Gary W. , Si Bingcheng
Published: July 2010

In situ measurement of soil hydraulic properties remains a challenge. This study presents new analytical expressions for estimation of soil hydraulic properties below a surface line source by means of multi‐purpose time domain reflectometry (TDR) probes and existing quasi‐analytical, steady‐state solutions for infiltration from a surface line source. Inverse procedures are used to estimate the inverse macroscopic capillary length scale, α, and the hydraulic conductivity at saturation, Ks, from pressure head (ψ), water storage (W), and conservative ionic tracer travel time (T) measured via multi‐purpose TDR probes placed at several depths below a line source with constant flux of water. Soil water content at saturation, θs, can also be estimated if prior information is available. The parameter and spatial sensitivities of each solution were calculated by means of sensitivity coefficients. The uniqueness of possible combinations of measurements to estimate α, Ks, and θs was tested by means of two‐dimensional response surfaces. Significant correlation exists between Ks and θs, and thus it is not possible to estimate both Ks and θs by globally minimizing the objective function. Combination approaches with W (i.e., ψ and W, T and W, or ψ and W and T) give unique estimates of α and Ks if either θs is known or prior information on θs is available.
Estimation of Soil Solution Electrical Conductivity from Bulk Soil Electrical Conductivity in Sandy Soils
Authors: Amente G. , Baker John M. , Reece Clive F.
Published: July 2010

Studies of solute transport through soil and attendant environmental impacts are hampered by the lack of methods for continuous monitoring of solute concentration. Measurement of bulk soil electrical conductivity (ECb) using time domain reflectometry (TDR) is a promising technique, but it is indirect, and estimation of solute concentration from such measurements requires a model relating soil solution electrical conductivity (ECw) to ECb Several models of varying complexity exist, but further testing is required to determine their relative merits and applicability. This study was conducted to determine the efficiency of various models that use different methods of estimating the tortuosity factor, Fg, in order to estimate ECw from ECb All models assume that the ratio of ECb/ECw is proportional to soil water content, θ, with Fg as the coefficient of proportionality. In this study, two types of models were compared, those in which Fg is obtained from soil hydraulic properties and those in which Fg is estimated as it is in gas diffusion models, except with θ rather than porosity as the independent variable. Measurements were conducted in a sandy soil, across a range of ECw from 0.10 to 0.56 S m−1 The models in which Fg is obtained from soil hydraulic properties did not perform as expected. The results with the gas diffusion analog models were variable; the most successful of these was based on the 1959 model of Marshall, in which Fg is a power function of θ, θb Optimal results were obtained with , not far from Marshall's suggested value of 0.5 for gas diffusion. We conclude that there is no benefit to the use of soil hydraulic properties in estimating ECw from ECb measurements, at least for sandy soils, where simpler relationships appear to provide superior results.
A profile cone penetrometer for mapping soil horizons
Authors: Rooney D. J. , Lowery B.
Published: July 2010

Accurate soil mapping at a fine scale is needed for site‐specific farming, research on solute transport, and many other applications requiring detailed analysis of both the depth and thickness of soil horizons. Soil mapping techniques currently used are too costly to address the spatial variability of soil mapping units. We propose the use of a profile cone penetrometer (PCP) to assist in mapping soil properties at a landscape scale. Data collected with the PCP show clear changes in soil properties with depth, and were confirmed using profile descriptions from soil pits as well as 4.3‐cm‐diam soil cores. Combining three‐dimensional PCP data with soil attribute information will provide a rapid and effective means to digitally update soil surveys and improve the efficiency and cost effectiveness of sampling techniques.
Evaluation of the Microwave Irradiation Method for Measuring Soil Microbial Biomass
Authors: Wang Weijin , Dalal Ram C. , Moody Phil W.
Published: July 2010

Soil microorganisms are an important and labile component of soil organic matter. We investigated the feasibility of measuring soil microbial biomass using microwave irradiation as a rapid and nontoxic alternative to chloroform fumigation. The efficacy of microwave irradiation was affected by the distribution pattern and location of soil samples in the oven, the amount of soil, soil moisture content, irradiation time, and soil properties. To ensure uniform and consistent microwave application to soil samples, we modified the microwave treatment procedure (i) by using a round sample rack to improve the uniformity of microwave delivery; (ii) by adjusting the moisture of different soils to the same percentage of their weight; (iii) by using a constant sample weight and irradiation time; and (iv) by grouping soil samples according to their clay contents. The results using 30 Australian soils, with a wide range in soil properties, showed that organic C released by microwave irradiation had weak or no correlation with the microbial biomass C measured by chloroform‐fumigation extraction, chloroform‐fumigation incubation, and substrate‐induced respiration methods; while the correlations between the measurements of the three conventional methods were generally close. The increase in extractable C after microwave treatment was often accompanied by an increase in the optical density of the soil extract at 410 nm, which was indicative of the liberation of humified substances by microwave irradiation. We conclude that the organic C liberated from soil by microwave irradiation may contain an appreciable portion of nonbiomass compounds.
An Unsaturated Transient Flow Method for Determining Solute Adsorption by Variable‐Charge Soils
Authors: Katou Hidetaka , Uchimura Koji , Clothier Brent E.
Published: July 2010

The amount of reactive ions adsorbed during transport in variable‐charge soils is often smaller than those predicted from batch adsorption experiments. This overestimation of adsorption for invading ions by the batch method is likely to be caused by excessive desorption of indigenous, strongly adsorbed ions. We propose an unsaturated transient flow method by which equilibrium adsorption of weakly reactive ions can be determined without causing appreciable desorption of indigenous ions. In our method, water is imbibed into horizontal columns packed with soil that has been mixed with a salt solution at different concentrations to attain adsorption equilibrium. We make use of the observation that during imbibition of water, the antecedent solution is pushed ahead by the invading solution and accumulates in the region beyond the plane of separation, with the solution concentration unchanged. From linear plots of the solute content vs. soil water content in this region, the amount of solutes adsorbed by soil and the equilibrium solution concentration prior to the water imbibition are obtained. The advantages of the method are that adsorption isotherms can be determined under conditions similar to those expected during transport processes in soil, and that it is exempt from uncertainty about attainment of adsorption equilibrium as in the miscible displacement methods. The proposed method is best suited for variable‐charge soils where adsorption of weakly reactive ions is largely due to an increase in the exchange capacity.
Phosphorus Loading Effects on Extracellular Enzyme Activity in Everglades Wetland Soils
Authors: Wright A.L. , Reddy K.R.
Published: July 2010

The impact of P loading to the northern Florida Everglades has been implicated in changing vegetation patterns, peat accretion rates, and other soil physico‐chemical properties. This investigation focused on determining the influence of P loading on the activities of various extracellular enzymes along a P‐enrichment gradient and relating measured enzyme activities to soil physico‐chemical parameters. Alkaline phosphatase activity (APA) was the only enzyme affected by P loading and was negatively related to soil P concentrations and microbial biomass C and P. Arylsulfatase, β‐d‐glucosidase, protease, and phenol oxidase were not affected by P loading and were not related to measured soil C, N, S, and P physical and chemical parameters. All enzyme activities were highest in the surface detritus layer and decreased with soil depth. Due to significant relationships between APA and soil and microbial P parameters, APA appears to be a useful indicator for assessing impacts of P enrichment in wetland soils.
Estimating Particle‐Size Distribution from Limited Soil Texture Data
Authors: Skaggs T. H. , Arya L. M. , Shouse P. J. , Mohanty B. P.
Published: July 2010

Particle‐size distribution is a fundamental physical property of soils. Because particle‐size data are frequently incomplete, it would be useful to have a method for inferring the complete particle‐size distribution from limited data. We present a method for estimating the particle‐size distribution from the clay (cl), silt (si), and fine plus very fine sand (fvfs) mass fractions (particle radii, r, between 25 and 125 μm). The method is easy to use, with the estimated distribution being given by a closed‐form expression that is defined explicitly in terms of cl, si, and fvfs. The accuracy of the method is evaluated using particle‐size data from 125 soils. The results show that the method should not be used when the silt fraction is greater than about 70%. For other soils, the estimated distribution agrees reasonably well with the true distribution, with the median level of accuracy being characterized by an average absolute deviation of 2% over 1 μm ≤ r ≤ 1000 μm, and a maximum absolute deviation of 9%.
Spatial Distributions of Soil Chemical Conditions in a Serpentinitic Wetland and Surrounding Landscape
Authors: Lee B. D. , Graham R. C. , Laurent T. E. , Amrhein C. , Creasy R. M.
Published: July 2010

Soils formed from serpentinite contain an abundance of Fe, Mn, Cr, Ni, and Mg, and low concentrations of the plant‐essential nutrients Ca and K. The resulting vegetation is commonly xeromorphic and characteristically stunted. This study was conducted to (i) determine the spatial distributions of heavy metals and exchangeable cations (Me) in an ultramafic wetland and surrounding landslide terrain, and (ii) to interpret the distributions relative to environmental conditions and pedogenic processes on the component landscape positions. Distributions of dithionite‐extractable metals (Md) and Me in surface soils (0–15 cm depth) were assessed by kriging and by landscape units, characteristic landscape position, soils, and vegetation. Abundance of Mes ranked in the following order: Mg > Ca ≫ K > Mn > Na > Ni. The Ca/Mg ratios range from 0.13 to 3.77 (mean 0.43), with the highest ratios in a landscape unit with nonserpentine metamorphic colluvium over serpentinitic residuum. Exchangeable cations are concentrated within the wetland relative to surrounding terrain. Dithionite‐extractable Fe, Mn, and Ni are concentrated in soils on the oxidizing, nonhydric lower landscape positions, near the hydrologic discharge point of the wetland. Chromium and Al are concentrated in the nonhydric upper landscape positions. Due to reducing conditions, the wetland contains low concentrations of Md relative to the surrounding nonhydric terrain. Large vegetation differences between moisture class coupled with moderate vegetation differences between landscape units within the same moisture class, suggest that vegetation occurrence within the study area is controlled primarily by hydrology, and secondarily by elemental conditions.
Multifractal Characterization of Soil Particle‐Size Distributions
Authors: Posadas Adolfo N. D. , Giménez Daniel , Bittelli Marco , Vaz Carlos M. P. , Flury Markus
Published: July 2010

A particle‐size distribution (PSD) constitutes a fundamental soil property correlated to many other soil properties. Accurate representations of PSDs are, therefore, needed for soil characterization and prediction purposes. A power‐law dependence of particle mass on particle diameter has been used to model soil PSDs, and such power‐law dependence has been interpreted as being the result of a fractal distribution of particle sizes characterized with a single fractal dimension. However, recent studies have shown that a single fractal dimension is not sufficient to characterize a distribution for the entire range of particle sizes. The objective of this study was to apply multifractal techniques to characterize contrasting PSDs and to identify multifractal parameters potentially useful for classification and prediction. The multifractal spectra of 30 PSDs covering a wide range of soil textural classes were analyzed. Parameters calculated from each multifractal spectrum were: (i) the Hausdorff dimension, f(α); (ii) the singularities of strength, α; (iii) the generalized fractal dimension, Dq; and (iv) their conjugate parameter the mass exponent, τ (q), calculated in the range of moment orders (q) of between −10 and +10 taken at 0.5 lag increments. Multifractal scaling was evident by an increase in the difference between the capacity D0 and the entropy D1 dimensions for soils with more than 10% clay content. Soils with <10% clay content exhibited single scaling. Our results indicate that multifractal parameters are promising descriptors of PSDs. Differences in scaling properties of PSDs should be considered in future studies.
Inspectional Analysis of Convective‐Dispersion Equation and Application on Measured Breakthrough Curves
Authors: Shukla M. K. , Kastanek F. J. , Nielsen D. R.
Published: July 2010

Several miscible displacement experiments were carried out in three 10‐, 20‐, and 30‐cm mollisol and antisol filled soil columns. A strong linear relationship between pore‐water velocity (v) and apparent diffusion coefficient (D) was obtained for both soil columns (r2 > 0.92). We also derived the nondimensional laws for equilibrium adsorption convective‐dispersion equation (CDE) using inspectional analysis, which reduced the physical constants and variables in CDE from seven to four nondimensional‐π quantities. After scaling, the times of effluent arrival were nearly the same and all the breakthrough curves (BTCs) coalesced into a very narrow region of scaled time.
Small‐Angle X‐Ray Scattering Study of the Quasi‐Crystal Structure of Montmorillonite‐CTAB in Suspension
Authors: Shang C. , Rice J. A. , Lin J. S.
Published: July 2010

The quasi‐crystals of hexadecyltrimethylammonium (CTA+)‐montmorillonite formed in suspension were investigated by small‐angle x‐ray scattering (SAXS). The d‐spacing of the quasi‐crystals increased from 17.1 to 21.7 Å, corresponding to an increasing surfactant loading from 20 to 250% of the clay's cation exchange capacity (CEC). One‐dimensional grating theory was used to describe the scattering in the Porod region so that the number of clay layers and crystal size were obtained. The quasi‐crystal reaches maximum size at a surfactant loading equal to the clay's CEC. The scattering peaks in the Porod region are due solely to quasi‐crystals. Small‐angle x‐ray scattering avoids intermediate peaks resulting from the artificial interstratification of free and complexed layers in conventional x‐ray diffraction analysis.
Soil Hydrology on an End Moraine and a Dissected Till Plain in West‐Central Indiana
Authors: Jenkinson Byron J. , Franzmeier Donald P. , Lynn Warren C.
Published: July 2010

Soil hydrologic properties are a function of precipitation (P)‐evapotranspiration relations, stratigraphy, and geomorphology. An understanding of soil hydrology helps us predict many soil and ecosystem properties. We studied soil hydrology on an end moraine and on a dissected till plain in west‐central Indiana. We measured hydraulic head, water table level, redox potential (EH), and temperature, with piezometers (0.25‐, 0.50‐, 1.0‐, 2.0‐, 4.5‐m depth), observation wells, platinum electrodes (0.25‐, 0.50‐, and 1.0‐m), and thermocouples (0.25‐, 0.50‐, 1.0‐, and 2.0‐m), respectively, in soils along two soil toposequences for 9 yr. Water table levels drop rapidly when hardwood trees first leaf out in the spring, and rise rapidly after the trees go dormant in the fall. The Thornthwaite model underestimates evapotranspiration in the forest in the spring. In the dissected plain underlain with dense till, water is held up by the slowly permeable till. Water moves from the interior of the till plain to the dissected bevel where it periodically rises within 1 m of the surface but does not cause redoximorphic features. Soils on the crest of a moraine are similar in morphology to those on the till plain bevel, but have essentially no high water table because there is no upslope contributing area to serve as a water source. In the wetter soils, reduction begins when a soil horizon becomes wet but not saturated, and proceeds more rapidly when the horizon is saturated. There is a lag period of 2 to 8 wk between initial saturation of the soil at 25 cm and minimum EH.
Spatially Explicit Treatment of Soil‐Water Dynamics along a Semiarid Catena
Authors: Chamran F. , Gessler P. E. , Chadwick O. A.
Published: July 2010

Volumetric soil‐water depth profiles at nine sample locations on a 2‐ha hillslope were monitored throughout the 1997‐1998 El Niño and the 1998‐1999 La Niña cycles. A hydrological model integrating the soil‐water measurements with digital terrain analysis and a one‐dimensional water balance model was developed to map dominant hydrological patterns of soil‐water storage and lateral flow redistribution. Statistical correlations between hydrologic behavior and the compound topographic index (CTI) generated from a digital elevation model (DEM) were used to generate spatially distributed input parameters of initial water storage and soil‐controlled evapotranspiration utilized in the model. The results suggest that differences in water storage and availability are highly modified by climatic conditions and local topography. Nearly three times higher than normal rainfall in the El Niño year caused deeper infiltration of water and led to significant subsurface water redistribution into the concave hillslope positions which remained moist throughout the 1998 summer. Water infiltration and distribution was diminished considerably in the drier than normal La Niña, and led to a complete dry‐down in 1999. Actual evapotranspiration was 87% of total precipitation during the El Niño, compared with 100% in the subsequent La Niña. The good correlation between modeled and measured water storage shows that even a simple one‐dimensional model combined with the appropriate input parameters is a suitable tool for estimating changes in soil‐water content on hillslopes where lateral flow is a significant functional component of the soil hydrology.
Modeling the Effects of Diffusion Limitations on Nitrogen‐15 Isotope Dilution Experiments with Soil Aggregates
Authors: Cliff John B. , Bottomley Peter J. , Haggerty Roy , Myrold David D.
Published: July 2010

An assumption inherent in isotope dilution methodologies is that of homogeneous distribution of label. This assumption may not hold, however, because of mass transfer limitations in most soil systems. The effects of mass transfer limitations on isotope dilution in soil aggregates with radii up to 0.36 cm were examined using spherical diffusion‐reaction models designed to simulate 15NH+4 isotope dilution experiments measuring gross production and consumption of NH+4 across a 24‐h period. Equations that described transport and reaction of NH+4 assumed Fickian diffusion, linear, equilibrium adsorption, zero‐order production of natural abundance 15N, and either pseudo‐first‐order or zero‐order consumption of NH+4 In the case of pseudo‐first‐order consumption, rate calculations were sensitive to the adsorption coefficient (emphasizing the need to interpret results as apparent rates), but not to other transport parameters. In the case of zero‐order consumption, both production and consumption rates were always underestimated. Errors increased as aggregate size increased and as effective diffusivity decreased. Increasing the consumption to production rate ratio increased the error in production rate estimates. Allowing the applied label to diffuse into soil aggregates for 24 h prior to initial time sampling decreased errors by a factor of about three (to <−8% relative error) in the largest aggregate size class. These simulations reemphasize the need to optimize experimental protocol when designing isotope dilution experiments in structured soils and suggest an equilibration period prior to initial time sampling will improve accuracy of reaction rate estimates obtained from isotope dilution experiments.
Infiltration and Surface Geometry Features of a Swelling Soil following Successive Simulated Rainstorms
Authors: Wells R. R. , DiCarlo D. A. , Steenhuis T. S. , Parlange J.-Y. , Römkens M. J. M. , Prasad S. N.
Published: July 2010

The theory of water movement in high shrink/swell soils has experienced consistent revision since Haines first presented the topic in 1923. Several aspects of the infiltration process in cracking soils have proven to be difficult to measure; seal/crust formation and properties, crack network patterns, preferential flow zones and contributions, and soil moisture determinations within the profile (near crack and near center of prismatic column) to name a few. Here, we used simulated rainstorms, laser measurements of surface elevation, needle‐penetrometer measurements, and mass measurements of infiltrating water over a 206‐ and 145‐d period to examine water movement and cracking patterns in a large sample box filled with a swelling clay soil. Water movement was restricted to the neighborhood of the crack zone, since the formation of a surface seal/crust prohibited infiltration into the surface of the prismatic columns of soil between cracks. Also, the location of cracks was observed to alternate between rainstorms. The alternating crack pattern led to more uniform wetting with depth as time increased and the number of rainstorms increased, thereby reducing the extent of preferential flow.
Root Distribution Relationships to Soil Properties in Missouri Oak Stands
Authors: Udawatta Ranjith P. , Henderson Gray S.
Published: July 2010

This study examined the feasibility of adapting a soil‐based productivity index (PI) to predict root distribution in Missouri oak (Quercus spp.) stands. Roots and soil were sampled to 150 cm in 58 plots in the Missouri Ozarks and Missouri River hills. Soil pH, bulk density, and moisture holding capacity were determined by horizon, and the data were used in equations designed to quantify “sufficiency” for root growth. The resulting sufficiency values were used to calculate individual and combined soil property indices for each plot. First, sufficiency values for combined indices were calculated in three ways—multiplicative, geometric, and arithmetic. Then, the indices were derived by multiplying individual or combined sufficiency values by a root index factor, which this study found to be representative of proportional root distribution in “ideal” soil, and then summing the weighted values. Of the individual indices, soil pH explained 30% of fine root length variability and 29% of the total root length variability. Neither soil bulk density nor soil moisture explained root length variability. In fact, these properties actually reduced predictability when included in combined indices. Of the combined indices, the multiplicative‐based index explained a greater percentage of root length variation than either the geometric‐ or arithmetic‐based indices. However, no combined index accounted for more than 11% of the variation in root length distribution. This suggests that, to be usable in forestry, the soil‐based productivity index needs to be refined and/or expanded to include variables such as nutrients and climate.
Kaolinite, Halloysite, and Iron Oxide Influence on Physical Behavior of Formulated Soils
Authors: West S. L. , White G. N. , Deng Y. , McInnes K. J. , Juo A. S. R. , Dixon J. B.
Published: July 2010

Soils of some tropical regions have low bulk density, high permeability, and resistance to erosion even under high rainfall. Soils with this combination of characteristics frequently contain halloysite and Fe oxides. We hypothesized that platy kaolinite particles form a more compact mass than tubular halloysite particles, and that Fe oxides promote porous aggregation. To test this hypothesis the settling densities were determined for soil analogs constructed of kaolinite and halloysite clays with ferrihydrite and nonionic, anionic, and cationic organic surfactants as organic matter proxies. The samples were mixed in water and compacted by centrifugation. The hydraulic conductivity of each kaolinite‐ and halloysite‐based mixture was determined with a falling head permeameter. Halloysite samples had lower bulk densities than kaolinite samples with the same centrifugation. The addition of ferrihydrite decreased bulk density of sets of both mineral mixtures. Numerous small particles of ferrihydrite adhered to halloysite tubes in contrast to larger oxide masses formed among clean kaolinite plates, as shown in transmission electron micrographs. The greater frequency of ferrihydrite particles associated with halloysite than kaolinite crystals provided more sites for inter‐particle bonding and clay aggregation. Cationic and neutral organic polymers decreased the bulk density of halloysite soil analogs. The kaolinite analog response to polymer treatment varied. Anionic polymers appeared to increase the bulk density of both mineral mixtures that is attributed to increased particle dispersion. These results support the hypothesis that clay morphology and bonding agents influence soil bulk density and hydraulic conductivity of fabricated clay soils.
Field Calibration of Water Content Reflectometers
Authors: Chandler D. G. , Seyfried M. , Murdock M. , McNamara J. P.
Published: July 2010

Field monitoring of volumetric soil water content (VWC) is critical for a variety of applications. Recently developed electronic soil water sensors provide a relatively inexpensive monitoring option. However, the calibration of these sensors is more sensitive to variations in soil properties than for time domain reflectometry (TDR), which is generally regarded as the best electronic means of VWC measurement and which has a relatively robust calibration. Field calibration incorporates the effects of within‐profile and between‐site soil variations and individual variability on sensor response. The objective of this study was to evaluate the effectiveness of using TDR to field‐calibrate the Campbell Scientific water content reflectometer (WCR), or CS‐615, which is an example of a newly developed sensor in widespread use. We found that (i) there was a strong, linear correlation between the WCR‐measured period and TDR‐measured VWC; (ii) the WCR calibration varied with soil type; (iii) calibration of individual sensors resulted in excellent agreement between TDR and the WCR measurements; and (iv) calibration resulted in improved description of soil water dynamics and improved precision of VWC estimates.
Frequency Domain Analysis for Extending Time Domain Reflectometry Water Content Measurement in Highly Saline Soils
Authors: Jones Scott B. , Or Dani
Published: July 2010

Water content and electrical conductivity of soils are routinely determined using time‐domain reflectometry (TDR) based on analysis of signal travel time and attenuation along embedded probes. In soils with appreciable salinity, time domain analysis becomes progressively inaccurate due to signal attenuation to the point of failure. Our objectives were to test whether dielectric permittivity, which is inextricable using TDR travel time analysis (TTA) in saline soils could be extracted using frequency domain techniques applied to waveforms from shorter TDR probes that reduce signal attenuation. The methodology was tested using coaxial cells and three‐wire TDR probes in sand and silt loam soil under a wide range of saturated solution soil electrical conductivities. Three different interpretation techniques were compared; conventional TTA, scatter function fitting (SFF), and resonant frequency analysis (RFA). Using a range of probe lengths (2, 3, 6, 10, and 15 cm) soil bulk dielectric permittivity estimates were obtained using all three techniques in solution electrical conductivities up to 48 dS m−1 Both SFF and RFA produced similar permittivity estimates, which generally increased with increasing solution electrical conductivity. Network analyzer permittivity measurements (0.5–1.5 GHz) were greater than estimates using TTA, which were both greater than values from SFF and RFA in a saturated silt loam soil. Although dependent upon dielectric permittivity and electrical conductivity, frequency domain analysis results indicate a 3‐cm probe is optimal for maintaining a interpretable scatter function in the TDR frequency band while providing maximum extension of dielectric determination under lossy conditions in saturated soils.
Decomposition of Nitrogen‐15 Labeled Hoop Pine Harvest Residues in Subtropical Australia
Authors: Blumfield Timothy J. , Xu Zhihong , Mathers Nicole J. , Saffigna Paul G.
Published: July 2010

Information on decomposition of harvest residues may assist in the maintenance of soil fertility in second rotation (2R) hoop pine plantations (Araucaria cunninghamii Aiton ex A. Cunn.) of subtropical Australia. The experiment was undertaken to determine the dynamics of residue decomposition and fate of residue‐derived N. We used 15N‐labeled hoop pine foliage, branch, and stem material in microplots, over a 30‐mo period following harvesting. We examined the decomposition of each component both singly and combined, and used 13C cross‐polarization and magic‐angle spinning nuclear magnetic resonance (13C CPMAS NMR) to chart C transformations in decomposing foliage. Residue‐derived 15N was immobilized in the 0‐ to 5‐cm soil layer, with approximately 40% 15N recovery in the soil from the combined residues by the end of the 30‐mo period. Total recovery of 15N in residues and soil varied between 60 and 80% for the combined‐residue microplots, with 20 to 40% of the residue 15N apparently lost. When residues were combined within microplots the rate of foliage decomposition decreased by 30% while the rate of branch and stem decomposition increased by 50 and 40% compared with rates for these components when decomposed separately. Residue decomposition studies should include a combined‐residue treatment. Based on 13C CPMAS NMR spectra for decomposing foliage, we obtained good correlations for methoxyl C, aryl C, carbohydrate C and phenolic C with residue mass, 15N enrichment, and total N. The ratio of carbohydrate C to methoxyl C may be useful as an indicator of harvest residue decomposition in hoop pine plantations.
Predicting Pesticide Transport in Mulch‐Amended Soils
Authors: Ma Liwang , Selim H. M.
Published: July 2010

With adoption of combine harvest technology, massive sugarcane (Saccharum Spp. Hyb.) residue is left on the soil surface following each harvest, which could affect the environmental fate and efficacy of applied pesticides in subsequent cropping seasons. The objective of this study was to quantify the retention characteristics and mobility of a commonly used herbicide, atrazine (2‐chloro‐4‐ethylamine‐6‐isopropylamino‐S‐triazine), in soils when sugarcane mulch residue was present. Specifically, adsorption and desorption kinetic batch experiments were performed to quantify atrazine retention by the mulch residue over time. Atrazine sorption exhibited time‐dependent behavior and was followed by slow release regardless of input concentration. A kinetic—equilibrium model based on a second‐order two‐site (SOTS) formulation was successful in describing atrazine adsorption versus time by the mulch residue. One set of model parameters was capable of describing atrazine release based on six successive desorption steps. As a test for the applicability of the model, data sets from two other experiments where sorption and release was measured for extended time periods (1348 and 2476 h) were successfully predicted by the SOTS model. Miscible displacement methods were used to measure the mobility of atrazine in packed columns where the mulch residue was mixed with a reference sand material or a Sharkey clay soil (very fine, smectitic, thermic Chromic Epiaquerts). Use of batch‐measured model parameters did not adequately describe atrazine mobility in the sand‐mulch column. In contrast, for a Sharkey‐mulch soil column, a two‐compartment SOTS model was successful in predicting atrazine breakthrough results where independently estimated parameters for the mulch residue and the soil matrix were used as the input parameters. Results also showed that mixing of mulch with soil created physical non‐equilibrium condition in the columns, which was responsible for errors in model predictions.
Continuous Measurements of Belowground Nitrous Oxide Concentrations
Authors: Drewitt Gordon , Warland Jon S.
Published: July 2010

Nitrous oxide released from soil is a concern since it can act as a potential atmospheric pollutant and it represents a loss of N from the soil. To better understand the factors controlling N2O production and transport, we developed a system to obtain continuous measurements from below the soil surface. The sampling system pulls small volumes of soil gas from buried sample probes through a tunable diode laser trace gas analyzer. The advantage of this system is that it measures concentrations spectroscopically, allowing regular, continuous measurements. This provides it with the distinct advantage of being able to capture short‐term changes in gas concentrations that may be important for nutrient and greenhouse gas budgeting. Furthermore, the system is relatively simple to install and could be integrated into existing field measurements of trace gas flux. Measurements of belowground N2O concentrations were obtained during the spring thaw from buried probes in a conventionally tilled field that was planted in soybean [Glycine max (L.) Merr.] the previous summer. Measurements showed that belowground N2O concentrations at the 25‐cm depth varied between 65 and 85 μmol mol−1 before snowmelt. After melting of the snow and the beginning of the soil thawing, N2O concentrations decreased to a value generally <1 μmol mol−1 During this period when belowground N2O concentrations were near atmospheric values, wind speed influenced concentrations, possibly through a pressure pumping effect.
Biological Activity of Humic Substances Is Related to Their Chemical Structure
Authors: Muscolo Adele , Sidari Maria , Attinà Emilio , Francioso Ornella , Tugnoli Vitaliano , Nardi Serenella
Published: July 2010

To understand if the biological activity of humic substances may be related to their molecular weight or chemical structure, two humic substances, derived from an Ah horizon of uncultivated couch grass [Elytrigia repens (L.) Desv. ex Nevski] and an Ah horizon of forest soil, were extensively characterized by means of different spectroscopic techniques (diffuse reflectance infrared Fourier transform [DRIFT] and 1H nuclear magnetic resonance [NMR]). The two humic substances, each separated in fractions with low (<3500 Da) and high (>3500 Da) relative molecular mass were compared for their effects on Pinus nigra J.F. Arnold callus. Growth of callus, the soluble sugar content, free amino acid pool, and the activities of the key enzymes involved in C and N metabolism were investigated. Callus was grown for a subculture period (28 d) on basal Murashige and Skoog medium plus humic matters with or without different hormones: indole‐3‐acetic acid, 2,4‐dichlorophenoxyacetic acid, or 6‐benzylaminopurine. The results of 1H‐NMR spectra and the DRIFT spectroscopy showed significant differences in the chemical composition between forest and grass humic substances. A large amount of aliphatic and H‐sugarlike component and an intense chemical shift of the β‐CH3 region in both grass humic fractions were observed, while high contents of betaine, organic acid, and COOH groups in both forest humic fractions were detected. A different biological activity between the grass and forest humic fractions was also observed. Thus, the different activity of the two humic substances used seems related to the diverse chemical composition rather than to different molecular weights.
Spirometry Longitudinal Data Analysis Software (SPIROLA) for Analysis of Spirometry Data in Workplace Prevention or COPD Treatment
Authors: Hnizdo Eva , Yan Tieliang , Hakobyan Artak , Enright Paul , Beeckman-Wagner Lu-Ann , Hankinson John , Fleming James , Lee Petsonk Edward
Published: July 2010

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of morbidity and mortality. Periodic spirometry is often recommended for individuals with potential occupational exposure to respiratory hazards and in medical treatment of respiratory disease, to prevent COPD or improve treatment outcome. To achieve the full potential of spirometry monitoring in preserving lung function, it is important to maintain acceptable precision of the longitudinal measurements, apply interpretive strategies that identify individuals with abnormal test results or excessive loss of lung function in a timely manner, and use the results for intervention on respiratory disease prevention or treatment modification. We describe novel, easy-to-use visual and analytical software, Spirometry Longitudinal Data Analysis software (SPIROLA), designed to assist healthcare providers in the above aspects of spirometry monitoring. Software application in ongoing workplace spirometry-based medical monitoring programs helped to identify increased spirometry data variability due to deteriorating test quality and subsequent improvement following interventions, and helped to enhance identification of individuals with excessive decline in lung function.
The Subsidy-Based Solar Energy Policy in Taiwan
Authors: Hu Jin-Li , Lin Jui-Chu , Yang Tzu-Cheng , Chi Meng-Chi
Published: July 2010

There are five major factors affecting the adoption of renewable energy for the households in Taiwan: price, environmental consciousness, education, geography, and building density. However, although people usually tend to be environment-friendly, the price is still the major concern for households in considering the adoption of renewable energy equipments. Therefore, subsidies have become the major policy instrument to promote household installation of renewable energy devices. This study takes the case of the solar water heaters (SWHs) as an example of how Taiwan subsidizes households to adopt renewable energy equipments.
Electoral Challenges of Moderate Factions: Main Streeters and Blue Dogs, 1994-2008
Authors: Lucas DeWayne L , Deutchman Iva E
Published: July 2010

In the contemporary age of party polarization, moderate members of Congress have found their electoral fortunes to be dependent upon their partys control of the House. Whether Democrat or Republican, members of moderate factions surprisingly receive considerably more supportin terms of electoral strategy and financeswhen their party is in the minority and less when it is in the majority. This paper examines the electoral challenges faced by members of the Democratic Blue Dog Coalition and the Republican Main Street Partnership in the election cycles of 1994 to 2008.
Redistricting in the U.S.: A Review of Scholarship and Plan for Future Research
Authors: Arrington Theodore S.
Published: July 2010

The nation-wide cycle of redistricting is the most consequential, repetitive decision-making process shaping the nature of American democracy. Because the arrangement of the districts forms an essential part of the rules of the game, the process by which they are drawn is meta-politics or a quasi-constitution making activity. The research on this process is voluminous and includes bits and pieces of the process. But the process is complicated, in part because the criteria for redistricting are in conflict with one another. The criteria include considerations of political geography, physical features, community of interest, one person one vote, race and ethnicity, partisanship, contiguity, compactness, recognition of local political boundaries, incumbents addresses, and desires for minimal change. The literature also covers the use of geographic information systems in the process and possible reforms. But no overall theory of redistricting has been developed which includes all these features.