bluuebunny/crossref_metadata_2025 huggingface dataset:
Determining the Hydraulic Properties of a Swelling Soil from a Transient Evaporation Experiment
Authors: Garnier P. , Rieu M. , Boivin P. , Vauclin M. , Baveye P.
Published: July 2010

Most methods used to determine the hydraulic properties of swelling soils (i.e., the shrinkage curve [e(θ)], the moisture retention curve [h(θ)], and the hydraulic conductivity curve [K(θ)]) are time consuming because they require measurements of several different parameters (either in separate experiments or by using very expensive equipment). We propose a simple evaporation experiment to simultaneously determine all three soil hydraulic properties. The method is illustrated using samples of a Vertisol from the Senegal River valley. The value of e(θ) is determined during the experiment by horizontal and vertical linear deformation measurements, whereas an inverse parameter estimation method is used to determine h(θT) and K(θ). This method relies on a water flow model that takes into account the three‐dimensional and anisotropic deformation of the soil. The reliability of the estimated parameter values was checked and we compared the results with those obtained by a multistep outflow experiment. Good agreement was found between the results of the different procedures. The sensitivity of the method to deformation was also analyzed. In the soil investigated, the inverse method does not seem to require the use of a water flow model that takes into account deformation. However, a correction for deformation is needed if the characteristic functions are sought in terms of the volumetric water content of the soil.
Apparatus for Constant‐Head Solute Transport and Soil Water Characteristic Determination
Authors: Langner H. W. , Wraith J. M. , Inskeep W. P. , Gaber H. M. , Huwe B.
Published: July 2010

We developed a system to impose, maintain, and monitor constant matric head (h) and water content (θ) within large soil cores during saturated or unsaturated flow. Critical elements include: (i) delivery of water and chemicals to the column inlet using a modified disk permeameter; (ii) paired time domain reflectometry (TDR) and transducer tensiometer sensors; and (iii) solenoid valves at the outlet for uninterrupted negative pressure and simultaneous collection of large effluent volumes. Use of TDR and tensiometry provides detailed water retention data and allows hydraulic conditions within the soil to be continuously monitored during single or multiple experiments using the same soil column. Our experiences have emphasized the need to measure soil column h rather than infer its status based on applied pressure.
Influence of Soil Organic Matter Removal and pH on Oxalate Sorption onto a Spodic Horizon
Authors: Bhatti J. S. , Comerford N. B. , Johnston C. T.
Published: July 2010

Oxalate is one of the dominant low molecular weight organic anions in many soils under forest ecosystems. Through its complexation reactions with Fe and Al, both in solution and at mineral surfaces, oxalate increases the availability of nutrients such as P in these soils. This investigation was designed to study (i) the influence of pH on the mechanism of oxalate sorption by the soil clay fraction and whole soil materials from a spodic horizon, and (ii) the effect of soil organic matter removal on oxalate sorption using Fourier‐transform infrared (FTIR) spectroscopy. The removal of soil organic matter and decrease in pH increased oxalate sorption significantly. There was a two‐ to threefold increase in oxalate sorption with removal of organic C at all pH values. Depending on pH, the molar ratio of OH ions released to oxalate sorbed was close to 1 or 2. These results suggest that oxalate formed mondentate and/or binuclear surface complexes at pH 3.5, and bidentate surface complexes at pH 4.5 and 5.5. With oxalate sorption, large amounts of organic C and Al were released from the soil clay fractions and whole‐soil samples. Seven to 10 mol oxalate kg−1 soil clay than by water.
Comparison of Reaction Products from the Transformation of Catechol Catalyzed by Birnessite or Tyrosinase
Authors: Naidja A. , Huang P. M. , Bollag J.‐M.
Published: July 2010

Both tyrosinase, a Cu‐containing polyphenoloxidase, and birnessite (δ‐MnO2) are able to catalyze the transformation of phenolic compounds through oxidative polymerization, a process that leads to humification, but the reaction mechanisms are not fully understood. The objective of this study was to characterize or identify the reaction products generated from catechol (1,2‐dihydroxybenzene) by birnessite or tyrosinase. Birnessite and tyrosinase catalyzed the transformation of catechol to oligomers, polycondensates, and fragments. The reaction products formed after catalysis by tyrosinase were brown colored, while those resulting from the birnessite‐catechol system were green colored; the former had a higher absorbance between 200 and 620 nm than the latter. This indicated a higher degree of aromatic ring condensation in products of the tyrosinase‐catechol system relative to those of the birnessite‐catechol system. In addition, the products of birnessite catalysis contained polycondensates and fragments, including aliphatic components, with lower molecular weights than did the products derived from catalysis by tyrosinase. Fourier‐transform infrared (FTIR) analysis and mass spectrometry indicated that the reaction products formed an organic coating on the birnessite granules.
Determining Soil Hydraulic Properties using Tension Infiltrometers, Time Domain Reflectometry, and Tensiometers
Authors: Wang Dong , Yates S. R. , Ernst F. F.
Published: July 2010

Tension infiltrometers have become a popular instrument for field determination of soil hydraulic properties. To develop and test different models for parameter estimation based on tension infiltrometer measurement, we obtained simultaneous measurements of transient tension infiltration rate, soil water content, and tension using small time domain reflectometry (TDR) probes and tensiometers installed at fixed locations relative to the infiltrometer disk. Infiltration was made with 10‐ and 20‐cm‐diam. disks under 1 and 5 cm of water supply tensions. The soil is an Arlington fine sandy loam (coarseloamy, mixed, thermic Haplic Durixeralf). Wooding's steady‐state approximate solution for water flow from a surface circular pond was used to estimate the saturated hydraulic conductivity (Ks) and an empirical parameter (αG) used in Gardner's exponential hydraulic conductivity function. These two parameters (i.e., Ks and αG) were then independently estimated using an integral form of the steady‐state Darcy‐Buckingham flux law. A sorptivity method was also proposed as an alternative to Wooding's steady‐state approach. Calculated Ks and αG with the Darcy‐Buckingham flux law method was in good agreement with estimates using Wooding's steady‐state approximation. The sorptivity method produced Ks estimates that were statistically similar to those obtained with Wooding's method. The K(h) inferred from measured θ(h) underestimated the conductivity close to saturation compared with estimates obtained from the infiltrometer measurements.
Proton Adsorption on a Titanium Oxide in the Presence of Bicarbonate
Authors: Schulthess C. P. , Belek J. Z.
Published: July 2010

The very high concentration of aqueous CO2 species below ground highlights a need to fully characterize the physicochemical behavior of this compound in the soil environment. This study focused on the adsorption of bicarbonates by a Ti oxide, and on its effects on the adsorption of protons, which was measured by the backtitration technique. The inorganic C adsorbed on the Ti oxide from pH 1.5 to 10 with a broad maximum at pH 4 to 6. For every molecule of inorganic C adsorbed (expressed as HCO3 adsorbed), an average of 2.3 protons were removed from the liquid phase (either by coadsorption or neutralization of the proton). The point of zero salt effect (PZSE) also increased from pH 5.7 to 6.2. The high stoichiometry of 2.3 suggests that the bicarbonate will also affect the desorption of cationic impurities; higher levels of Na, Ca, and Mg were measured in the liquid phase in the presence of inorganic C at pH 4. This study indirectly highlights that modeling the adsorption of protons by an oxide (even a “simple” one like Ti oxide) can be easily complicated by the presence of low levels of inorganic C or the presence of adsorbed cationic impurities.
Intercalation of Hydroxy‐Aluminosilicate and Hydroxy‐Aluminum in Montmorillonite and Resultant Physicochemical Properties
Authors: Sakurai K. , Huang P. M.
Published: July 2010

Both hydroxy‐aluminosilicate (HAS) and hydroxy‐Al (HyA) ions can be adsorbed into the interlayer spaces of montmorillonite (Mt), resulting in an expanded structure; however, the differences in the adsorption and the surface properties of the intercalated clay complexes still remain to be established. The objective of this study was to investigate the influences of the coexistence of silicic acid with HyA ions on the formation and surface properties of the HAS‐Mt complexes, in comparison with the HyA‐Mt complex and Mt. Most of the intercalation reactions of HAS and HyA ions by Mt came to apparent completion within 10 min. Compared with the original Mt, the HyA‐Mt complex had more external specific surface, pore area, and pore volume, and less internal specific surface; the HAS‐Mt complex had less external and internal specific surface, pore area and pore volume. The transmission electron micrographs and the analysis of the particle‐size distribution by small‐angle x‐ray scattering indicated that both HyA‐Mt and HAS‐Mt complexes formed domains of clay particles associated into larger particles. The HAS‐Mt complex exhibited a higher point of zero salt effect (PZSE) value than the HyA‐Mt complex. The pH‐dependent cation‐exchange (CEC) value was greater in the HAS‐Mt complex than in the HyA‐Mt complex; therefore, the variable charge in the former was more dominant than in the latter. The surface chemistry of HAS‐ and HyA‐intercalated clay complexes pertaining to dynamics of nutrients and pollutants in various pedogenic environments merits close attention.
Automated Near‐Continuous Measurement of Carbon Dioxide and Nitrous Oxide Fluxes from Soil
Authors: Ambus P. , Robertson G. Philip
Published: July 2010

Trace gas fluxes often show temporal variability on the order of hours and accurate quantification may be difficult without continuous or near‐continuous measurements. We developed an automated near‐continuous trace gas analysis system (NCTGAS) to measure soil‐atmosphere gas fluxes on a several‐times‐per‐day basis. In this system, air is circulated in a closed sample loop between fully automated flow‐through chambers and a photoacoustic infrared trace gas analyzer (TGA). The TGA quantifies infrared active gases at ambient levels within 2 to 3 min. We tested sensitivity, stability, and calibration of the TGA, and the ability of the NCTGAS to measure fluxes of CO2 and N2O. In addition to static tests, fluxes of CO2 and N2O were simulated by bleeding known quantities of these gases into a test chamber. Gas samples were simultaneously analyzed by TGA and removed for independent analysis of CO2 by conventional infrared gas analysis and for N2O by gas chromatography. The TGA‐based flux measurements were statistically identical to the independent measurements of both CO2 and N2O. In situ fluxes of CO2 and N2O measured by the NCTGAS were 105 ± 6 and 93 ± 10%, respectively, of those measured from hand‐drawn samples. The TGA was as or more stable than conventional means for measuring CO2 and N2O in air at ambient concentrations, and was equally sensitive across the range of concentrations normally encountered in field measurements. Fast response time and ease of use offers significant advantages over conventional gas chromatography.
Three‐Parameter Soil‐Water Transient Equations in Horizontal Water‐Transport Analysis
Authors: Guerrini Ivan A. , Swartzendruber D.
Published: July 2010

For data obtained from horizontal soil column experiments, the determination of soil‐water transport characteristics and functions would be aided by a single‐form equation capable of objectively describing water content θ vs. time t at given position xt. Our study was conducted to evaluate two such possible equations, one having the form of the Weibull frequency distribution, and the other being called a bipower form. Each equation contained three parameters, and was fitted by nonlinear least squares to the experimental data from three separate columns of a single soil. Across the θ range containing the measured data points obtained by gamma‐ray attenuation, the two equations were in close agreement. The resulting family of θ(xf,t) transients, as obtained from either equation, enabled the evaluation of exponent n in the tn dependence of the positional advance of a given θ. Not only was n found to be <0.5 at low θ values, but it also increased with θ and tended toward 0.5 as θ approached its sated (near‐saturated) value. Some quantitative uncertainty in n(θ) does arise due to the reduced number of data points available at the higher water contents. Without claiming non‐Boltzmann behavior (n < 0.5) as necessarily representative of all soils, we nonetheless consider n(θ) to be worthy of further study for evaluating its significance and implications.
Aluminum Speciation in Aluminum‐Silica Solutions and Potassium Chloride Extracts of Acidic Soils
Authors: Hiradate Syuntaro , Taniguchi Satoru , Sakurai Katsutoshi
Published: July 2010

To differentiate chemical species of Al in soil solutions, a method using nuclear magnetic resonance (NMR) was applied to laboratory preparations of hydroxyaluminum (HyA) and hydroxyaluminosilicate (HAS) ions ([OH]/[Al] = 2.0), and 1 M KCl extracts from acidic soils. The Al in a Al‐OH‐Si(OH)4 mixture was separated into three fractions: Al13 ([AlO4Al12(OH)24(H2O)12]7+), AlSYM, and AlNON. The Al13 and AlSYM were quantitatively determined by 27Al‐NMR at 63 and 0 ppm, respectively. The AlNON was defined as the Al that cannot be determined by 27Al‐NMR. The AlSYM was attributed to electrically symmetric octahedral Al including monomer (and dimer) HyA ions, and the AlNON was attributed to electrically asymmetric Al including HAS and polymer HyA ions. The concentrations of Al13 decreased with increasing Si/Al molar ratio of the mixed solutions, and Al13 was not detected at Si/Al ≥ 0.28. With increasing Si/Al molar ratio, the concentration of AlSYM increased slightly, while AlNON increased significantly. In the KCl extracts from soils, the Al13 was not detected at all. This result suggests that Al13 is not formed in these soils, or that the persistence of Al13 in the soil solution is strongly inhibited by adsorption or precipitation reactions. The presence of organically complexed Al (AlORG) was also directly detected in KCl extracts from upper horizons by 27Al‐NMR spectra. The chemical shift of resonance peak of AlORG was close to that of the 1:1 complex of Al oxalate. On average, 92 and 96% of the KCl‐exchangeable Al existed as AlSYM and AlSYM plus AlORG, respectively.
Revegetation in Semiarid Zones: Influence of Terracing and Organic Refuse on Microbial Activity
Authors: Garcia C. , Hernandez T. , Albaladejo J. , Castillo V. , Roldan A.
Published: July 2010

Revegetation of areas under semiarid conditions is difficult due to both the water shortage and the poor quality of the soils of semiarid areas. Two techniques of soil management (manually and mechanically built terraces), as well as soil amendment with organic materials were used for revegetation in a semiarid area. In this work the effect of such techniques on the microbial activity of a soil revegetated with Aleppo pine (Pinus halepensis Miller) was studied. The content of the different labile C fractions studied (water‐soluble C, water‐soluble carbohydrates, and polyphenol compounds) substantially increased in soils with mechanically built terraces and with addition of organic refuse. The highest values of these labile C fractions were found in soil samples collected in spring (rainy season) while those collected in January (dry season) showed the lowest values. The activity of oxidoreductases such as dehydrogenases as well as that of hydrolases involved in the biogeochemical cycles of important nutrients (ureases, proteases, phosphatases, and β‐glucosidases) were stimulated by the addition of organic matter to the soil. The lowest values of microbial biomass and enzyme activities were detected when revegetation was carried out on mechanical terraces without addition of organic materials. The simultaneous use of both soil management techniques, mechanical terracing and amendment with organic refuse, clearly improved soil microbial activity and hence soil biological quality. Plant growth was also improved with these techniques.
Factor Analysis of Nutrient Distribution Patterns under Shrub Live‐Oak in Two Contrasting Soils
Authors: Brejda John J.
Published: July 2010

In shrub‐dominated ecosystems, many soil properties are correlated, confounding changes in nutrient distribution associated with soils and shrub canopies. The objectives of this research were to: (i) identify underlying patterns in soil properties using factor analysis, and (ii) analyze factor scores to determine how the factor patterns varied between soils, canopy covers, and depth. White House (fine, mixed, thermic Ustic Haplargid) and Romero (loamy‐skeletal, mixed, nonacid, thermic, shallow Ustic Torriorthent) soils were sampled at 0‐ to 4‐ and 4‐ to 8‐cm depths under shrub live‐oak (Quercus turbinella Greene) canopies and adjacent open areas and analyzed for sand, silt, and clay contents, cation‐exchange capacity (CEC), pH, organic C, total N, extractable P, and exchangeable K, Ca, and Mg. A three‐factor model accounted for 81.2% of the total variation in the data. The first factor had high positive loadings on organic C, total N, and extractable P, and represented aggrading soil processes produced by accumulated litter and organic matter under shrubs. The second factor had high positive loadings on silt and clay contents and exchangeable K, had high negative loading on sand content, and was influenced by textural changes resulting from the interaction between shrub canopies and the two soils. The third factor had high positive loadings on exchangeable Ca, Mg, and CEC, and varied significantly between the two soils but was not affected by the presence of shrub live‐oak canopies. Factor analysis provided a statistical tool for grouping the 11 correlated soil variables into three uncorrelated factors. Analysis of factor scores allowed independent assessment of soils, shrub cover, depth, and their interactions on soil properties.
Analytical Solutions for Solute Transport in Finite Soil Columns with Arbitrary Initial Distributions
Authors: Leij Feike J. , Toride Nobuo
Published: July 2010

Analytical expressions were derived for the solute concentration in soils with a nonuniform initial distribution and a finite outlet condition assuming a zero gradient at the soil outlet. The advection‐dispersion equation (ADE) was solved by successively using a Laplace transform with respect to time, variation of parameters, and two different inversion procedures. Solutions for two resident concentrations and a flux‐averaged concentration were derived for arbitrary and pulse‐type initial distributions. The solutions are applicable for a wide range of conditions. Particular attention was paid to cases involving small Peclet numbers and large dispersive fluxes associated with steep fronts in the initial distribution. Flux‐averaged concentrations may become negative or exceed the initial concentration, while solutions for the resident concentration, derived for first‐ and third‐type inlet conditions, can predict a substantial amount of upstream solute transport due to dispersion. This suggests that the conventional ADE is not always suitable to describe initial value problems where travel times are typically short and large concentration gradients may occur.
Reduction and Oxidation Effect on the Solubility and Transformation of Iron Oxides
Authors: Brennan E. W. , Lindsay W. L.
Published: July 2010

Reports on the solubility of Fe during fluctuating redox conditions in soils and sediments are often difficult to interpret. This study was undertaken to examine the solubility relationships of Fe in suspensions of amorphous Fe(OH)3, Fe2O3(hematite), and soils subjected to changing redox conditions. A decrease in pe + pH was accomplished by the addition of organic matter and H2(g) in soils, and by H2(g) with a Pt catalyst in Fe(III) oxide suspensions. Addition of H2(g) and a Pt catalyst to Fe(III) oxide suspensions resulted in their dissolution and subsequent precipitation of two distinct Fe3O4 products. With small additions of O2 (0.2 mL of air), equilibrium was maintained with Fe3O4(magnetite). X‐ray diffraction confirmed its presence. When large amounts of atmospheric O2(g) were added (15 mL of air), the precipitate designated Fe3O4(amorp) was formed with a mean log of the equilibrium constant based on activities (Ko) of 40.65 ± 0.11. X‐ray diffraction showed this precipitate to be amorphous. This precipitate controlled Fe solubility within the pe + pH range of 4.0 to 12.7. In soil suspensions subject to changing redox, the Fe3O4(amorp) precipitate and Fe(OH)3(amorp) appear to control Fe solubility. Crystalline Fe(III) oxides including Fe2O3(hematite) and FeOOH(goethite) can only control Fe solubility under more highly stable, oxidizing conditions. Only with prolonged and intensive reduction is Fe3O4(magnetite) expected to form and control Fe solubility.
Alleviation of Copper Rhizotoxicity by Calcium and Magnesium at Defined Free Metal‐Ion Activities
Authors: Parker David R. , Pedler Judith F. , Thomason David N. , Li Huiying
Published: July 2010

The common “hardness cations”, Ca and Mg, are at least partially capable of alleviating the toxicities of metal ions, but quantitative data for their effect on Cu rhizotoxicity are lacking. We used 2‐d root elongation of wheat (Triticum aestivum L., cv. Yecora Rojo) in a simple medium (≥0.2 mM CaCl2) as a sensitive bioassay for examining how Ca, Mg, and pH affect Cu rhizotoxicity. A fourfold increase in solution CaT from 1 to 4 mM showed a slight alleviation of toxicity, but the effect could be completely ascribed to changes in ionic strength and thus in Cu2+ activity. Subsequently, a 25‐fold range in CaT (17‐fold range in Ca2+ activity) was found to improve Cu‐inhibited root elongation by some 30 to 35%. Increases in solution Mg2+ activity were equally or slightly more effective than comparable increases in free‐ion activity [denoted by parentheses, i.e., (Ca2+)] of Ca in alleviating Cu stress, an unexpected result because of reports of selective binding of Ca by apoplastic sites. Neither cation alleviated Cu rhizotoxicity as profoundly as they do with other metals such as Al. Lowering pH from 6.5 to 5.5 alleviated Cu stress slightly; a further decrease to pH 4.5 was more effective. Finally, seedlings were reared en masse in nine treatments selected from the previous root elongation studies, and root tips were analyzed for operationally defined apoplastic and symplastic Cu. Growth inhibition was only weakly correlated with symplastic Cu (or with apoplastic or total Cu), and the results suggested that Ca and Mg (but not H) afford some physiological protection against Cu that is not explained by simple competitive inhibition of Cu accumulation in the apical tissues.
Hydrology and Hydric Soil Extent within a Mollisol Catena in Southeastern Minnesota
Authors: Thompson James A. , Bell Jay C. , Zanner C. William
Published: July 2010

A landscape perspective is essential when examining the relationships among soil hydrology, hydric soil conditions, and soil hydromorphic properties because pedogenic processes, which are mainly driven by the presence and flow of water, are not restricted to a vertical soil profile. The objectives of this study were to: (i) examine the soil geomorphic properties that control water movement over and through soils of a catena in southeastern Minnesota, (ii) describe this water movement using soil water monitoring data and terrain analysis, and (iii) relate these monitoring and modeling results to the distribution of hydric soils in this landscape. Local shallow groundwater flow is lateral along this hillslope and is governed by parent material stratigraphy, particularly the presence of a sandy colluvium subsoil layer over dense till in lower landscape positions. The topographic influence on surface and near‐surface water flow and storage predicts saturated surface conditions farther upslope of the drainageway int he vicinity of low‐order, low‐relief drainages perpendicular to the drainageway. The hydric soil boundary also occurs farther upslope in the vicinity of these same low‐order drainages.
High‐Resolution Time Domain Reflectometry Coil Probe for Measuring Soil Water Content
Authors: Nissen H. H. , Moldrup P. , Henriksen K.
Published: July 2010

Time domain reflectometry (TDR) is becoming a widely used nondestructive method for measuring soil‐water content (θ), but relatively little effort has been put into the development of TDR equipment and especially TDR probes. Therefore, TDR has been used with only limited success for measuring small spatial scale variations in θ. In this study a small‐scale TDR probe (length = 15 mm, diameter = 3.6 mm), applicable with common TDR equipment and easy and inexpensive to produce, was developed. Travel time in the probe is prolonged by forcing the electromagnetic waves to travel in a coil surrounded by four grounded wires. The apparent relative dielectric permittivity (Ka) measured by the coil probe (Ka, coil) was calibrated against Ka measured by a standard two‐rod TDR probe without a balun (Ka, ref) in (i) five soils during transient evaporation, and (ii) air and seven fluids. Calibration in air and fluids was fast and reliable compared with transient‐state calibration in soil. A two‐phase dielectric mixing model was used to describe the contributions of the probe materials and the surrounding media to Ka, coil. Soil volume of influence was found to be approximately 180 mm3, implying that the coil probe measurement can be considered close to a point measurement. By introducing the coil principle, a reduction in probe length of a factor of five was achieved without loss in the sensitivity of the probe to changes in the Ka of the surrounding soil.
Nitrogen Management for High Yield and Quality of Citrus in Sandy Soils
Authors: Alva A. K. , Paramasivam S.
Published: July 2010

We are in the process of developing N best management practices for citrus in sandy Entisols to increase N uptake efficiency and to minimize NO3 leaching below the rooting depth. We evaluated the effects of N sources as either dry granular form (DGF), fertigation (FRT), or controlled‐release fertilizer (CRF), and rates (56–280 kg N ha‐1 yr‐1) with optimum irrigation management on: (i) the fruit yield and quality and leaf nutrient concentrations of bearing ‘Hamlin’ orange [Citrus sinensis (L.) Osbeck] trees on ‘Cleopatra’ mandarin (Citrus reticulata Blanco) rootstock (planted in 1974) grown in a Tavares fine sand (hyperthermic, uncoated Typic Quartzipsamments) and (ii) changes in NO3‐N status in soil solution sampled from the vadose zone both within and below the root zone. For the DGF and FRT sources, 3‐yr mean fruit yield increased with an increase in N rates in the range of 112 to 224 kg ha‐1 yr‐1. For further increase in N rate, the fruit yield showed a diminishing response, which was quite marked for the DGF. The N requirements for 1 Mg of fruit, mean across all N rates, were 1.79, 2.58, and 2.75 kg N for the CRF, FRT, and DGF sources, respectively. Leaf N concentrations were maintained within the optimal range (25–27 g kg‐1) at N rates ≥168 kg ha‐1 yr‐1, regardless of source of N. Various N rates and sources did not significantly affect the fruit size, nor juice quality parameters. The improved management of irrigation and fertilizer placement and timing of application contributed to minimized leaching of NO3‐N below the root zone.
Evaluation of a Model for Predicting Compressibility of Forest Soils
Authors: Smith C. W. , Johnston M. A. , Lorentz S. A.
Published: July 2010

Soil compressibility is an important soil physical property in the prediction of compaction behavior. The compression index, C, as a measure of compressibility, was determined for a wide range of South African forest soils and compared with existing models that utilize clay content as the independent variable. These models were tested using a model performance technique that distinguished between systematic (bias) and nonsystematic (random) errors. The maximum compression index, Cmax, was adequately predicted for all soil orders in this study and possessed a relatively low systematic error. The average compression index, Cmod, which was calculated in this study as the average of C values across a wide range of water contents, was generally underpredicted and showed a slightly higher systematic error than with Cmax. It is concluded that the slightly better performance of the models in predicting Cmax was due to the models being developed on moist to wet soils (Ψp > −100 kPa) when compression is at a maximum. Since compaction can also occur under moist to dry conditions, our results indicate that modelling compaction behavior for soils that occur in regions with a pronounced dry season will require compression indices developed across a wider range of water contents than is currently the case.
Estimating Soil Hydraulic Conductivity and Macroscopic Capillary Length from the Disk Infiltrometer
Authors: Zhang Renduo
Published: July 2010

The disk infiltrometer is increasingly used to measure in situ soil hydraulic properties in the field. Several procedures have been proposed for determining soil hydraulic conductivity from disk infiltrometer data. However, the procedures require steady‐state infiltration rates at several tensions, which limits their applications in the field. In this study, two methods were developed to estimate soil hydraulic conductivity and macroscopic capillary length using soil water fluxes at any infiltration time under the disk infiltrometer. The proposed procedures do not require steady‐state infiltration rates but infiltration data at any time. Therefore, the time required for field infiltrometer experiments can be dramatically reduced. Meanwhile the new procedures provide high estimation accuracy of soil hydraulic conductivity and macroscopic capillary length. Extensive numerically simulated data were used to examine the methods for various soils and different radii and tensions of the disk infiltrometer. The proposed methods are especially useful for estimating soil hydraulic conductivity and macroscopic capillary length of fine‐textured soils, using infiltration data collected during a short experiment period with a relatively large infiltrometer.
Stability of Arsenate Minerals in Soil under Biotically Generated Reducing Conditions
Authors: Rochette E. A. , Li G. C. , Fendorf S. E.
Published: July 2010

Mining activities and arsenical pesticide applications can introduce arsenate compounds into soils and sediments. Under water‐saturated (flooded) soil conditions, arsenate solids are subjected to biotically generated reducing conditions and may undergo reductive dissolution. While thermodynamic calculations have been used to predict the conditions under which mineral‐associated As undergoes reduction, there is relatively little data from systems in which well‐characterized arsenate solids have been subjected to reducing conditions, and a limited amount of information about the reduction of mineral‐bound arsenate. In this study, the behavior of five arsenates was observed under reducing conditions generated by flooded soils. The apparent solubility of the arsenates decreased in the order CaHAsO4 = Na2HAsO4·7H2O > AlAsO4·2H2O > MnHAsO4 > FeAsO4·2H2O under oxic conditions; under anoxic conditions (redox potential <0 mV) the apparent solubility was FeAsO4·2H2O ≥ CaHAsO4 = Na2HAsO4·7H2O > AlAsO4·2H2O > MnHAsO4. Calcium and sodium arsenates completely dissolved under the initial oxidizing conditions. X‐ray absorption near‐edge structure (XANES) spectroscopy indicated that As in AlAsO4·2H2O rapidly transformed to solid‐phase As(III). Manganese arsenate yielded the least solution and solid‐phase As(III) of all of the minerals. Iron arsenate underwent reductive dissolution, releasing As(III) to solution and solid phases, and thus may yield solution or solid‐phase As(III) if prolonged anoxic conditions prevail.
Classing the Soil Skeleton (Greater than Two Millimeters): Proposed Approach and Procedure
Authors: Corti G. , Ugolini F. C. , Agnelli A.
Published: July 2010

In soil science, analytical procedures apply almost exclusively to the fine earth (<2 mm). Rock fragments or skeleton (>2 mm) are regarded as inert and discarded during sieving; however, we have found that the clasts display physical and chemical properties that can equal or surpass those of the fine earth. These properties depend largely on the degree of alteration of the clasts. In light of these findings, we developed a method to separate the rock fragments into weathering classes. This method has been applied to five European skeleton‐rich soils derived from different parent materials. Color intensity, roughness and irregularities of the surfaces, cracks, and surface features of the exposed minerals were considered reliable criteria for the separation of the clasts. We noticed also that the degree of alteration of the clasts corresponds to size: as size decreased, weathering increased. Consequently, sieving could be used for separating the weathering classes. On the basis of these criteria, clasts were differentiated into highly, moderately, and slightly altered. There are statistically significant differences among the weathering classes in terms of bulk density, porosity, organic C, total N, and cation‐exchange capacity. There are no statistically significant differences in pH. The results confirm that the procedure separates relatively homogeneous and different classes of rock fragments. We also compared the characteristics of the soil skeleton to those of the fine earth and fresh rock. We concluded that not characterizing the skeleton of the soils may provide distorted information on the capability of these substrata.
Properties of Permafrost Soils on the Northern Seward Peninsula, Northwest Alaska
Authors: Höfle Claudia , Ping Chien‐Lu , Kimble John M.
Published: July 2010

Soil processes in permafrost regions differ markedly from those of the mid and low latitudes. Permafrost soils are cold during the short growing season and frozen the rest of the year. This study was conducted to describe permafrost soils on the tundra coastal plain of northern Seward Peninsula with emphasis on soil characteristics below the active layer and cryogenic structures, both aspects which were widely neglected in previous studies of permafrost soils. We used cryogenic structures to determine active layer depths. In describing these soils, we applied the previous soil taxonomy and tested the utility of the new Gelisol order. Seven pedons were excavated and described in different topographic positions. Most pedons are influenced by frost action, as evidenced by irregular and broken horizons and weakly developed soils. Mineral horizons have predominantly reduced colors. Organic horizons of 7‐ to 50‐cm thickness occur in the study area. All soils contain segregated ice and ice wedges. Segregated ice includes ice lenses, ice nets, and ataxitic ice concentrations at the base of the active layer. With the identification of these cryogenic features, it was possible to determine active layer depths independently of thaw season. For describing the properties of permafrost soils, the new Gelisol order is shown to be a significant improvement on the previous soil taxonomy.
Evaluating Central Tendency and Variance of Soil Properties within Map Units
Authors: Hammer R. David , Young Fred J. , Williams Frederick
Published: July 2010

Users are demanding that soil surveys contain statistical information about soil and map unit properties. Numerous sampling and statistical methodologies are available, but statistical methods should be appropriate for both sampling methods and data distributions. Rigorous investigations of soil property distributions are rare, and statistical methodologies have received little attention for soil survey applications. Two hypotheses were tested: (i) frequency distributions of soil properties within map units are non‐normally distributed, and (ii) variability estimates will depend on the statistical assumptions and methods. Twelve transects were randomly selected in a Boone County, Missouri soil survey map unit and 12 soil attributes were investigated from a population of 120 soil cores. Three methods were used to estimate variances: (i) simple random sampling, (ii) cluster sampling, and (ii) two‐stage random sampling. Frequency distributions were significantly skewed for 11 of the soil properties. The median is an appropriate estimator of central tendency for these properties. The random sampling approach provided the samplest variances, but is conceptually questionable. Two‐stage sampling is conceptually most correct, but requires dubious assumptions about population size. Non‐parametric confidence intervals for variable medians were appropriate, but are wide for most properties. None of the applied assumptions and techniques are universally applicable. Statistical assumptions and methodologies should be tested across a spectrum of depositional, weathering, and land‐use conditions to determine the most suitable approaches for particular user needs and soil conditions.
Landscape and Pedogenesis of an Oxisol‐Inceptisol‐Ultisol Sequence in Southeastern Brazil
Authors: Anjos L. H. , Fernandes M. R. , Pereira M. G. , Franzmeier D. P.
Published: July 2010

The topographic sequence of Oxisols, Inceptisols, and Ultisols is frequently observed in tropical hilly surfaces in the southeastern region of Brazil. The purpose of this study was to relate pedogenesis to major geomorphic surfaces (MGS) in the Caetés watershed, located in Paty do Alferes, Rio de Janeiro State. The landscape is characterized by steep bedrock hills and cliffs of pre‐Paleozoic gneiss, granite, and related metamorphic rocks rising above long, nearly level, accordant ridge crests, convex hills, and narrow fluvial plains. Intense soil development, with deep weathering and kaolinite formation in the gneiss‐granite rock, took place on the ridges and convex hills. Six pedons were examined using field investigation and laboratory soil characterization techniques. The degree of pedogenesis on the various geomorphic surfaces supports the landscape evolution theories of Penck and King. A Typic Hapludox, with the greatest degree of pedogenesis, formed on the stable summit position, MGS1. The upper part of the retreating slope, MGS2, bevels MGS1, and the material eroded from MGS2 moved downslope and formed a surface with lower gradient, MGS3. Dystrochrepts are on shoulder positions and shallow Hapludox are on backslope positions of the geomorphic surface MGS2, and Kandiudults formed on footslopes, MGS3. Eutrochrepts are on the youngest surface MGS4, a toeslope position.
Water and Erosion Management with Multiple Applications of Polyacrylamide in Furrow Irrigation
Authors: Sojka R. E. , Lentz R. D. , Westermann D. T.
Published: July 2010

Polyacrylamide (PAM) in furrow irrigation water eliminates 94% of runoff sediment. Higher infiltration (15–50%) can result in upperfield overirrigation. We hypothesized that PAM would lengthen advance time, but that interactions with flow rate and wheel‐track (WT) furrows would occur, influencing erosion and infiltration with potential for improved water management. A 2‐yr study conducted on 1.5% slope Portneuf soil (Durinodic Xeric Haplocalcid) was irrigated with 10 g m‐3 PAM in advancing 23 L min‐1 furrow streams (reduced to 19 L min‐1 after advance) (PAM treatment, P) or without PAM (control, C). Initial inflows in 1994 were 23 L min‐1 (normal flow rate, N) or 45 L min‐1 (high flow rate, H) with or without PAM. The application of PAM at 23 L min‐1 (PN) increased 2‐yr mean advance time 33% and reduced runoff soil loss 88% compared with controls (CN). Polyacrylamide applied at 45 L min‐1 (PH) reduced advance time 8% and soil loss 75% compared with CN, whereas untreated 45 L min‐1 inflows (CH) cut advance time 42% but raised soil loss 158%. The CH and PH raised infiltration 11 and 35% more than CN respectively. Polyacrylamide halted erosion in all furrows, but in WT furrows had no effect on advance time and little infiltration effect after two or three irrigations. This is mainly attributed to erosion and deposition increasing control‐furrow wetted perimeters; accumulated PAM may also slightly affect seal conductivity. Polyacrylamide raised aggregate stability from 54 to 80% in 1993 and from 63 to 84% in 1994. In 1994, PAM reduced soil strength in furrows from 1.7 to 1.1 Mpa.
Macroporosity and Hydraulic Properties of Earthworm‐Affected Soils as Influenced by Tillage and Residue Management
Authors: Trojan M. D. , Linden D. R.
Published: July 2010

Macropores affect infiltration of water and solutes in soil. A field study was conducted to determine the effect of tillage‐residue management on earthworm development of macropore structure and the infiltration properties of a silt loam soil cropped in continuous corn. Tillage treatments included rototilled and nontilled soils, with or without residues, and innoculated with earthworms. Infiltration properties were measured with an instantaneous infiltration test of a 1.61 cm pulse of 0.5% methylene blue solution and by measuring steady‐state infiltration rates at +5, 0, −3, and −12 cm pressures. There were no significant tillage‐residue effects on steady‐state infiltration rates. The time required to reach steady state was 930 and 1020 s in treatments with residues, compared to 180 and 415 s in treatments without residue. Dye solution infiltrated in 22 and 217 s in no‐till and tillage‐with‐residue treatments, respectively, compared to >544 s in the remaining treatments. Estimates of effective porosity calculated using infiltration data and by counting stained macropores with depth were 0.85 and 1.3% in no‐till and 0.99 and 0.29% in tillage‐with‐residue treatments, respectively. In no‐till treatments, large quantities of dye solution, unaccounted for by steady‐state measurements, infiltrated rapidly and were stored in deep, surface‐connected earthworm macropores. In tillage‐with residue treatments, infiltration of dye solution, unaccounted for by macropore stained count measurements, occurred along partially incorporated residue pieces. Measurements of infiltration properties should include measurements of early infiltration and storage in macropore systems (ponded tests) and of steady‐state infiltration into the soil matrix (tension infiltrometry) once the macropore system has filled with water.
Field Calibration of a Neutron Moisture Meter in Vertisols
Authors: Corbeels M. , Hartmann R. , Hofman G. , Van Cleemput O.
Published: July 2010

Accurate calculation of water use efficiency is critical in evaluating innovative crop management practices under limited moisture conditions. The use of a neutron moisture meter is advantageous where repeated, non‐destructive measurements are needed, but it requires a particular calibration procedure in Vertisols. The purpose of this study was to produce a field procedure for unbiased volumetric moisture content calculations using a neutron moisture meter. Two methods of calibrating a neutron moisture meter in the field were compared. The methods differed in their soil sampling procedures. The first method employs undisturbed core and clod sampling adjacent to the access tubes. This method is destructive with respect to the access tube. The second method employs disturbed soil sampling using a screw auger a few meters from the access tubes. This method is less laborious and non‐destructive. Undisturbed soil samples adjacent to the access tube are representative for the sphere of influence of the neutron moisture meter and their bulk density‐moisture content relationships follow a normal one‐dimensional shrinkage model. The precision of the calibration was increased by correcting for changes of bulk density with changes of water content. The two methods of calibrating gave highly significant (P < 0.001) correlation coefficients. The second calibration method, however, introduced a bias of ≤20% at the dry end of the moisture range. At wilting point this bias was 10%. Separate calibration equations were necessary for the different horizons of the soil. Based on the calibration with correction for bulk density effect, a polynomial function can be derived that relates neutron count ratio with gravimetric water content; thus, we assumed one‐dimensional shrinkage. For volumetric moisture determinations at field level, gravimetric water content was converted to volumetric on the basis of a three‐dimensional isotropic shrinkage model.
Time Variance Analysis of Preferential Solute Movement at a Tile‐Drained Field Site
Authors: Lennartz B. , Michaelsen J. , Wichtmann W. , Widmoser P.
Published: July 2010

Preferential flow has been identified as an important secondary process to transport through the soil matrix in controlling solute movement in soils. However, it remains unknown to what extent a fast‐transporting flow regime governs solute leaching and whether it persists for various seasons at field scale. For 3 yr, KBr was applied in late autumn to the surface of a tile‐drained field site (0.5 ha in size) and monitored in drain outflow for 5 mo each year. All three seasonal breakthrough curves (BTC) were dominated by an early first concentration maximum and intensive tailing, indicating preferential flow to be a strong intrinsic soil property at the experiment site. A bimodal probability density function (pdf) was adequate to describe the concentration courses of the first 2 yr of investigations. The coefficient of determination was not satisfying when the model was fitted to the BTC of the last season, which was the only one to have a distinct secondary (matrix) peak. The optimized weighting factor combining the two pdfs suggested that preferential transport mechanisms governed the flow process to about 60% during all 3 yr. Simple linear regression analysis among flow rates and solute concentrations showed that both measures increased and decreased simultaneously during the early stages of the first test, which was interpreted as a confirmation of the dominance of preferential flow. The same method, however, revealed that Br‐ was leached predominantly through the soil matrix during the corresponding observation period of the last season.