bluuebunny/crossref_metadata_2025 huggingface dataset:
Aluminum Leaching by Mineral Acids in Forest Soils: II. Role of the Forest Floor
Authors: James Bruce R. , Riha Susan J.
Published: July 2010

To simulate the effects of forest floor organic horizons on leaching of labile and nonlabile forms of Al from underlying mineral soil horizons by acid precipitation, albic (E), ochric (A), and spodic (Bs) mineral horizons were leached in the laboratory with 1.0 mM HNO3, 0.5 mM H2SO4, or NH4NO3 control solutions at ionic strength 0.01 with or without an Oi‐Oe‐Oa forest floor horizon sequence (FF) above each mineral horizon. Adding 2 and 0.5 cmolc (H+)/kg to the organic horizons and mineral soils, respectively, simulated snowmelt additions to the soils in mountainous regions of the northeastern USA, where lake acidification has been attributed to acid precipitation leaching of forest soils. Total Al concentrations in leachates from soil columns containing the E or A horizon below the FF were greater than the sum of the concentrations in leachates from the FF and mineral horizon when leached separately. This positive synergistic behavior of the FF‐mineral horizon sequences was also observed in the FF‐Bs horizon sequence when leached with the control solution, but the synergism was negative for both forms of Al when leached with the acids. Sulfuric acid leached less Al from the Bs horizon than did HNO3, regardless of the presence of an FF, but HNO3, H2SO4, and control solutions leached similar concentrations of Al from the E and A horizons. The FF effects on the mineral soil leachates were attributed to effects of Ca, SO4, NO3, and dissolved organic C leached from the FF to the mineral horizons since the FF removed nearly all added H+.
An Economical, Digital Meter for Gypsum Soil Moisture Blocks
Authors: Fowler W. B. , Lopushinsky W.
Published: July 2010

Most meters for soil moisture blocks are designed for use with relatively moist soils. This paper describes a meter that utilizes a frequency output proportional to block resistance and that is usable over a relatively wide range of soil moisture. Advantages of this meter are digital display, easy and reliable operation, low power drain, and simple economical design. It is stable with changes in temperature, lead length to sensors, and battery voltage. The meter functions satisfactorily with several types of commercially available gypsum blocks and provides good resolution of matric water potential in the range of −0.06 to −1.5 MPa.
Effect of Access Hole Properties on Soil Water Content Determination by Neutron Thermalization
Authors: Amoozegar A. , Martin K. C. , Hoover M. T.
Published: July 2010

Installation of snugly fitted neutron access tubes in uniformly sized holes is difficult to achieve in many soils. This is especially true for areas not readily accessible by heavy machinery. We evaluated the effect of access hole diameter and a kaolinite soil slurry placed around loosely fitted access tubes on soil water content determination by neutron thermalization. Uniformly sized 5.1 (control hole), 7.6, and 9.1‐cm diam. holes, and a nonuniformly sized 5.5‐ to 6.75‐cm diam. hole were constructed at the vertices of five 80‐ by 80‐cm square plots on a Cecil soil (clayey, kaolinitic, thermic Typic Hapludult) within a small pasture. An additional uniformly sized 5.1‐cm diam. hole was constructed 80 cm from the control hole at each plot. A 2‐in. Al irrigation pipe was used as access tubing. The access tubes were fitted tightly in the 5.1‐cm holes and were placed at the center of the larger holes. A kaolinite‐soil slurry was placed around the access tubes in the nonuniformly sized holes. Count ratios obtained at various depths in each hole type were linearly regressed against the count ratios for the corresponding control hole at each plot. While there was a statistically significant one to one relationship between the count ratios in the control and 5.1‐cm holes, the coefficient of determination (r2) was only 0.69. The r2's for the relationship between the count ratios for the control hole and the other three hole size treatments were between 0.61 and 0.72, and the regression coefficients (b) decreased with increasing access hole diameter. The calibration curve r2's for the 5.1‐, 7.6‐, 9.1‐cm holes and the slurry backfilled holes were 0.71, 0.62, 0.76, and 0.61, respectively. The slope of the calibration curves generally increased with increasing hole size indicating some loss of sensitivity with the larger holes.
A Simple Approximate Equation to Calculate Diffusivities from One‐Step Outflow Experiments
Authors: Valiantzas J. D.
Published: July 2010

Gardner's approximation for determining soil water diffusivities, D(Θ), from one‐step outflow experiments may deviate significantly from actual D(Θ) values. By the systematic analysis of a weighting function which corrects the Gardner's solution, a new simple and accurate equation is derived. Numerical outflow experiments were performed for a variety of arbitrary D(Θ) functions to demonstrate the validity of the equation. Results indicate that the suggested procedure is applicable even for nonlinear ln D(Θ) functions and is more accurate than other previous methods. The present equation has been applied to analyze one‐step outflow experiments in two soils. Numerical predictions of the outflow volumes are in good agreement with laboratory measurements.
Competitive Ion Exchange Behavior on Oxides
Authors: Schulthess C. P. , Sparks D. L.
Published: July 2010

Cation adsorption data using MnCl2 and the proton isotherm of a Si oxide were compared with pH as the variable. The cation adsorption data quantitatively correlated with the proton isotherm analysis; the H+/Mn2+ exchange ratio was 6.0. The presence of adsorption plateaus are due to pH‐dependent (step) reactions; this was suggested as the only reasonable explanation for adsorption isotherms covering several pH units. These plateaus are very important to surface adsorption modeling, and may be significant in determining experimental conditions for other soil and colloidal research. The proton isotherm obtained using the backtitration technique had some pH‐ and salt‐dependent shifts that may involve competitive reaction mechanisms between the ions in solution and the oxide surface. Cation adsorption studies were also used to determine the total number of sites available; this resulted in an initial estimate of 13.6 µmol m−2. The authors review several topics related to ion exchange modeling and data interpretation; emphasis is placed on avoiding an oversimplified view of the chemical nature of the solidaqueous phase.
Kinetics of Calcium‐Magnesium Exchange on Soil Using a Stirred‐Flow Reaction Chamber
Authors: Seyfried Mark S. , Sparks Donald L. , Bar‐Tal Asher , Feigenbaum Sala
Published: July 2010

Ion exchange reaction kinetics may significantly affect effluent concentrations under both laboratory and field conditions. One limitation to the study of exchange reaction kinetics has been the lack of appropriate methods. A stirred‐flow method that uses a constantly stirred reaction chamber with constant, steady inflow of the reactant solution and outflow of reactants and products was tested. The method allows for continuous sampling and accommodates a wide range of soil particle sizes. The basic assumption of a well mixed solution in the chamber has not been tested, however. That assumption was tested over a wide range of flow rates and found to be applicable. The measurable reaction rates using the stirred‐flow method were estimated using a simple empirical equation that allowed the use of the reaction half‐time (t1/2) to describe reaction rates. Values of t1/2 of 3 min and greater were detectable while a 0.3 min t1/2 was not detectable under the experimental conditions. Calcium‐Mg exchange on a Nordya sandy loam (Typic Rhodoxeralf) soil from Israel was investigated. Measured effluent concentrations were compared with values calculated assuming no adsorption preference for Ca or Mg, and assuming local equilibrium between adsorbed and solution phases prevailed. Effluent concentrations were accurately predicted when the reaction direction was from equilibrium with Ca solution to equilibrium with Mg, but not for the reverse. These results suggest that either the local equilibrium or the nonpreference assumption was not appropriate. Flow rate reduction and stoppedflow experiments indicated that local equilibrium prevailed. Equilibrium exchange isotherms obtained using the chamber indicated a preference for Ca over Mg.
Rheology of Mixed Kaolinite‐Montmorillonite Suspensions
Authors: Keren R.
Published: July 2010

The rheological characteristics of mixed kaolinite‐montmorillonite suspensions as a function of adsorbed ion (Na+ or Ca2+), montmorillonite concentration and suspension pH were studied in aqueous medium at a total clay concentration of 50 g kg−1 and 25 °C. The suspensions of kaolinite showed a Newtonian rheology regardless of the adsorbed ion and pH, indicating that neither structural breakdown nor orientation occurs during the flow. Non‐Newtonian rheology was observed when small amounts of montmorillonite (saturated by Na+ or CA2+ ions) were introduced into the kaolinite suspensions at pH values of 4.0 and 7.0. An association between kaolinite and montmorillonite platelets appears to take place, with the intensity (as inferred from the extrapolated shear stress and viscosity) higher at pH 4.0 than at pH 7.0. This association is probably due to the attraction between the positive charge on the pH‐dependent charge surfaces of kaolinite and the negative charge associated with the planar surfaces of montmorillonite. When the pH increases well above the point of zero charge of the pH‐dependent charge surfaces, the association between kaolinite and montmorillonite platelets is negligible.
Specificity of Arrowleaf Clover for Rhizobia and Its Establishment on Soil From Crimson Clover Pastures
Authors: Weaver R. W. , Sen D. , Coll J. J. , Dixon C. R. , Smith G. R.
Published: July 2010

Successful establishment of clover (Trifolium spp.) on soil requires that the appropriate rhizobia are present to establish an N2 fixing association. Experiments were undertaken in the laboratory to determine if the rhizobial requirements of arrowleaf clover (Trifolium vesiculosum Savi) were different from those of crimson clover (Trifolium incarnatum L.) because arrowleaf clover is often being sown in pastures that have previously grown crimson clover. Generally, rhizobia capable of nodulating crimson clover were also able to nodulate arrowleaf clover but fixed little N2. Soil collected from nine pastures that were growing crimson clover and had never been planted to arrowleaf clover contained rhizobia capable of effectively (nodules fixed N2) nodulating arrowleaf clover. Protein profiles of rhizobia isolated from nodules of arrowleaf and crimson clover grown on soil from one of the nine locations indicated that at least 12 rhizobial strains were present, and those that selectively nodulated crimson clover generally were not able to fix N2 or showed delayed nodulation on arrowleaf clover. When arrowleaf clover was grown on the same soil, four of the five strains that formed nodules on its roots were effective. It appears that arrowleaf clover was able to select effective rhizobia from a mixed population and that it may be successfully established on fields that have grown crimson clover, even though the rhizobial requirements for the two hosts are different.
Effect of Bedrock Porosity on Soils Formed from Dolomitic Limestone Residuum and Eolian Deposition
Authors: Levine S. J. , Hendricks D. M. , Schreiber J. F.
Published: July 2010

Differences in the weathering characteristics of dolomitic limestones have resulted in the formation of Haplustalfs and Calciustolls located in the northwestern Colorado Plateau of Arizona. The establishment of effective porosity in the parent rock has controlled important pedogenic processes such as decalcification and silicate clay illuviation. The underlying carbonate strata, the Kaibab Formation, are complex limestone‐dolomite‐chert marine rocks of Permian age. Pleistocene age meteoric waters have caused the dissolution and partial removal of CaCO3 and the establishment of a porous dolomite crystal framework. Under these conditions, soils forming in residuum are able to decalcify and to form argillic horizons. However, in more resistant limestones, compaction during burial has resulted in a nonporous micrite that retards calcite removal by meteoric waters. Under these conditions, soil profiles maintain a high CaCO3 content and silicate clay illuviation does not occur. Eolian dust is also important to soil formation on the Colorado Plateau; in particular, quartz in the coarse silt fraction (31–44 µm), and quartz and biotite in the very fine and fine silt fractions (2.0–11 µm). Micaceous clay minerals of residual and eolian origin are converted to montmorillonite in the Alfisols. A probable sequence of events for this transformation to occur is: (i) the removal of calcite from the dolomitic limestone bedrock and the formation of a dolomite crystal framework, (ii) the slow dissolution of dolomite and release of Mg2+ into solution, (iii) the incorporation of Mg2+ into the octahedral layer of the mica and the release of K+ from the mica interlayer position, and (iv) the illuviation of montmorillonite to form the argillic horizon.
Nutrient Flux Through a Loblolly Pine Forest Floor Using Simulated Rainfall
Authors: Duffy P. D. , Schreiber J. D. , McDowell L. L.
Published: July 2010

Simulated rainfall was applied to 1‐m2 forest floor plots in a 45‐yr‐old loblolly pine (Pinus taeda L.) plantation using a multiple‐intensity simulator. On Day 1, 127.0 mm was applied and on Day 2, 76.2 mm. Runoff, collected at intervals throughout the applications, was analyzed for total organic C (TOC), PO4‐P, NH4‐N, and NO3‐N. Deionized water (mean pH 5.3) and simulated acid rain (mean pH 4.2) were applied to two separate, replicate plots. The simulated acid rain reduced NH4‐N concentrations in runoff from 0.08 to 0.04 mg L−1 but did not affect TOC or PO4‐P. The TOC and PO4‐P concentrations in runoff from all simulated rainfall applications were 18 and 0.011 mg L−1, respectively. The NO3‐N concentration was 0.02 mg L−1 for nonacid applications; the effects of acid applications on NO3‐N were not determined because of analytical problems. Nutrient flux during nonacid rainfall applications for TOC, PO4‐P, NH4‐N, and NO3‐N were, respectively, 5.2, 0.003, 0.021, and 0.006 mg m−2 mm−1 of applied rainfall. The pH was higher in runoff than in the applied acid rainfall but lower than in the applied nonacid rainfall.
Aluminum Precipitation and Dissolution Rates in Spodosol Bs Horizons in the Northeastern USA
Authors: Dahlgren R. A. , Driscoll C. T. , McAvoy D. C.
Published: July 2010

The kinetics of Al precipitation/dissolution reactions in Spodosol Bs horizons from sites at Hubbard Brook, NH and Bear Brook, ME were examined. A mechanical vacuum extractor was employed to draw solutions through soil columns at solution/soil residence times between 0.3 and 100 h. Equilibrium was approached from conditions of both undersaturation and oversaturation to determine if a particular soil mineral controlled Al3+ activity. Column leachates were analyzed for major solutes followed by chemical speciation and calculation of mineral saturation indices. Our results showed that apparent equilibrium with respect to Al(OH)3 solubility was readily obtained from both conditions of undersaturation and oversaturation within 0.3 h. Computed saturation indices, for an Al(OH)3 mineral with log K25C = 8.1, were identical at all examined residence times. Aquo Al (Al3+) within soil solutions may be regulated by the hydroxy‐Al interlayer of expansible 2:1 layer silicates. Soil solutions from Bear Brook also reached apparent equilibrium with imogolite at residence times in excess of 10 h. The laboratory results compared favorably with saturation indices calculated from stream and soil solutions at these sites.
Development Rates of Late Quaternary Soils, Silver Lake Playa, California
Authors: Reheis Marith C. , Harden Jennifer W. , McFadden Leslie D. , Shroba Ralph R.
Published: July 2010

Soils formed on alluvial fan deposits that range in age from about 35 000 to 200 yr BP near Silver Lake playa in the Mojave Desert permit study of the rates of soil development in an arid, hyperthermic climate. Field‐described properties of soils were quantified and analyzed using a soil development index that combines properties and horizon thicknesses. We compared the variability in index values from five independent descriptions of the same soil profile with the variability in values from four soils of the same age described by different people. The variability due to description accounts for between 30 and 80% of the total variability (that due to both the soils and description) for the properties described, which emphasizes the need for consistent soil descriptions. Pedogenic CaCO3 (as indicated by color), pH increase, and dry consistence appear to change with age at linear rates, whereas rubification appears to change at a logarithmic rate. The linear rates are best attributed to the progressive accumulation of CaCO3‐ and salt‐rich eolian dust derived from the playa and other more distant sources. The total‐texture values of soils on fans older than 10 000 yr BP are similar, which suggests that playas in this area may have been wet enough to restrict the availability of fines from these sources for many thousands of years prior to 10 000 yr BP. Index values for most properties of soils on the lower fans adjacent to the playa increase at faster rates than those of soils of the same age on the upper fans farther from the playa, probably due to the proximity to this local dust source. Equations derived from regressions of soil age and properties can be used to estimate ages of undated, lithologically similar deposits in similar climates and geomorphic settings.
Classifying Soils for Acidic Deposition Aquatic Effects: A Scheme for the Northeast USA
Authors: Lee J. J. , Lammers D. A. , Stevens D. L. , Thornton K. W. , Wheeler K. A.
Published: July 2010

The Direct/Delayed Response Project (DDRP) is estimating the number of lakes and streams in three U.S. regions that might become acidic due to current or altered levels of acidic deposition, and the long‐term time scales involved. Because of the influence of soils on aquatic chemistry, DDRP acquired data on soils that were mapped, sampled, and analyzed consistent methods across the regions. In the northeastern USA, about 600 soils (mainly phases of soil series) were identified during mapping of 145 watersheds. Because statistically adequate sampling of every soil was impractical, the soils were grouped into 38 sampling classes. Each of these classes was sampled across several (usually eight) watersheds. The properties of soils on specific watersheds (or portions of watersheds) can be estimated from the regional means and variances of the sampling classes and the percent occurrence of sampling classes on each watershed. This paper describes how the sampling classes for the northeastern USA were developed, the definitions of the classes, and the characteristics of soils within the classes. A preliminary statistical test indicates that the occurrence of sampling classes on watersheds is a significant predictor of Acid Neutralizing Capacity class of the corresponding lakes. Final evaluation of the utility of this scheme will come from the very extensive data analysis and modeling tasks of the DDRP.
Fertilizer Phosphorus Recommendations for Winter Wheat in Terms of Method of Phosphorus Application, Soil pH, and Yield Goal
Authors: Fiedler R. J. , Sander D. H. , Peterson G. A.
Published: July 2010

The objective of this study was to predict the most profitable amount of P fertilizer applied to winter wheat in terms of grain yield increase as influenced by soil test P, method of P application, and projected yield level. Winter wheat (Triticum aestivum) was grown in 22 field experiments between 1978 and 1982 with treatments consisting of six P rates applied with the seed and broadcast. The soils were Keith‐Holdrege and Uly‐Colby silt loam (fine‐silty, mixed mesic Typic Argiustolls). Yield increase to applied P was related by multiple regression to rate and method of P application, soil P level, soil pH, and grain yield level (R2 = 0.76, SE = 0.20 Mg ha−1). This function estimates maximum profit at specific fertilizer and grain prices. The regression function provides a mathematical solution for incorporating yield goal into fertilizer P recommendations. The model shows that P requirements for winter wheat increase as the yield level increases. Most importantly, the model indicates that it is economically prohibitive to follow the traditional recommendations of doubling the rate of broadcast P compared to seed applied P for winter wheat. When grain yields are increased with applied P, seed applied P results in much higher grain yield increase per kilogram of applied P than broadcast P. This results in being able to pay for more P when seed applied than broadcast. At medium and low levels of soil P, seed application resulted in 2 to 4 times more profit from fertilizer P application than broadcast P.
Analysis of Water Flow under Trickle Irrigation: II. Experimental Evaluation
Authors: Lafolie F. , Guennelon R. , van Genuchten M. Th.
Published: July 2010

A numerical solution for predicting soil water content distributions during trickle irrigation on stratified and anisotropic soils was compared with data from a field experiment carried out on a loamy clay soil using 24 field plots irrigated at different rates and frequencies. The unsaturated hydraulic conductivity was estimated from measured soil water retention and saturated hydraulic conductivities. Observed volumetric soil water contents and saturated areas on the soil surface were compared with model predictions. The effects of anisotropy and soil surface crusting on experimental and calculated soil water distributions were also investigated. Relatively good agreement was obtained between predicted and measured soil water content distributions vs. depth. The shape of the observed wetted soil volume was also predicted reasonably well. The effects of possible errors in the hydraulic characteristics on calculated water content distributions are discussed.
Method for the Sequential Extraction of Organic Matter from Soils and Soil Fractions
Authors: Schnitzer M. , Schuppli P.
Published: July 2010

The extraction of organic matter (OM) from soils is one of the unresolved problems in soil chemistry and biochemistry. To contribute to the solution of this problem, we developed a procedure for the extraction of OM in which the following sequence of extractants is used: (i) n‐hexane; (ii) chloroform; (iii) 0.1 M Na4P2O7 solution under N2; (iv) 0.5 M NaOH solution under N2; and (v) distilled H2O. The n‐hexane extracts alkanes and fatty acids; chloroform removes fatty acids, long‐chain alcohols, and wax esters; 0.1 M Na4P2O7 solution extracts OM “complexed” to metals and clays; whereas 0.5 M NaOH and H2O remove “free” OM, that includes less decomposed materials. The method was tested on three soils and 25 particle‐size fractions separated from these soils, which varied in mineralogical composition and OM content. Our data show that 0.1 M Na4P2O7 solution extracts relatively more OM from finer soil particles than from coarser ones while the reverse is true for 0.5 M NaOH solution. In general, OM is more readily extracted from soils low in clays than from those rich in clays. Between 35.4 and 80.9% of the soil‐C and between 21.0 and 75.6% of the soil‐N are solubilized. Determinations can be made at each step of the procedure of how much of the initial OM and which major components are extracted. Humic acids isolated from the 0.1 M Na4P2O7, 0.5 M NaOH and H2O extracts have analytical characteristics which are very similar to those of typical soil humic acids.
Cone Index Values Diagnostic of Where Subsoiling Can Increase Corn Root Growth
Authors: Vepraskas M.J. , Wagger M.G.
Published: July 2010

To identify root restrictive layers in a field using a penetrometer, a diagnostic cone index (CI) value indicative of restricted root growth must be known for the particular soil and crop. This investigation identified diagnostic CI values indicative of where corn (Zea mays L.) root abundance could be increased by subsoiling. Two tillage treatments were evaluated in seven Typic and Arenic Paleudults from 1985 through 1987. Penetrometer readings were made weekly in the plant row of both tillage treatments to a depth of 0.4 m. Roots were described primarily between 77 and 90 d after planting (DAP). Root observations were expressed on a proportional basis and were termed relative root abundance. Regression analyses showed that relative root abundance in the chiseled treatment was related to mean CI, depth, and clay percentage (R2 = 0.85). By 77 to 90 DAP, subsoiling significantly (P> 0.10) reduced mean CI as compared to the chiseled treatment at depths below 0.1 m, while significant increases in relative root abundance as a result of subsoiling were found primarily at 0.3 to 0.4 m. Diagnostic CI values for the chiseled treatment were identified where relative root abundance could be increased by subsoiling. Diagnostic CI values decreased with soil depth and increased with clay percentage. For a depth of 0.35 m, subsoiling was estimated to increase root abundance where the mean CI over a 3‐ to 5‐wk period was greater than approximately 1.5, 3.0, and 4.5 MPa for soil layers having clay percentages of 4, 12, and 20%, respectively.
Calibration of Nitrogen and Phosphorus Soil Tests with Yield of Proso Millet
Authors: Rodriguez J. B. , Peterson G. A. , Westfall D. G.
Published: July 2010

Current fertilizer recommendations for proso millet (Panicum miliaceum L.) are based on soil test calibrations developed for related crops such as corn (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench]. Therefore, their accuracy may be questionable. A study was initiated to correlate and calibrate the AB‐DTPA, Olsen P, Bray P‐1, and Mehlich P‐1 soil tests for P and the soil profile NO3‐N test with proso millet yields. Most of the soils studied were Argiustolls. Fourteen dryland field experiments were conducted from 1985 through 1987 in eastern Colorado. The experiments were N and P factorials with N levels of 0, 22, 45 and 67 kg ha−1 and P levels of 0, 8, and 17 kg ha−1. Profile soil samples were taken and analyzed for P by each of the soil P tests and for extractable NO3‐N. Grain yield was measured at maturity. Critical levels were established for each soil P and N test. Critical levels (point below which response to fertilizer is expected) were 6, 12, 20, and 35 mg kg−1 of P (0‐15‐cm sample depth) for the AB‐DTPA, Olsen P, Bray P‐1, and Mehlich P‐1 tests respectively. For N the critical level was 58 kg ha−1 in the 0‐ to 90‐cm soil profile. Soil test categories for each P test were established. The amount of P needed to correct deficiency and obtain maximum yield was 16, 12, 7 and 0 kg ha−1 for VL, L, M, and H categories, respectively. The amounts of N were 45, 25, 15 and 0 kg ha−1 for the respective categories.
Analytical Extensions of the Discrete Interface Penetration Model for Dynamic Permeability Analysis
Authors: Jennings Aaron A. , Ravi Varadhan
Published: July 2010

Discrete interface penetration modeling has recently been proposed to quantify the phenomenological domain response to permeants that substantially alter soil's hydraulic conductivity. Analytical solutions are presented here for a dual‐interface model compatible with constant‐head, constant‐flux, or falling‐head permeameter testing. It is demonstrated that the nondimensional transient saturated hydraulic conductivity response K̄(t) is independent of permeameter design. Solutions are also presented for the transient potential field φ̄(X,t) and interface locations X̄1(t), X̄2(t) that would accompany the infiltration episode.
Cadmium Buffering Capacity and Accumulation in Swiss Chard in Some Sludge‐Amended Soils
Authors: Kuo S.
Published: July 2010

Cadmium sorption by soils could be an important factor regulating the plant availability of soil Cd. Five soils containing varying amounts of Cd resulting from previous sludge application were analyzed for residual Cd availability under field conditions using Swiss chard (Beta vulgaris L.) as an indicator plant. The Cd accumulation was not highly correlated with DTPA (diethylene‐triamine‐pentaacetic acid)‐extractable Cd (R2 = 0.53). This result may be explained by a dissimilar response of plant Cd and DTPA Cd to soil pH. However, DTPA extracted 50 to 75% of sorbed Cd, depending on soil type. The recovery was little affected by the quantity of Cd sorbed. As such, DTPA Cd could be used to predict Cd accumulation by converting it to the quantity of Cd sorbed (Cds). The Cds was combined with the pH‐dependent Cd buffering capacity (BC) to obtain Cds/BC, an intensity factor for soil Cd. The buffering capacity is defined as the slope of the Cd‐sorption isotherm. The Cds/BC and plant Cd were highly correlated over all the soils, using the Michaelis‐Menten equation as a model (R2 = 0.83).
Factors Influencing Soil Structural Stability within a Growing Season
Authors: Perfect E. , Kay B. D. , van Loon W. K. P. , Sheard R. W. , Pojasok T.
Published: July 2010

Temporal fluctuations in soil structural stability within cropping treatments are often as large as differences between crops during the growing season. The relative importance of soil moisture, roots, and microbial biomass as factors contributing to this variation were investigated. Research was conducted on a fine‐silty, mixed, mesic Typic Eutrochrept intergrading to a fine‐silty, mixed, mesic Typic Haplaquept soil near Elora, ON. Six perennial forage treatments, established 2 yr previously, were compared with spring‐seeded conventional and zero‐till corn (Zea mays L.). The plow layer of each cropping treatment was sampled at monthly intervals. A combination of wet sieving and turbidimetry was used to provide a rapid assessment of wet aggregate stability (WAS) and dispersible clay (DC), respectively. On average, the forages had significantly less DC and greater WAS than the two corn treatments. Structural stability was found to decrease with increasing soil water content (r = 0.80 for DC and r = 0.74 for Was, both significant at P = 0.01). The corn soil experienced less extreme drying in the spring. Stepwise multiple‐regression analyses selected soil moisture and microbial biomass (in that order) as significant predictors of structural stability within the growing season. Using both parameters, it was possible to explain up to 85% of the temporal variation in DC and WAS on a by‐treatment basis.
Tillage Effects on the Spatial and Temporal Variations of Soil Water
Authors: Zhai R. , Kachanoski R. G. , Voroney R. P.
Published: July 2010

The objective of this study was to examine the effect of tillage on the spatial and temporal variability of soil water content of the surface layer (0–0.2 m) under a corn (Zea mays L.) crop. Soil water content was measured nondestructively every 1 to 2 d in fall moldboard (CT), 1‐yr no‐tillage (SNT), and longer term (>15 yr) notillage (LNT) plots using permanently placed time domain reflectometry (TDR) transmission line probes. The plots are located near Guelph, ON, Canada on a Typic Hapludalf (loam) soil. Sampling sites were in the corn row, directly between corn rows (interrow), and halfway between the row and interrow (quarter row). Systematic spatial differences in soil water content, within and between tillage treatments, were observed throughout the entire growing season. Large differences between CT and both LNT and SNT early in the season were attributed to increased evaporation in CT caused by spring secondary tillage. The drying rate in the LNT interrow position was much lower than the CT and SNT interrow drying rates. Soil water recharge from rainfall was distributed systematically in space because of canopy interception and subsequent stemflow. Crop residue on the soil surface of the no‐till treatments intercepted a significant amount of rainfall and reduced soil water recharge by 14 and 35% in the SNT and LNT treatments, respectively. The tillage treatments affected the temporal dependence of the spatial variability of soil water and the spatial dependence of the temporal variability.
Isolate Selection and Phosphorus Interaction of Vesicular‐Arbuscular Mycorrhizal Fungi in Biomass Crops
Authors: Hung L. L. , Sylvia D. M. , O'Keefe D. M.
Published: July 2010

Industrial sweet potato [Ipomoea batatas (L.) Lam, cv. White Star] and Napiergrass (Pennisetum americana × P. purpureum hybrid triploid PI 300086) have good potential for biomass energy systems. The objective of this research was to evaluate vesicular‐arbuscular mycorrhizal (vam) fungi for their ability to provide P to these crops across a range of soil P. To select effective vam fungi, cuttings of sweet potato were inoculated with nine isolates of fungi and were grown in soil with no P addition. Plants were evaluated after 3, 7, and 11 wk. To determine the range of soil P where these crops respond to vam fungi, experiments were conducted with sweet potato and Napiergrass, using at least two vam fungi and five P additions ranging from 0 to 198 mg P kg−1 of soil. Plants were evaluated after 4 and 16 wk. Sweet potato response to vam fungi ranged from growth enhancement to growth depression, compared to control plants. Both inter‐ and intraspecific fungal variation was observed. Total biomass production at 11 wk was correlated positively with root colonization at 3 wk, but not at 7 or 11 wk. Mycorrhizal dependency for both biomass plants decreased with P addition; nonetheless, growth was greater for plants inoculated with vam fungi and with up to 23 mg added P kg−1. The apparent ineffectiveness of the indigenous vam fungi, and the responsiveness of these biomass crops to selected vam fungi within a practical range of fertilizer P, may provide an opportunity for inoculation.
Relating High Soil Test Phosphorus Concentrations to Plant Phosphorus Uptake
Authors: Yerokun Olusegun A. , Christenson D. R.
Published: July 2010

The median P soil‐test concentration in Michigan has increased above the point at which a yield response is expected from fertilizer P application. This study was conducted to determine whether several soil‐P extractants reflect plant P uptake under high residual soil P conditions and to estimate the reduction in soil‐test P concentration as a result of crop removal. Initial P concentrations of the surface 0‐ to 15‐cm layer of ten Michigan soils were determined with Bray‐Kurtz P1, Bray‐Kurtz P2, Olsen, and anion‐exchange resin (AER) as extracting solutions. Ten consecutive crops were grown for 5 wk each on each soil. Phosphorus uptake by each crop was calculated from yield and composition. Linear correlation coefficients among the Bray‐Kurtz P1 and P2, Olsen P and AER P methods ranged from 0.79 to 0.99. Linear correlation coefficients between initial test P concentrations and cumulative P uptake were from 0.40 to 0.74. The highest correlation was with the Olsen extractant and the lowest was with Bray‐Kurtz P1 (1:20). A comparison of change in extracted soil‐P content with P uptake showed that the Bray‐Kurtz P1 extractant at a soil/solution ratio of 1:20 and the Bray‐Kurtz P2 extractant most closely estimated the magnitude of P removed by plants. On the cultivated soils, there was a change of 0.13 to 0.31 mg P kg−1 soil in the Bray‐Kurtz P1 soil test for each mg P kg−1 soil removed by plants.
Characteristics of “Coal Bloom” Horizons in Undisturbed Forest Soils in Eastern Kentucky
Authors: Sainju U. M. , Kalisz P. J.
Published: July 2010

Weathered coal seams (blooms) commonly occur at depths <150 cm under benches on steep slopes in eastern Kentucky. Since blooms are within the reach of tree roots and are C‐rich, they may affect nutrient availability and tree growth. This study was conducted to characterize the properties of blooms, and to examine growth and nutrient uptake by trees grown on blooms in the greenhouse. Samples were collected from eight profiles and properties of blooms were compared with those of overlying A horizons. Blooms occurred at a median depth of 68 cm and were generally loamy; coarse‐fraction concentrations were <100 g/kg, and bulk densities ranged from 0.56 to 1.25 Mg/m3. Compared with overlying A horizons, blooms had higher C (median values, 216 vs. 37 g/kg), total N (4.0 vs. 1.9 g/kg), and C/N ratios (48 vs. 21), and lower Ca (0.2 vs. 0.8 cmolc/kg), P (1 × 10−3 vs. 7 × 10−3 g/kg), and mineralizable N (8 × 10−3 vs. 50 × 10−3 g/kg). Available water capacity of disturbed samples (range 0.13–0.32 m3/m3) and pH (3.4–5.0) were similar for blooms and A horizons. Root densities were much greater in A horizons, but densities in blooms were greater than predicted for horizons formed at the same depth in colluvium. Yields and nutrient concentrations of yellow poplar (Liriodendron tulipifera L.) grown in the greenhouse on blooms were low, probably due to a shortage of available N. Blooms are of low fertility and apparently do not affect forest composition under natural conditions.
Water Vapor Transport through a Flail‐Chopped Corn Residue
Authors: Tanner C. B. , Shen Y.
Published: July 2010

Crop residue at the soil surface is known to decrease evaporation, and measurements have shown that wind increases evaporative loss through residues; however, to our knowledge, measurements of water vapor flux through residues have not defined their vapor conductance. The objective of this study was to measure the water vapor transport through crop residues in a wind tunnel and under natural wind and to parameterize the vapor conductance in a way useful for modeling the energy balance of conservation‐tillage systems. The vapor conductance of flail‐chopped corn (Zea mays L.) residue laid over large vapor sources (0.15 by 1.2 m) at different vapor‐pressure gradients was measured in still air and under winds. In still air, the vapor conductance of 10 samples of residue (areal density = 0.4 kg m−2; average thickness = 11 mm) averaged 2.2 mm s−1 at 20 °C and was not significantly different than the conductance of a similar thickness of air. Error in the measurement (CV = 13%) was sufficient that porosity and tortuosity effects on conductance could not be determined. Buoyancy‐driven convection in the flail‐chopped residue was negligible under much greater buoyancy instabilities than are likely to occur in the field. The vapor conductance (h) of nine samples of residue measured in a wind tunnel increased linearly with wind speed (V) measured at 1 m above the residue: h = (2.2 mm s−1) (1 + 0.89V), with a standard error of estimate (Syx) of 1.82 mm s−1. The regression coefficients of vapor conductance vs. wind found in the wind tunnel and under natural winds did not differ at P = 0.25. Based on our experience, measurements of conductance of other residues would be done much more easily in a suitable wind tunnel than in the field, and with the same results.
Water‐Drop Kinetic Energy Effect on Infiltration in Sodium‐Calcium‐Magnesium Soils
Authors: Keren R.
Published: July 2010

The effect of the complementary adsorbed ion (Ca vs. Mg) in the presence of Na on seal formation and water infiltration in two soils (Calcic Haploxeralf and Typic Rhodoxeralf) at several kinetic energies of water drops was studied using rain simulators. The infiltration rate (IR) of the soils was lower for the Na‐Mg soils than for the Na‐Ca soils at the studied kinetic energy range of the water drops (3.2–22.9 kJ m−3). The higher the kinetic energy, the steeper the drop in IR. The steady‐state IR and the cumulative water depth required to reach steady‐state IR were both decreased with increasing kinetic energy of the water drops. Adsorbed Mg on montmorillonitic soils had a specific effect on IR whether or not the soil contained CaCO3. Aggregates with adsorbed Na and Ca ions were more stable than those with adsorbed Na and Mg ions when they were exposed to water drops having a kinetic energy in the range of 8.0 to 12.5 kJ m−3. The specific effect of Mg on IR was explained by the presence of Mg ions on the external surfaces of the clay tactoids and the larger hydration shell of the Mg ion compared to Ca.
Phosphate Adsorption and Desorption by Goethites Differing in Crystal Morphology
Authors: Torrent J. , Barrón V. , Schwertmann U.
Published: July 2010

Goethite is an important component influencing phosphate adsorption in many soils and sediments. Little is known, however, about the relationships between crystalline properties and phosphate adsorption and desorption by this mineral. In this study we investigated the phosphate adsorption and desorption properties of 31 synthetic goethites differing widely in specific surface area, crystal morphology, and AIOOH mole fraction. The amount of phosphate adsorbed per unit surface area at pH 6 and an equilibrium concentration of 6 mg P L−1 was similar for all goethites (x̄ = 2.51, SD = 0.17 µmol P m−2), suggesting that the common crystal faces have similar P‐sorbing capacities. This condition is compatible with the existence of only (110) faces; in fact, according to transmission electron microscope (tem) observations, both natural and synthetic goethites seem to be bound by only (110) faces. The amount of phosphate nonextractable by 0.1 M KOH, and the amount not extracted by dissolving one layer of one‐unit‐cell thickness with an acid (HCl‐H2SO4) treatment, are related to crystal morphology: samples consisting of thin, multidomainic laths retain more P than those having thick, monodomainic crystals. It is hypothesized that the presence of V‐shaped interdomainic grooves and/or the slit‐shaped macropores of multidomainic laths accounts for stronger P bonding and/or low accessibility of the hydroxyl or hydronium ions.
Crust Formation Effects on Soil Erosion Processes
Authors: Moore Daniel C. , Singer Michael J.
Published: July 2010

Soil seals and crusts reduce soil infiltration rates and increase soil strength. How they affect the erosion process is not entirely clear. Effects of soil crusts at different stages of formation on soil erosion processes were analyzed and presented within the context of a model that divides crust formation into pre‐runoff, increasing runoff, and steady‐state runoff stages. Soil detachment trends accompanying crusting were characterized for Capay silty clay loam (fine, montmorillonitic, thermic, Typic Chromoxerert), Jacinto loam (fine‐loamy, mixed, thermic Mollic Haploxeralf), and Gridley coarse sandy loam (Typic Argixeroll). Soils crusts were formed on 61 by 61 cm2 plots inclined at 9% slopes using simulated rainfall applied at 42.5 mm h−1 as 3.2‐mm‐diam. drops falling 2.5 m. Photographs of crust surfaces were taken at selected times to provide additional morphological evidence to support conclusions drawn from erosion data. Soil splash and runoff materials were collected at intervals, and selected samples were analyzed for particle size distribution. In all three soils, erosion rates reached maximums during the period of increasing runoff, then decreased and tended toward equilibrium levels during the final, steady‐state runoff period. This suggests that crust formation decreases soil erodibility under these steady erosivity conditions. Splash erosion rates peaked during the period of increasing runoff, while wash erosion rates displayed a gradual increase over the periods of increasing and steady‐state runoff. These trends are related to the decreasing size and degree of aggregation of surface material available for detachement, and the buildup of a layer of overland flow that appeared to enhance splash detachment while retarding splash transport. Between‐soil differences in the rate of soil crust development, as inferred from progression through the three runoff stages, suggest an interaction between initial soil texture and soil aggregate stability.
Sampling Device to Extract Inclined, Undisturbed Soil Cores
Authors: Vepraskas M. J. , Hoover M. T. , Beeson J. L. , Carpenter M. S. , Richards J. B.
Published: July 2010

A sampling device was constructed to extract undisturbed cores of soil or similar material at angles between 0 and 90° from the vertical. The sampler consisted of a hydraulic cylinder suspended from an arm of a backhoe. Undisturbed cores (76‐mm in ht. by 76‐mm in diam.) were collected in metal rings, which were inserted into a Uhland‐type sample holder. The hydraulic cylinder pushed the sample holder into the soil material and also extracted it. Twenty‐five undisturbed, inclined cores could be collected with this device in 3 hr by three people. Saturated hydraulic conductivity was measured on 120 saprolite cores using a double‐ring permeameter to assess boundary flow. No boundary flow was detected between the sample ring and core edge. Examination of the cores' internal fabric, as seen in thin sections made from each of the 120 cores, confirmed that the cores were virtually undisturbed.
Quantification of Postsettlement Deposition in a Northwestern Illinois Sediment Basin
Authors: Kreznor W. R. , Olson K. R. , Jones R. L. , Johnson D. L.
Published: July 2010

The purpose of this study was to quantify the postsettlement deposition in a 24 900‐m2 (2.49‐ha) sediment basin with a single outlet in a 105 400‐m2 (10.54‐ha) watershed and estimate the sediment delivery to a first‐order stream in northwestern Illinois. Methods included direct measurements of the eroded sediment deposited in the sediment basin. Buried A horizons (dated using fly ash as a time marker) identify the presettlement (≈1854) surface, which was overlain by as much as 116 cm of sediment. Volume of the sediment within the basin was calculated at 11 394 m3 with a weight of 16 480 Mg. The modern soils of the sediment basin were characterized, classified, and the spatial variability of the sedimentation process was examined. Based on representative measurements of postsettlement sediment delivery obtained from research of drainage basins having similar size or soil characteristics, it was inferred that 20 975 Mg of sediment was delivered to the stream with a total of 37 455 Mg of soil being removed from the watershed hillslopes as a result of accelerated soil erosion. The measured rate of postsettlement sediment accumulation has been approximately 0.34 cm yr−1. Based on the tightly packed deposits, redeposition probably occurred as overland flow during storm events, rather than as overland flow occurring after a rainfall or as rain‐splash transport. However, machinery traffic and cultivation could have contributed to the high soil bulk density. Intensive cultivation, biotic activity, and freeze‐thaw are probably responsible for destroying any evidence of stratification.
Release of Nonexchangeable Potassium from a Highly Weathered, Forested Quartzipsamment
Authors: Comerford N. B. , Harris W. G. , Lucas D.
Published: July 2010

Long‐term K supply is often considered a function of the amount of K‐bearing minerals present. Hydroxy‐interlayered vermiculite (HIV) is a ubiquitous secondary mineral of the southeastern lower Coastal Plain and is now known to be associated with nonexchangeable K in these soils. Oxalate has also been shown to exist in millimolar quantities in these soil solutions. The objective of this study was to test the effect oxalate has on the potential solubility of K in a forested Quartzipsamment containing appreciable HIV in the < 50‐µm fraction, but no other detectable K‐bearing minerals. Samples were prepared, chemically extracted, and extracting solutions analyzed for K. We found that: (i) K can be released from clay and silt fractions by oxalate concentrations ranging from 1 to 150 mM and pH 3 to 6; (ii) sequential extractions with oxalate removed the most K during the first extraction with the silt being depleted of readily released K after three to four extractions but with the clay releasing K continuously over seven extractions; (iii) low pH was as effective in the release of K as oxalate at higher pH; (iv) after a 210‐ to 240‐d incubation of the extracted samples, re‐extraction resulted in high levels of K being released, even from the silt fraction that had been previously depleted; (v) electron microprobe analysis and K x‐ray images suggested that K contents were higher in the center of the phyllosilicate grains than near the edges.