bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon, Nitrogen, and Sulfur Pools in Particle‐Size Fractions as Influenced by Climate
Authors: Amelung W. , Zech W. , Zhang X. , Follett R. F. , Tiessen H. , Knox E. , Flach K.‐W.
Published: July 2010

The response of soil organic matter (SOM) dynamics to climate change may be deduced from changes in the distribution of SOM among different C pools. The distribution of soil organic carbon (SOC), total N, and total S in particle‐size fractions were measured to assess the influences of climate. Clay (<2 µm), silt (2–20 µm), fine sand (20–250 µm), and coarse sand (250–2000 µm) fractions were obtained from composite soil samples from the top 10 cm of 21 native grassland sites along temperature and precipitation transects from Saskatoon, Canada, to southern Texas, USA. The clay fraction contained about 43% of the total SOC, 56% of the total N, and 62% of the total S. The SOC and total‐N concentrations in the clay fraction, relative to those in the bulk soil, increased significantly across sites with increasing annual temperature, decreasing annual precipitation, and decreasing clay content (multiple R2 = 0.80*** [significant at P = 0.001] for SOC and 0.83*** for N); the concentration of SOM in the fine sand fraction showed the opposite trends. Principal axis component analyses confirmed that both clay and fine sand fractions comprised sensitive SOC and N pools related to climate, whereas S seemed to be controlled by factors other than those regulating the dynamics of SOC and N. These results suggest that SOM is preferably decayed from pools of the fine sand fractions with increasing temperature, resulting in a relative enrichment of SOM stabilized on clay.
Zinc and Cadmium Effects on Rhizobia and White Clover using Chelator‐Buffered Nutrient Solution
Authors: Ibekwe A. M. , Angle J. S. , Chaney R. L. , van Berkum P.
Published: July 2010

Toxicity of metals to plants and microbes depends on the chemical activities of metals in the soil solution. To examine the effects of Zn2+ and Cd2+ activities on white clover (Trifolim repens L.), Rhizobium leguminosarum bv. trifolii, the infection process, and nodulation, a growth chamber study was conducted. The chelator EGTA [ethylenebis(oxyethylenetrinitrilo) tetraacetate] was used to buffer Zn2+ and Cd2+ activities in nutrient solution from pZn2+ = 8.0 to 5.0 and pCd2+ = 10.5 to 8.0 mol L−1. Plants grown in pZn2+ = 5.0 and pCd2+ = 8.75 and 8.65 were stunted and chlorotic with interveinal necrosis. Shoot concentrations of Zn and Cd averaged >200 and 40 mg kg−1, respectively, in these treatments. This resulted in a 60% yield reduction for plants grown in pZn2+ = 5.0. In pCd2+ = 8.75 and 8.65, 40 and 60% yield reductions, respectively, were observed. In treatments where mineral N was supplied to plants, 20 to 35% greater shoot yield was recorded compared with plants inoculated with rhizobia, presumably due to a period of starvation for N due to the delay in the onset of fixation. Nodulation was observed at all Zn2+ and Cd2+ activities. At pCd2+ = 8.75 and 8.65, however, there was a delay in nodulation. Most nodules were effective in N2 fixation irrespective of Zn2+ and Cd2+ activity. Enumeration of viable cells showed a significant decline of total cell counts from 105.5 cells mL−1 in the control to 105.0 and 104.5 cells mL−1 at the highest Zn2+ and Cd2+ activities, respectively. At the activities studied, Cd was more toxic to rhizobia and nodulation than Zn. At the highest Cd2+ activity, however, plants were killed within 48 h due to metal toxicity. This technique showed for the first time that toxicity of Zn and Cd was greater to plants than to rhizobia.
Two Indices of Soil Structure Based on Prediction of Soil Water Processes
Authors: Geeves G. W. , Murphy B. W. , Cresswell H. P.
Published: July 2010

Evaluation of soil structure should reflect the nature and degree of soil physical limitations to land use for local climatic conditions. This can be achieved through mechanistic simulation of soil‐plant‐atmosphere processes. We propose two alternative indices of soil structure, based on predicted infiltration. The potential runoff index (PRI) is the runoff predicted from a 1‐in‐20‐yr average recurrence interval storm event of 30‐min duration using an event‐based soil water infiltration model that utilizes Richards' equation. The runoff recurrence index (RRI) is the average recurrence interval of a 30‐min duration storm of intensity just sufficient to result in runoff. These indices were applied to data from 37 sites (mainly Palexeralfs, but including Natrixeralfs, Rhodoxeralfs, and Haploxeralfs) in southeastern Australia, where rainfall partitioning between infiltration and runoff can significantly affect agricultural production. Sites with different land use histories were ranked on the basis of the RRI. Woodland sites have a significantly greater mean ranking (mean ranking [RRI] = 33.5), indicating more favorable soil structure, compared with less conservative agricultural land uses such as heavily grazed pasture (mean ranking = 11.7) or intensively cultivated cropping where stubble was not retained (mean ranking = 12.4). Both indices integrate the effects of soil structure, as represented through soil hydraulic properties, with local rainfall characteristics. They also account for soil horizon interactions influencing infiltration. The saturation‐excess runoff generation predicted for 12 of the 37 sites indicates that structural amelioration of B horizon soil should be a high priority at these sites.
Forest Soil Sulfur in the Adirondack Mountains: Response to Chemical Manipulations
Authors: Mitchell Myron J. , Santore Robert C. , Driscoll Charles T. , Dhamala Bhesh R.
Published: July 2010

Chemical manipulations were conducted on plots during the growing seasons from 1991 through 1993 in four forest ecosystems (Woods Lake [WL], Pancake‐Hall Creek [PHC], Huntington Forest [HF], and Pack Forest [PF]) in the Adirondack Mountains of New York. Sulfate was added as (NH4)2SO4 (all sites at 1000 and 2000 molc ha−1 yr−1), H2SO4 (WL and HF at 1000 molc ha−1 yr−1), or (Ca,Mg)SO4 (WL and HF at 1000 molc ha−1 yr−1). At WL and HF additional sets of plots were also treated with HNO3 (1000 molc ha−1 yr−1). Soil solutions were sampled at 15 and 50‐cm depths. Changes in the S constituents of the soil were evaluated by buried mineral soil bags installed below the forest floor. Additions of SO2−4 increased solution SO2−4 and total S and phosphate‐extractable SO2−4 in soil. Although organic S constituted >71% of the total soil S, no treatment effects on organic S were found. The response of SO2−4 was not influenced by the form of addition. Extractable sulfate and soil solution SO2−4 both increased with increases of (NH4)2SO4. For the three hardwood sites (WL, PHC, and HF), there was a positive relationship (P < 0.05) between soil solution SO2−4 concentration at 15 cm and extractable SO2−4 in soil bags, suggesting that these Haplorthod soils responded similarly to S inputs. For the Typic Udipsamment at PF, beneath red pine (Pinus resinosa Aiton), no such relationship was found. The similarity of response of Haplorthod soils suggests that similar soils across the Adirondack Mountains will show synchronous responses to S inputs.
Nonhydrolyzable Organic Nitrogen in Soil Size Separates from Long‐term Agricultural Experiments
Authors: Leinweber P. , Schulten H.‐R.
Published: July 2010

Total N (Nt), hydrolyzed N, NH3‐N, and nonhydrolyzed N were determined in soil particle‐size separates from unfertilized or manured treatments in five long‐term (15–108 yr) experiments in Germany. The concentrations of all N fractions (i) increased with decreases in particle size and (ii) were higher in samples from manured treatments. Irrespective of particle size and soil management, nonhydrolyzed N accounted for 7 to 31% of Ni (mean: 19%). On average, 53% of nonhydrolyzed N could be volatilized by pyrolysis. Field ionization mass spectra of the pyrolyzates of two hydrolysis residues showed that N heterocycles are major constituents of nonhydrolyzed N. In addition, 28 to 34% of total ion intensity was assigned to low‐mass N compounds and aliphatic nitriles and amides. Shifts to higher volatilization temperatures with maxima at 450 to 520°C in the thermograms of all N compounds indicated that chemical stability, or strong bonds to soil minerals, are main reasons for the resistance of these molecules to acid hydrolysis. Curie‐point pyrolysis‐gas chromatography/mass spectrometry using a N‐selective detector and library searches enabled the identification of aliphatic, carbocyclic, and aromatic amines and nitriles, benzothiazole, substituted imidazoles, substituted pyrroles and pyrrolidine, substituted pyrazoles, an isoquinoline derivative, substituted pyrazines and piperazine, pyridine, and methylpyridine. In addition, low‐mass N compounds such as hydrocyanic acid, N2, nitrogen monoxide, isocyanomethane, and hydrazoic acid were assigned so that, in total, 37 compounds were identified in the pyrolyzates of nonhydrolyzed N. Within this fraction, we distinguished (i) proteinaceous materials, nonhydrolyzable probably due to binding or occlusion by pedogenic oxides, and (ii) highly alkyl‐substituted N heterocycles, which are structural constituents of stable humic substances.
Soil Solution Speciation of Lead(II): Effects of Organic Matter and pH
Authors: Sauvé Sébastien , McBride Murray , Hendershot William
Published: July 2010

The effects of adjusting the levels of soil organic matter in a Pb‐contaminated soil on the solubility and free Pb2+ speciation were studied within the pH range 3 to 8. A contaminated orchard soil containing 284 mg Pb kg−1 was treated with leaf compost to increase soil organic matter and with H2O2 to decrease it, yielding six soil organic matter levels between 25.6 and 83.7 g C kg−1. The equilibrated solutions were then analyzed for total dissolved Pb by graphite furnace atomic absorption spectrometry and for labile Pb by differential pulse anodic stripping voltammetry (DPASV). The labile Pb values were used to calculate the free Pb2+ activity based on the assumption that organo‐Pb complexes are not DPASV‐labile. The data showed that 30 to 50% of dissolved Pb is present as soluble OM complexes at low pH and up to 80 to 99% at near‐neutral pH. The solubility of Pb shows a linear decrease from pH 3 to 6.5 and is independent of soil organic matter in that pH range. From pH 6.5 to 8, higher pH promotes the formation and dissolution of organo‐Pb complexes, which increase Pb solubility. In this pH range, higher organic matter content results in higher concentrations of dissolved and labile Pb.
Survival of Pseudomonas fluorescens 2‐79RN10 in Clay Powders Undergoing Drying
Authors: Morra Matthew J. , Chaverra Martha H. , Dandurand Louise‐Marie , Orser Cindy S.
Published: July 2010

Although clay minerals differentially alter bacterial survival during desiccation, the mechanism responsible is speculative. Our objective was to determine how clay water content might control the enhanced survival of Pseudomonas fluorescens (Migula) 2‐79RN10 in the presence of various clays. Pseudomonas fluorescens 2‐79RN10 was suspended in phosphate buffer, mixed into Ca2+‐saturated pyrophyllite, kaolinite, clinoptilolite, and montmorillonite (0.5 mL of cell suspension g−1 clay), and air dried at 20°C. Bacterial colony‐forming units (CFU), gravimetric water, and water activity (aw) were determined when mixed and at 9, 14, 19, 28, and 48 h after mixing. Bacterial survival was greatest in air‐dried montmorillonite and lowest in kaolinite. The rate of change in aw, final aw values, and rate of gravimetric water loss were similar for all clays. However, aw values during the initial stage of drying varied because the same cell‐suspension volume was amended to equivalent weights of clays possessing different surface areas. The length of time prior to decreases in aw varied in the order: kaolinite > clinoptilolite > pyrophyllite > montmorillonite, a sequence inversely proportional to survival. Alteration of clay particle size and amendment with different cell‐suspension volumes showed that increased bacterial survival could be achieved by shortening the time aw remained elevated. Increased survival of 2‐79RN10 is thus promoted by cell‐clay interactions resulting from more rapid decreases in aw values during the initial stages of drying. Our results have relevance to bacterial survival in clay formulations and soil.
Human‐Influenced Soils from an Iron and Steel Works in Naples, Italy
Authors: Buondonno C. , Murolo M. , Pugliano M. L. , Ermice A. , Buondonno A.
Published: July 2010

The study of soils formed by human activities is one of the concerns of modern pedology. In Italy, data on highly human‐disturbed soils are not available. We investigated the soils from a recently dismantled iron and steel production plant, and compared them with natural soils in undisturbed adjacent areas. The industrial activity in question started 80 yr ago. The dominant morphology of the disturbed soils results from the stratification of materials used in and derived from the industrial process, which were variously mixed with earthy materials. Layers with variable thickness occur up to the 2‐m depth. The spoil layer sequence is rarely interrupted by an applied natural soil, or in situ formed horizons, indicating the continuity of material deposition. Natural subsurface primary horizons are either obliterated or highly disturbed. We also recognized highly disturbed soils without significant spoil materials. All soils show high variability in their characteristics. They also have morphological and chemical features, such as horizonation, pH, organic C and total N content, distinctly different from those of natural soils. Problems emerged in classifying the investigated soils consistently with the current requirements of the U.S. soil taxonomy. To overcome such difficulty, we propose the adoption of the foundric subgroup of the Xerorthents. Such soils may be of interest in the discussion of the International Committee on Anthropogenic Soils (ICOMANTH), which is charged with studying and defining criteria for an appropriate taxonomic classification of highly human‐influenced soils.
Duripans of Southwestern Idaho: Polygenesis during the Quaternary Deduced through Micromorphology
Authors: Blank R. R. , Cochran B. , Fosberg M. A.
Published: July 2010

There is uncertainty regarding the pedogenesis of duripans on the Owyhee Plateau of southwestern Idaho. Micromorphology was used to deduce the role of polygenesis in their formation. Data suggest that during the Pleistocene, duripans were cyclically subaerially exposed, then recovered by eolian dust. Two lines of evidence indicate past duripan exposure. First, sinuous laminar fabrics with lenticular voids, which occur within most duripan plates, are similar to the fabrics produced in arid regions by the action of lichens and cyanobacteria at the soil surface. Second, a laterally extensive air‐fall tephra layer in the middle of a duripan plate was deposited at one sampling location, indicating the duripan or protoduripan was exposed at the ground surface. A suggested model to explain the data is as follows: (i) during cold stages of the Quaternary, periglacial processes, possibly assisted by eolian deflation, caused the truncation of loose soil material overlying the duripan; (ii) cryptogamic organisms then colonized the exposed duripan surface and produced distinctive fabrics; (iii) in response to the increased production and delivery of eolian dust during interglacials, the duripan was recovered. Pedogenesis during interglacial times resulted in precipitation of CaCO3, thereby thickening the upward‐developing duripan and preserving micromorphological signatures of subaerial exposure. At higher elevations in this region, large‐scale removal of unconsolidated soil may have occurred during full glacial stages of the middle and earlier Pleistocene. Maximal development of duripans may require polygenesis.
Kinetics of Crop Residue Decomposition: Variability among Crops and Years
Authors: Gilmour John T. , Norman Richard J. , Mauromoustakos Andy , Gale Paula M.
Published: July 2010

A kinetic description of crop residue decomposition makes assessment of the global C cycle and nutrient cycling possible for a wide variety of crop production systems. It was the objective of this study to compare decomposition kinetics of soybean [Glycine max (L.) Merr.], rice (Oryza sativa L.) and grain sorghum [Sorghum bicolor (L.) Moench.] residues for 3 yr to determine if variability among years was similar to that among crops. Crop residues were incorporated into a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf) soil and incubated at 25°C under optimum soil moisture for 54 to 66 d. Initial (0–2‐wk) decomposition was related to crop residue organic N and C/N ratio, while subsequent decomposition was not related to these factors. Decomposition data were evaluated using first‐order kinetics and sequential and simultaneous decomposition models. As a result of the variability among crops and years, which was not related to residue characteristics (organic N or C/N ratio), it was concluded that mean estimates of rate constants and the rapid fraction would provide a reasonable estimate of crop residue decomposition for a variety of crops using either decomposition model. For the sequential model, mean rapid‐ and slow‐fraction rate constants were 0.025 and 0.0091 d−1, respectively, while the rapid fraction was 31%. Parallel values for the simultaneous model were 0.21 and 0.0080 d−1 and 20%.
Redox Status, Poultry Litter, and Phosphorus Solubility in Atlantic Coastal Plain Soils
Authors: Vadas P. A. , Sims J. Thomas
Published: July 2010

Artificially drained, agricultural soils in Delaware's Inland Bays watershed are high in P from poultry litter and fertilizer applications. The potential loss of P from these soils to drainage waters during soil reduction and reoxidation was investigated. Soil from three artificially drained, cultivated fileds and two wooded areas was collected and characterized as Fallsington sandy loam (fine‐loamy, mixed, mesic Typic Ochraquult), Pocomoke loamy sand (coarse‐loamy, siliceous, thermic Typic Umbraquult), and Osier loamy sand (siliceous, thermic Typic Psammaquent). Topsoils, unamended and amended with poultry litter (PL), and subsoils were reduced for 28 d and reoxidized for 14 d at 25 and 35°C. The soils were analyzed for pH, redox potential (Eh), soluble P and Fe2+, and P fractions (unoccluded Fe‐P and Al‐P, occluded Fe‐P and Al‐P, and Ca‐P) under oxidized, reduced, and reoxidized conditions. Reduction decreased Eh to moderately reduced (200–350 mV) and reduced (−100 to 100 mV) values, and increased pH (0.8 ± 0.1) and soluble Fe2+ (44 ± 24 mg/kg). Reoxidation returned Eh, pH, and Fe2+ to near initial values. Reduction increased soluble P in unamended cultivated topsoils (0.69 ± 0.42 mg/kg), decreased soluble P in amended cultivated topsoils (1.42 ± 1.31 mg/kg), but had little effect in subsoils or wooded soils. Reoxidation decreased soluble P in cultivated topsoils, but increased soluble P in subsoils and wooded soils. Reduction increased the extractability of all P fractions in cultivated topsoils (20 ± 12 mg/kg), but increased only Ca‐P extractability in subsoils and wooded soils (9 ± 3 mg/kg). Reoxidation decreased the extractability of these fractions to near initial values.
In Situ Estimation of the Gaseous Nitrous Oxide Diffusion Coefficient in a Sandy Loam Soil
Authors: van Bochove Eric , Bertrand Normand , Caron Jean
Published: July 2010

The estimation of gas exchanges with the soil is important when assessing gas emission to the atmospheric environment or gas consumption by the soil. This estimation often requires the measurement of the diffusion coefficient of the investigated gas. The aim of this study was to develop an experimental method creating limited soil disturbance and based on simple calculation procedures to determine the diffusion coefficient, Ds, for N2O in soils. This objective was achieved using a N2O mass flow meter that supplied a continuous and constant flow of gas from below the soil surface until a steady‐state N2O concentration gradient with depth was obtained. The coefficients of diffusion were calculated daily for 6 d, under steady‐state concentration gradient, using Fick's first law. The mean value of the diffusion coefficient for N2O was 1.26 × 10‐6 m2 s‐1 (CV = 25%) at 0.16 m3 m‐3 of air‐filled porosity. This value was validated by a transient‐state laboratory method using soil cores and compared with empirical estimations of Ds from air‐filled porosity determinations. The two experimental methods produced similar values for Ds and both provided more accurate estimates than the empirical models. The proposed method can be applied to other gases provided an empirical model relating Ds to Do (gas diffusivity in free air) is first established. A theoretical study identified the threshold air‐filled porosity values below which the flux density must be adjusted to maintain the validity of the Ds calculations.
Estimating Microscale Spatial Distribution of Conductivity and Pore Continuity using Computed Tomography
Authors: Rasiah V. , Aylmore L. A. G.
Published: July 2010

Despite the importance of information on the spatial distribution of unsaturated hydraulic conductivity (Kus) at microscale in soil, experimental determination of this property is difficult. The objectives of this study were to: (i) seek a simple, but reliable, procedure for the estimation of Kus at microscale and (ii) determine the sensitivity of the estimates to wetting‐induced changes in selected structural parameters (porosity, ɛ, surface fractal dimension, D, and pore continuity, PC). Using computer‐assisted tomography (CAT), spatial distributions of soil water content (θ) and changes in ɛ that occurred during wetting were monitored at 2 by 2 mm resolution at 1‐cm depth increments in water‐stable (WSA) and unstable aggregate (USA) columns. The Fuentes theoretical equation, which requires data on saturated hydraulic conductivity (Kɛ), θ, ɛ, and D, was used for the estimation of the spatial distribution of Kus. The spatial distribution of θ in WSA columns ranged from 0.113 to 0.327 cm3 cm‐3 and from 0.175 to 0.567 cm3 cm‐3 in the USA columns. The spatial distribution of ɛus ranged from 0.46 to 0.74 and was used in the computation of D and PC. Values of Kɛ ranged from 0.006 to 0.745 cm h‐1. The spatial distribution of Kus ranged from 6.87 × 10‐4 to 1.49 × 10‐2 cm h‐1 in WSA compared with 7.3 × 10‐4 to 4.11 × 10‐2 cm h‐1 in USA. Pore continuity, θ, D, and initial aggregate diameter (x) accounted for 94 to 95% of the variability in Kus distributions. The results indicate that reliable estimates of Kus distributions at microscale can be computed from single‐source CAT‐derived data on θ and ɛ.
Use of Statistical Tests to Describe the Basic Distribution Pattern of Iron Oxide Nodules in Soil Thin Sections
Authors: Arocena J. M. , Ackerman J. D.
Published: July 2010

Soil formation is often associated with the spatial reorganization of soil components, particularly Fe oxides. However, the methods available to describe the spatial distribution of Fe oxides generally lack measurable parameters that allow comparison between different types of soils. In this work, we demonstrate the use of statistical methods (e.g., χ2 goodness‐of‐fit test, mean, variance, and cluster coefficient) to describe the basic distribution pattern of Fe oxide nodules in soil thin sections. Using a computer, we mapped the spatial distribution (i.e., x and y coordinates) of Fe oxide nodules in six soil thin sections from the B horizons of three sandy soils from Alberta, Canada. We calculated the statistical tests at a range of grid sizes (2–10 mm) with a Fortran program to (i) examine the effect of grid size on the statistical description of the distribution and (ii) determine the “appropriate scale of observation” for each thin section. We defined this scale as the grid size at which the mean number of observation is at least five, which was found to vary in size from 5 to 9 mm in our samples. We recommend the determination of the appropriate scale of observation before any statistical description of the Fe nodule distribution. In all but one of our six samples, the statistical distribution of nodules was clustered; the remaining one was uniform in distribution. The methods described in this study provide statistical methods whereby results from different studies can be compared.
Least Limiting Water Range: Traffic and Long‐term Tillage Influences in a Webster Soil
Authors: Betz C. L. , Allmaras R. R. , Copeland S. M. , Randall G. W.
Published: July 2010

Rooting is a continuous response to the soil physical environment, but root responses in the field are sufficiently complex to require a least limiting approach. Rooting limitations of available water, soil aeration, and penetration resistance are linked into a least limiting water range (LLWR) as a function of bulk density (ρb). The LLWR concept and associated measurements were used to evaluate the impact of tillage and tracking on root and hydrologic environment at two depths in a poorly drained clay loam: (i) the 5‐ to 10‐cm depth in nontracked and tracked interrows of three long‐term tillage treatments (chisel plow, CH; moldboard plow, MB; and no tillage, NT); and (ii) a plow pan at 25‐ to 30‐cm depth. Soil shrinkage, ρb, saturated hydraulic conductivity, water retention characteristic (WRC), and penetration resistance characteristic (PRC) were all measured in undisturbed soil cores (5 cm long by 5 cm in diameter). Both the WRC and PRC included ρb as an independent variable. Linearized fits of the WRC and PRC, with R2 > 0.70, were sensitive to tracking and to CH vs. MB tillage; compaction in the plow pan and tracking in the NT reduced by 75% the impact of ρb on the PRC. Tracking reduced the LLWR as much as 0.04 to 0.06 m3 m‐3 in CH and NT treatments, but the reduction in the MB treatment was <0.02 m3 m‐3. Penetration resistance was more limiting than the wilting point in the NT treatment and the plow pan, but not in treatments receiving annual tillage. Aeration was more limiting than available water in the NT and plow pan than in the MB and CH. The LLWR portrayed a major soil structural impact on physical control of rooting. Soil hydraulic properties associated with the LLWR explained a compaction and drainage problem with conservation tillage that can be linked to shallow penetration of tillage tools in this poorly drained soil.
Hydraulic Gradient, Aging, and Water Quality Effects on Hydraulic Conductivity of a Vertisol
Authors: Moutier M. , Shainberg I. , Levy G. J.
Published: July 2010

Aging, manifested by an increase with time of the aggregate mechanical strength, has been reported recently to affect the response of a soil to water quality. However, experimental evidence demonstrating its effect on the hydraulic conductivity is lacking. We present the results of aging, hydraulic gradient, and water quality effects on the saturated hydraulic conductivity of disturbed smectitic soil samples (A horizon, Chromic Haploxerert). The effects of two hydraulic gradients (2.9 and 12) and two leaching durations (3–4 and 20 h) were tested. Soil consecutively leached with 0.5, 0.05, 0.01, and 0.003 M Cl‐ solutions (Na adsorption ratio, SAR = 10) or 0.5, 0.01 M Cl‐ solutions and deionized water (SAR = 0). The saturated hydraulic conductivity of the soil decreased with an increase in soil exchangeable Na percentage and a decrease in total electrolyte concentration. Also, the relative hydraulic conductivity of the soil decreased from 1.1 to 0.94 when subjected to a high‐hydraulic gradient treatment, and subsequently increased to 2.32 under prolonged leaching with 0.01 M Cl‐ solution of SAR = 0. This decrease was attributed to the compression of clay particles at the column outlet. The subsequent increase in hydraulic conductivity was ascribed to thixotropic stabilization of the clay fabric and cohesive bond development. The effects of hydraulic gradient and aging were less pronounced in soil in equilibrium with solution of SAR = 10 because the higher sodicity increased the repulsion forces between clay particles, thus reducing clay‐to‐clay contact. Some practical consequences were postulated concerning aging effect under field conditions.
Eolian and Associated Pedogenic Features of the Jornada Basin Floor, Southern New Mexico
Authors: Gile Leland H.
Published: July 2010

In the Jornada Basin floor of southern New Mexico, some eolian deposits are distinct whereas others are not readily identifiable, because slopes grade smoothly into adjacent deposits that differ greatly in age and morphology, with little or no landscape evidence to suggest such differences. This study was conducted to determine if soil characteristics would be helpful in establishing a chronology for eolian deposits in this setting. Totals of pedogenic carbonate at three sites and observations at other sites indicate at least six episodes of substantial erosion and deposition since downcutting of the Rio Grande Valley began in middle to early Pleistocene time. The first episode is recorded by ancient longitudinal dunes that occur just east of the Rio Grande Valley. Prominent stage V carbonate horizons in the dunes indicate that they probably started to form soon after valley entrenchment began. The second episode is marked by a late Pleistocene deposit with a stage III horizon and 289 kg m‐2 of carbonate. The third episode is recorded by a younger late Pleistocene deposit with a weaker stage III horizon and 137 kg m‐2 of carbonate. For the fourth episode, stage I carbonate associated with a late Holocene deposit totals 7 kg m‐2. One historical deposit accumulated during the fifth episode, soon after the 1880s and the introduction of large numbers of cattle. The final episode occurred after the great drought of 1951–1956. Both historical deposits consist of fresh‐appearing, stratified sediments. The late Holocene and late Pleistocene deposits may be eolian correlatives of drought‐caused alluviums. Pedogenic carbonate is a major morphological and analytical tool for estimating soil and landscape age, for determining possible eolian‐alluvial correlatives, and for estimating the timing of climatic changes and eolian events. Subtle erosion and deposition can profoundly alter the evolutionary progression from stage III to stage IV carbonate.
Calcified Fungal Filaments in the Petrocalcic Horizon of Eutrochrepts in Beauce, France
Authors: Bruand Ary , Duval Odile
Published: July 2010

Calcified filaments could be responsible for the induration of petrocalcic horizons, although they are absent or very rare in petrocalcic horizons with a porosity filled by needle‐fiber and micro‐rod calcite. The aim of this study was to show that calcified filaments were also numerous in these petrocalcic horizons, thus ensuring their high cohesion. Samples were collected in petrocalcic horizons of Eutrochrepts in Beauce, France. They were studied by scanning electron microscopy, and chemical analyses were performed using an energy dispersion spectrometer microprobe. Observations of fragments in the secondary electron mode showed a close packing of needle‐fiber calcite with micro‐rod calcite without any visible calcified filament. In the backscattered electron mode, observations showed numerous rounded voids, 0.5 to 1.0 µm in diameter within the packing of microrods. These voids and their walls exhibited similar morphological characteristics to those of the calcified filaments described earlier and interpreted as the remains of fungal hyphae. Chemical analysis of the rounded voids' walls, needle‐fiber calcite, and micro‐rod calcite revealed the presence of C and Ca as main elements and secondarily of Al and Si, but their respective compositions were not significantly different (P = 0.05). The C/Ca atomic ratio indicated that the analyses did not avoid resin, and that they cannot be used for discussion of calcite or calcium oxalate presence.
Depth‐Incremental Soil Properties under No‐Till or Chisel Management
Authors: Logsdon S. D. , Kaspar T. C. , Cambardella C. A.
Published: July 2010

Comparisons of bulk density between no‐till and chisel management systems have produced conflicting results in different studies. These conflicting results have been due to averaging across large depth increments (up to 30 cm) and by ignoring traffic patterns when sampling. A few studies have measured 2‐cm depth increments for soil from tilled plots, but few, if any, have measured 2‐cm incremental soil properties from no‐till and compared them with similar measurements from tilled management systems. The objective of this study was to compare no‐till and chisel management system effects on 2‐cm increments of the vertical soil properties both for sites with and without controlled wheel traffic in corn (Zea mays L.)‐soybean [Glycine max (L.) Merr.] rotation. The controlled traffic site consisted of Muscatine (Fine‐silty, mixed, mesic, Aquic Hapludoll) and Tama (Fine‐silty, mixed, mesic Typic Argiudoll) soils, and the site without controlled traffic had Downs soil (Fine‐silty, mixed, mesic Mollic Hapludalf). We collected soil samples in 2‐cm increments to the 30‐cm depth. On controlled traffic plots for the 0‐ to 2‐cm increment, soil bulk density from no‐till plots was less than from chisel plots for half of the cases, but for the 6‐ to 18‐cm depths, soil from no‐till was more dense than soil from chisel plots 61% of the time. There was no significant soil bulk density difference between tillage treatments for plots without controlled traffic. Results of tillage on residue, organic C, and crop yield were inconsistent. Chisel management did not result in less dense soil than no‐till unless traffic was carefully controlled.
Solute Movement in Uncropped Ridge‐Tilled Soil under Natural Rainfall
Authors: Jaynes Dan B. , Swan J. B.
Published: July 2010

Point injection of N fertilizers within the ridge of ridge‐tilled soils has shown promise in reducing nitrate leaching in short‐term rainfall simulation studies, but it has not been studied under natural rainfall throughout the growing season. At two uncropped locations, we measured the leaching of tracers injected into different ridge positions in established ridge‐tilled plots that were leached by natural rainfall. A point injector was used to inject conservative anionic tracers 100 mm below the soil surface every 38.1 mm along ridge‐top, ridge‐shoulder, and furrow positions. Movement of tracers was measured four times after tracer application by triplicate soil sampling with a 38.1‐mm‐diam. soil probe to a maximum depth of 1.22 m. Sample collection spanned a period of 102 d with 282 mm of cumulative precipitation after tracer application at the Boone site and 97 d with 314 mm of precipitation at the Treynor site. Mass recoveries of furrow‐applied tracer was significantly lower (P = 0.05) than ridge‐applied tracer on the last two sampling dates at both sites. There was no consistent difference in mass recoveries between tracers applied at ridge top compared with shoulder positions. Furrow‐applied tracer had lower concentrations in the soil profile than tracers applied to ridge‐top and shoulder positions after 40 d and 76 to 129 mm of precipitation. Tracer movement was essentially vertical below the ridges, with ≥96% of the recovered ridge‐applied tracer found below the ridges. Lateral spreading was more pronounced under the furrows, with ≥49% of the recovered furrow‐placed tracer found below the furrows. Fertilizer injection within the ridge shows promise for reducing leaching and potentially increasing nutrient availability to plants.
Seed‐Zinc Concentration and the Zinc‐Efficiency Trait in Navy Bean
Authors: Moraghan John T. , Grafton Kenneth
Published: July 2010

Some navy bean (Phaseolus vulgaris L.) cultivars are susceptible to Zn deficiency. Norstar and Voyager are examples of Zn‐efficient cultivars; Avanti and Albion are examples of Zn‐inefficient cultivars. The objective of this study was to compare growth and Zn accumulation, especially in seed, of these four cultivars. In field and greenhouse experiments, except under extremely low soil‐Zn levels, the two Zn‐efficient cultivars contained >25% higher seed‐Zn concentrations than did the two Zn‐inefficient cultivars. Both Albion and Avanti, but not Norstar and Voyager, were Zn deficient at a field site with a relatively high level of Zn (1.7 mg kg−1) extractable by diethylenetrinitrilopentaacetic acid (DTPA). The Zn‐efficiency trait was associated with higher levels of Zn in plant tops and was not associated with differences in P or Fe nutrition. Zinc deficiency delayed pod maturity most in the two Zn‐inefficient cultivars. Analysis for Zn in seed from routine breeder‐yield trials, in which a Zn‐efficient cultivar is not Zn deficient, is proposed as a suitable technique for selecting navy bean genotypes that are both agronomically Zn efficient and better sources of Zn for human nutrition.
Mineralogy and Water Quality Parameters in Rill Erosion of Clay–Sand Mixtures
Authors: Bradford J. M. , Blanchar R. W.
Published: July 2010

Accuracy of the prediction of rill erodibility can be improved, in part, through an increased understanding of soil variables controlling particle detachment. To test the hypothesis that rill erodibility of clay–sand mixtures increases (i) as the dominant clay mineral changes from montmorillonite to illite to kaolinite, (ii) as total salt in the eroding fluid decreases, and (iii) when Ca is replaced by Na, concentrated flow erosion tests were conducted by mini‐flume test procedures. Chelsea fine sand was mixed with 2 to 20% (w/w) Ca or Na forms of either kaolinite, illite, or montmorillonite, and water to a moisture potential of −490 Pa. Rill erodibility of Ca–montmorillonite–sand mixtures was 4 to 40 times less than for Ca–illite–sand and Ca–kaolinite–sand mixtures. Na–montmorillonite–sand mixtures were one‐half as erodible as Ca–montmorillonite, while Na–kaolinite and Na–illite were 3 to 25 times as erodible as their Ca forms. Decreasing salt concentration of the eroding fluid from 0.01 to 0.001 M in all cases decreased the critical shear stress value on average 0.8 Pa. Decreasing the salt concentration from 0.1 to 0.001 M had no effect on the erodibility of Ca–kaolinite and Na–montmorillonite, but increased the erodibility of Ca–illite and Ca–montmorillonite. The erodibility of clay–soil mixtures decreased from 9.6 to 0.04 ms m−1 as the water holding capacity of the clay in the mixture increased from 0.2 to 6.9 g g−1 and appears to be related to the effective surface area of the clay.
Bromide Leaching on a Piedmont Toposequence
Authors: Olson G. L. , Cassel D. K.
Published: July 2010

Solute leaching on the field‐scale is a poorly understood, complex process affected by local soil variation and landscape position. We hypothesized that Br ion leaching is a function of landscape position in a well‐structured, clayey soil on a Piedmont toposequence that had been in pasture for the previous 30 yr. Dry KBr, mixed with sand at a ratio of 12 g sand to 1 g KBr, was surface‐applied at a rate of 314 kg Br ha−1 on 24 May 1994 along two transects and allowed to move into the soil under natural rainfall conditions. Soil cores 0.90‐ and 2.00‐m‐long were taken 13 June and 20 Dec. 1994, respectively (corresponding to 20 and 210 d after Br application and 15 and 63 cm rain, respectively). The cores were subdivided into increments 10 or 15 cm, oven dried, and analyzed for Br. Centers of Br mass at both sampling times were significantly deeper in the footslope position (31 and 82 cm for June and December, respectively) compared with the shoulder and linear slope positions combined (25 and 70 cm for June and December, respectively), which was possibly due to lower clay contents (44 vs. 50% clay) and lower water retention (37 vs. 43 cm in the top meter in December) for the footslope vs. the linear and shoulder slopes combined, respectively. Predicted leaching depths were calculated from measured soil water content profiles and were positively correlated with observed depths to the center of Br mass for the Dec. 20 sampling (r2 = 0.35, P < 0.007). Anion leaching may be partially controlled by landscape position, and soils susceptible to initial rapid leaching may not necessarily be susceptible to sustained rapid leaching throughout the year.
Belowground Nutrient Dynamics Following Three Harvest Intensities on the Pearl River Floodplain, Mississippi
Authors: Schilling E. B. , Lockaby B. G. , Rummer R.
Published: July 2010

The influence of clear and partial cut harvests on belowground nutrient cycling processes was examined on the Pearl River floodplain, Mississippi. Foci examined by this study included fine root biomass and detritus, fine root production, fine root nutrient contents, soil respiration rates, and microbial biomass C, N, and P during the first year post‐harvest. Both the clearcut and partial cut initially reduced fine root biomass; however, fine root biomass levels within each treatment did not differ at this study's conclusion. Bimonthly fine root production within both the clearcut and partial cut declined initially following harvest; however, net primary production was greatest within the clearcut, followed by the partial cut, and lowest within the control. Soil respiration rates showed strong seasonal trends; however, increased soil respiration rates within the clearcut and partial cut were not found until almost 1 yr post‐harvest. Decreased microbial biomass C levels were observed following both harvests. Only the clearcut treatment significantly reduced microbial biomass N. No treatment effects were found regarding microbial biomass P. Herbaceous and woody vegetation recolonization was vigorous within the clearcut and partial cut harvests, strongly influencing fine root production levels and soil respiration rates. It appears that fine roots from naturally recolonizing vegetation play a large role in belowground C storage following disturbance. The rapid increases in fine root production and biomass following both silvicultural methods indicates that, within these ecosystems, the negative influences of harvesting on belowground C and nutrient pools may be short lived.
Spatial and Temporal Variability of Extractable Lipids as Influenced by Cropping History
Authors: Dinel H. , Nolin M.C.
Published: July 2010

Tillage and crop rotations may alter soil organic matter (SOM) content and quality. Organic matter content can be satisfactorily assessed by determining total organic matter and C content, but easily obtainable, reliable, and highly sensitive indicators of its quality are still lacking to assess its biological, chemical, and physical functions. The spatial and temporal distributions of diethyl ether–(DEE) and chloroform‐(CHCl3) extractable lipids and gravimetric DEE/CHCl3 and CHCl3/total extractable lipids (TEL) ratios were evaluated as indicators of organic matter quality in two soils of Agri‐Food Canada cropping system fields situated in Qu e ´ bec. Diethyl ether and TEL were significantly (P ≤ 0.001) more abundant under perennial than annual crops, indicating that the perennial crops were better suppliers of easily biodegradable organic matter. Chloroform‐extractable lipids remained relatively constant under both crop rotations, indicating that soil biochemical inertness was relatively the same. Spatial and temporal distributions of these indicators of soil organic matter quality closely correlated with total organic C and clay contents. The DEE/CHCl3 and CHCl3/TEL ratios proposed for assessing organic matter quality were very sensitive (P ≤ 0.01) in detecting changes in SOM status resulting from crop rotations and tillage practices.
Effect of Long‐Term, Biennial, Fall‐Applied Anhydrous Ammonia and Nitrapyrin on Soil Nitrification
Authors: Shi W. , Norton J. M.
Published: July 2010

Long‐term dryland wheat plots were established in northwestern Utah and maintained for 8 yr in a 2‐yr wheat‐fallow rotation. Nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyrindine] was applied with anhydrous ammonia (NH3) in the fall preceding wheat growth to retard nitrification. Our objective was to determine the effects of long‐term, biennial application of anhydrous NH3 with and without nitrapyrin on soil nitrification. We were particularly interested in the potential residual effects of the long‐term repeated applications of anhydrous NH3 and nitrapyrin. Nitrification potentials were measured in control (no added N) soil, or soil fertilized with anhydrous NH3 with or without nitrapyrin for both rotation phases. Nitrification potentials were higher in soils receiving anhydrous NH3 than in the control soil during the cropped rotation. Nitrification potentials in soils receiving anhydrous NH3 with nitrapyrin were similar to those of the control soils during the entire wheat fallow rotation period. Further, nitrification potentials in soils with a history of nitrapyrin use were significantly lower than in soils without nitrapyrin use when measured after 2 yr. We observed a transient increase in nitrification potentials with the application of anhydrous NH3 that did not last in the fallow year, suggesting that the long‐term, biennial application of anhydrous NH3 at a rate of 50 kg ha−1 had no residual effect on soil nitrifier population size. In contrast, our results suggest that the long‐term, biennial application of nitrapyrin did have a residual effect on soil nitrifier populations that lasted at least 2 yr.
Predicting Soil Phosphorus Buffer Coefficients Using Potential Sorption Site Density and Soil Aggregation
Authors: Wang X. , Jackman J. M. , Yost R. S. , Linquist B. A.
Published: July 2010

The phosphorus (P) buffer coefficient, a ratio of the increase in extractable P to the amount of applied fertilizer P, is a source of considerable uncertainty in determining the amount of fertilizer needed to meet crop P requirements. The use of clay as a predictor of the P buffer coefficient has been suggested for soils of similar mineralogy. However, it has not been satisfactory for soils with a wide range of soil mineralogies but relatively high clay content. The objective of this study was to improve the prediction of buffer coefficients using soil characteristics associated with the process of P sorption, such as mineralogy, surface area, and aggregation. The soil P sorption site density, estimated from detailed clay mineralogy, and reactive mass, the fraction of the total soil mass in the surface aggregates where newly added P can be sorbed, were used to predict the buffer coefficient. The P buffer coefficients of 10 soils with a wide range in P sorption were estimated by Mehlich 3, modified Truog, and 0.5 M NaHCO3 extractants for incubation periods of 32 and 180 d. The inclusion of P sorption site density and reactive mass substantially improved predicting the P buffer coefficients when compared with the P buffer coefficients predicted by only soil clay content. Statistical models showed that the P buffer coefficients were negatively correlated with both log of the P sorption site density and reactive mass. Thus, soils with fewer P sorption sites, lower reactive mass, and larger aggregate size will tend to have higher buffer coefficients, indicating that a greater portion of the added P remains plant available.