bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐Term Soil Chemistry Changes in Aggrading Forest Ecosystems
Authors: Knoepp Jennifer Donaldson , Swank Wayne T.
Published: July 2010

Assessing potential long‐term forest productivity requires identification of the processes regulating chemical changes in forest soils. We resampled the litter layer and upper two mineral soil horizons, A and AB/BA, in two aggrading southern Appalachian watersheds 20 yr after an earlier sampling. Soils from a mixed‐hardwood watershed exhibited a small but significant decrease in soil pH. Extractable base cation content declined substantially in both mineral horizons. For example, Ca2+ levels in the A horizon fell from 236 kg ha−1 in 1970 to 80 kg ha−1 in 1990. Proportionally, the decline was greatest for Mg2+, which dropped from 111 to 20 kg ha−1. A white pine (Pinus strobus L.) plantation was planted in 1956, after clear‐felling hardwoods and recutting sprouts for 15 yr. Soil pH and base cation concentrations declined in the A horizon from 1970 to 1990. Soil pH declined from 5.9 to 5.0 and Ca2+ levels from 534 to 288 kg ha−1. Cation content did not change significantly in the AB/BA soil horizon. Nutrient budgets were constructed using these soil and litter data plus existing data on weathering rates, forest productivity, and hydrologic fluxes and associated chemistry. Decreases in soil base cations and soil pH are attributed to leaching and to the sequestration of nutrients in biomass.
Phosphate Sorption in Relation to Extractable Iron and Aluminum in Spodosols
Authors: Yuan G. , Lavkulich L. M.
Published: July 2010

Phosphorus is an important plant nutrient and of concern from the environmental point of view. Numerous studies on the relationship between P sorption characteristics and other soil properties have been done; however, most of these studies do not include originally sorbed (oxalate‐extractable) P (Po). Since Po accounts for 17 to 66% of the total sorption capacity (Po + Xm, where Xm is the P sorption maximum) in 43 Spodosol samples from British Columbia, Canada, it should not be ignored in P sorption models. The good correlations between oxalate‐extractable Fe and Al (Feo + Alo) and P sorption parameters (Po, Xm, or Po + Xm) indicate amorphous Fe and Al oxides are the major P sorbents in the soils studied. Phosphorus sorption capacity is predictable from Alo and Feo by two existing models. The relationship between organically complexed Al and P sorption parameters may be important in forest and soil management, since the organically complexed fraction is relatively easily altered if environmental factors or management practices change.
Micromorphological Characteristics of Long‐Term No‐Till and Conventionally Tilled Soils
Authors: Drees L. R. , Wilding L. P. , Karathanasis A. D. , Blevins R. L.
Published: July 2010

Conservation tillage practices have been shown to affect a number of soil physical properties, but less is known about their effect on the size, shape, and arrangement of soil constituents. To evaluate soil structural differences between tillage treatments, six paired conventionally tilled and no‐tilled plots of Maury silt loam soil (fine, mixed, mesic Typic Paleudalf) were analyzed. Oriented undisturbed samples (16 by 9.5 by 5.5 cm) were taken from each plot at depths of 0 to 5, 10 to 15, and 20 to 25 cm. The samples were impregnated with polyester resin and two vertical thin sections were prepared from each sample. The micromorphic features were described, and the size (equivalent spherical diameter), shape, and orientation of pores and aggregates were measured using an interactive image analysis system. The no‐tilled plots had platy structure near the surface and interconnection of fine pores (50–100 µm) throughout the profile. Eartbworm channels with excrement infillings were abundant in the no‐till plots at all depths, but absent in conventionally tilled plots. The conventionally‐tilled soil was composed of granular and fragmented structural units with no evidence of earthworm activity. The no‐till plots contained about 11% pore area >50 µm, compared with about 16% for conventional tillage management. However, the no‐till plots have an average pore size (0.18–0.26‐mm diam.) that is greater than the conventionally tilled plots (0.12–0.17‐mm diam.). The finer aggregate size of the conventionally tilled plots (0.25–0.39‐mm diam.) compared with the no‐till plots (0.41–1.08‐mm diam.) is probably due to plowing and disking.
Determining Almond Root Zone from Surface Carbon Dioxide Fluxes
Authors: Ben‐Asher J. , Cardon G. , Phene C. J. , Hutmacher R. B. , Peters D. , Rolston D. E. , Biggar J. W.
Published: July 2010

Size and distribution of roots in the soil is affected by irrigation method and water quantity and quality. The number of replications required to characterize it at a significant level is so large that it cannot be included in routine sampling. Our objective was to evaluate the effects of irrigation regimes on almond (Prunus amygdalus Batsch. cv. Butte) root zones from measurements of surface CO2 flux. A dynamic chamber quantifying the spatial distribution of CO2 fluxes at the soil surface was used to predict root distribution as affected by experimental treatment in an almond orchard. The treatments were two rates of water application by trickle irrigation and two salinity levels. Roots were sampled in a trench 3‐m width by 2‐m depth that exposed soil profiles. Soil‐surface CO2 flux was described by a descending function of the distance from the trunk of the tree. This function was combined to another regression model estimating the depth of the root zone from CO2 flux measurements. The combined model was used to describe the shape and the size of the root zone. Results show that favorable treatments are characterized by a larger root volume. The depth of the roots may exceed 1.5 to 2.0 m and lateral expansion 2.5 to 4.0 m even when water is applied by drip irrigation.
Clay Dispersion in Relation to Sodicity, Electrolyte Concentration, and Mechanical Effects
Authors: Curtin D. , Steppuhn H. , Selles F.
Published: July 2010

Clay dispersion is one of the major processes causing structural problems in lands irrigated with sodic waters. The dispersion characteristics of a group of prairie soils (Haploborolls) from southern Saskatchewan (Canada) were determined after reaction with solutions that had a range of sodium adsorption ratios [SAR = Na/(Ca/2)1/2, where concentrations are expressed in mmolc L−1], and electrolyte concentrations. When the input of mechanical energy was high (i.e., 16‐h shaking), a well‐defined threshold electrolyte concentration existed at each SAR, below which extensive clay dispersion occurred. The threshold concentration for dispersion ranged from 1 to 3 mmolc L−1 at SAR 0 and increased linearly as SAR increased to reach 21 to 50 mmolc L−1 at SAR 40. In contrast, when dispersion was measured after minimal shaking by hand, distinct thresholds were absent. Instead, dispersion increased gradually at each SAR as electrolyte concentration decreased. Threshold concentrations determined with low‐energy inputs are likely to be most indicative of field dispersibility. Such threshold values can be substantially lower than those measured using vigorous agitation techniques, particularly when sodicity levels are low. Our results do not support recent reports that silt dispersion is a better indicator of structural stability in the presence of exchangeable Na than is clay dispersion. Such findings are probably the result of an experimental artifact caused by the inappropriate use of Stokes' law in estimating the particle size distribution of soil suspensions. Simple tests of clay dispersibility in water or of aggregate stability may be useful in screening soils for sensitivity to sodic irrigation waters.
Long‐Term Management and Clay Dispersibility in Two Haploborolls in Saskatchewan
Authors: Curtin D. , Campbell C. A. , Zentner R. P. , Lafond G. P.
Published: July 2010

The water dispersibility of clay influences soil physical properties such as water infiltration, surface crusting, and water erosion. The development of the Water Erosion Prediction Project (WEPP) model, which uses water‐dispersible clay in the algorithm for estimating interrill erosion, has created a need to understand the factors controlling clay dispersibility. This study evaluated the effects of long‐term (≥24 yr) crop rotations and management on water‐dispersible clay in two contrasting soil types in southern Saskatchewan. Cultivated soils were 0.4 to 21 times more dispersive than nearby grassland soils. Among the rotation treatments, a 6‐yr rotation, which included 1 yr of summer fallow, 2 yr of spring wheat (Triticum aestivum L.), and 3 yr of bromegrass (Bromus inermis Leyss.)‐alfalfa (Medicago sativa L.) hay, had the greatest impact, giving dispersible clay values (151–244 g kg−1) that were substantially lower than those for continuous wheat (361–441 g kg−1) and wheat‐fallow rotations (354–483 g kg−1). Fallow frequency and fertilizer treatment had little effect. Water‐dispersible clay was negatively correlated (r = −0.79*** and −0.86***) with wet aggregate stability. The results suggested that both of these characteristics are influenced by organic binding agents produced during crop growth. Although soil management had a major effect on clay dispersibility, total clay content may be the dominant factor when a wide range of cultivated soil types are considered. However, management history and aggregate stability data should be taken into account when attempting to predict dispersible clay from total clay content.
Modeling Oxygen Diffusion in Aggregated Soils: II. Anaerobiosis in Topsoil Layers
Authors: Renault Pierre , Sierra Jorge
Published: July 2010

Denitrification may appear in soil anaerobic regions. In order to estimate the anaerobic fraction of a soil, a finite element method was used to simulate O2 diffusion and consumption in topsoil layers. The soil is considered as a set of aggregates of various shapes and dimensions. Their external transport areas are reduced by contacts between the aggregates and by areas covered with water in the intercrumb pore space. In some simulations, the role of water from the intercrumb pore space in partially occluding the aggregate surface area has not been taken into account. In this case, anaerobiosis only becomes significant near saturation and is due to the reduction of the intercrumb O2 diffusion. When water of the intercrumb pore space is considered, anaerobiosis appears at lower water contents and is due primarily to the reduction of the aggregate external transport area. In this case, O2 concentration in the intercrumb pore space is high at all depths, except near soil saturation. The results of this study were compared with some published relationships between the water saturation level and denitrification, obtained from experimental data. There is a good agreement between our calculations and these functions. In addition, our simulations show that the relationship between the soil anaerobic fraction and the water content is highly dependent on soil structure, soil temperature, and microbial activity. Thus, multiplicative functions are inadequate to describe the effects of water and temperature on soil anaerobiosis or denitrification.
Evaluation of a Mechanistic Model of Potassium Uptake by Cotton in Vermiculitic Soil
Authors: Brouder S. M. , Cassman K. G.
Published: July 2010

The Cushman‐Barber model was evaluated for K uptake by cotton (Gossypium hirsutum L.) from vermiculitic soils of high K‐fixation capacity and low solution‐phase K+ concentration. On these soils, cotton exhibits late‐season K deficiency while other crop species remain unaffected. Four soil treatments of NH4‐N, K, or both were combined factorially in a vertically split‐pot system to create eight plant treatments of different uniform and nonuniform soil nutrient environments. Depending on the treatment, initial model output produced both substantial under‐ and overpredictions of whole‐plant K accumulation. Model precision was greatly improved by changing the Michaelis‐Menten kinetic parameters for uptake at the root surface to reflect differences in shoot K/N balance, a more accurate measure of plant K demand in the presence of variable soil N supply. Regression revealed a linear relationship between the predicted and the observed K uptake (r2 = 0.87) but, across treatments, the model underpredicted accumulation by 43%. Model predictions were further improved by estimating soil buffer capacity from a Langmuir fit of a K adsorption isotherm rather than from the relationship between exchangeable solid‐phase and solution‐phase K pools. Sensitivity analyses were performed to identify key determinants of cotton K acquisition from vermiculitic soils of high K‐fixation capacity. The analyses demonstrated that both Michaelis‐Menten kinetic and soil supply parameters were strong determinants of K uptake on these soils and thus warrant more emphasis than previously suggested by model validations conducted on soils with greater K supply and less K‐fixation capacity.
Leaching Characteristics of Repacked Soil Columns as Influenced by Subsurface Flow Barriers
Authors: Kiuchi M. , Horton R. , Kaspar T. C.
Published: July 2010

Reducing the leaching of NO−3‐N is of great interest. The effects of different types of subsurface barriers on delaying and reducing anion leaching and the effect of barrier size on anion leaching were investigated. Three repacked soil columns filled with soil from a Sparta loamy fine sand (sandy, mixed, mesic Entic Hapludoll) mapping unit were used to run Cl− breakthrough experiments under saturated, steady‐flow conditions. Subsurface barriers used were no barrier (NB), a polyethylene disk placed above the Cl−, the same disk placed below the Cl−, a compacted soil layer created outside of the column and placed above the Cl− (CA), and a compacted layer formed in situ above the Cl−. Compared with NB, all barriers tested delayed initial breakthrough of Cl− and reduced peak Cl− concentration. Subsurface barriers delayed occurrence of the peak concentration, indicating that harriers prolonged residence time of Cl− in the soil column. Among subsurface barriers used, the CA was most effective in delaying and reducing Cl− leaching. Initial breakthrough of Cl− was delayed by 0.9 relative pore volumes, and peak concentration was reduced by >50% with the CA treatment compared with the NB treatment. The occurrence of the peak concentration was also delayed by 1.2 relative pore volumes. Compared with the NB treatment, a 3‐cm plastic disk, just large enough to cover the applied Cl−, reduced peak concentration of Cl−. A 5‐cm‐diam. barrier also delayed initial breakthrough of Cl−, reduced peak concentration by 40%, and delayed occurrence of the peak by 0.6 pore volumes.
Model Comparison of Unsaturated Steady‐State Solute Transport in a Field Plot
Authors: Costa Jose Luis , Knighton R. E. , Prunty Lyle
Published: July 2010

Models of solute movement in soil are seldom compared using independently generated data. The objectives of this study were to leach Br− through a Hecla fine sandy loam (sandy, mixed Aquic Haploboroll) and to compare the results with four previously published solute transport models. Solute was applied over the surface of four 9‐m2 subplots within a 65.5‐m2 plot and leached at constant rates: 1.28, 2.53, 4.28, and 5.94 µm s−1. Soil solution samples were taken from 0.3‐, 0.6‐, 1.0‐, 1.5‐, 2.0‐, 2.3‐, and 2.5‐m depths. At the same depths, water content and soil suction were measured using a neutron probe and tensiometers. Data from this experiment were used to evaluate four solute transport models. Model performance was evaluated using the observed to expected sum‐of‐squares ratio, the normalized objective function, and the Kolmogorov‐Smirnov statistic. A numerical finite‐difference solution of the convective‐dispersive equation (LEACHM) was more successful in predicting solute movement under unsaturated steady‐state conditions than the analytical solution for the convective‐dispersive equation (CDE), the continuous‐time Markov process (CTMP), or the transfer function model (TFM). The CTMP model predicts observed solute concentration better than the TFM. The TFM needs to be calibrated by a solute transport experiment while CTMP requires water flow and soil moisture as input data.
Extractable Soil Boron and Alfalfa Uptake: Calcium Carbonate Effects on Acid Soil
Authors: Su Chunming , Evans L. J. , Bates T. E. , Spiers G. A.
Published: July 2010

Since soil tests for B in fine‐textured soils give inconsistent predictions and the amendment of acidic soils with CaCO3 is a common practice, the suitability of extractants for plant‐available B in a CaCO3‐amended clayey soil was studied. This research investigated the pH effect on B adsorption, the changes in the amounts of hot‐water‐extractable B (HW‐B), mannitol‐extractable B (MANN‐B), and soil solution B (SOLN‐B) as a result of B and CaCO3 addition to a silty clay soil (a clayey, mixed, mesic Typic Humaquept) with an initial pH of 4.2. The relationship between the amounts of extractable B and B uptake by alfalfa (Medicago sativa L.) was also studied. Amounts of extractable B in soil were in the order HW‐B > MANN‐B > SOLN‐B, decreasing with increasing pH and after growth of alfalfa. Addition of 2.5 and 5.0 g CaCO3 kg−1 increased alfalfa dry matter yield; whereas addition of 0.5 and 1.5 mg B kg−1 had no effect. In the absence of added B, the B concentration in alfalfa shoots decreased with increasing pH. Linear correlations between B concentration in alfalfa shoots and extractable B in soil were significant for all three cuts and for all three extractants. Total uptake of B was significantly correlated with all forms of extractable B except HW‐B for the third cut only. Inclusion of pH improved the relationship for the other cuts. The dilution of B in plant shoots by CaCO3‐stimulated growth may result in B deficiency.
Tillage, Residue, and Rainfall Effects on Movement of an Organic Tracer in Earthworm‐Affected Soils
Authors: Trojan M. D. , Linden D. R.
Published: July 2010

A field study was conducted to determine the effects of tillage, residue, and rainfall on the movement of rhodamine WT (C29H29N2O5Na2Cl), a strongly adsorbed organic dye, in earthworm‐affected soils. Rhodamine WT was uniformly applied to the surface of two separate, 0.063‐m2 areas within either no‐till or conventionally tilled treatments in the presence or absence of residues. One area was exposed to a high intensity rainfall of 12 mm, whereas the second area received 193 mm of rainfall in 13 events during a 28‐d period. Following rainfall, soils were excavated in layers to a depth of 40 cm and dye concentrations were determined. For the single rain event, dye concentration at the 28‐ to 40‐cm depth was 1.20 and 0.63 mg kg−1 in the no‐till and conventionally tilled treatments containing residues, respectively, compared with concentrations near the detection limit (0.10 mg kg−1) in treatments without residues. For multiple‐rain plots, dye concentrations of 1.80 and 0.93 mg kg−1 were detected at the 28‐ to 40‐cm depth in the no till with surface residue and no till without residue treatments, respectively, compared with concentrations near the detection limit for the conventionally tilled treatments. Staining patterns indicated that earthworm channels were responsible for dye movement below 20 cm. The differences in dye movement for single‐ and multiple‐rain events suggests that properties of the macropore system, such as continuity and surface position, control preferential flow under differing tillage, residue, and rainfall conditions.
Legume Green Manures and Conservation Tillage for Grain Sorghum Production on Prairie Soil
Authors: Sweeney Daniel W. , Moyer Joseph L.
Published: July 2010

With increased emphasis on conservation tillage, information is needed on the use of spring‐ or fall‐seeded legumes as green manures for eastern Great Plains grain sorghum [Sorghum bicolor (L.) Moench] production. This study was conducted to determine whether legumes can be beneficial to subsequent grain sorghum crops grown in conservation tillage systems on prairie soil. Comparisons included the effects of (i) red clover (Trifolium pratense L.) and hairy vetch (Vicia villosa Roth) before grain sorghum vs. continuous grain sorghum, (ii) reduced or no‐tillage, and (iii) fertilizer N rates on grain sorghum grown on two sites of a Parsons silt loam (fine, mixed, thermic Mollic Albaqualf). Surface soil at Site 1 was higher in pH (7.2 vs. 6.2), P (12 vs. 4 mg kg−1), and K (80 vs. 60 mg kg−1) than at Site 2. Yield of the first sorghum crop after legume kill‐down in 1987 ranged from 79 to 131% more than for continuous grain sorghum. At the higher fertility Site 1, red clover residual increased yields to 3.7 from 2.7 Mg ha−1 with continuous grain sorghum in the third year; at the lower fertility Site 2, the legume residual did not influence yield after the first year. First‐year grain sorghum yielded 1.1 to 1.6 Mg ha−1 more with reduced tillage than with no‐tillage, but the difference was less in subsequent years. In 1987, yield was not affected by fertilizer N even following grain sorghum, but the response was significant in subsequent years. Low N response on this high organic matter prairie soil contributed to uncertain fertilizer N equivalencies and suggested other non‐N benefits from the legumes.
Detachment of Soil by Flowing Water Under Turbulent and Laminar Conditions
Authors: Nearing M. A. , Parker S. C.
Published: July 2010

Fluid turbulence of water flowing over soil surfaces imparts instantaneous and localized levels of shear stress to the fluid‐solid interface that are much greater than the average shear stress of flow. It has been hypothesized that these high levels of instantaneous shear are the driving mechanism for detachment of cohesive soil by flowing water. The purpose of this study was to test the hypothesis that detachment of soil by flowing water at a given shear stress is dependent on turbulence. Detachment rates of three soils were measured in a hydraulic flume at seven combinations of flow depth and bed slope under both turbulent and laminar flow conditions. For all soils and all slope/depth treatments, detachment was dramatically greater for the turbulent case compared with the laminar case. Detachment that occurred under laminar flow conditions was thought to be due in part to localized turbulence associated with pitting of some of the samples.
Denitrification in Soil Aggregates Analyzed with Microsensors for Nitrous Oxide and Oxygen
Authors: Højberg Ole , Revsbech Niels Peter , Tiedje James M.
Published: July 2010

Denitrification in soil microenvironments is difficult to study by conventional techniques. By use of O2 and N2O microsensors, it was possible to study the spatial distribution of oxygen respiration and denitrification in soil aggregates kept at field capacity. Aggregates with diameters of 20 to 25 mm often contained anaerobic centers but exhibited only low rates of denitrification due to a limiting availability of electron donors. Addition of organic matter such as clover leaves or tryptone to the surface of the aggregates greatly stimulated respiratory activity and caused anoxia and high rates of denitrifying activity within the organic hot‐spot and in the underlying soil. Due to imbalance between N2O production and N2O reductase activity, the creation of a hot‐spot led to an initial accumulation of N2O even when acetylene was absent. Denitrification within the center of a hot‐spot rapidly became limited by the diffusional supply of NO−3, even when the underlying soil contained 5 mM NO−3, and such hot‐spot centers depleted of NO−3 served as sinks for N2O while N2O concentrations of up to 400 µ M were building up immediately below. The bulk N2O production rate of the soil was thus the result of a net production in some microenvironments and simultaneous net consumption in other microenvironments.
Rapid Bioassay for Inhibitory Rhizobacteria Using Digital Image Analysis
Authors: Doty J. A. , Kennedy A. C. , Pan W. L.
Published: July 2010

Current methods for assaying the potential effects of rhizobacteria on plant growth are tedious and time consuming. A rapid, automated bioassay has been developed using a flatbed scanner and digital image analysis. Comparisons were made between manual measurements of root length and computed values based on an edge discrimination image analysis procedure. The assay consisted of bacterial cultures of filtrates added to 18 mL of 0.9% agar in square petri plates. Seeds were planted along a marked axis and incubated for 4 d at 15°C, and then the roots were measured. Total root length measurements for the two methods, manual and image analysis, were well correlated (r2 = 0.94), and both were equally able to identify bacteria inhibitory to plant growth. Root measurements by the scan method were five times faster than the manual method. Each sample required 53 s to read with the scan method vs. 250 s with the manual method. The scan method provides a quick and accurate method for screening inhibitory activity of rhizobacteria based on seedling root length and has potential in the screening of toxic substances of other origin.
Soils of the Red Fir Forest‐Barrens Mosaic, Siskiyou Mountains Crest, California
Authors: Laurent T. E. , Graham R.C. , Tice K. R.
Published: July 2010

In the crest areas of northern California and southern Oregon mountains, Shasta red fir (Abies magnifica var. shastensis Lemmon) forests are often interspersed with irregularly shaped, 0.1‐ to 50‐ha openings that contain only sparse prostrate forbs and sub‐shrubs amid mostly bare and gravel‐paved soil. We investigated these forest‐barrens associations to determine if soil differences could help explain the cause of the barrens. While the soils (Xerumbrepts) are morphologically similar in many respects, burrowing by abundant pocket gophers (Thomomys sp.) in the barrens produced thicker umbric epipedons than in the forests, where pocket gophers are absent. The only significant soil chemical differences detected between sites were lower concentrations of Ca and Mg in the barrens surface soils. In contrast, base cations accumulate in the forest A horizons as a result of biocycling. While the origin of the barrens remains unknown, herbivory by pocket gophers is a major factor in maintaining the barren conditions and their activity ultimately accounts for most soil chemical and morphological differences.
Temperature‐Dependent Measurement Errors in Time Domain Reflectometry Determinations of Soil Water
Authors: Pepin S. , Livingston N. J. , Hook W. R.
Published: July 2010

With the recent development of improved time domain reflectometry (TDR) probe design, measurement systems, and calibration procedures, it is now possible to detect and quantify the effect of temperature on the soil apparent dielectric constant (Ka). We investigated measurement errors in Ka associated with soil temperature variations and compared measured changes in Ka with those predicted by a dielectric mixing model. After confirming the accuracy and resolution of our measurement system with a series of measurements on distilled water, we measured changes in Ka with temperature for a range of soil types, including sand, loam, and peat, at soil water contents (θv) ranging from 0.09 to 0.81 m3 m−3. The measured variation with temperature in the dielectric constant of distilled water (0.322°C−1) was very close to that reported in the literature (0.356°C−1). In soils, changes in Ka with temperature were highest at high water contents. For soils near saturation, the overall changes observed in Ka with temperature were lower than those predicted by the dielectric mixing model by 17% for sand, 24% for loam, and 39% for peat. These results suggest that the temperature dependence of the dielectric constant of water in a soil matrix is lower than that of bulk water. Absolute water content errors increased linearly with the size of the water fraction, ranging from 8.75 × 10−5 m3 m−3°C−1 at 0.05 m3 m−3 soil water content to 1.40 × 10−3 m3 m−3°C−1 at 0.80 m3 m−3 soil water content. To obtain the highest measurement accuracy, particularly at higher θv, we suggest that a temperature correction of 0.00175θv °C−1 be employed.
Fragipan Genesis in Polygenetic Soils on the Springfield Plateau of Missouri
Authors: James H. R. , Ransom M. D. , Miles R. J.
Published: July 2010

Soils on broad ridgetops of the Springfield Plateau in southwestern Missouri typically are covered by a silty mantle about 1 m thick, have developed from multiple parent materials, and contain a fragipan. The objectives of this study were to identify the parent materials, assess the influence of parent material stratigraphy on fragipan expression, and determine processes of fragipan genesis. Two pedons each of Creldon (fine, mixed, mesic Mollic Fragiudalfs) and Captina (fine‐silty, siliceous, mesic Typic Fragiudults) soils were investigated using field, soil characterization, and micromorphological techniques. The parent materials were Late Wisconsinan loess, erosional lag concentrate, and cherty limestone residuum. A composite paleosol developed in the lower two parent materials was merged with the modern soil. Since the composite paleosol was acid and highly weathered, illuviation of carbonates from the overlying loess had minimal effect on the paleosol. Clay and silt, however, were illuviated from the loess into the composite paleosol. The parent material strongly influenced fragipan expression. A fragipan formed only in the erosional lag concentrate, which was probably deposited as a slurry. Micromorphological examination showed close packing of particles in the fragipan. Depth distributions of Al, Si, Mn, and Fe extracted in sodium citrate‐bicarbonate‐dithionite were not useful in establishing if one or more of these constituents was a chemical cement of the fragipan. Close packing of skeleton grains was most responsible for fragipan genesis in these soils and could have resulted from physical ripening of the erosional lag concentrate.
Organic Matter Role in Illitic Soil Colloids Flocculation: III. Scanning Force Microscopy
Authors: Heil Dean , Sposito Garrison
Published: July 2010

In previous papers of this series, the flocculation of illitic colloids separated from Hanford sandy loam diminished with the presence of organic matter that can form coatings on soil colloids. The purpose of this study was to apply scanning force microscopy to image both geologic specimen illite and the Hanford (coarse‐loamy, mixed, nonacid, thermic Typic Xerorthent) soil colloids directly to provide visual evidence of the coatings. Scanning force micrographs showed differences in particle morphology and surface features between the soil and the specimen illite particles that were not interpretable exclusively in terms of organic coatings but did indicate the presence of surface roughness that could inhibit flocculation of the soil illite particles.
Field Method for Measuring Mobile/Immobile Water Content and Solute Transfer Rate Coefficient
Authors: Jaynes D. B. , Logsdon S. D. , Horton R.
Published: July 2010

Numerous field and laboratory studies have documented the occurrence of preferential transport of solutes due to a fraction of the soil water being immobile and not taking part in the transport process. Domain models have been developed that describe these processes, but before we can apply them routinely, we need methods for measuring the required model parameters, particularly the fraction of immobile water to total water θlm/θ and the exchange coefficient between the mobile and immobile domains, α. We developed a field method for measuring both θlm/θ and α. The method uses a sequence of conservative anionic tracers consisting of Br−, pentafluorobenzoate, o‐trifluoromethylbenzoate, and 2,6‐difluorobenzoate infiltrated with time through a tension infiltrometer. Previous studies have confirmed that these tracers have very similar transport properties in a wide range of soils. The method was applied to an undisturbed loam and a greenhouse soil as an initial test of the approach. Calculated θim/θ fractions averaged 0.69 and ranged from 0.25 to 0.98, while calculated α values averaged 0.0081 h−1 and ranged from 0.0030 to 0.021 h−1. These values compare well with values reported earlier by other investigators. The method is simple and allows routine measurement of transport properties of field soils. The method can also be used to validate the applicability of domain models to specific soils.
Near‐Infrared Analysis as a Rapid Method to Simultaneously Evaluate Several Soil Properties
Authors: Ben‐Dor E. , Banin A.
Published: July 2010

The near infrared analysis (NIRA) approach was studied to examine its capability for predicting spectral feature soil properties from the reflectance curves in the near infrared (NIR) region (1–2.5 µm) of arid and semiarid soils. High‐resolution diffuse reflectance spectra (3113 spectral points) in the NIR region were recorded for 91 soil samples from Israel. Six soil properties (clay content, specific surface area, cation‐exchange capacity, hygroscopic moisture, carbonate content, and organic matter content) were measured by routine methods employed in soil laboratories. An empirical model to predict each property from its spectral signature was developed by adapting the NIRA technique. Several data manipulations were used to obtain optimum performance. The optimum performance of all properties was found to be between 25 and 63 spectral points. Strong support for the NIRA capability was provided by its ability to examine most of the spectral assignments. A slight bias was observed for the prediction of both organic matter and hygroscopic moisture, suggesting that more attention in the prediction of these constituents is required. It was concluded that NIRA is a promising method for rapid and nonrestrictive analysis of soil materials, and further study of the synergism between NIRA and soil materials is recommended.
Hydrologic Tracer Effects on Soil Microbial Activities
Authors: Groffman Peter M. , Gold Arthur J. , Howard Galen
Published: July 2010

While much research has shown that the commonly used hydrologic tracers Br−, Cl−, and pentafluorobenzoic acid (PFBA) are not affected by soil microbial processes, much less work has gone into analysis of the effects of these tracers on microbial activity. In this study, we analyzed the effects of Br−, Cl−, and PFBA at 100 mg kg−1 concentration on soil respiration, denitrification, N mineralization, and nitrification in a forest soil under laboratory conditions. Chloride and Br− inhibited all activities other than denitrification and PFBA stimulated respiration and denitrification. Mechanisms for the observed effects may be related to the effects of these anion tracers on soil solution cation activities and microbial membrane processes. The results suggest that effects on microbial activities should be considered when tracers are used in studies of the fate and transport of pollutants that are affected by microbial processes.
Slope Class Maps from Soil Survey and Digital Elevation Models
Authors: Hammer R. D. , Young F. J. , Haithcoate T. W. , Wollenhaupt N. C. , Barney T. L.
Published: July 2010

Special‐purpose land use maps based on slope attributes from digital elevation models (DEMs) often are produced with geographic information system technology. Field verification is lacking for accuracy and precision of computer‐generated slope class maps from 10‐ and 30‐m DEMs, a standard USDA (1:24 000) soil survey, and field‐measured slopes. Two 16‐ha sites in Atchison County, Missouri, were selected, flagged on 10‐m grids, and the slope was field measured for each grid cell. The field‐measured slope class maps were templates for cell‐by‐cell comparisons with the computer‐generated slope classes. More than 50% of the areas were classified into correct slope classes with 10‐m DEM maps. The 30‐m DEM maps were 30 and 21% correctly classified in the two study areas. Two iterations of low‐pass filters increased the accuracy of the 10‐m derived maps, but decreased the accuracy of one 30‐m derived map. Soil survey techniques correctly classified >30% of each area, but did not capture landscape heterogeneity. The GIS‐produced maps underestimated slopes on convexities and overestimated slopes on concavities. Slope class maps from 10‐m DEMs have potential use for soil survey and land use planning.
Methane and Carbon Dioxide Dynamics in a Northern Hardwood Ecosystem
Authors: Yavitt J. B. , Fahey T. J. , Simmons J. A.
Published: July 2010

There is evidence that oxidation of CH4 to CO2 by methanotrophic bacteria in forest soil is a major sink for atmospheric CH4, even though growth of the bacteria on such low CH4 concentrations (<1.7 µL L−1) is perplexing. Measurements of CH4 and CO2 in a northern hardwood ecosystem in the Adirondack Park in the state of New York indicated that: (i) soil CH4 concentrations were mostly higher than the concentration of CH4 in forest air, with concentrations as high as 500 µL L−1 at the 0.1‐m depth in the early and late parts of the growing season; (ii) soil CO2 concentrations ranged from the atmospheric level to as high as 19 000 µL L−1 at the 0.2‐m depth in midsummer; (iii) net consumption of atmospheric CH4 emission by soil in midsummer averaged only 0.25 mg m−2 d−1, which is low compared with findings for most forest ecosystems; and (iv) methanogenesis occurred in soil samples throughout the profile when incubated anaerobically as well as aerobically with CH3F to inhibit methanotrophs. The prominent activity of methanogenic bacteria producing CH4 in the spring and autumn could support the growth of methanotrophic bacteria that otherwise consume atmospheric CH4 when methanogens are not active. Therefore, CH4 dynamics in this Spodosol represent the balance between CH4 production and CH4 oxidation, which is similar to the CH4 dynamics in many wetland ecosystems.
Soil Pedotransfer Functions for Four Mexican Soils
Authors: Bell M. A. , van Keulen H.
Published: July 2010

Simulation models for design and testing of different land use management options require detailed soil data inputs, which are often not available. Under such circumstances, pedotransfer functions (PTF) can be used to predict soil properties such as cation‐exchange capacity (CEC) and moisture retention. We developed PTF for CEC and moisture retention at −1500 kPa for soils from four contrasting agro‐ecological environments in Mexico. The PTF relating CEC to clay content, soil organic matter content (SOM), and pH explained 96% of the variability. Analysis of the residuals showed the effects of clay at three sites and SOM at all sites to be similar, despite quite distinct agro‐ecological conditions and a wide range of SOM levels (8.0–40.0 g kg−1). The PTF, using SOM, clay, and pH, explained 93% of the variability across the four sites in moisture retention at −1500 kPa, and residuals showed similar behavior across the sites for both SOM and clay. Additionally, PTF from the literature for CEC and moisture retention at −1500 kPa were tested for the study data and adequate fits were found. Apart from PTF prediction, confidence in model output depends in part on the variability of soil properties at a site. Despite considerable absolute variation in soil properties among sites, the relative variability (i.e., coefficient of variation [CV]) across sites was quite similar, with electrical conductivity and micronutrient concentrations showing the highest CV, and pH, −1500 kPa soil moisture retention, and CEC the lowest; the latter results provided some degree of confidence in the application of PTF. The SOM content was strongly related to altitude and to silt + clay content.
Horizontal Groundwater Flow Patterns Through a Cypress Swamp‐Pine Flatwoods Landscape
Authors: Crownover S. H. , Comerford N. B. , Neary D. G. , Montgomery J.
Published: July 2010

Groundwater movement in the surficial aquifer of the lower Coastal Plain cypress swamp‐pine flatwoods landscape of the southeastern USA is poorly documented. This study was conducted to define the patterns of horizontal groundwater flow through a typical landscape with particular attention to water exchange between cypress swamps and the surrounding areas. One hundred and twenty shallow water table wells 1 m deep were installed in a 42‐ha study area, one‐third of which was covered by pond cypress (Taxodium ascendens Brongn.) swamps. Water tables were measured approximately every 2 wk for 2 yr and the data were used to map water table elevation. Directions of horizontal groundwater flow were inferred from the water table topographic maps. Measured hydraulic heads were combined with saturated hydraulic conductivities to estimate groundwater flux. Most of the groundwater flowed through the swamps in response to the generalized surface elevation pattern. For selected ponds, the ground‐water also flowed from the swamps to the surrounding areas. It was uncommon for groundwater to flow into the ponds from the entire surrounding area. The pattern of groundwater exchange between the swamps and the surrounding area was related to the average water table depth: the deeper the average water table, the greater chance for groundwater to flow from the swamp into the surrounding area. Waterflow rates were estimated to be <56 cm d−1. These groundwater flow patterns are different from the generally accepted pattern of water flow and should be useful in defining the hydrologic cycle of these landscapes.
Soil Water Pressure Measurements in Subzero Air Temperatures
Authors: Gorden D. S. , Veneman P. L. M.
Published: July 2010

Air temperatures below freezing often preclude soil water pressure measurements with tensiometers. The use of antifreeze solutions facilitates tensiometer use in weather when air temperatures are below 0°C yet the soil remains unfrozen. We studied the applicability of methanol concentrations ranging from 100 to 500 cm3 L−1. Soil water pressures were measured with ceramic cup tensiometers installed at 15‐cm depth within 38‐L‐capacity buckets. Experimental temperatures were ‐2, 0, 5, and 15°C. The pressures ranged from 0 to −60 kPa. Readings of the tensiometer with the methanol‐water mixture were within 0.6 kPa of that of the tensiometer with pure water. No statistically significant difference (α = 0.05) in soil water pressure was found between the methanol‐water mixtures and the pure water system using 1:1 lines and the Wilcoxon signed rank test for paired data. The results indicate that field tensiometer data may be collected in unfrozen soils by the use of the appropriate methanol concentration based on the temperature range expected.
Phenolic Acid Redox Properties: pH Influence on Iron(III) Reduction by Caffeic Acid
Authors: Deiana Salvatore , Gessa Carlo , Marchetti Mauro , Usai Marianna
Published: July 2010

Phenolic acids are of great interest to soil chemists because their redox properties affect the availability of micronutrients to plants. In order to provide information about the mechanisms that regulate the reduction of Fe(III) at the soil‐root interface, the redox activity of caffeic acid (CAF) at different pH values in aqueous solution was investigated. The kinetics of the redox reaction was studied by using systems with Fe(III)/CAF molar ratios ranging from 1.1 to 10.9. At pH < 3, all systems showed the highest redox capacity: a maximum of nine electrons for each molecule of CAF was released at a Fe(III)/CAF molar ratio of 10.9. At pH > 3, the redox capacity dramatically decreased and was very low above pH 4. At pH > 4, the reduction of Fe(III) was considerably inhibited due to the formation of Fe(III)‐CAF complexes as well as of Fe(OH)3 precipitates, which are active in the adsorption of CAF. The amount of Fe(II) determined after 24 h of reaction suggests that not only the aquo ion, but also the hydrolized Fe(III)‐soluble species, are active in the oxidation of the organic molecule. At about pH 4, the ultraviolet/visible spectra revealed the presence of Fe(III)‐CAF complexes, which gave rise to the formation of a black polymeric product. The infrared spectra of this product suggest that the CAF molecule interacts with the positively charged hydroxide through the carboxylate groups. The reaction was not influenced by the presence of metal ions such as Cu(II), Ni(II), Mn(II), Fe(II), and Zn(II). We have proposed a mechanism of the reduction and complexation process consistent with our results.
Dynamics of Soil Organic Matter and Corn Residues Affected by Tillage Practices
Authors: Angers D. A. , Voroney R. P. , Côté D.
Published: July 2010

This study was conducted to determine the influence of tillage practices on the decomposition of corn (Zea mays L.) residues and turnover of soil organic matter (SOM). Measurements of δ13C were made of the whole soil, the microbial biomass, and two particle‐size fractions (<50 and >50 µm) in soils that had been under corn production for 11 yr and from an adjacent meadow. Meadow‐derived C in total SOM (0–24 cm) decreased under corn cropping at the same rate under all tillage treatments. Corn‐derived C was evenly distributed with depth in the moldboard plow treatment and accumulated at the surface in the shallow, reduced‐tillage treatments. The incorporation of corn residue C into SOM in the 0‐ to 24‐cm layer was not significantly affected by tillage and was estimated to be ≈41 g C m−2 yr−1, which represents ≈30% of the corn residue inputs. Both the macroorganic matter (>50 µm) and microbial biomass had a greater enrichment (up to 35%) in corn‐derived C than either the whole soil or the microorganic matter (<50 µm), indicating that these pools are important recipients of plant residue inputs. Nevertheless, the microorganic matter was also a significant sink for C input, acounting for ≈50% of the total corn‐derived C remaining in the surface (0–8 cm) soil. Under the conditions of this study, tillage practices influenced the vertical distribution of SOM and corn residues but had no detectable effect on SOM turnover and on the fate of corn residues when the whole Ap horizon was considered.
Bacterial Transport and Phenanthrene Biodegradation in Soil and Aquifer Sand
Authors: Devare Medha , Alexander Martin
Published: July 2010

Remediation of contaminated soil by inoculated bacteria requires movement of the bacteria to the site of contamination. Addition of a phenanthrene‐metabolizing Psudomonas sp. to the surface of 1.5‐cm columns of sterile or nonsterile soil or aquifer sand resulted in the rapid mineralization of phenanthrene present in the top 0.4 cm of sand or soil columns receiving intermittent or no water flow. However, the surface‐inoculated pseudomonad mineralized little of the substrate present in the bottom 0.4‐cm portion of nonsterile soil or aquifer sand that had been sterilized prior to inoculation, although mineralization occurred at the bottom of nonsterile aquifer sand. Little biodegradation was evident if the bacterium and the substrate were both at the bottom part of columns of soil and aquifer sand receiving intermittent flows of water, although rapid biodegradation occurred at this site in soil if the water flow was constant. Only ≈1% of the added cells passed through the soil after passage of ≈1.5 pore volumes of water, although ≈4% passed through the aquifer sand. We suggest that bacteria added to the soil surface or to aquifer solids for biodegradation may not be transported sufficiently to reach organic pollutants at sites distant from channels or macropores.