bluuebunny/crossref_metadata_2025 huggingface dataset:
Compositional and Solubility Relationships Between Aluminum‐hydroxyinterlayered Soil‐Smectites and Vermiculites
Authors: Karathanasis A. D.
Published: July 2010

Coarse clay fractions (2–0.2 µm) of selected soil samples containing variable quantities (10–52%) of Al‐hydroxyinterlayered smectite (HISM) or vermiculite (HIV) were investigated by XRD, thermal, elemental and solution composition analyses. The HISM vs. HIV nature of the sample was determined from the smectitic or vermiculitic origin of the sample and by alkylammonium ion exchange, expansion with glycerol and resistance to collapse after K‐saturation and heating at 300° and 550 °C. X‐ray diffraction and thermal analysis of tetradecylammonium exchanged clays and structural formulae calculations indicated all hydroxyinterlayered minerals, except for one HISM, to have high layer charge deficiencies (X > 0.5 equivalents per 0.5 unit cell). A greater portion of the total charge deficiency was satisfied by [Al(OH)x]3‐x in HIV minerals which resulted in generally higher free energies of formation (ΔG°f). Hydroxyinterlayered smectites on the other hand, exhibited higher cation exchange capacities and higher OH/Al ratios in the hydroxyinterlayer material. Compositions of soil solutions in contact with these minerals supported a metastable HISM region in relatively Si‐enriched solutions and a metastable or stable HIV region in somewhat Si‐deficient solutions comparable to those supporting the stability of kaolinite. Structural formulae‐ and soil solution‐ compositions of the studied samples appeared to be consistent with the dynamic nature of these minerals in soil environments in terms of mineralogical distribution, physicochemical behavior, and stability.
Mineralization of Phosphorus in Sludge‐Amended Soils Monitored by Phosphorus‐31‐Nuclear Magnetic Resonance Spectroscopy
Authors: Hinedi Zeina R. , Chang A. C. , Lee R. W. K.
Published: July 2010

The purpose of the experiment was to observe the changes occurring in the different phosphorus (P) pools in sludge‐amended soils during incubation using 31P nuclear magnetic resonance spectroscopy (31P NMR) to qualitatively and quantitatively register P transformations. An acid and an alkaline soil were each incubated with sludges that underwent different digestion processes. The 31P NMR spectra of those soils after 1, 28, 70, and 140 d of incubation showed that P diesters completely hydrolyzed after 28 d of incubation in both soils, irrespective of the type of sludge incorporated. After 140 d of incubation, P monoesters were still detected in the acid soil while they had completely hydrolyzed in the alkaline soil. Pyrophosphates were detected after 70 d of incubation in the alkaline soil and 140 d of incubation in the acid soil. The study suggested that acidity has an adverse effect on the microbial degradation of P monoesters and pyrophosphates in sludge‐amended soils.
Nonbiological Nitrous Oxide Production from Vadose Soil Catalyzed by Galvanized Steel Tubing
Authors: Parkin T. B. , Codling E. E.
Published: July 2010

Studies of microbial processes in the vadose zone are hampered by difficulties in obtaining uncontaminated samples. We initiated a study in 1985 to quantify microbial denitrification in the vadose zone of agricultural land located in the Atlantic Coastal Plain. In the initial stages of this study, deep soil cores (360 cm) were collected and subcored with sterile galvanized steel tubes to eliminate contamination by surface soil. We observed N2O production from subsoil incubated with C2H2 in galvanized tubes, but in the same soil incubated anaerobically with added glucose and NO−3, denitrification activity was not detected. Subsequent comparisons of N2O production in surface and subsurface soil incubated in galvanized and plastic tubes indicated that chemodenitrification was the likely mechanism responsible for the N2O production observed in soil contained in galvanized steel tubes. These results suggest that, in field or laboratory experiments designed to investigate soil‐N transformations, galvanized steel enclosures should be used with caution.
Denitrification Hysteresis During Wetting and Drying Cycles in Soil
Authors: Groffman Peter M. , Tiedje James M.
Published: July 2010

Denitrification response to soil moisture was studied in soils undergoing either wetting or drying cycles to determine if denitrification‐soil water relationships were independent of antecedent moisture conditions. Intact, field moist soil cores were brought into the laboratory and subjected to either wetting or drying phase treatments. In the drying phase treatment, soils were wet to saturation and then progressively dried to field capacity, 60% water‐filled porosity and 20% water‐filled porosity with denitrification measured at each moisture condition. In the wetting phase treatment, soil cores were first dried to 20% water‐filled porosity and were then progressively wet to 60% water‐filled porosity, field capacity, and saturation. Denitrification showed a hysteretic response to soil moisture when drying and wetting phases were compared. In the drying phase, rates of denitrification decreased dramatically as soils were dried from saturation to field capacity, with further decreases in activity observed at 60 and 20% water‐filled porosity. In the wetting phase, denitrification activity sharply increased immediately after rewetting soils from 20 to 60% water‐filled porosity, with only slight increases observed as soils were wet further to field capacity and saturation. The hysteretic response was observed in three soils of markedly different texture. Denitrification dynamics in the wetting phase were strongly correlated with pulses of C and N mineralization caused by stress of microbial biomass by drying and rewetting. Models of denitrification driven by soil moisture need to consider hysteretic effects if they are to accurately predict denitrification activity in the field.
Tillage Effects on Availability of Nitrogen to Corn Following a Winter Green Manure Crop
Authors: Sarrantonio M. , Scott T. W.
Published: July 2010

Field studies were conducted in 1984 through 1986 to investigate the release of inorganic N to corn (Zea mays L.) following a winter annual green manure crop of hairy vetch (Vicia villosa Roth) that had either been plowed down to 22 cm (conventional tillage, CT), or killed and left on the surface (no‐till, NT). Soil samples were taken regularly throughout the season at three depths (0–7.5 cm, 7.5–22 cm and 22–45 cm) and analyzed for inorganic N. Crop growth and N uptake, as well as various other plant, soil and environmental parameters were also monitored. First year data (1985) show that soil inorganic N concentration in vetch treatments was higher under CT than NT, and it was more evenly distributed throughout the plow layer. Both corn yields and N uptake, however, were significantly higher in the NT system, probably because of higher soil moisture content in a dry summer. Vetch did not stimulate significant yield increases over 0‐N control plots in either tillage system, although there was greater N uptake by corn in vetch treatments. Under NT, 29% of the original N in the above‐ground vetch biomass was measured either as soil inorganic N or corn N. Under CT, 56% of the original vetch N was measured. A repeat of the first experiment was conducted in 1986. Again, higher levels of inorganic N occurred under CT than under NT where vetch had been grown. Contrary to the results of 1985, corn yields were significantly higher in CT treatments than NT treatments at all N levels, and both corn yield and N uptake were significantly higher in vetch treatments than control treatments under both tillage systems. Maximum inorganic N levels were measured in late October in 1986, when 22% and 55% of the original vetch N was measured under NT and CT tillage systems, respectively.
Effect of Zinc Deficiency on Growth, Phosphorus Concentration, and Phosphorus Toxicity of Wheat Plants
Authors: Webb Michael J. , Loneragan Jack F.
Published: July 2010

In some previous experiments, Zn deficiency has enhanced P accumulation in old leaves to toxic concentrations by enhancing the rate of P absorption. This research was undertaken to examine the relationship of Zn deficiency to P accumulation and toxicity in young wheat plants (Triticum aestivum L. ‘Gamenya’) grown in a complete nutrient solution with 1000 µM phosphate and either with or without 2.5 µM Zn. Mild Zn deficiency depressed shoot but enhanced root DM and this change was almost paralleled by P distribution. Severe Zn deficiency enhanced P concentration to 3 to 4% in old leaves and the marked necrotic symptoms were attributed to combined Zn deficiency and P toxicity. It depressed whole plant dry matter (DM) by 40% but P content by only 10%. It severely depressed DM distribution but enhanced P distribution to shoots thus doubling shoot P concentration. Short term and long term estimates indicate that mild Zn deficiency had only a transient effect in enhancing Pi absorption rate as severe Zn deficiency substantially depressed it. Thus, Zn deficiency enhanced P concentrations to toxic levels in old leaves through the cumulative effects of responses at three tiers of structural organization: (i) in the whole plant, it depressed DM more strongly than P content, (ii) between roots and shoots, it depressed that proportion of total DM which was present in shoots while increasing that of total P, (iii) within shoots, it concentrated P in old leaves by depressing new growth.
Evaluation of Soil Variability in Northwest Florida Using Geostatistics
Authors: Ovalles F. A. , Collins M. E.
Published: July 2010

The objectives of this research were to (i) investigate the use of geostatistics in studying the spatial variation of previously statistically selected soil properties in northwest Florida; (ii) have a better interpretation of how the variability in the selected soil properties is related to a physiographic region; and (iii) determine areas where sampling density should be increased. Two sets of data from 151 pedons in a 380‐ by 100‐km irregular grid were used. The sets of data were composed of (i) sand, clay, and organic carbon (OC) contents on a weighted average basis; and (ii) A horizon clay and OC contents. Direction‐independent and direction‐dependent semivariograms were calculated and observed semivariograms indicated drift in the data. Therefore, residuals were used to compute new semivariances. Drift was reduced, but local trends still remained. Semivariograms of sand, clay, and OC contents were anisotropic. Organic carbon content semivariograms exhibited a pure nugget effect indicating a large point‐to‐point variation at short distances and an absence of spatial correlation at the sampling scale used. Kriged data and standard error diagrams of soil properties were related to the five physiographic regions in northwest Florida. The variability shown by these diagrams may be a consequence of the different topography, geology, and management of the area. Reliability (kriged) diagrams were helpful in locating areas of large standard error, such as the northeast edge of the Dougherty Karst physiographic region, that require an increase in sampling intensity to improve the precision of the estimates.
Calciustolls in Central Texas: II. Genesis of Calcic and Petrocalcic Horizons
Authors: West L. T. , Wilding L. P. , Hallmark C. T.
Published: July 2010

Soils on hillslopes in the Grand Prairie and eastern Edwards Plateau regions of Texas are developed from multiple facies of interbedded weakly to strongly indurated Cretaceous limestones. Most contain either calcic or petrocalcic horizons. Stable C isotope analysis of the carbonate‐enriched horizons from seven pedons sampled in this area permitted quantification of the amount of pedogenic carbonates. Features indicative of carbonate translocation and accumulation were observed in the soils. However, reconstruction analysis indicated that none of the calcic horizons and few of the petrocalcic horizons contained more carbonates than the parent limestone. Microfabric development in calcic horizons supports loss of carbonates as a major process in these horizons. The pedogenic nature of most of the carbonates in calcic horizons is attributed to in situ recrystallization of the parent limestone. Petrocalcic horizons commonly had areas of strongly indurated limestone in matrix interiors, and micromorphic observations indicated that much of the pedogenic carbonates in these horizons was also the result of in situ recrystallization of the limestone. Petrocalcic horizons occurred on all landscape positions. Their occurrence and position in the profile appears to be related to an indurated limestone bed within the normal depth of wetting. The development of calcic and petrocalcic horizons primarily by recrystallization rather than translocation and accumulation of carbonates contrasts with the commonly accepted model for formation of these horizons.
Chemical, Mineralogical, and Physical Property Differences Between Moderately and Severely Eroded Illinois Soils
Authors: Nizeyimana E. , Olson K. R.
Published: July 2010

The effects of degree of erosion on the chemical, mineralogical, and physical properties of seven Illinois soils were evaluated. At each site, separate map units of moderately and severely eroded phases of a soil series were located in the same field. These paired erosion phases occurred as a consequence of slight differences in slope gradient, slope shape, or slope length within a landscape position. Soil descriptions were made from pits located within each eroded phase of all seven soil series. Soil samples were taken with depth to measure the chemical, mineralogical, and physical properties of each phase of all soil series. The magnitude and direction of change in these parameters varied with soil series. For most soils studied, degree of erosion significantly reduced the organic C, and water storage porosity values of the Ap horizons. Clay mineral type estimates of the Ap horizons of severely eroded soils changed measurably as a result of thinner topsoils permitting the tillage equipment to mix underlying Bt horizon materials higher in hydrous mica or smectite into the topsoil. With increased degree of erosion, pH, cation exchange capacity, K and base saturation value trends varied with soil series. Erosion of soils with root restricting layers, such as dense subsoils, resulted in these layers occurring closer to the surface and in lower profile water storage capacities. Most of the soil property differences between moderately and severely eroded phases of a soil series would reduce the ability of the soil to produce crops. Successful management techniques for the restoration of the productivity of eroded soils will need to modity the chemical, mineralogical, and physical properties of the severely eroded soils.
Reactions of Ammonia and Urea Hydrolysis Products with Soil
Authors: Kissel D. E. , Cabrera M. L. , Ferguson R. B.
Published: July 2010

A quantitative description of pH changes in N fertilizer application zones is needed to predict the degree of NH3 formation in the soil solution. In particular, the pH changes following surface application of urea determine in part the degree of NH3 formation and possible loss by volatilization. The objectives of our study were to compare the rise in soil pH following addition of urea and NH4OH to soil, and evaluate the importance of inorganic C reactions to any differences in the rise in pH caused by the two respective N sources. Titration curves with urea or NH4OH as a base were used to determine differences in the patterns of pH change. Up to pH 8.2, soil pH was raised identically by NH4OH and urea that had been completely hydrolyzed. Above pH 8.2, urea was less effective than NH4OH in raising soil pH. The lower effectiveness of urea was due in part to the urea‐C not forming CO2 but remaining as HCO−3 and CO2−3 in the soil solution. Part of the CO2−3 precipitated as CaCO3 when enough urea was added to raise soil pH to 8.8. At a lower application rate of urea, which resulted in a soil pH of 7.15, no CaCO3 was detected. These results demonstrate the importance of inorganic C from urea hydrolysis in providing resistance to a pH increase above pH 8.2 in concentrated fertilizer application zones.
Reversible and Irreversible Dehydration of Hydroxy‐Interlayered Vermiculite from Coastal Plain Soils
Authors: Harris W. G. , Hollien K. A.
Published: July 2010

Dehydration behavior of hydroxy‐interlayered vermiculite (HIV) from three coastal plain soils was studied using x‐ray diffraction (XRD) and thermal analysis. Relative humidity (RH) at 25 °C had little effect on HIV 001 XRD peaks, except for a 0.01 to 0.05° 2θ shift at RH ≈ 0%. Heating to 50 °C shifted peak positions 0.10 to 0.20° 2θ for fine silts and 0.05 to 0.10° 2θ for coarse clays. Effects of 50 °C treatment were largely reversed by re‐wetting, indicating that H2O re‐entered interlayers. Heating to 115 °C broadened peaks and produced shifts of up 0.40° 2θ. Dehydration at ≥ 115 °C was essentially irreversible, as indicated by lack of 001 expansion and failure to regain full sample weight at 100% RH. Peaks were markedly broadened and attenuated by heating to 165 and 225 °C, with full width at half maxima approaching 1.0° 2θ. No significant peak in the 1.0‐nm region developed from interlayer collapse, even at 550 °C. Reversible dehydration may be attributable to free‐H2O loss from interpolymer zones at temperatures below the onset of significant polymer dehydration. The data suggest that attraction between dehydrated polymers and 2:1‐layer surfaces exceeds hydration forces, resulting in irreversible collapse and variable interlayer thickness. Re‐entry of H2O into interlayers could be sterically impeded by the dehydrated polymers themselves or by their binding effect on layers. The 1.4‐nm mineral in the soils studied exhibits thermal properties more consistent with HIV than an alternative vermiculite‐kaolin intergradient structure.
A Computer Simulation of Fe(III) and Fe(II) Complexation in Nutrient Solutions: II. Application to Growing Plants
Authors: Schwab A. P. , Lindsay W. L.
Published: July 2010

A computer model developed by the authors accurately predicted the chelation of ferrous and ferric ion as a function of pH and redox potential in nutrient solutions. Experiments were conducted to establish the apparent redox potential (4 < pe + pH < 7) imposed by roots of efficient and inefficient soybean plants (Glycine max L.). Using this information, equilibrium Fe2+ concentrations were controlled by adjusting the concentrations of the chelating agents. Iron‐59 uptake was correlated with log[Fe2+] for concentrations between 10−6.5 and 10−9.2 mol Fe2+/L in the experimental nutrient solutions.
Edaphic and Reclamation Aspects of Vesicular‐Arbuscular Mycorrhizae in Wyoming Red Desert Soils
Authors: White J. A. , Munn L. C. , Williams S. E.
Published: July 2010

Three Aridisols and an Entisol in the Red Desert of southwest Wyoming were surveyed for vesicular‐arbuscular mycorrhizal (VAM) fungal biomass. The survey was conducted to determine attenuation of VAM fungal biomass in profiles of these arid soils, to examine possible edaphic influence on VAM fungal distributions and to evaluate the potential of these soils in providing VAM fungal biomass for use in reclamation. Fungal biomass levels—as indicated by fungal spore densities and bioassay percent infections—was apparently related to morphological and chemical properties that differ between individual soils and their associated vegetation. While fungal spore densities generally attenuated with depth in the Aridisols, the Torrifluvent retained high densities of spores (up to 81 spores g−1 soil) to a depth of 140 cm. The VAM fungal biomass attenuation in relatively deep horizons of these arid soils may still allow adequate formation of propagules for use in reclamation of disturbed lands.
Minirhizotron Installation Techniques for Investigating Root Responses to Drought and Oxygen Stresses
Authors: Box J. E. , Smucker A. J. M. , Ritchie J. T.
Published: July 2010

Estimation of plant root activities by the minirhizotron technique is a nondestructive approach for observing root responses to the soil environment, yet few such observations have been made. The purpose of this report is to compare methods for installing minirhizotron tubes in separate experiments located in two regions of the USA. Transparent plastic tubes were installed at acute angles of 0.8 and 1.2 rad to the surfaces of sandy loam (Typic Hapludult and Typic Hapludalf) soils located in Georgia and Michigan. Soil cores were removed from these low expansion‐contraction soils using Giddings hydraulic power samplers. Both ends of the minirhizotrons were stoppered and the aboveground portion of the tube surfaces were made opaque before inserting. The excellent soil to minirhizotron wall interfaces provided clear and high contrast root images that were observed and video recorded. These procedures provided information which indicate that short‐term drought results in root losses near the soil surface and large increases in deep root growth. Uninterrupted O2 stress substantially reduced growth of wheat (Triticum aestivum L.) roots throughout the rhizosphere.
Effects of Soil Flooding on Selenium Transformations and Accumulation by Rice
Authors: Mikkelsen Robert L. , Mikkelsen Duane S. , Abshahi Akbar
Published: July 2010

The fate of Se in flooded soil is not well known. This greenhouse study was conducted to determine the fate of Se in flooded soil and to determine the effects of Se on plant growth. Rice plants (Oryza sativa L. cv. M101) were grown in pots containing Panoche loam soil (fine‐loamy, mixed, calcareous, thermic Typic Torriorthents) to which 0, 1.5, 3, and 6 mg Se kg−1 as Na2SeO4 was added. Rice was grown in continuously flooded or nonflooded (upland) soil. The flooded treatments were amended with organic matter (OM) at concentrations of 0, 2.5, and 5 g cellulose kg−1. Soil solution samples were taken weekly from the flooded treatments and analyzed for pH, Eh, EC, and Se concentration and Se oxidation state. Plants were harvested and analyzed for Se at three plant growth stages. Selenate soil solution concentrations were reduced 95% after 6 and 10 wk following flooding for the 5.0 and 0 g OM kg−1 treatments, respectively. Selenite in solution reached a maximum concentration (340‐1920 µg Se[IV] L−1) 5 to 8 wk after flooding and then decreased to trace levels (<0.5 µg L−1). Selenium accumulated in all rice plant parts in direct proportion to the added Se. Plants grown in flooded soil with added OM had tissue Se concentrations <20% that of rice grown without added OM or in upland conditions. Selenium phytotoxicity symptoms were observed in plants grown in flooded soil without OM and in the upland soil when Se was added. Tissue Se concentrations associated with a 10% reduction in shoot dry matter were 160 and 81 mg Se kg−1 for upland and flooded rice (without added OM). No Se‐induced yield loss occurred when OM was added to flooded soil. Flooding those soils containing Se[VI] may be an effective way to reduce soluble Se concentrations in soil to nontoxic concentrations.
Orientation of Planar Voids in Vertisols and Soils with Vertic Properties
Authors: Bui E. N. , Mermut A. R.
Published: July 2010

The length, orientation, and area percentage of planar voids >75 µm in soil thin sections of several Vertisols from India and Ghana, and clayey soils with vertic properties from Saskatchewan were measured using an image analyzer. Cumulative lengths of planar voids for 10° intervals were expressed as a percentage of total length and plotted in polar coordinates to show the orientation of these voids. The orientation of planar voids was anisotropic in all the soils studied. The percentage of vosepic plasmic fabric (porostriated birefringence fabric) was determined by averaging counts from 40 fields of view under a petrographic microscope. The clay soils from Saskatchewan showed a predominance of vertically oriented planar voids; these probably developed as shrinkage cracks during drying. In the Vertisols from India, in accord with parallelepiped natural structural aggregates described for this soil order, the dominant orientation of planar voids was at an angle of 15° to 60° oblique to the horizontal, in either direction of the first or second quadrant. In those from Ghana, planar voids were oriented at various oblique angles as well as vertically. Together with plasmic fabric analysis, planar void orientation patterns were useful in determining whether soils have been subjected to stress‐strain forces.
Morphology of Calcite Crystals in Clast Coatings From Four Soils in the Mojave Desert Region
Authors: Chadwick Oliver A. , Sowers Janet M. , Amundson Ronald G.
Published: July 2010

Pedogenic calcite‐crystal coatings on clasts were examined in four soils along an altitudinal gradient on Kyle Canyon alluvium in southern Nevada. Clast coatings were studied rather than matrix carbonate to avoid the effects of soil matrix on crystallization. Six crystal sizes and shapes were recognized and distinguished. Equant micrite was the dominant crystal form with similar abundance at all elevations. The distributions of five categories of spar and microspar appear to be influenced by altitudinally induced changes in effective moisture. In the drier, lower elevation soils, crystals were equant or parallel prismatic with irregular, interlocking boundaries while in the more moist, higher elevation soils they were randomly oriented, euhedral, prismatic and fibrous. There was little support for the supposition that Mg2+ substitution or increased (Mg + Ca)/HCO3 ratios in the precipitating solution produced crystal elongation.
Estimation of Unsaturated Hydraulic Conductivity from Field Sorptivity Measurements
Authors: White I. , Perroux K. M.
Published: July 2010

Measurement or estimation of the unsaturated hydraulic conductivity of soils, K(Ψ), is of central importance to the understanding of soil‐water flows in many areas of hydrology and agriculture. Here we derive approximations that relate K(Ψ) to sorptivity, S0, measured over a range of negative supply pressures. We test the approximations against the Green‐Ampt, Knight, and Broadbridge‐White models of soil hydraulic properties. The last model covers the range from a Green‐Ampt like model to the weakly nonlinear Knight model. One of the derived approximations is found to give K(Ψ) accurate to within 5% over the entire range of soil‐water potential and the full range of the single Broadbridge‐White model parameter. Comparison of estimates of K(Ψ) using this approximation with conventionally determined K(Ψ) for repacked and intact soil samples shows good agreement. In an application of the technique we use measurements of S0 to identify the effect of rain, falling at the end of a severe drought, on K(Ψ) of the surface soil. We adapt these measurements to pinpoint the changes in characteristic pore size brought about by the rain. In addition, we show how the macroscopic capillary length of a soil may be estimated from sorptivity measurements at any supply pressure. One of the principal advantages of the technique is that measurements of sorptivity sample shallow soil depths. The technique therefore is suited to layered soils, shallow surface soils and soil tillage studies.
Potassium in Atlantic Coastal Plain Soils: I. Soil Characterization and Distribution of Potassium
Authors: Parker D. R. , Sparks D. L. , Hendricks G. J. , Sadusky M. C.
Published: July 2010

Corn (Zea mays L.) grown on sandy Atlantic Coastal Plain soils is often unresponsive to applications of K fertilizer. As part of a field study on the response of irrigated, intensively managed corn to K applications, we characterized four representative Hapludults from the Delaware Coastal Plain and evaluated their K status. The soils were generally quite sandy with maximum clay contents of 11.4 to 26.5%, had low (≤2.0%) organic matter contents, and had correspondingly low cation exchange capacities (1 to 4 cmolc kg−1 by summation). The clay fractions were dominated by kaolinite and hydroxy‐interlayered 2:1 expansible minerals; the latter may play a crucial role in the overall chemistry of K in these soils. The soils were quite high in total K, with means for the four soils (across horizons) ranging from 23.6 to 43.9 cmolc kg−1, and this was ascribed to the K‐rich parent material and relatively young age of these soils. Most (97–98%) of the total K was in mineral forms, and the majority (65–87%) was in the sand fractions, virtually all as K‐feldspars. Exchangeable and nonexchangeable (fixed) K levels were relatively low and were of comparable magnitude. Consideration of particle size distribution, K distributions, and published studies of weathering rates suggested that the sand fractions of these soils represent significant sources of plant‐available K.
Estimating Soil Salinity from Saturated Soil‐Paste Electrical Conductivity
Authors: Rhoades J. D. , Manteghi Nahid A. , Shouse P. J. , Alves W. J.
Published: July 2010

A method is presented for estimating the electrical conductivity of the saturated soil‐paste extract (ECe) from measurement of the electrical conductivity of the saturated soil‐paste (ECp) and estimated saturated soil‐paste water content (SP), for purposes of soil salinity appraisal. The method is suitable for both field and laboratory applications. Empirical relations are provided to estimate values of several parameters required for the method. The appropriateness of the method was tested using two groups of soil samples, one of which varied widely in geographical sources and parent materials, in addition to texture and salinity. The method estimated the soil salinities very accurately (r2 > 0.9; slope ≈ 1.0; intercept ≈ 0.0).
Soil Electrical Conductivity and Soil Salinity: New Formulations and Calibrations
Authors: Rhoades J. D. , Manteghi N. A. , Shouse P. J. , Alves W. J.
Published: July 2010

A new model describing the relation between bulk soil electrical conductivity (ECa), volumetric content (θw) and electrical conductivity of soil water (ECw) is given along with supporting evidence for its validity. The new model distinguishes between the water and salt present in the soil in the “immobile” (fine pores) and “mobile” (large pores) phases. It provides a possible physical meaning to the transmission coefficient (T) previously used in an earlier model and eliminates a limitation of that model which existed under conditions of low salinity. New empirical relations are provided to estimate the parameters needed in the new and old models in order to utilize them for diagnosing soil salinity, in terms of the electrical conductivity of the extract of saturated soil pastes (ECe).
Hydrogen Sulfide Production from Cysteine (Cystine) in Soil
Authors: Morra M. J. , Dick W. A.
Published: July 2010

Hydrogen sulfide (H2S) production in aerobic soils amended with cysteine (cystine) is thought to result from cystathionase γ‐lyase (EC 4.4.1.1) activity. This enzyme yields thiocysteine (2‐amino‐2‐carboxylethyl hydrodisulfide), which reacts spontaneously with free sulfhydryl groups to produce H2S. Hydrogen sulfide, however, may also be produced in soil as a result of sulfate reduction. This work was conducted to evaluate the physical and chemical parameters that affect H2S production in cystine‐amended soil and to test the hypothesis that sulfate reduction is involved. Hydrogen sulfide, evolved from 4 g of soil placed in a 25‐mL Erlenmeyer flask, was trapped in a center well containing pleated filter paper and 0.5 mL of 1 M zinc acetate. Three soils brought to a water potential of −0.033 MPa and incubated at 37 °C with 50 µmol L‐cystine evolved 2.08 to 3.62 mg H2S‐S kg−1 soil 24 h−1. Maximum rate of H2S evolution occurred at 57°C. Propargylglycine (12.5 mmol kg−1 soil), a specific inhibitor of cystathionine γ‐lyase, reduced H2S evolution by 90 to 98%. Incubating the soils under waterlogged conditions also reduced H2S evolution in two of the three soils studied, with no change observed in the third soil. Hydrogen sulfide evolution was not affected by the addition of 12.5 mmol kg−1 soil of sulfate or nitrate, thus providing additional evidence that sulfate reduction was not involved. The apparent Michaelis constant (Km) value for H2S production from cystine in soil was 2.3 mmol kg−1 soil. It is concluded that production of H2S in soil, which is a significant reaction of the S cycle, can occur as a result of the mineralization of cysteine (cystine) via participation of the enzyme cystathionine γ‐lyase.
Pedogenic Carbonates in a Calciaquoll Associated with a Recharge Wetland
Authors: Knuteson J. A. , Richardson J. L. , Patterson D. D. , Prunty Lyle
Published: July 2010

Calcic horizon formation was studied in an Aeric Calciaquoll (Bearden series) adjacent to an occasionally ponded Typic Argiaquoll (Lindaas series) on the Lake Agassiz Plain of eastern North Dakota. Carbonates in the Calciaquoll accumulated from groundwater additions. Soil water monitoring during a year with near‐normal rainfall and temperatures showed that an upward soil water flux existed during a 13‐wk period from late spring through midsummer. Unsaturated hydraulic conductivity (UHC) values indicated that the 2BC horizon controlled upward water flux in this soil. Upward water movement through this horizon during the 14‐wk period was estimated to be 36 mm. In late summer, evapotranspirative demand far exceeded the UHC of the horizon. As the soil dried, UHC values were further reduced. Assuming time of soil formation of 4000 to 9000 yr and detrital carbonate mineral levels of 10 to 15% by weight, annual additions of calcium carbonate equivalent (CCE) to the calcic horizon range from 0.1 to 0.2 mol m−2 yr−1 in this soil based on the amount of carbonate in the calcic horizon. Annual average levels of CCE in rising groundwater must be between 2.6 and 8.2 mmol kg−1 for the observed amount of carbonate to accumulate. The current amount of CCE in calcic horizon soil solution, as estimated by mathematically concentrating saturation past soluble ions to the observed constant water content, was 3.5 mmol kg−1, a value within the range estimated.
Landscape and Soil Property Effects on Corn Grain Yield Response to Tillage
Authors: Simmons F. W. , Cassel D. K. , Daniels R. B.
Published: July 2010

Deep tillage practices such as chiseling and in‐row subsoiling generally increase crop yields on well‐drained sandy soils of the Atlantic Coastal Plain. Although attempts have been made to relate deep tillage response to measurable soil physical and chemical properties, little information is available relating within field corn (Zea mays L.) yield responses to topographic factors. This study was initiated to analyze the interactive effects of landscape and soil properties with tillage treatment on corn yields. Disking (D), chiseling (C), and in‐row subsoiling/bedding (SB) tillage treatments were applied across a Norfolk‐Wagram (Typic and Arenic Paleudults) complex. Grain and stover yields and grain weights, were measured in 1984 and 1985. Deep tillage provided a 25% yield increase compared to disking both years. Of all soil‐related variables examined, in‐row curvature explained the most yield variability. Grain yields in concave plots were more sensitive to changes in curvature than those in convex plots. Landscape influence on yields was greatest in 1985, a year with severe early season drought. Yield components at footslope and deep linear slope positions were greater than those of the interfluve and shallow linear slope positions. At the footslope position in 1984, SB increased yields more than C, suggesting that SB promotes higher yields than C when soil moisture conditions are favorable. Shallow tillage (treatment D) was the most susceptible of the three tillage treatments to yield reductions at drought‐prone landscape positions.
Oxygen Flux, Air‐filled Porosity, and Bulk Density as Indices of Vertisol Structure
Authors: Hodgson A. S. , MacLeod D. A.
Published: July 2010

The structure of irrigated Vertisols in Australia is frequently damaged by cultivating wet soil. This may reduce crop growth and yield, but there is a lack of suitable indices that characterize the physical damage to the soil. Oxygen flux density (F), air‐filled porosity (ε), and bulk density (ρb) were compared as indices of soil structure in undisturbed soil cores of a cracking gray clay (Vertisol, Typic Pellustert) at Narrabri, New South Wales, Australia. All three parameters were measured on the same cores. The soil had received two cultivation treatments: cultivating when wet and cultivating when dry. Samples were taken from each treatment on six occasions over a range of soil‐water content at five depth increments from 0 to 0.075 m to 0.4 to 0.475 m. Wet cultivation decreased F and ε relative to dry cultivation at most sampling times, but effects on ρb were smaller and inconsistent. All three parameters increased as gravimetric water content (θg) decreased. The variation of each parameter with respect to θg was obtained by linear regression, and the ratio of the slopes of these regressions between the two cultivation treatments was called the sensitivity ratio. Sensitivity ratios for F, ε, and ρb were 22.7, 6.9, and 1.2, respectively, for the 0.2‐ to 0.275‐m depth, which was most affected by cultivation treatments. Low sensitivity of ρb was related to low ε of the wet soil, which precluded compaction during wet cultivation. The sensitivity of ε was attributed to the greater structural shrinkage (conservation of pore volume on drying) observed in soil cultivated when dry compared to soil cultivated when wet. The high sensitivity of F is related to the dependence of F on ε and on the tortuosity and continuity of air‐filled pores, all of which appeared to be adversely affected by wet cultivation. Oxygen flux density is therefore recommended as the most sensitive of the three indices for detecting structural changes.
Soil Macropore Size Distribution from Water Breakthrough Curves
Authors: Radulovich R. , Solorzano E. , Sollins P.
Published: July 2010

A new method for characterizing macropore size distribution is presented for a well‐aggregated Oxic Dystropept at La Selva, Costa Rica, known to exhibit macropore flow. Samples were taken as undisturbed cores from a secondary forest and an abandoned pasture. The method is based on hydraulic principles including the Poiseulle equation, and on water breakthrough curves obtained by timing and measuring water flow through the cores from a drained state (simulating field capacity) to a saturated steady‐state flow condition. Application of the method to the La Selva soil (0‐ to 20‐cm depth) yielded macropore radii between 50 and 200 µm, with a peak between 80 and 140 µm. The macropore size distributions thus obtained were coupled to micropore size distributions calculated from moisture release curves to yield a set of complete pore size distributions. The method is simple, and the results are based on dynamic measurements, making them more applicable to flow models.
Aluminum Fractionation of Soil Solutions from Unperturbed and Tephra‐Treated Spodosols, Cascade Range, Washington, USA
Authors: Dahlgren R. A. , Ugolini F. C.
Published: July 2010

Fractionation of aqueous Al was investigated in leachates from a subalpine Spodosol (Typic Cryohumod) located in the Cascade Range of Washington state. Leachates were collected from major genetic horizons with tension lysimeters during the fall, winter, and spring seasons. Solutions were collected from unperturbed profiles and from profiles that had received artificial additions of Mt. St. Helens tephra 4 yr prior to this study. Fractionation of Al was performed by a column cation exchange technique that minimized alterations in pH and ionic strength during the fractionation procedure. Organically complexed Al was the dominant form of soluble Al in the Oa, E, and Bhs horizons, while organically complexed and inorganic forms were nearly equal in the Bs horizon. These results are consistent with the metal‐fulvate theory of podzolization. The effects of tephra deposition were only apparent in the Bs horizon, where inorganic Al concentrations were twice the concentrations measured in nondisturbed profiles. Laboratory experiments showed that the ability of natural organic acids in soil solutions to complex Al increased as the pH was increased from 3.8 to 5.0. Aqueous Al3+, added as AlCl3 to solutions at pH = 4.5, was found primarily as organic complexes when organic C/metal atomic ratios were >50. At organic C/metal ratios <50, the additional Al was found primarily in inorganic forms.
A Comparison of Mineral Weathering Trends Between Two Management Systems on a Catena of Loess‐Derived Soils
Authors: Karathanasis A. D. , Wells K. L.
Published: July 2010

This study was an attempt to predict potential long‐term mineralogical transformation trends in soils under continuous no‐tillage management using the in situ soil solution composition as a sensitive index of changes occurring in the soil system. Mineralogical and soil solution compositions of surface and subsurface horizons of a catena of loess‐derived soils (Memphis, Grenada, Calloway) under continuous (16 yr) no‐till (NT) and conventional‐till (CT) management suggested a shift in weathering patterns as a result of the differential tillage management. This shift was evident primarily as a buffer effect of the NT management on drainage characteristics. Interstitial soil solutions of surface NT horizons were generally two to three times higher in Si and K than respective surface CT horizons. The elevated soluble Si and K concentrations maintained in the NT horizons correlated well with increases in organic matter content. The Si‐enrichment of the NT‐solutions combined with the reduced Al3+ activities, due to increased complexation, appeared to favor a hydroxyinterlayered vermiculite/vermiculite metastable state over the hydroxyinterlayered vermiculite/kaolinite of the CT system. This slowdown of the weathering process under continuous NT management should have important implications on K equilibria of these soils.
Microscopic and Ultramicroscopic Porosity of an Oxisol as Determined by Image Analysis and Water Retention
Authors: Bui E. N. , Mermut A. R. , Santos M. C. D.
Published: July 2010

Detailed analysis of soil porosity in an Oxisol from Brazil was performed by image analysis in order to understand the unique water retention behavior of Oxisols. In addition to pores, the quantification of skeleton grains and plasma was made by image analysis of thin section micrographs. Due to the high quantity of skeleton grains and micro‐aggregates, interaggregate pores formed a network of interconnected simple and compound packing voids. Interaggregate porosity was an average of 39% for the profile. Micro‐aggregates of about 50‐ to 100‐µm in size were impregnated with Spurr's resin and ultrathin sections were made to measure ultramicroscopic pores. Image analysis of the transmission electron microscope (TEM) micrographs indicated approximately 9% intra‐aggregate pores. Ultramicroscopic pores were formed by the arrangement of kaolinite, halloysite and Fe‐ and Ti‐bearing minerals, with an average area of 1250 nm2. Their circularity was low, reflecting their irregular outline and high number of protrusions. The combined use of petrographic, TEM and image analysis techniques can complement other methods used to determine soil porosity and can provide a better understanding of the nature of the porosity of soils because it allows for quantification of size and shape of microscopic and ultramicroscopic pores as well as visual appreciation of their spatial arrangement.
Spatial Variability of Saturated Hydraulic Conductivity of the Subsoil of Two Forested Watersheds
Authors: Wilson G. V. , Alfonsi James M. , Jardine P. M.
Published: July 2010

Subsurface flow has been shown to be greater in soils with spatially dependent hydraulic properties. The objective of this study was to quantify the spatial dependency in saturated hydraulic conductivity, Ksat, of two potential shallow waste disposal sites in eastern Tennessee. The Guelph Permeameter was used to determine Ksat of the subsoil of two forested watersheds, Walker Branch and Melton Branch. The simultaneous equations approach resulted in more than 50% negative Ksat values and was concluded to be invalid for these forested subsoils. As an alternative, flux density was used as an index of the saturated hydraulic conductivity for spatial correlation analysis and for determination of scaling factors. the spatial realizations of hydraulic conductivity for both watersheds were found to be intrinsic random functions of order zero, i.e., stationary, with a generalized covariance function for Walker Branch consisting of a pure nugget and for Melton Branch a nugget with a linear term. Semivariograms revealed no spatial dependency for separation distances >4.2 m at Walker Branch. Spatial dependency at Melton Branch for separation distances <30 m was described by an exponential model. The hydraulic conductivity of Walker Branch subsoils had a greater arithmetic mean (1.50 vs. 0.76 × 10−5 m s−1) and greater random variability than Melton Branch subsoils. These findings suggest that soils common to Walker Branch Watershed are hydrologically preferable for shallow waste disposal.
Diffuse Reflectance and Transmission Fourier Transform Infrared (DRIFT) Spectroscopy of Humic and Fulvic Acids
Authors: Baes A. U. , Bloom P. R.
Published: July 2010

The infrared spectra of a humic and a fulvic acid from a peat were obtained using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and were compared with transmission Fourier transform infrared (FTIR) spectra using KBr pellets. The DRIFT spectra showed similar resolution to KBr pellet transmission spectra. Elimination of interference due to water bands is easy with DRIFT and possible changes in the spectra due to modification of H bonding and ionization of carboxylate groups in the KBr pellet is avoided. Comparison of the DRIFT spectra of humic substances with the DRIFT spectra of some reference compounds suggests that phenolic OH groups in fulvic acids are more H‐bonded than those in humic acids, but the COOH groups are similarly H‐bonded. Comparison of the C=O stretching band with those of the reference compounds suggests that either intramolecular H‐bonding between COOH and phenolic OH is not significant in humic substances or alkyl COOH groups contribute considerably in the 1720 cm−1 band. The DRIFT spectra of Na and Cu(II) forms of humic acid powders show the capability of the method for metal‐ion binding studies. The possibility of using DRIFT spectroscopy for quantitative and semiquantitative evaluation is suggested by the similarity in the Kubelka‐Munk transformed DRIFT spectra and absorbance spectra using KBr pellets.