bluuebunny/crossref_metadata_2025 huggingface dataset:
Infiltration as Affected by Long‐term Use of Sodic‐Saline Water for Irrigation
Authors: Hadas A. , Frenkel H.
Published: July 2010

Infiltration rates and hydraulic conductivity of two fields were determined to evaluate the long‐term impact of irrigation with saline‐sodic water [electrical conductivity (EC) = 5.6 mmho/cm and sodium adsorption ratio (SAR) = 26] and the benefit of gypsum treatments. Field 1 had been irrigated for 2 years and field 2 for 8 years. Infiltration rates were measured by a constant head method and hydraulic conductivity by Bower's method using distilled water (to simulate rainwater) and the saline‐sodic irrigation water. Results indicated that the infiltration rates of the gypsum‐treated plots were higher than the nontreated plots for each field, and the infiltration rate of the soil irrigated with sodic‐saline water for 8 years was greater than the infiltration route of field irrigated for 2 years. The latter difference was related to different crust structures found in the two fields. Hydraulic conductivities and infiltration rates of soil crusts were calculated for rainfall and for irrigated conditions. The results are discussed in view of the existence of CaCO3 and gypsum in the original and treated soil, respectively. Some estimates of calculated final infiltration rates under rainfall conditions are presented.
Bacterial Utilization of Simple Alcohols and Their Influence on Saturated Hydraulic Conductivity
Authors: Frankenberger W. T. , Troeh F. R.
Published: July 2010

Two simple alcohols (methanol and n‐propanol) were used to leach saturated soil columns for 2,000 hours, and changes in saturated hydraulic conductivity (Ksat) over time were determined. For both alcohols and a distilled water treatment, Ksat was found to decrease with time, attaining a constant value after approximately 1,500 hours. The addition of simple alcohols reduced Ksat considerably when compared with the flow rate of distilled water in soils. Initial decreases in Ksat were attributed to structural breakdown of unstable aggregates and expansion of clays, but the final portion of conductivity‐time curves was probably due to microbial action, in which soil pores became clogged with products of growth and cells. The pH values of effluents collected from soils treated with simple alcohols were lower than those of the added influents. Soils leached with distilled water became more acidic than those leached with methanol and n‐propanol. Phosphatase activity was assayed in each soil column, and results showed greater activities in the oxidized zones of soils. The magnitude of phosphatase activities in the oxidized zones of the treated soils were consistently higher in the following order: methanol > n‐propanol > distilled water. The decrease in Ksat of soils treated with simple alcohols was related to acid phosphatase activity, in that, as phosphatase activity increased, Ksat decreased.
Factors Affecting the Mobility and Plant Availability of Boron in Some Western Oregon Soils
Authors: Parker D. R. , Gardner E. H.
Published: July 2010

Surface soil from five diverse soil series was used to investigate the influence of soil properties and constituents on the mobility of boron (B) in a greenhouse study. Using pots 16.5 by 18.5 cm in diameter, from 13 to 61% of a 2.0 mg/kg liquid application of B was recovered in 25 cm of leachate. Recovery of B decreased with increased soil organic matter, clay, and free Fe and Al oxide content, but statistical separation of the effects of individual components was complicated by intercorrelations among these soil properties. No effect of soil pH on B mobility over a range of 5.4 to 7.5 was observed.

Following leaching, the soils were cropped with New Zealand white clover (Trifolium repens L.). Yield differences were not correlated with hot water‐extractable B levels ranging from 0.47 to 2.34 µg/g or with B applied at planting. Plant B concentrations were high, ranging from 60 to 150 µg/g. As the range in hot water‐soluble B values encompassed current concepts of deficiency levels in western Oregon soils, the merits of investigating soil‐B critical levels under greenhouse conditions are questioned.

A balance sheet approach indicated that soils have reserves of leachable and plant‐available B not detected in the conventional hot water extraction. The boron‐supplying power of these soils varied both within and among soil series and depended on soil properties and the amount of B in the soil system.
Soil Fertility Changes following Clearcut and Whole‐tree Harvesting and Burning in Central Michigan
Authors: Adams Paul W. , Boyle James R.
Published: July 2010

Soil fertility (available Ca, Mg, K, P, and total N) was evaluated at the time of and 1 and 5 years after clearcut and whole‐tree harvest of adjacent oak‐aspen forests. Surface mineral soil at both sites showed increased K and decreased N concentrations 1 year following harvest. A wildfire that burned both sites shortly thereafter generally increased the nutrient concentrations at each site, but smaller increases occurred at the whole‐tree harvest site. Five years after cutting (4 years after burning) soil Ca and P levels at both sites were higher than the concentrations at the time of harvest, while K and N were similar to original levels. Calcium and Mg concentrations at the clearcut site were 88 and 75% higher than the levels at the whole‐tree site 5 years after harvest. The increased soil fertility observed could provide a valuable nutrient supply to the succeeding forest stand, but net nutrient outputs through harvest and burning could also eventually reduce the already low productivity of these sites.
Electromagnetic Determination of Soil Water Content Using TDR: I. Applications to Wetting Fronts and Steep Gradients
Authors: Topp G. C. , Davis J. L. , Annan A. P.
Published: July 2010

The time‐domain reflectometry (TDR) technique has been demonstrated to be a viable method for determining soil water content in uniformly wet soils. The TDR response in nonuniformly wet soils was examined herein both theroetically and experimentally. An extensive set of experiments was carried out in a controlled laboratory test facility which permitted synthesis of steep water content gradients and wetting fronts. The water content measured by the TDR technique has been found to be the same as the average water content to within 0.01 cm3cm−3 in extremely nonuniform conditions. This result is quite surprising at first but is readily explained by the nature of the dielectric constant and water content relationship. The TDR technique has also been found useful in detecting and monitoring the progression of wetting front advance through a soil.
Soil and Rhizosphere Microorganisms in Amended Coal Mine Spoils
Authors: Fresquez P. R. , Lindemann W. C.
Published: July 2010

Topsoil is usually respread over strip‐mined land during reclamation. In some instances, spoil could be used as a medium for revegetation. The objectives of this study were to compare microbial parameters in spoil and soil and determine the effect of spoil amendment on these microbial parameters.

Representative samples from a topsoil stockpile, a nonvegetated spoil, a reclaimed area, and an adjacent undisturbed surface soil were collected from the San Juan coal mine near Farmington, N. Mex. Additional samples of spoil and stockpiled topsoil were used in a greenhouse pot experiment to determine the influence of spoil amendment on microbial parameters. The treatments included spoil, spoil plus topsoil inoculant, spoil plus alfalfa hay and fertilizer (both with and without topsoil inoculant), and spoil plus gamma‐irradiated sewage sludge (both with and without topsoil inoculant). The pots were planted to Bouteloua gracilis and microbial determinations of the spoil made after 5 months. Later the same pots were replanted to Atriplex canescens and microbial determinations made of the rhizosphere 7 months after planting. Microbial parameters measured included numbers of aerobic heterotrophic bacteria, Streptomyces, fungi, ammonium oxidizers, and aerobic asymbiotic nitrogen fixers, dehydrogenase activity, and fungal genera distribution.

The undisturbed soil and reclaimed area had comparable microbial numbers, dehydrogenase activity, and fungal genera distribution. Microbial numbers and dehydrogenase activity of stockpiled topsoil and nonvegetated spoil were low and the fungal genera distribution was narrow.

Topsoil inoculation did not increase microbial parameters of the spoil or of the rhizosphere of A. canescens. Spoils appeared to be unable to support an active and varied indigenous flora or the microorganisms introduced by the topsoil inoculant. Organic amendment of either sludge or alfalfa increased all microbial parameters. The increased numbers, dehydrogenase activity, and distribution of fungi were particularly evident in the rhizosphere. Providing an available carbon source was more critical in stimulating an active and varied spoil microflora than was supplying an inoculant source.
Statistical Analysis of Crop Yield Under Controlled Line‐source Irrigation
Authors: Bresler E. , Dagan G. , Hanks R. J.
Published: July 2010

The line‐source sprinkler irrigation system produces a water application pattern which is uniform along the length of the plot and variable across the plot. This ensures a high degree of uniformity of deterministic water application along strips parallel to the sprinkler line and minimizes effect of irrigation variability upon yield in such strips. Statistical techniques are applied to analyze yield results obtained from controlled line‐source field experiments. The spatial statistical structure of the crop yield is determined. The completely random component of yield is separated from the one displaying a spatial structure attributed to soil properties. Two of the three experimental fields considered display the complete random component solely, so that the usual statistical inference techniques are applicable. In one field the crop yield has a spatial statistical structure and the experimental plot seems to be smaller than the correlation scale, indicating that yield average and variance estimates depend on the size of the field. The main conclusions are: (i) statistical stationarity is achieved when yield is scaled with respect to its average for a constant irrigation level; (ii) soil variability has a large effect on yield; and (iii) the latter has a spatial structure which has to be inferred in order to carry out statistical analysis independent of field size.
Use of Circular Polarization on Soil Thin Sections to Distinguish Voids from Mineral Grains
Authors: Ruark G. A. , Veneman P. L. M. , Mader D. L. , Waldron P. F.
Published: July 2010

Application of crossed‐polarized (XP) light to thin sections of soil often results in images where the assessment of patterns of void distribution is complicated by the extinction of anisotropic mineral grains which have their optical axes exactly parallel to the plane of polarized light. A low cost system utilizing circularly polarized (CP) light rectifies this problem and is described in detail. Thirty‐three thin sections were photographed under both XP and CP light. The resulting 35‐mm color slides were examined with a Quantimet 720 Image Analyzer. A paired t‐test showed a highly significant reduction in void space estimates using CP light indicating a correction for mineral grain extinction. The photographs resulting from this method give consistent and accurate representation of parameters of voids regardless of sample orientation.
Effect of Grass, Legume, and Tree Roots on Soil Shearing Resistance
Authors: Waldron L. J. , Dakessian S.
Published: July 2010

Plants enhance soil stability against downslope mass movement through the removal of soil water by transpiration and by the mechanical reinforcement of their roots. To assess the magnitude of this reinforcement, direct shear measurements were made on 0.25‐m diam cylindrical soil columns packed both homogeneously and in layers which simulated water and/or root‐impeding horizons. In all cases the matric potential was adjusted to zero before shearing. Twelve plant species were used including seven grasses: Phalaris tuberosa, Lolium rigidium, Dactylis glomerata, Bromus mollis, Sorgum bicolor sudanense, Triticum oestivum, Hordeum vulgare. Two legumes were used: Vicia dascarpa, Medicago sativa. and two trees were used: Pinus ponderosa and Quercus agrifolia.

The ratio of the shear resistance at 25‐mm displacement of the rooted and unrooted specimens was used as a measure of root reinforcement. Roots of several grasses planted in early fall and sheared the following spring gave about a threefold increase in shear resistance at the 0.3‐m depth in homogeneous saturated clay loam. In the same material, roots of oak produced a similar increase only after 3 years' growth. One‐year‐old alfalfa produced a fourfold increase. At the 0.45‐m depth at the interface between soil and a dense gravel‐sand mixture simulating weathered rock, yellow pine gave a 1.5‐fold increase after 16 months and a 2.5‐fold increase after 52 months. Hardinggrass was almost equally effective after only 7 months.

In almost all cases where roots increased soil shear resistance, the resistance continued to increase beyond 25‐mm displacement so that the selection of 25‐mm displacement was conservative, i.e., it may underestimate the root reinforcing effect.

Factor of safety calculations for shallow planar slides using measured shear strengths show that plant roots can make large increases in slope stability.
Carbon‐13 Nuclear Magnetic Resonance Spectra of some Fungal Melanins and Humic Acids
Authors: Lüdemann H. D. , Lentz H. , Martin J. P.
Published: July 2010

A study was made to compare the 13C‐NMR (Carbon‐13 nuclear magnetic resonance) spectra of a variety of fungal melanins with that of soil and Leonardite peat humic acids. The spectra were made in 5% wt/wt solution in 0.1N NaOD in D2O using the Fourier transform technique. All of the polymers gave complex 13C NMR spectra with strong signals, shoulders, or plateaus in the area of resonance for aliphatic, peptide, polysaccharide, aromatic, and carboxylic acid groups. The soil humic acid and all the original fungal melanins except that from Stachybotrys atra showed strong peaks or shoulders at about 20, 25, 28, 35, 40, 58, 75, 80, 110, 120, 130, 136, 175, and 180 ppm. The study gives further evidence that many fungal melanins are similar to soil humic acids in their chemical structure.
Lime Requirement Determination for Attaining pH 5.5 and 6.0 of Coarse‐textured Soils using Buffer‐pH Methods
Authors: Tran T. S. , van Lierop W.
Published: July 2010

In this experiment, we sought to verify the precision of the Shoemaker et al. (SMP), Yuan, Woodruff, and Mehlich lime requirement (LR) methods as proposed and modified for measuring the LR of 37 acid coarse‐textured soils to attain pHs 5.5 and 6.0. The SMP buffer was tried at initial buffer pH levels of 7.5, 7.0, 6.5, 6.0, and 5.5 as a single‐buffer (SB) method or double‐buffer (DB; McLean et al.) modification. Results indicate that linearity of the relationship between incubation LR and soil‐buffer pH increased as the initial buffer pH approached the desired soil pH. This comparison also disclosed that after recalibration the SMP‐SB method was as accurate and precise as the more complex SMP‐DB procedure for determining LR (5.5) and LR (6.0) rates. The most advantageous way of using the SMP‐SB method for determining these LR rates was with the customary initial buffer pH of 7.5 but calculating the prescribed rates with a curvilinear instead of the more common linear buffer calibrations.

The Yuan buffer was evaluated at initial buffer pH levels of 7.0, 6.5, and 6.0 both with single‐ and double‐buffer methodologies. This comparison revealed that the Yuan‐DB procedure, though among the most precise tested for LR (6.0), was appreciably less precise for determining LR (5.5) rates. Nonetheless, the Yuan buffer was as precise for determining LR (6.0) rates and substantially more precise for prescribing LR (5.5) rates when used as a SB instead of its usually proposed more complex DB methodology.

The Woodruff buffer was as precise as any for determining LR (6.0) rates, but its precision was substantially lower for LR (5.5). As proposed, the Mehlich method was probably the most accurate method tested for determining LR (5.5) rates, because this method prescribed on the average 111% of the incubation values and the prescribed and incubation values were closely related (r = 0.938**). This study revealed that most buffers can be used for determining LR (5.5) or LR (6.0) rates after appropriate calibration. Regression equations are, accordingly, provided for calculating or adjusting LR rates to pH 5.5 or 6.0 for the methods and modifications tested. Results also indicate that buffer calibrations are valid for a wider range of mineral soils than used in this study.
Use of Discriminant Analysis for Classification of Fertilizer‐Responsive Sites
Authors: Comerford N. B. , Fisher R. F.
Published: July 2010

The use of soil‐extractable phosphorus (P) was evaluated as a means for classifying P‐deficient soils. Two P extractants, ammonium acetate (pH 4.8) and double acid (Melich I), were employed as guides to P‐deficient soils. Surface soil‐extractable P was not useful for determining a P‐deficient site; however, either extractant, when used to a total depth of 60 cm, produced acceptable discriminatory power. The depth of soil sampling was as important or more important than the extraction used. Measurements of rooting depth such as drainage class and depth to a spodic horizon, argillic horizon, or mottles were useful variables for diagnosing nutrient‐deficient sites when combined with extractable P. The use of discriminant analysis in predicting fertilizer response is discussed.
A Timesaving Technique for Measuring Respiration Rates in Incubated Soil Samples
Authors: Edwards Nelson T.
Published: July 2010

A method for determining CO2 efflux rates from large soil samples (50 to 200 g) is described. The method permits the measurement of cumulative CO2 efflux from large numbers of incubated samples in about 2 min/sample. The apparatus includes a CO2 scrubber, soil incubation jars, flow meter, drying column, dilution jar, and infrared gas analyzer. Results obtained using this method were less variable than results obtained with a Gilson differential respirometer when a homogeneous forest soil sample was tested.
Effects of Sawlog vs. Whole‐Tree Harvesting on the Nitrogen, Phosphorus, Potassium, and Calcium Budgets of an Upland Mixed Oak Forest
Authors: Johnson D. W. , West D. C. , Todd D. E. , Mann L. K.
Published: July 2010

Whole‐tree harvesting increased the export of biomass N, P, K, and Ca by 2.6, 2.9, 3.1, 3.3, and 2.6 times, respectively, compared to sawlog harvesting in an upland mixed oak forest in eastern Tennessee. Whole‐tree harvesting after leaf fall reduced the potential drains of N, P, K, and Ca by 7, 7, 23, and 5%, respectively, compared with potential removal by harvesting during the growing season. Due to low soil Ca content and high Ca content in woody tissues, whole‐tree harvesting depleted total ecosystem Ca to a much greater extent than N, P, or K. Soil reserves and atmospheric inputs may be adequate to sustain total N, P, and K supplies with whole‐tree harvesting, but soil amendments may be necessary to sustain Ca supplies.
A Method of Collecting Soil Solutions from Flooded Soils
Authors: Fox R. , Rolfe G.
Published: July 2010

A procedure and soil water sampling unit are described for obtaining soil solution samples from flooded soils. The low oxidation‐reduction potentials of soil solution samples should be preserved by extracting the samples under an atmosphere of nitrogen. Standing floodwaters do not inhibit the collection of samples.
The Cross‐Coupling Transport Coefficient for the Steady Flow of Heat in Soil Under a Gradient of Water Content
Authors: Chu Shu‐Yuan , Sposito Garrison , Jury William A.
Published: July 2010

A theoretical discussion based on the thermodynamics of irreversible processes (TIP) is given concerning the flux equations for the coupled, steady flows of water and heat in a soil as formulated by Jury and Miller. It is shown that a unique definition of the heat flux vector in a coupled flow process is not possible within the context of TIP alone, although differences between heat flux vectors can be defined uniquely. It is shown also that any set of coupled expressions for simultaneous, steady water and heat flow in soil that is compatible with TIP can be used to derive the Jury‐Miller formulation of the flux equations by means of linear transformations. Moreover, the cross‐coupling coefficient that links the heat flux to the gradient of water content vanishes identically in this formulation. However, a particular definition of the heat flux is implied by the Jury‐Miller equations and its relationship to the measured heat flux cannot be established solely by the methods of TIP. An examination of the data on heat and water flow reported by Jury and Miller indicated that the experimental sensitivity was not sufficient to discriminate among several alternative definitions of the heat flux that can be developed within TIP. This result serves to emphasize the point that the identification of the heat flux actually measured in a coupled flow experiment must be on the basis of either a theoretical model of the coupled flow processes or an application of the general equation of total energy balance.
Biodegradation, Stabilization in Humus, and Incorporation into Soil Biomass of 2,4‐D and Chlorocatechol Carbons
Authors: Stott Diane E. , Martin J. P. , Focht D. D. , Haider K.
Published: July 2010

14C‐labeled catechol, 4‐chlorocatechol, and 4,5‐dichlorocatechol readily linked into model peroxidase humic acid‐type polymers, with 84 to 96% recovery of the 14C‐activity in the reaction mixtures. The 4,5‐Dichlorocatechol was the least reactive. 2,4‐D did not link into the polymers. The biodegradation of labeled catechol, 4‐chlorocatechol, and 4,5‐dichlorocatechol, free and linked into model polymers and of 2,4‐D, a fungal melanin, ferulic acid, wheat straw, and glucose were followed over 6‐month and 1‐year incubation periods in four soils, and the distribution of the residual activity in biomass, new humus, and 6N HCl hydrolyzable substrates was determined. The rate and extent of degradation depended upon the substrate, the concentration, and the soil. The 2,4‐D was rapidly degraded with 86 to 94% of the side chain and 73 to 85% of the ring‐14C evolved as CO2 over 1 year. Only 38 to 50% of the catechol, 22 to 63% of the 4‐chlorocatechol, and 22 to 62% of the 4,5‐dichlorocatechol carbons were lost over 1 year indicating substantial stabilization of these compounds, probably by enzymatic polymerization reactions. Catechol, 4‐chlorocatechol, and 4,5‐dichlorocatechol incorporated into model polymers were still more stable with 6 to 22, 8 to 42, and 13 to 43%, respectively, of the 14C evolved as CO2.

After 1 year, about 3 to 8, 2 to 14, 1 to 7, 0 to 8, and 2 to 15% of the residual 14C activity from catechol, 4‐chlorocatechol, 4,5‐dichlorocatechol, the ring portion, and the side chain of 2,4‐D, respectively, was present in the biomass. The amount of residual C in the biomass from the catechols incorporated into the model polymers was very low and varied from 0 to 3%. The amounts of the residual 14C solubilized upon 6N HCl hydrolysis were related to the extent of biodegradation of the substrates. With highly degraded substrates, such as side chain 2,4‐D, glucose and wheat straw carbons the major portion of the residual C was lost upon hydrolysis. With highly resistant substrates such as catechol, the model polymers, and the fungal melanin, the major portion was not lost upon hydrolysis. The other substrates gave intermediate values.
Relationship of Topography to Soils and Vegetation in an Upper Michigan Ecosystem
Authors: Pregitzer Kurt S. , Barnes Burton V. , Lemme Gary D.
Published: July 2010

The influence of topography on soil development and classification and the interrelationships among soils and forest composition are poorly understood in Upper Michigan. Topographic plant‐soil interrelations are important because plants are increasingly being used to indicate environmental conditions and potential forest productivity. Our objectives, therefore, were to study the effect of topography on soil development and classification, soil nutrient status, and forest composition over a classical toposequence. An 8‐ha portion of a steep watershed was topographically mapped, and soils and plants were sampled and analyzed using established techniques. In addition, the distributions of selected ground flora species were mapped over the landscape. Results indicate a strong correspondence between the distribution of plants, soil development and classification, and soil nutrient status. Soils ranged from a Lithic Dystrochrept in the upper slope through a Typic Dystrochrept, Entic Haplorthod, Dystric Eutrochrept, and finally a Terric Borosaprist in the toeslope; this is considerable variability within a horizontal distance of 300 m. Soil nutrient status varied along with soil development and was strongly related to topographic position. For these coarse‐textured soils, increased content of macronutrients is closely associated with increased content of soil organic matter. For example, in the surface soil of a colluvial soil profile we found that soil nitrogen was roughly 10 times greater than in the subsoil; this large difference in soil nitrogen was closely associated with large amounts of soil organic matter in the surface soil. Within the highly variable landscape, forest composition followed variability in soil development, soil organic matter, and soil nutrient status. Groups of ground flora species were closely associated with these soil and topographic variations.
Mineralogy of Saudi Arabian Soils: Central Alluvial Basins
Authors: Viani B. E. , Al‐Mashhady A. S. , Dixon J. B.
Published: July 2010

These investigations were conducted to provide basic soil chemical, physical, and mineralogical data for an area of Saudi Arabia that had not been studied and for which greatly increased agricultural development is anticipated. Fourteen soils were collected from two arid interior basin areas of Saudi Arabia. The silt and clay mineralogy was studied using x‐ray diffraction, differential thermal analysis, and electron microscopy. Quantitative estimation of clay‐sized minerals was based on a combination of chemical and x‐ray diffraction techniques. The calcareous soils of the central basins show minimal profile development. Particle‐size classes range from sandy‐skeletal to fine silty. Soils with shallow water tables are saline with large SAR values. The clay minerals in soils of the basins are primarily inherited. Soils developed in alluvium from mixed igneous rocks have clay fractions in which smectite > mica > kaolinite > chlorite, palygorskite, vermiculite. Soils formed from Permian sedimentary rocks have kaolinitic clay fractions. It is postulated that the central basins do not receive sufficient Si inputs for palygorskite neoformation and it is though that palygorskite is detrital, originating from easternregion Tertiary rocks. The soil clays of the central hasins have greater smectite contents than those of the kaolinitic western highland soils and palygorskite‐rich eastern‐region soils.
Transformation of Smectite to Kaolinite in Naturally Acid Soil Systems: Structural and Thermodynamic Considerations
Authors: Karathanasis A. D. , Hajek B. F.
Published: July 2010

Four acid montmorillonitic soil profiles were sampled to study thermodynamic‐stability relationships and chemical weathering of soil minerals. Solid‐ and solution‐phase characterization indicated smectite to be the metastable precursor of kaolinite with the highest rate of transformation occurring in topsoil horizons. Structures of Al‐saturated smectites were found to be nonideal with respect to excess structural OH‐ water and below normal (≈550°C) dehydroxylation temperatures. Structural and thermochemical data suggested the weathering sequence was montmorillonite → beidellite → kaolinite. The smectite → kaolinite transformation appears to be a combination of dissolution‐precipitation and structural reorganization processes. Excess structural OH‐ in the beidellitic structure seems to have played a key role in the transformations. Montmorillonite → beidellite and beidellite → kaolinite transformations were favored in the more weathered topsoil horizons where solutions were undersaturated with respect to amorphous SiO2. Kaolinite precipitating from supersaturated solutions appeared to have a range in crystallinity and standard free energy of formation (ΔGof), approaching those of halloysite at high solution silica activities.
Experimental Verification of a Model to Predict Soil Moisture and Temperature Profiles
Authors: Lascano R. J. , van Bavel C. H. M.
Published: July 2010

A model was used to calculate water and temperature profiles over 30 d for a bare soil profile, using the hydraulic characteristics of the soil and standard meteorological data as input. The model was also used to determine the spatial variability of the calculated values, using the concept of similar media. The calculated profiles were compared to actual measurements, made periodically over the same period of time. The predicted water content values for different soil layers were within 1 standard deviation of the average measured values. The predicted temperature profiles were within 1° C of the measured values. The estimate of the spatial variability of the calculated values of water content was comparable to the variance of the measured values. Hence, it is concluded that the model was adequate to its purpose, under the conditions of the verification made.
A Comparison of Diffusion and Distillation Methods for Preparing Samples for 15N Analyses
Authors: Adamsen F. J. , Reeder J. D.
Published: July 2010

This study was conducted to compare a distillation method with tube diffusion for the preparation of samples for 15N analyses. Standard samples [1 mg of N as (NH4)2SO4] with various 15N excess contents (0, 3, or 10 atom % excess 15N) were distilled or diffused and compared with nondiffused, nondistilled standards. There were no significant differences between treatments at the 0% level of enrichment. However, at the 3 and 10% levels of enrichment, both distilled and diffused standards were significantly lower than the nondistilled, nondiffused standards. No significant differences (p < 0.05) were found between HCl and H2SO4 as trapping solutions. The data indicate that diffusion is an acceptable alternative to distillation, since the 15N values are comparable and the precision is slightly better.
Adsorption of Cd(II) and Cu(II) by Na‐Montmorillonite at Low Surface Coverage
Authors: Inskeep William P. , Baham John
Published: July 2010

Montmorillonite has a heterogeneous charge distribution, and it is important to determine whether constant potential edge sites or constant charge sites control metal adsorption. The pH dependence of metal adsorption provides insight into the adsorption mechanism as well as being an important variable that will determine the solubility of Cd or Cu in soil systems. Adsorption of Cu and Cd by Na‐montmorillonite (2 g L−1) in 0.01M NaClO4 was measured over a pH range from 4 to 8.5 under humidified N2 gas. With the exception of experiments for Cu adsorption > 10 µM CuT, total soluble metal values were undersaturated with respect to known metal hydroxide solid phases. Kinetics for the adsorption of 50 µM CdT and CuT were rapid, with equilibrium occurring within 30 min. Experimental data for initial metal concentrations ranging from 50 to 0.1 µM yielded linear adsorption isotherms over the pH value range studied. Initial metal concentrations represent from 6 to 0.01% of the total sites available for metal binding, assuming an average of 0.8 mmol charge g−1 of clay. The pH dependence associated with Cd and Cu adsorption was reversible and much lower than observed for oxide minerals or for precipitation reactions. Adsorption of 2 µM CdT by 2.0, 0.2, and 0.02 g of clay L−1 suspensions showed that the fractional coverage of Cd on montmorillonite increased when the solid concentration decreased. As the fractional coverage approached saturation on the calculated amount of constant potential edge sites, the pH dependence increased and approached expected values of pH dependent charge on constant potential sites. This suggests that constant potential edge sites may primarily be responsible for Cd and Cu adsorption at low adsorption densities.
Soil Acidity and Liming: II. Evaluation of Using Aluminum Extracted by Various Chloride Salts for Determining Lime Requirements
Authors: Oates Kenneth M. , Kamprath E. J.
Published: July 2010

Neutralization of soil Al to a minimum value is one approach to liming acid soils. The objective of this study was to determine which chloride extracting solution removed the quantity of soil Al that readily reacts with limestone and reduces the Al saturation to < 15%. Soils were incubated for 8 weeks after being limed at rates needed to neutralize the Al removed by KCl, LaCl3, and CuCl2. Six soils with a range in organic matter contents were used. When the Al extracted by KCl was used to predict the lime rate, soils containing organic matter had a large amount of residual KCl‐extractable Al and a soil pH below 5.0. The lime rate predicted by the Al removed with LaCl3 reduced the residual Al to < 15% Al saturation for all soils. If residual Al is the criterion for evaluating limed soil, then LaCl3 is the best extracting solution. The LaCl3 not only removes the same amount of Al as KCl from the clay fraction of the soil, but also removes organically bound Al that influences the soil solution Al.
Relative Erodibility of 20 California Range and Forest Soils
Authors: Trott Kenneth E. , Singer Michael J.
Published: July 2010

Erodibility research on California upland soils has indicated that the Universal Soil Loss Equation's K nomograph may not account for all of the factors affecting erodibility of western upland soils. To further investigate this, laboratory rainfall simulation on 0.6‐ by 0.6‐m plots of sieved soil at 9% slope was used to measure relative erodibility of 20 upland soils, including two soils from terraces of the Sacramento River. The most powerful predictor in a stepwise multiple regression of erodibility, on a mass basis, was a combined smectite plus vermiculite clay mineralogy term. Also included in the four‐variable regression equation was bulk density, pyrophosphate‐extractable Fe + Al, and the standard texture term M. R2 for the equation was 0.800. Smectite plus vermiculite, M, a clay mineralogy‐pyrophosphate Fe + Al interaction term, pH, organic matter, oxalate Fe + Al, and vermiculite were the seven significant terms in the equation predicting soil loss on a volume basis. This equation had an R2 of 0.772. For now, the best available tool for predicting erodibilities of western upland soils appears to be the Universal Soil Loss Equation erodibility nomograph. However, results of this study show that because of the large differences in parent materials and soil‐forming conditions that distinguish midwestern from western soils, consideration of soil mineralogy in future predictive work may improve the predictive capacity of the nomograph.
Water Budget of an Eastern Deciduous Forest Stand
Authors: Luxmoore R. J.
Published: July 2010

Soil water content and soil matric potential were monitored during 2 years at two neighboring ridge‐top sites in an oak‐hickory stand on a Typic Paleudult forest soil with cherty silt loam texture. Hydraulic gradients and soil water contents showed distinct seasonal variation. Soil water dynamics and water budgets were simulated with a soil‐plant‐atmosphere water flow model using meteorologic, soil, and plant characteristics estimated for the two sites. A seasonal pattern of soil water drainage and upward fluxes was predicted by the model that corresponded with the field‐determined hydraulic gradients. Recharge of water up into the root zone (0‐ to 90‐cm depth) from lower depths was predicted to contribute an average of 9 and 29% of the soil evaporation plus transpiration water loss at the two sites. Total evapotranspiration, including interception evaporation, was similar at the two sites; however, the greater upward water flux at one site compensated for the lower soil water capacity in the root zone at that site. There were significant differences between calculated and simulated daily drainage rates. Simulated soil water contents for the two study sites differed somewhat from measured values obtained on specific days. At longer time scales, the annual water budgets simulated for the sites were similar and were in reasonable agreement with measurements from a local watershed study. Annual evapotranspiration was predicted to be 74.5 cm for the ridge‐top forest stand, somewhat higher than the average of 70.5 cm estimated for the whole watershed.
Transformation of Incubated Micronutrient Chelates in Calcareous Soils
Authors: Ryan John , Hariq S. N.
Published: July 2010

Micronutrient chelates have been introduced as fertilizing materials to overcome deficiencies mainly in calcareous soils, and to maintain effectiveness for a significant period of time. However, few studies have examined changes in applied chelates over a normal growing season, and some selected soil and environmental properties which influence these changes. Laboratory incubation studies, up to 168 d, were conducted to evaluate the influence of associated properties in several soils and, added CaCO3 (0, 2.5, 5.0, and 10.0% wt/wt), temperature (5, 15, 25, and 35°C) and wetting‐drying (up to four weekly cycles) on the persistence of applied FeEDDHA and Zn‐, Mn‐, and CuEDTA. Incubated samples were extracted with water and then with DTPA‐extraction solution. Recovery varied with the metals in each soil. After 168 d, 32 to 56% of the applied Fe and <13% of the applied Cu and Zn was extracted by both solutions. Loss of Mn from MnEDTA was essentially complete within 2 d. Decreased metal extractability appeared to be related to the organic matter content of each soil. Applied CaCO3 depressed recovery with no significant difference between application rates. Metal extraction also decreased consistently with increasing temperature and with the number of wet‐dry cycles compared to constantly moist samples. The results have implications for arid‐region soils where chelates are used under irrigation and high soil temperatures.
Linearized Moisture Flow with Root Extraction Over Two‐Dimensional Zones
Authors: Warrick A. W. , Lomen D. O.
Published: July 2010

A solution of Richards' equation is developed for flow from a two‐dimensional, rectangular source or sink. The soil is assumed uniform with the unsaturated hydraulic conductivity exponentially related to pressure head. Steady‐state conditions are used, although a time‐dependent solution is discussed. The results are useful for approximating any two‐dimensional, explicitly defined root extraction pattern. This is possible by superimposing several rectangles to give the desired effect. Calculations are rapid with negligible computer time. Several examples are given appropriate for trickle irrigation, including stratified uptake regions, noncontiguous extraction zones, and a nonsymmetric case.
Adsorption of Oxamyl and Dimecron in Montmorillonite Suspensions
Authors: Bansal O. P.
Published: July 2010

Adsorption of oxamyl and phosphamidon (Dimecron) was determined from dilute solutions of montmorillonite saturated with different cations, e.g., Li+, Na+, K+, Cs+, Fe3+, and Al3+. Adsorption of oxamyl was found to be greater than adsorption of Dimecron. The shapes of the isotherms depended on the exchangeable cations. The adsorption varied directly with the polarizing power of the exchangeable cation and inversely with changes in temperature, organic matter, and ionic strength up to 0.6, after which it became constant. The enthalpy changes (ΔH°) calculated from the temperature coefficient of the equilibrium constant showed that the process is exothermic. The adsorption of pesticides on montmorillonite gives rise to an entropy loss that is higher for trivalent cations. Various studies, e.g., infrared (IR) and x‐ray, as well as thermodynamic parameters and Freundlich adsorption isotherms, revealed the existence of protonation or coordination (or both) between exchangeable cations of clay and oxygen of > C=0 group of the pesticides. However, desorption studies showed the presence of physical adsorption.
Trace Metal Chemistry in Arid‐Zone Field Soils Amended with Sewage Sludge: III. Effect of Time on the Extraction of Trace Metals
Authors: Sposito Garrison , LeVesque C. S. , LeClaire Joseph P. , Chang A. C.
Published: July 2010

The surface horizons of two arid‐zone field soils that either had received amendments of composted sewage sludge annually since 1975, or had received amendments of liquid sludge between 1976 and 1978, were fractionated by sequential extraction for 4 years annually, beginning in 1979, to compare the solid‐phase forms of Ni, Cu, Zn, Cd, and Pb. The total concentration of each trace metal in the soils continually receiving composted sludge increased with time, whereas the total concentration of the metals in the soil that had received liquid sludge until 1978 did not increase with time. Regardless of the time variation of total metal concentration, the percentages of the metals in either the EDTA (ethylenedinitrilote‐traacetic acid)‐extractable fraction or the HNO3‐extractable fraction often tended to increase with time in the soils. This trend was more evident in the lighter‐textured field soil receiving composted sludge. It was concluded that the observed increase in EDTA‐extractable trace metals with time could be the result of the formation of trace metal carbonates accompanying the gradual mineralization of the organic matter in the applied sludge in the soil environment.
Changes in Phosphorus Adsorption Associated with Aging of Aluminum Hydroxide Suspensions
Authors: Sims J. T. , Ellis B. G.
Published: July 2010

Phosphorus adsorption by “pure” Al‐OH suspensions was examined as a function of pH of Al‐OH precipitation, length of incubation, and ionic strength. Changes in P adsorption were measured through use of Langmuir isotherms after 30, 180, and 365 d of incubation. Physical characterization of changes in the Al‐OH suspensions was accomplished through x‐ray diffraction and scanning electron microscopy. Aging of Al‐OH suspensions reduced their capacity for P adsorption, and while Al‐OH precipitated at pH 5.5 initially adsorbed more P than that precipitated at pH 7.0, the difference became insignificant within 90 d. Reducing the ionic strength of the Al‐OH suspensions by dialysis produced gibbsite and caused a decrease in the P adsorption maxima (Langmuir b value), further evidence that the polymerization/crystallization process is an important control of Al‐OH reactivity for P.
The Effect of Temperature on Decomposition at Optimum and Saturated Soil Water Contents
Authors: Clark M. D. , Gilmour J. T.
Published: July 2010

A laboratory study was conducted to evaluate the effect of temperature on decomposition in a silt loam soil under saturated (0.32 g/g) and optimal (0.19 g/g) soil water contents. Sewage sludge was the carbon substrate. Cumulative CO2‐C data were obtained for three temperatures (14, 22, and 30°C), and two substrate groups (rapid, intermediate) for the saturated and optimal water contents. Decomposition followed first‐order kinetics. The temperature effect for each substrate and water content was described by regressing the natural logarithm of the first‐order rate constant on the inverse of the absolute temperature. No significant differences in slopes between substrates within a water content were found for these regressions. Slopes were significantly different between water contents. The slopes were −8975 and −2660 K for the unsaturated and saturated soils, respectively. At saturation the much smaller rate of change in the rate constant, k, with temperature (slope) indicated that temperature had a much smaller influence on decomposition rate under saturated than under unsaturated conditions. Intercepts from the above regressions were significantly different between substrates and water contents. For the unsaturated soil, intercepts were 25.86 and 29.41 for the rapid and intermediate substrates, respectively. Parallel intercepts at saturation were 3.48 and 2.36, respectively. Differences in intercepts between water contents combined with slopes resulted in smaller k values for the saturated soil. These results pointed out that a single equation describing the effect of temperature on the first‐order rate constant should not be applied to the decomposition of organic matter in both unsaturated and saturated soils.
Complementary Methodologies to Delineate the Composition of Rhizobium trifolii Populations in Root Nodules
Authors: Dughri M. H. , Bottomley P. J.
Published: July 2010

Three methods of strain identification were used to determine the composition of the Rhizobium trifolii population in nodules formed on subterranean clover (Trifolium subterraneum L. cv. Mt. Barker) inoculated with a soil suspension. Sodium dodecyl sulfate polyacrylamide gradient gel electrophoresis (SDS‐PAGGE) was used in a microslab system to elucidate the protein profiles of 22 isolates of R. trifolii. Tube agglutination serological tests carried out with antisera raised to four isolates showed that four groups of isolates could be recognized. Only four isolates out of 22 agglutinated with more than one antiserum, although they reacted with only one antiserum in the gel‐immune‐diffusion test. One isolate did not react with any of the four antisera. No group of isolates dominated the nodule population. Gel‐immune‐diffusion analysis showed that isolates from two of the four groups were serologically identical whereas isolates from the other two groups were serologically heterogeneous. Isolates within all four serogroups were subdivided further according to their protein profiles. Many of the isolates within individual groups had very closely similar or identical profiles whereas others were very distinct. Isolates identified as very similar or identical by SDS‐PAGGE had the same symbiotic effectiveness on T. subterraneum. The data illustrate the need for multiple methods of identification for the best delineation of the composition of the nodule population.
Effect of Entrapped Air on ECa vs. ECw Calibration Curves as Measured in a Soil Column
Authors: Frenkel H. , Nadler A. , Shainberg I.
Published: July 2010

Measurements of soil electrical conductivity, ECa, for assessing soil solution salinity, ECw, use calibration curves obtained in the field or in the laboratory. It has been found that calibration curves obtained in the laboratory on water‐saturated soil columns are very sensitive to entrapped air which affects the calibration slope of ECa − ECw by 25% or more. This difference in the slope is as large as the difference in slopes between soils having 25 and 50% clay. Displacing the entrapped air with CO2 before saturation reduces the problem and produces a more accurate calibration curve.
Two Types of Soil Anisotropy Induced by the Passage of a Wetting Front
Authors: Dexter A. R.
Published: July 2010

Disks of soil were wetted from a point on their diameters. The tensile strength of the soil disks was measured using the Brazilian crushing test. Tensile strength was measured both in the direction of wetting and at right angles to the direction of wetting. These values were different, which indicated that the passage of the wetting front had made the soil anisotropic. The soil tensile strength was smallest either in the direction of wetting or at right angles to it. Some possible consequences of these changes for the processes of formation of natural soil structures are discussed.