bluuebunny/crossref_metadata_2025 huggingface dataset:
Sulfate Retention by an Acid BE Horizon of an Ultisol
Authors: Hue N. V. , Adams Fred , Evans C. E.
Published: July 2010

Many apparently conflicting reports on sulfate (SO2‐4) retention by soils suggest that a single, inclusive mechanism may not be adequate in explaining SO2‐4‐soil reactions and that additional experimentation is needed for different soils. An acid Benndale (Typic Paleudults) BE horizon, predominantly kaolinite and gibbsite in the clay fraction, was initially treated with either five lime rates or five gypsum rates. After 14‐d of incubation at field capacity, previously limed soils were amended with gypsum, and previously gypsum‐treated soils were limed. All samples were again incubated moist for 14 d, after which soil solutions were displaced and their chemical compositions determined. The sequence of Ca(OH)2 and CaSO4 additions did not affect SO2‐4 retention. Furthermore, SO2‐4 retention isotherms indicated that multiple mechanisms were involved because at low pH (<5.1) an adsorption‐precipitation type mechanism dominated, while at high pH (>5.6) electrolyte adsorption was dominant. This was further supported by the decrease in the ratio of OH‐ gain to SO2‐4 retention as soil pH increased. Sulfate retention was also accompanied by an increase in total exchangeable cations. Cation increases, however, varied with pH and SO2‐4 rates. The combined increases in OH‐ and exchangeable cations, particularly at low pH and high SO2‐4 rates, are inexplicable with current SO2‐4‐soil reaction models.
Fertilizer Nitrogen and Nitrogen‐15 in Three Warm‐season Grasses Grown on a Florida Spodosol
Authors: Impithuksa V. , Blue W. G.
Published: July 2010

Recovery of fertilizer N in plant tops is generally considered to be about 50% of that applied. With increasing cost of fertilizer N and concern for environmental contamination by N lost from soilplant systems, it is important that absorption of fertilizer N be maximized. Introduced warm‐season grasses have different morphological characteristics, and they may differentially absorb N. To investigate this possibility, a field study with enriched 15NH415NO3 was superimposed in March 1977 on a nontracer N experiment with three warm‐season grasses—Ona stargrass (Cynodon nlemfuensis Vanderyst), Transvala digitgrass (Digitaria decumbens Stent), and Pensacola bahiagrass (Paspalum notatum Flugge)— on EauGallie fine sand (sandy, siliceous, hyperthermic Alfic Haplaquods) at the Agricultural Research Center, Ona, FL. Two N rates (100 and 200 kg ha−1) were the subplots, and three times of 15N‐labeled fertilizer N application were the sub‐subplots. In 1977, quantities of total and 15N‐labeled fertilizer N in forages did not differ among grass species, but they were largest in the Pensacola bahiagrass stolon‐root mass. Recovery of fertilizer N in forage as averages of the two N rates and the three times of 15N‐labeled fertilizer application was 35, 40, and 35% of that applied to Ona stargrass, Transvala digitgrass, and Pensacola bahiagrass, respectively; 13, 9, and 20% of that applied was in the stolon‐root masses; and 22, 17, and 20% of that applied was in the soil presumably in organic form, since it was neither water‐soluble nor exchangeable. Approximately 50% of the N in forages came from the 15N‐labeled fertilizer and 50% from nonfertilizer sources, Recoveries of fertilizer N in soil‐plant systems were 70, 66, and 75% of that applied to Ona stargrass, Transvala digitgrass, and Pensacola bahiagrass, respectively. The sums of fertilizer N in forages from 1977 and 1978, and in the stolon‐root masses and soil at the end of 1978, did not differ significantly from amounts accounted for at the end of 1977. Results from the study indicated (i) essentially equal quantities of labeled N in the three soil‐warm season grass systems, (ii) relatively large retention of labeled N in these sandy soils, and (iii) a large amount of nonfertilizer N in forages in 1977, the year of 15N‐labeled fertilizer application.
Availability and Transformation of Applied Phosphorus In Calcareous Lebanese Soils
Authors: Ryan J. , Hasan H. M. , Baasiri M. , Tabbara H. S.
Published: July 2010

Though the initial reactions of P in soils are important with respect to plant growth and efficient fertilizer use, the reactions that occur with time have received less research attention, and may have even more important implications for these aspects. In order to monitor changes in applied P after fertilization, six calcareous soils were incubated up to 200 d with P solutions and periodically extracted with NaHCO3, and inorganically fractioned. Soil batches were equilibrated with P solutions ranging from 0 to 40 mg P L−1 for adsorption isotherm data after 0, 60, and 200‐d incubation. Desorption curves were obtained by water extraction for eight consecutive days. Extractable P values declined rapidly within the first day, and uniformly thereafter. The amounts of P retained against NaHCO3 extraction were closely related to citrate‐dithionite‐bicarbonate (CDB)‐Fe. With the longer incubation period, generally less P was released in the water extraction. Similarly, desorbed P was inversely related to CDB‐Fe. While P additions mainly enriched the NH4Cl‐ and NaOH‐P fractions, the amounts recovered decreased with time. Increasing prior soil‐P contact time also caused a shift in the adsorption isotherms, reflecting changes in retained P and the soils' retention capacity. Thus, free Fe oxides may modify longer‐term P reactions and residual P availability in CaCO3‐rich soils.
Measurement of Shear Strength and Bulk Density of Soil Aggregates
Authors: Benjamin J. G. , Cruse R. M.
Published: July 2010

A method was developed to measure soil aggregate shear strength and bulk density at soil water matric potentials <0. Strength measurements were made with the Swedish fall‐cone penetrometer, and bulk density measurements were made by gamma‐ray attenuation. The method allowed both density and strength measurement on the same aggregate. Tests were conducted at soil water matric potentials of −0.2, −1.1, and −4.0 kPa. As the matric potential decreased, the shear strength of the soil aggregates increased. The method described by this paper is an improvement on the standard wet‐sieve technique for determination of aggregate stability as follows: (i) it allows the measurement of aggregate strength at matric potentials <0, (ii) the strength measurement is in units of stress, and (iii) the aggregate density as well as aggregate strength can be measured on each sample. The disadvantage is that aggregates with diameters ≥ 2 cm are required for the measurement.
Statistical Analysis of Sorghum Yield: A Stochastic Approach
Authors: Morkoc F. , Biggar J. W. , Millar R. J. , Nielsen D. R.
Published: July 2010

The spatial variability of the yield of a sorghum (Sorghum vulgare Pers.) crop irrigated by a two line source sprinkler system is analyzed. This system, with two different qualities of irrigation water, produced a uniform water but varying salt application between the irrigation lines. On the outside of the irrigation lines both the amount of applied water and salt varied. Maximum yield was obtained around the low salt line and the yield decreased from the low (EC = 1.50 dS m−1) to high (EC = 4.02 dS m−1) salt line. On the outside of the irrigation lines the sorghum yield decreased approximately linearly with distance from each sprinkler line. The sorghum was harvested with 1‐m sampling intervals along five 45‐m transects normal to the irrigation lines. Sample autocorrelation function (SACF) of the mean yield showed high correlation values at the first two lags and a slow decay thereafter, indicating the nonstationary behavior caused by the controlled water application. A fourth‐order polynomial removed the deterministic component of the yield. The sample autocorrelation function of the residuals showed spatial structure with a significant peak at lag 1 and indicated that the stationarity condition is achieved. Further analysis of the residuals using the sample partial autocorrelation function (SPACF) revealed significant peaks at lags 1 and 2. The behavior of SACF and SPACF indicated that the spatial structure of residuals related to the effect of soil salinity variation on the sorghum yield is well described by a second order autoregressive process with a white noise (identically and independently distributed with mean (x) zero and variance σ2).
Ethylene Biosynthesis in Soil: I. Method of Assay in Conversion of 1‐aminocyclopropane‐1‐carboxylic Acid to Ethylene
Authors: Frankenberger W. T. , Phelan Patrick J.
Published: July 2010

Ethylene (C2H4) is a common biologically active secondary metabolite produced by soil microorganisms which can have a tremendous potential impact on crop yield. Methionine (MET) has been shown to be the major substrate for C2H4 biosynthesis in higher plants and soil microorganisms. Although 1‐aminocyclopropane‐1‐carboxylic acid (ACC) is an intermediate in the conversion of MET to C2H4 in plant tissues, the immediate precursor of C2H4 and its biosynthetic pathway in soils has yet to be established. The primary objective of this study is to develop a method of assay to characterize the microbial conversion of ACC to C2H4 in soil. Results showed that the rate of C2H4 released from soil was enhanced with increasing pH (up to pH 9.0). The reaction rates of this transformation approached zero‐order kinetics when 9.9 mM ACC was added to soils. Under standard conditions, the accumulation of C2H4 was linear with time of incubation for at least 7 d. Maximum reaction rates in the conversion of ACC to C2H4 were observed at 50°C with enzyme denaturation occurring at 55°C. ACC derived‐C2H4 production in soils was enhanced under highly oxidized conditions and severely inhibited under anaerobiosis. Among various pretreatments that affected the conversion of ACC to C2H4, toluene, CoCl, and oscillation enhanced C2H4 biosynthesis, whereas, DMSO, formaldehyde, EDTA, 2‐mercaptoethanol, 2,4‐dinitrophenol, NaF, KCN, KNO2, and KNO3 inhibited this reaction.
Specific Adsorption of Lithium, Sodium, Potassium, and Strontium to Montmorillonite: Observations and Predictions
Authors: Nir S. , Hirsch D. , Navrot J. , Banin A.
Published: July 2010

The adsorption of Li, Na, K, Cs, and Sr to montmorillonite is studied within the framework of a model that accounts for specific binding as well as adsorption in the double layer region. Variations in solution concentrations of cations due to adsorption are explicitly considered. The experimental data include adsorption measurements in binary and ternary systems of cations as well as adsorption data taken from the literature. Solution and adsorbed concentrations of cations are well simulated and predicted by the calculations for a wide range of variations of cation ratios, ionic strengths, and clay concentrations. The values determined for the binding coefficients are: KLi = 0.6 M−1, KNa = 1 M−1, KK = 2 M−1, KCs = 200 M−1.
Specific and Nonspecific Cation Adsorption to Clays: Solution Concentrations and Surface Potentials
Authors: Nir Shlomo
Published: July 2010

A model for cation adsorption to negatively charged surfaces is developed by taking into account specific cation binding to the surface sites and adsorption in the double layer region. Equations are given for any combination of mono and divalent cations in solution and for one type of binding site. Variations in solution concentrations of cations due to adsorption are explicitly included in the model in the framework of an iterative procedure. The results indicate that a Langmuir type of adsorption isotherm may represent the data over a certain range of cation concentrations. When a certain cation is present in such small concentrations that it does not affect the surface potential, then an increase in its concentration results in a proportional increase in its adsorbed amount. For a wide range of concentrations the amount of cation adsorbed appears to be independent of its concentration in solution. However, the adsorbed amounts are very sensitive to cation competition. An increase in the concentration of surface sites results in as reduction in the fractional binding per sits. A source of difference between sorption and desorption of cations is explained.
Evaluation of Potassium Quantity‐Intensity Relationships by a Computer Model Employing the Gapon Equation
Authors: Evangelou V. P. , Karathanasis A. D.
Published: July 2010

The influence of cation exchange selectivity coefficients on quantity‐intensity (Q/I) relationships of soil systems was evaluated by the Gapon equation. Computer simulations of potassium Q/I plots revealed that the linear potential buffering capacity for K+ (PBCK), when exchangeable K+ constitutes a minor portion of the CEC, depends on the magnitude of the soil CEC and the Gapon exchange selectivity coefficient (KG). This dependency is valid only if the Q/I plot is directly K‐(Ca + Mg) interaction dependent. Upon increasing the CEC and KG, PBCK increases since PBCK = CEC KG. At low KG values the CEC has a lesser influence on increasing the PBCK, and at low CEC values the KG has a smaller influence on the magnitude of the PBCK. The PBCK is also inversely related to soil K‐loading but the influence of K‐loading on the magnitude of PBCK, appears to be important only when exchangeable K+ represents a significant portion of the CEC. The influence of K‐loading on the magnitude of PBCK, however, appears to be considerable only at K‐loading values much higher from those encountered in most agricultural soils. These findings are supported by data available in the literature.
Coastal Plain Soils of Southeastern Nigeria: I. Morphology, Classification, and Genetic Relationships
Authors: Lekwa G. , Whiteside E. P.
Published: July 2010

Fourteen pedons developed within the Coastal Plain Sands of southeastern Nigeria were investigated. Laboratory studies included particle size distributions on all pedons plus <0.2‐µm clay, pH, organic C, total N, cation exchange capacity, exchangeable bases, and extractable Al on nine of them. X‐ray analyses of selected clay samples and micromorphologic studies of thin sections of some horizons were also made. Exchangeable bases and base saturation percentages were low for these deeply weathered soils and they had low cation exchange capacities. X‐ray diffraction analyses of clay indicated the predominance of kaolinite. In most of the selected soils isotic and undulic plasmic fabrics characterized the micromorphology, indicating relatively advanced weathering stages. Ferri‐argillans were occasionally observed in the deeper horizons in accord with their higher clay and Fe2O3‐d contents (see part II, this issue). Litho‐, topo‐, climo‐ and possible chronosequences of soils were proposed. Biosequences were not clearly evident. Classification according to the U. S. Soil Taxonomy system indicated that most of the pedons were Ultisols (fine‐loamy or coarse‐loamy) with one Dystropept (coarse‐loamy) and one Tropaquod (sandy). Typic Paleustults (fine‐loamy) represented most soils on the higher (older?) physiographic surfaces. Three Typic Paleudults (fine‐loamy), an Arenic Paleudult (coarse‐loamy), a Typic Paleaquult (coarse‐loamy), and a Typic Tropaquult (fine‐loamy) were found on lower land surfaces nearer the coastline. All pedons are in siliceous, isohyperthermic families. Most of the well‐drained soils were found to be Dystric Nitosols according to the FAO/UNESCO World Soil Map legend. Gleyic Acrisols were proposed for the more poorly‐drained associates of Nitosols. A Gleyic Podzol (with a spodic B) and a Dystric Cambisol (with a cambic horizon) were also represented.
Field Aging of Transparent Polyethylene Mulches: II. Influence on the Effectiveness of Soil Heating
Authors: Avissar R. , Naot O. , Mahrer Y. , Katan J.
Published: July 2010

Photometric properties of transparent polyethylene (PE) mulches change significantly during prolonged field utilization. In order to test and explain the effects of these changes on the temperature regime of mulched soil, we developed a one‐dimensional numerical model, which simulates the microclimate of mulched soils. The model consists of three layers: soil, plastic, and the air enclosed between them. Given the thermal and hydraulic properties of the soil, the photometric properties of the plastic, and appropriate climatic conditions, the model computes the diurnal variation in temperature and humidity of the different layers. Field measurements verify the model's ability to predict the temperature regimes of mulched soils. Both numerical and field experiments show that mulching the soil with PE sheets previously used during one solarization season, rather than new ones, results in more effective heating of the soil and, therefore, faster killing of pathogenic soil fungi. This is explained by the relatively higher reflectance of new mulch, due to the condensation of small water droplets on its inner surface. Recycling polyethylene sheets, previously used for agricultural purposes, provides an extremely inexpensive method for soil mulching.
Physical and Chemical Properties of a Haploxeroll after Fifty Years of Residue Management
Authors: Pikul J. L. , Allmaras R. R.
Published: July 2010

Greater inference about the value of long‐term crop residue management requires that soil chemical properties be measured together with soil physical properties. After 54 yr of several different crop residue management treatments in a winter wheat (Triticum aestivum L.)‐fallow system in the Pacific Northwest, soil bulk density (ρb), saturated hydraulic conductivity (Ksat), soil water desorption curves (SWDC), soil organic carbon, and soil pH were all used to quantify the soil physical and chemical state. All wheat straw, chaff, and manure additions were incorporated by spring plowing in an alternating winter wheat‐fallow rotation. The residue treatments were: (i) straw, (ii) straw plus 22 Mg/ha strawy manure, (iii) straw burned in the fall, and (iv) straw plus 90 kg/ha of N as NH4NO3 broadcast before seeding. Straw return in treatments 1, 2, and 4 depended especially on the N added. Soil ρb at 0.02‐m increments was used to locate compacted layers. Respective tillage pan ρb for treatments 1, 2, 3, and 4 were 1.3, 1.2, 1.3, and 1.2 Mg/m3; respective Ksat, using a double tube method, were 0.34, 0.85, 0.29, 0.23 µm/s. Respective Ksat, above the tillage pan, using an air‐entry permeameter were 1.08, 2.24, 1.52, and 2.36 µm/s. Average ρb and Ksat distinguished between treatments with low vs. high return of residue. SWDCs in the plow layer and tillage pan reflected the degree of soil compaction within and among treatments. No treatment differences in Ksat or ρb were found below the tillage pan. The Ksat in the tillage pan, relative to overlying and underlying layers, indicated that the tillage pan governs water flow in this soil. Soil pH of the Ap horizon was 5.6, 6.1, 5.4, and 4.8 for treatments 1, 2, 3, and 4, respectively; respective percent organic carbon was 1.14, 1.53, 1.07, and 1.25. The Ksat in the tillage pan was maintained at a high level only where residue additions were increased and soil pH maintained above 5.6.
Simulated Acid Rain Effects on Jack Pine Seedling Establishment and Nutrition
Authors: MacDonald Neil W. , Hart James B. , Nguyen Phu V.
Published: July 2010

A greenhouse study examined the effects of simulated acid rain on jack pine (Pinus banksiana Lamb.) seedling development and the Grayling sand (Typic Udipsamments) growth medium. Five rain pH levels (2.0, 2.5, 3.0, 4.0, 4.7) and two soil horizons (A/E, Bw1) were included as levels of factors. Soil pH decreased only at rain pH 3.0 and below. Exchangeable Ca and Mg were reduced at pH 2.0 in A/E horizon soil only. Germination of jack pine was inhibited at pH 2.0 on both soils. Mortality of germinants was over 95% on both soils at pH 2.0, 42% on A/E soil at pH 2.5, and 2 to 13% in other treatment combinations. Seedling top weight increased and root weight decreased on both soils at pH 2.5. In seedlings grown at pH levels 2.5 to 4.7, tissue concentrations of N, K, Ca, Na, Mn, Zn, and Al increased, but P and Mg were reduced, as rain pH decreased. At pH 2.5, Al toxicity and deficiencies in P and Mg were indicated. Simulated rain approximating pH levels typical of precipitation in northern lower Michigan (> 3.0) did not adversely affect jack pine regeneration or soil properties of the Grayling sand during the 75‐d study.
Determination of the Gibbs Free Energy of Formation of Magnesite by Solubility Methods
Authors: Kittrick J. A. , Peryea F. J.
Published: July 2010

The current values reported for the Gibbs free energy of formation for magnesite [MgCO3(s)] are bimodally grouped, centered at −1012 kJ mol−1 and in the range −1026 to −1030 kJ mol−1. The solubilities of three natural magnesites in aqueous solution were determined in order to verify the appropriate values. The samples were equilibrated at high solid‐to‐liquid ratios with solutions that were initially undersaturated or supersaturated with respect to magnesite. The chemical activities of pertinent system components at equilibrium were measured analytically or calculated using an ion‐association computer model. The results of 50 solubility determinations yielded a mean Gibbs free energy of formation of −1026.0 ± 2.1 kJ mol−1. Identical values were obtained from undersaturation, using an immiscible displacement technique, and from supersaturated initial conditions. These data suggest that the more negative values reported for the Gibbs free energy of formation are correct; hence, magnesite will be the only thermodynamically‐stable Mg carbonate phase in surface or near‐surface geochemical environments. The attainment of equilibrium in initially undersaturated systems containing either magnesite only or a mixture of magnesite, kaolinite, and montmorillonite was not impeded by the presence of soluble silicon (Si). This observation indirectly discounts the hypothesis that dissolved Si may form magnesium silicate coatings on magnesite surfaces, thus limiting the rate of dissolution and preventing the establishment of chemical equilibrium.
Leaching of Herbicides Through Undisturbed Cores of a Structured Clay Soil
Authors: White R. E. , Dyson J. S. , Gerstl Z. , Yaron B.
Published: July 2010

The leaching of the herbicides bromacil and napropamide through large undisturbed cores of a structured Evesham clay (Aquic Eutrochrept) was studied under continuous and discontinuous watering regimes and at different initial moisture contents. A greater proportion of both herbicides was leached from initially dry cores (θ = 0.24) than from prewet cores (θ = 0.35). This was consistent with differences in the amount of herbicide retained in the soil, most of which was retained in the top 0.05 m. Continuous leaching resulted in greater herbicide breakthrough than did the discontinuous treatment, presumably because some herbicide diffused from the conducting channels into the soil aggregates during the quiescent period, where it was less susceptible to subsequent leaching. At a continuous input rate of 12 mm h−1 to initially dry soil, 85% of the applied napropamide (Kd = 17.7 L kg−1) and almost 100% of bromacil (Kd = 1.73 L kg−1) were leached out of the soil by one pore volume of water. Chloride was used as a tracer for water flow through the soil. Chloride breakthrough curves were analyzed using a transfer function equation, which yielded the median travel time of a solute molecule in the soil. It is suggested that preferential flow of water down cracks and channels between soil aggregates led to short travel times and apparently low volumes of soil water participating in solute transport (θst). The θst values were inversely correlated with the percentages of the applied herbicides that were leached.
A Critical Evaluation on the Use of Kinetics for Determining Thermodynamics of Ion Exchange in Soils
Authors: Ogwada R. A. , Sparks D. L.
Published: July 2010

Thermodynamics of K‐Ca exchange were compared using equilibrium and kinetic approaches in two Delaware soils. The classical Argersinger theory was employed for the equilibrium approach, while a kinetic approach was studied using miscible displacement, batch, and vigorously mixed batch techniques. These three techniques were used to determine how diffusion affects the comparison between thermodynamic parameters using kinetic and equilibrium approaches. Rate coefficients and energies of activation were profoundly affected by the type of kinetic technique employed and their magnitude was in the order: vigorously mixed batch > batch > miscible displacement. Energies of activation for adsorption (Eaa) in the two soils ranged from 7.42 kJ mol−1 using the miscible displacement technique to 32.96 kJ mol−1 with the vigorously mixed batch, while energies of activation for desorption (Ead) ranged from 11.87 to 42.1 kJ mol−1 for the two methods, respectively. The magnitude of the Eaa and Ead values indicated pronounced diffusion effects in the miscible displacement and batch techniques, which were greatly reduced with the vigorously mixed batch method. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) calculated using the equilibrium and kinetic approaches compared very well in trend, and gave the same inferences of ion behavior for the two soils studied. However, except for the vigorously mixed batch technique, the magnitude of the thermodynamic parameters for the two approaches compared poorly. For example, the ΔG° values calculated using the equilibrium approach avg 4.67 kJ mol−1 for the two soils, while they avg 4.92 kJ mol−1 with the vigorously mixed batch, 2.12 kJ mol−1 with the batch, and 2.12 kJ mol−1 with the miscible displacement. The degree of comparison between the two approaches was directly related to the extent of diffusion controlled exchange. When the influence of diffusion was significantly reduced, as with the vigorously mixed batch technique, our data would indicate that a kinetic approach can be successfully used to gather thermodynamic information about a soil system.
Soil Physical Properties as Influenced by Cropping and Residue Management
Authors: Skidmore E. L. , Layton J. B. , Armbrust D. V. , Hooker M. L.
Published: July 2010

Alternate methods of residue management for reduced tillage under irrigation and in double cropping systems are constantly being sought. One method that is becoming increasingly popular is residue burning. Knowing how to best manage crop residues to maintain desirable soil physical properties for decreasing erosion and increasing crop yields in these cropping systems is a problem. This study was conducted to determining the influence of several methods of residue management for winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] on physical properties of Richfield silty clay loam (fine, montmorillonitic, mesic Aridic Argiustolls). Residue management treatments were: residue removed by burning, residue removed by baling and hauling, incorporation of the residue produced during the immediate past cropping season, and incorporation of twice the amount of residue produced by the crop. Most of the soil physical properties measured were not influenced by either grain sorghum or wheat residue management treatments; however, they differed between crops. The soil aggregates from the sorghum plots were smaller, more fragile, less dense, less stable dry, and more stable wet than the aggregates from the wheat plots. The pore size distribution of the soil from the Ap horizon of the sorghum plots was more conducive to water infiltration. The saturated hydraulic conductivity was several times greater in the soil cores obtained from the sorghum plots than those obtained fro the wheat plots.
Optimal Ratios of Saline and Nonsaline Irrigation Waters for Crop Production
Authors: Dinar Ariel , Letey J. , Vaux H. J.
Published: July 2010

Increased demands for freshwater in irrigated agriculture might be offset in some instances by substituting saline waters when they are available. The purpose of this paper is to present a quantitative method for determining the optimal mix of saline and nonsaline waters for crop production. Equal yield curves (isoquants), which quantify the extent of substitutability between waters of different qualities when constant yield is sought, were derived from crop‐water production functions for waters of different qualities computed from a previously published model. Isoquants were derived for several crops for relative yield (RY) values of 1.0, 0.9, and 0.8. The waters considered for mixing were nonsaline waters and waters of electrical conductivity (EC) equal to 4, 6, or 11 dS/m. Extending the supply of water by combining nonsaline and saline water is not always technically or economically feasible, and depends on specific crop and water pricing situations. The technical and economic feasibility of mixing waters of different quality increases as the EC of the saline water decreases, crop tolerance to salinity increases, desired RY decreases, or the relative price of saline to nonsaline water decreases.
Soil Compaction from Harvesting and Site Preparation in the Upper Gulf Coastal Plain
Authors: Gent J. A. , Morris L. A.
Published: July 2010

The impact of intensive forest management practices on the physical properties of a Typic Paleudult was examined to a depth of 0.3 m by collecting 7.6‐cm core samples before harvest, after harvest, and after site preparation. Whole‐tree harvesting of a 22‐yr‐old loblolly pine (Pinus taeda L.) plantation caused significant changes in bulk density to a depth of 0.23 m outside of skid trails, and 0.30 m in primary skid trails. Subsequent chop/burn and shear/windrow site preparation treatments had little added impact on bulk density. Post site preparation differences in aeration porosity and saturated hydraulic conductivity among treatments were nonsignificant.
An Electrical Readout System for Tensiometers
Authors: Lowery B. , Datiri B. C. , Andraski B. J.
Published: July 2010

Commercially available pressure transducers (PTs) and tensiometers were combined to continuously monitor in situ soil pore‐water pressure. The transducers were calibrated over a range of 0 to −76.5 kPa and a temperature range from 5 to 40°C. A single calibration equation corrected for zero offset and a small temperature‐induced variation. Field temperature fluctuations between 10 and 30°C had little effect on results from PTs connected to constant pressures of −5 and −11.5 kPa. Wetting fronts were easily mapped with outputs from tensiometers placed at three different depths. From these field data, prior water history and diurnal changes in soil pore‐water pressure were easily obtained. Given variable field conditions, results from the PTs agreed well with closely‐placed Bourdon gauge tensiometers.
Artificial Intelligence, Cognitive Science, and Measurement Theory Applied in Soil Classification
Authors: McCracken Ralph J. , Cate Robert B.
Published: July 2010

Recent advances in artificial intelligence and related fields have relevance to problems encountered in soil classification. Expert systems can be used to strengthen efforts to update and revise soil classification, to maintain large data bases such as Soils‐5, and to involve field personnel in technical evaluation programs. Expert systems may also be applied to other areas of soil science, where judgement and practical experience by experts can be computerized, such as soil management recommendations on irrigation, fertilizer use, and erosion control. Cognitive science research aimed at better understanding of the fundamental aspects of mental representation and categorization may provide stimuli to research on improvements in soil classification. Understanding of the theory of measurement can lead to more efficient, less arbitrary use of quantification techniques in the description and interpretation of soils. The purpose of this paper is to draw to the attention of pedologists and other soil scientists the potential usefulness of recent advances in artificial intelligence, cognitive science, and measurement theory. Following an introduction to these fields, we provide suggestions and specific examples regarding their application to soil classification. Our hope is that this introduction will encourage soil scientists to learn more about these disciplines and consider additional applications to soil science.
Air Encapsulation: II. Profile Water Storage and Shallow Water Table Fluctuations
Authors: Fayer M. J. , Hillel D.
Published: July 2010

In a wet soil, volumetric encapsulated air contents can easily approach 0.06 m3 m−3. The objective of this study was to determine, through simulation, the effect of air encapsulation on profile water storage and shallow water table fluctuations and whether air encapsulation should be considered in modeling field events. Using a two‐dimensional soil moisture code that included a routine designed to model air encapsulation, we simulated profile water storage changes during hypothetical rainfall events and water table responses during actual rainfall events. The simulation results indicated that, following the infiltration of 10 mm of water, profile moisture content differences with and without air encapsulation would be <0.01 m3 m−3 and thus may not be measurable in the field with a neutron probe. Water table levels, however, rose significantly higher in the profile when air was encapsulated. Depending on the initial depth of the water table and the moisture characteristic, the water table rises were two to five times those when air was not encapsulated. For water tables located within 1.3 m of the surface, application of the model to actual rainfall events improved the fit to the measured water table data. In those situations where water table level predictions are important (e.g., wetlands, stream banks), researchers should consider air encapsulation in their analysis of water table fluctuations.
Fluridone Retention and Release in Soils
Authors: Weber J. B. , Shea P. H. , Weed S. B.
Published: July 2010

Aqueous adsorption/desorption studies showed that fluridone [1‐methyl‐3‐phenyl‐5(3‐trifluoromethyl) phenyl]‐4‐(1H)‐pyridinone) adsorbed to both organic matter and montmorillonite clay surfaces in 18 soils. Adsorption ranged from a high of 0.81 mmol/kg on Earle clay (Vertic Haplaquets) [3.7% organic matter (OM), 59% clay] to a low of 0.02 mmol/kg on an Amarillo loamy sand (Aridic Paleustalfs) (0.5% OM, 8% clay). Fluridone adsorption was highly correlated with montmorillonite clay or organic matter contents of the soils, but the highest correlation coefficients (r = 0.92) resulted when adsorption was correlated with both clay and organic matter contents. Adsorption isotherms for fluridone on three soils (Earle and Tunica [Vertic Haplaquets], and Falaya [Aeric Fluvaquents] were of the S‐type on soils containing low amounts of organic matter and high amounts of montmorillonite clay, and of the L‐type on soils high in organic matter and with low mixed clay mineralogy (Cape Fear [Typic Umbraquults] and Drummer [Typic Haplaquolls]). Isotherms for soils low in organic matter and clay content (Fincastle [Aeric Ochraqualfs] and Norfolk [Typic Paleudults]) were linear (C‐type) or of the L‐type. Fluridone adsorption increased by 38 to 42% when solution pH was decreased from 6.4 to 3.5 and the herbicide was not readily desorbed with water at the low pH level (11–27% released), suggesting that the weakly basic herbicide protonated and was bound by cation exchange forces. Large amounts (58%) were desorbed with water where adsorption occurred at higher pH levels (6.4), suggesting that only physical binding was involved. Incubation of fluridone adsorbed on soil pellets under wet, 50°C conditions reduced fluridone that could be displaced with water by 10 to 20%, as compared with incubations at 25°C, or incubations under dry conditions (25 or 50°C), suggesting that climatic factors may affect adsorption/desorption, mobility in soil, bioactivity, and persistence of the herbicide. X‐ray diffraction studies revealed that the herbicide was adsorbed in the interlayer surfaces of montmorillonite clay and Δd spacing ranged from 0.2 to 0.4 nm.
A Computer Simulation Model for Soil Genesis Applications
Authors: Levine Elissa R. , Ciolkosz Edward J.
Published: July 2010

A two horizon computer model was developed to simulate leaching and acidification processes occurring in the solid phase of soils of humid, temperate climates. The model used linear equations to describe processes of sulfate adsorption, cation exchange, mineral weathering, and precipitation and dissolution of sesquioxides within the soil. Standard soil characterization and precipitation chemistry data were used as inputs to quantitatively predict changes in soil properties over time. T‐test analysis showed no significant difference at the 0.01 level between field values and those predicted by the model for base saturation, pH, and exchangeable cations. Two examples illustrated the application of the simulation model for soil genesis investigations. In the first example, acidic soils with low buffer capacities reached 60% base saturation (Ultic Hapludalfs) and 35% base saturation (Typic Hapludults) sooner than more basic soils. Using regression analysis (excluding soils with high amounts of exchangeable bases), base saturation decreased at a rate of 0.01%/yr under deciduous forest, and 0.02%/yr under coniferous forest at precipitation pH 4.1. At precipitation pH 5.5, the rate of change was much slower. In the second example, a change in soil pH over time was predicted at precipitation pH values of 4.1 and 5.5 under deciduous and coniferous forest vegetation. In all simulations, a “steady state” soil pH level was predicted, with soils under coniferous forest reaching this level sooner than those under deciduous forest. The steady state pH was lower under precipitation pH 4.1 than under pH 5.5.
Pedogenesis on the Edwards Plateau, Texas: I. Nature and Continuity of Parent Material
Authors: Rabenhorst M. C. , Wilding L. P.
Published: July 2010

Of 15 pedons sampled on the Edwards Plateau of Texas, four were evaluated to determine the relative contribution of limestone weathering and airborne dust additions to soil formation. Although dusts were collected at measurable rates, silt grain morphology by scanning electron microscopy indicates that dusts are not accumulating on stable land surfaces. Euhedral, prismatic quartz grains were prominent components of residues from hard crystalline limestones. These grains were used as marker minerals in identifying parent material discontinuities. Quartz grain morphology, particle size distribution, elemental assay, and mineralogical data indicate lithologic discontinuities between the solum and subjacent limestone. Noncarbonate residues from petrocalcic horizons show varying degrees of similarity to the overlying sola and subjacent limestone. These soils appear to have formed from overlying limestone residuum, rather than from the underlying rock, which is different in character.
Soils of the Mall in Washington, DC: II. Genesis, Classification, and Mapping
Authors: Short J. R. , Fanning D. S. , Foss J. E. , Patterson J. C.
Published: July 2010

The soils on the Mall in Washington, DC have formed in about 6 m of miscellaneous fill deposited in repeated applications to the site during filling operations. Some limited pedogenesis has occurred; cambic, or cambic‐like B horizons were recognized in 26% of the profiles examined. Buried A horizons were found in 42% of the profiles. Classification of these soils using Soil Taxonomy alone was not satisfactory, as variations in organic matter with depth caused many of the soils to be placed in Fluv‐classes that connoted deposition of the parent material as alluvium and did not show unique accessory characteristics such as high bulk density. Proposed Urbic and Spolic subgroups of Udorthents and Ochrepts, with criteria to exclude them from Fluv‐classes, were utilized to classify these soils in a manner more consistent with their genesis and characteristics. A detailed soil map was prepared for the Mall using the proposed classification, and recommendations are made for mapping such highly manipulated areas.
Soil Nutrient Distribution Under and Adjacent to Singleleaf Pinyon Crowns
Authors: Everett Richard , Sharrow Steven , Thran Diana
Published: July 2010

Soil nutrient concentrations were examined by horizon and distance from the tree stem of singleleaf pinyon (Pinus monophylla Torr. & Frem.). Documenting tree impact on the soil system provided insights into observed understory distribution patterns and variations in understory yield among soil microsites reported previously. Nutrient concentrations were greater under the crowns of trees than in soils between trees. Cluster analysis showed a maximum of 80% similarity in the distribution among exchangeable K+, Na+, Ca2+, Mg2+; extractable Zn2+, Cu2+, Mn2+, Fe3+, SO2‐4, PO3‐4; water soluble C, mineralizable‐N, pH, total soluble salts, and HCO‐3 in relation to soil depth and distance from the tree. Soil nutrients and other measured parameters segregated into two main clusters based on distribution patterns. Extractable PO3‐4, Fe3+, Mn2+, Cu2+, Zn2+, mineralizable‐N, water soluble C, and HCO‐3 were found in highest concentrations at the soil surface. Exchangeable Ca2+, Mg2+, Na+, K+, total soluble salts, and pH had highest values in subsurface horizons. Phosphate, K+, pH, total soluble salts, and Na+ significantly increased from the interspace soils to soils under the tree canopy. Phosphate, mineralizable‐N, Zn2+, Fe3+, and HCO‐3 declined rapidly in concentration from surface to subsurface horizons under the tree crown. Small root density was directly correlated to concentrations of mineralizable‐N, Zn2+, Mn2+, Cu2+, and Fe3+. Nutrient accumulation in conjunction with soil moisture, light, and allelopathic effects is speculated to confer a competitive advantage to the tree species at the expense of the associated understory.
Microwave Drying of Clays for X‐ray Diffraction Analysis
Authors: McCallister D. L.
Published: July 2010

Clay specimens were dried in a microwave oven on glass slides for x‐ray diffraction analysis and their patterns compared with those produced by the standard air‐drying method. Drying a smectite clay at 50 or 100% power, while rapid, produced an irregular clay surface and thus a poor quality diffraction pattern. Drying at 10% power, on the other hand, gave results equivalent to air drying for hydrous mica, smectite, and kaolinite clays. Even fully expanded, glycerol treated smectite was unaffected. Equally acceptable results were found for clays fractionated from an Upshur Bt2 horizon (fine, mixed, mesic Typic Hapludalfs); a Dandridge Bw1 horizon (clayey‐skeletal, mixed, mesic Lithic Ruptic Alfic Eutrochrepts); and a Westmoreland Bt2 horizon (fine‐loamy, mixed, mesic Ultic Hapludalfs). Rapid microwave drying of highly expansible clays from a Sharpsburg A horizon (fine, montmorillonitic, mesic Typic Hapludalfs) produced severe cracking, and a poor diffraction pattern, however. Microwave drying is a rapid method of producing specimens for x‐ray diffraction that does not affect any mineralogical properties visible in the diffractogram.
Percolation of Water Below an Irrigated Field
Authors: Rice Robert C. , Bowman Robert S. , Jaynes Dan B.
Published: July 2010

Deep percolation of excess irrigation water was measured on a 0.62‐ha bare soil field. Deep percolation rates were determined from bromide added to the soil as a tracer. Core samples were taken at a depth to 2.7 m within 14 subplots after each irrigation. The depth of the maximum bromide concentration was uniformly distributed over the field. The average deep percolation rate was determined from the arithmetic mean of the tracer velocities and water content. The deep percolation rate calculated from the tracer velocities was about five times greater than determined from a water balance. The discrepancy between the tracer and water balance rates indicates that much of the water is moving in preferential paths. The water balance may overestimate the travel times of solutes and pollutants to the groundwater.
Soil‐water Determination Using Fiber Optics
Authors: Alessi R. S. , Prunty Lyle
Published: July 2010

Light transmission through a 1.0‐mm diam quartz rod was found to be consistently related to the water status of the surrounding soil. Increased soil water resulted in decreased light transmission. The measurements were made using a modified Tempe cell containing glass beads and a very fine sandy loam soil material. The major components of the measurement system were a quartz rod, a lightemitting diode, a phototransistor, fiber optic cable, and connectors. The rod was in the shape of a loop centered in the cell and separated from direct contact with the surrounding soil by a small pocket of glass beads. Increasing levels of air pressure were applied at the Tempe cell inlet; drainage volume and instrument voltage were recorded at equilibrium. These data were analyzed separately with pressure and volumetric water content as independent variables. The voltage had a highly significant response to either independent variable and there was no significant difference between slopes or intercepts of regression lines across repeated desorption cycles. The range of volumetric water content measured in the experiment was 0.10 to 0.40. It was concluded that this technique of soil water measurement is feasible and deserves further research.
Effects of Phenolic Compounds on Nitrification in Soil
Authors: McCarty G. W. , Bremner J. M.
Published: July 2010

Recent literature reflects considerable interest in the hypothesis that climax vegetation inhibits nitrification in soil and that this is due to the production in such vegetation of phenolic compounds that inhibit oxidation of NH+4 by nitrifying microorganisms. This hypothesis is based largely on the detection of tannins and phenolic acids in climax vegetation and in soil under such vegetation and on a report that very small amounts of these phenolic compounds completely inhibited NO‐2 production in an aqueous suspension of soil treated with (NH4)2SO4 and a nutrient solution suitable for growth of Nitrosomonas. To test the validity of this hypothesis, we studied the effects of different amounts of eight phenolic acids (p‐hydroxy‐benzoic acid, p‐coumaric acid, vanillic acid, ferulic acid, caffeic acid, ellagic acid, gallic acid, and chlorogenic acid) and five tannins [mangrove (Rhizophora mangle), quebracho (Quebrachia lorentzii), mimosa (Albizia julibrissin), chestnut (Castanea dentata), and sumac (Rhus coriaria)] on nitrification in soils incubated at 30°C after treatment with (NH4)2SO4. These studies provided no support for the hypothesis that climax vegetation inhibits nitrification in soil by producing phenolic compounds because they showed that phenolic acids and tannins did not significantly affect nitrification in soil even when the amounts applied greatly exceeded the amounts that have been reported to inhibit nitrification or to occur in soil.