bluuebunny/crossref_metadata_2025 huggingface dataset:
Backtitration Technique for Proton Isotherm Modeling of Oxide Surfaces
Authors: Schulthess C. P. , Sparks D. L.
Published: July 2010

Batch potentiometric titration analyses were made on a γ‐Al2O3 colloidal suspension and interpreted in terms of the electroneutrality principle. Three titration methods involving a singular reference curve were compared. The first reference used was theoretical, the latter two were representative supernatant curves: an electrolyte solution, and an aliquot of the zero point of titration (ZPT) supernatant. All three methods resulted in similar charge isotherms and a zero point of charge (ZPC) = 8.60. A fourth titration method was developed involving each supernatant of the batch titration sample to act as a unique reference. This latter method is a backtitration technique which accounts for all sources that also consume H+ ions, leaving the difference to be the adsorbed proton concentration only. The NaClO4 electrolyte solution used is postulated to be adsorbed with competitive cation and anion exchange mechanisms with a point of zero salt effect (PZSE) = 7.50.
Nitrogen Mineralization Kinetics with Different Soil Pretreatments and Cropping Histories
Authors: Beauchamp E. G. , Reynolds W. D. , Brasche‐Villeneuve D. , Kirby K.
Published: July 2010

A laboratory study was conducted to determine how soil pretreatment (air‐drying, freezing, and field‐moist) and cropping history affects the kinetics of N mineralization. Although most researchers suggest that net N mineralization behaves according to first order kinetics, some have suggested that this process is better described with zero order kinetics. It was hypothesized that the air‐drying pretreatment may be largely responsible for an N mineralization pattern which may be described by first order kinetics. Experimental data showed that net N mineralization followed a first order kinetics pattern regardless of pretreatment. However, the air‐drying pretreatment enhanced N mineralization during the first 7 d of incubation. The traditionally used first order kinetics model (Model I) was extended to take into account an “easily” mineralized N fraction (Ne) mostly released during the first 7 d of incubation. This amended model (Model II) generally provided a much better fit to the experimental data, especially for the air‐drying pretreatment. As a result of the flush of mineralized N during the first 7 d, the total quantity of N released with air‐drying was considerably greater than with the freezing or field‐moist pretreatments. Organic N was released in a linear manner over the 42‐d incubation period and comprised about 10% of the total N released. Since this organic N would probably be mineralized, the total N leached was used to determine mineralizable N values (No) and rate constants (k). Mineralizable N values for bromegrass (Bromus inermis) and alfalfa (Medicago sativum) soils were generally higher than those for corn (Zea mays L.) whereas cropping history had no apparent effect on the k value. There were no significant effects of soil pretreatment on No or k values produced with Model II whereas differences occurred with Model I.
A Closed, Well‐oxygenated System for the Determination of the Emission of Carbon Dioxide, Nitrous Oxide, and Ammonia
Authors: Fine P. , Feigin A. , Waisel Y.
Published: July 2010

A simple closed system was set up for the measurement of CO2, N2O, and NH3 emission from soil samples kept under well‐oxygenated atmosphere. The system is an adaptation of a method suggested by Cornfield (1961a). Carbon dioxide is precipitated from the atmosphere as BaCO3, while O2 is generated from a BaO2 solution in equivalent amounts. With the aid of the proposed method, the simultaneous and quantitative determination of the mineral N forms in soils, of the gaseous N forms, and of CO2 may be performed even in well‐oxygenated conditions. Tests carried out in incubated soilsludge mixtures indicated that gaseous N forms may constitute a large fraction of the organic N ammonified. This may result in an underestimation of the mineralization potential of the organic N. Gas measurement may be needed where losses of N gases are likely or for the testing of the suitability of incubation techniques for the assessment of N mineralization capacities. The method is especially useful for the study of C and N dynamics in soil‐sludge mixtures.
Suspension Concentration Effects on Depositional Crusts and Soil Hydraulic Conductivity
Authors: Shainberg I. , Singer M. J.
Published: July 2010

Depositional crusts form when turbid water infiltrates into soils. These crusts may reduce water infiltration rates. The effect of four concentrations of fine particles (0, ∼0.25, ∼0.5, and ∼1.0%) and two electrolyte concentrations (0.001 M and 0.005 M Cl‐) on water infiltration rate was studied. Infiltration and hydraulic conductivity (HC) of two nonsodic soils were not affected by leaching with the salt solutions because the electrolyte concentration in the percolating water was sufficient to prevent clay dispersion and swelling in the soils. The clay and silt that deposited at the soil surface decreased the water infiltration rate. The HC of the depositional crust was 2 and 3 orders of magnitude less than the HC of bulk soils in the 0.005 M and 0.001 M solutions, respectively. The rate of crust formation and the decrease in infiltration rate increased with increase in the solids concentration. Applying a −1.5‐kPa potential reduced crust HC but had no effect on soil HC. The effect of a potential was more pronounced on the crust deposited from the 0.005 M suspensions than on crust deposited from 0.001 M suspensions.
Effects of Dissolved Organic Carbon and Sulfate on Aluminum Mobilization in Forest Soil Columns
Authors: Evans Andrew
Published: July 2010

A column study was conducted using a Cecil soil that was leached with various combinations of SO2‐4 and dissolved organic carbon (DOC), with the eluent pH adjusted to 4.6. Aluminum mobilization increased in the order SO2‐4 < DOC + SO2‐4 < DOC with Al being present primarily as Al in the 1000 to 2500 molecular aggregate range (MAR). The addition of SO2‐4 to the soil resulted in a reduction in DOC in the <1000 (MAR) with a corresponding increase in the 1000 to 2500 and 2500 to 5000 (MAR). Subsequent leaching with SO2‐4 after DOC treatment reduced Al mobilization. The number of pore volumes of eluent required for SO2‐4 break‐through decreased with elevated DOC levels in solution. Preliminary results suggest that SO2‐4 and organic species <1000 (MAR) compete for similar adsorption sites.
Soil Disturbance by Skyline Yarding vs. Skidding in a Loamy Hill Forest
Authors: Miller James H. , Sirois Donald L.
Published: July 2010

Soil disturbance was assessed on harvested units of mature southern pines (Pinus spp.), where a part of each unit was logged with a cable skyline system and a part with rubber‐tired ground skidders. Effects of the two methods of harvesting were studied by aerial and ground surveys. Cable yarding required 2% less acreage in landings than skidding, and yarding corridors occupied 12% less area than skid trails. Physical and chemical analyses of surface soils (upper 15 cm) showed that loam soils with clay subsoils were most severely affected by the displacement of topsoil after both methods of logging. On 8 to 14% of both logged areas, harvesting activities resulted in significant reductions in organic matter, available moisture holding capacity, and available P, Ca, and K. Silt loam soils were severely compacted by cable yarding in the corridors that consistently ran upslope creating the greatest erosion potential. It is concluded that the carefully planned use of skyline cable systems would minimize the area affected by severe soil disturbance and should be considered for future harvesting in this Jocale.
A Freezing Technique for Sampling Skeletal, Structureless Forest Soils
Authors: Froehlich H. A. , Miles D. W. R.
Published: July 2010

A technique was developed to take large undisturbed samples in forest soils with high coarse‐fragment content. Each sampling site was wetted with water, a metal pin was driven into and carefully removed from the soil, and liquid N2 was poured into the resulting hole. A frozen sample up to 200 mm in diam and 450 mm deep could be excavated and transported frozen to the laboratory. This sampling technique allowed measurement of bulk density, particle size distribution, and organic matter characteristics. The large size of the samples permitted sampling of soils with coarse fragments up to 85 mm in diam.
Soil‐water Properties as Affected by Twelve Annual Applications of Cattle Feedlot Manure
Authors: Sommerfeldt T. G. , Chang C.
Published: July 2010

A long‐term study was set up to determine the effects of annual applications of manure, at rates in excess of the recommended, on a Dark Brown Chernozemic (Typic Haploborolls) soil. Cattle (Bos taurus) feedlot manure was applied at 0, 30, 60 and 90 Mg ha−1 to nonirrigated and 0, 60, 120, and 180 Mg ha−1 to irrigated land at the Lethbridge Research Station. Soil‐water properties of the soil at 0‐ to 15‐ and 15‐ to 30‐cm depths, as affected by the manure, are reported. In the surface 15 cm of soil, the mean volume of plant‐available water retained by the soil between 20 and 1500 kPa tension decreased with increasing rates of manure on both the nonirrigated and irrigated blocks of land. The saturated hydraulic conductivity of the soil cores and the infiltration rate of the soil in the field were unaffected by the applied manure.
Influence of Spatially Variable Soil Hydraulic Properties on Predictions of Water Stress
Authors: Anderson S. H. , Cassel D. K. , Skaggs R. W.
Published: July 2010

Models are often used to predict drainage system effects on crop production. Variability of soil hydraulic properties on predictions made by many models have not been evaluated. This study evaluated several methods for predicting water transport properties and corn (Zea mays L.) stress as influenced by variable soil hydraulic properties in a field of Portsmouth sandy loam (Typic Umbraquults). Upflux, drainage volume, and infiltration parameters as functions of water table depth were predicted using hydraulic conductivity and soil water retention functions for three soil horizons measured at 150 locations in a field. Crop stress due to both deficient and excess soil water conditions and relative crop yield were estimated using DRAINMOD, a water management simulation model, for three selected methods of averaging soil property inputs. Small differences existed among the three approaches for the 30‐yr average relative corn yield. Large differences in relative corn yield occurred in dry years indicating that the variability of the soil properties was important to consider in predicting crop stress during relatively dry years. More information for the field soil‐drainage response was obtained using the individual locations method which allowed soil property inputs to vary from location to location at each of the 150 points in the field. However, the field averages approach is more practical because fewer data are required to perform the necessary computations and only a 3% difference in the 30‐yr relative yield resulted between the individual location and field average methods.
Estimating Soil Water Content Using Cokriging
Authors: Yates S. R. , Warrick A. W.
Published: July 2010

Using cokriging estimates, and estimation variances of the gravimetric moisture content (GMC) were made using one and two additional random functions: the bare soil surface temperature and the percent sand content. The semivariograms and cross‐semivariograms were obtained as well as the sample correlation between the GMC and the auxiliary functions. Various measures of the differences and quality of the estimates for kriging and cokriging were calculated and compared on the basis of the sample correlation and whether the auxiliary random functions were over‐sampled with respect to the GMC. The average estimation variance for cokriging compared to kriging was reduced for all levels of absolute sample correlation considered (i.e., 0.15‐0.83). The mean sum of squares error between the actual and estimated values obtained by the jack‐knifing technique was found to be lower for cokriging when compared to ordinary kriging when highly correlated auxiliary random variables were used but could be greater than that of ordinary kriging for less correlated auxiliary variables. It was found that the additional complexity of cokriging may be justified when the magnitude of the sample correlation exceeded 0.5 and the auxiliary functions were over‐sampled with respect to the GMC.
Steady Three‐dimensional Absorption in Anisotropic Soils
Authors: Philip J. R.
Published: July 2010

Exact solutions are given for steady absorption from spheroidal cavities into soils with axisymmetric anisotropy independent of moisture potential. The needle, sphere, and disc are special cases. Apart from their direct relevance to systems with gravity negligible, our results yield the leading terms of expansions describing steady infiltration into such soils for small and moderate values of the dimensionless cavity length. The effectively wetted region is a spheroid with aspect ratio µ, where µ2 is the anisotropy. The analysis suggests that, in anisotropic soils, vertical conductivity influences the capillary component of flow much more strongly for disc permeameters than for borehole permeameters. Generalizations of the problem solved in detail involve (i) inequality of the three conductivity principal components, (ii) cavity axes skew to conductivity axes, (iii) ellipsoidal cavities. Any one, combination of two, or all three, of these generalizations leads to essentially the same mathematical problem with the solution expressible in terms of the incomplete elliptic integral of the first kind.
Solute Transport Through a Stony Soil
Authors: Schulin R. , Wierenga P. J. , Flühler H. , Leuenberger J.
Published: July 2010

Movement of tritium and Cl‐ was studied through undisturbed, unsaturated columns of a Rendoll soil (Eutrochreptic rendoll) containing between 50 and 55% by volume of stones. The columns, 30 cm in diameter and 50 cm long, were leached at a steady flow rate varying from 0.16 to 41 cm/d. Breakthrough curves from these stony soils were smooth and mostly symmetrical, especially for the lowest flux. Based on an analysis with the classical two‐parameter convection‐dispersion equation, it was found that the dispersion coefficient was linearly related to pore water velocity with an average dispersivity of about 4 cm. The difference between the retardation factors for Cl‐ and tritium averaged 0.16 pore volumes. Using a four‐parameter transport equation with exchange between mobile and immobile liquid phases, an immobile water fraction of 15% was found, independent of the leaching rate. The four‐parameter model provided no better fit to the experimental data than the two‐parameter model for the lowest flux and only slightly better fits for all the other cases. This indicates that nonequilibrium conditions between mobile and immobile phases were of minor importance in modeling solute transport through this stony soil.
Populations of Bradyrhizobium japonicum in Fields Cropped with Soybean‐Rice Rotations
Authors: Weaver R. W. , Morris D. R. , Boonkerd N. , Sij J.
Published: July 2010

The population density of Bradyrhizobium japonicum in soil, before planting, largely determines the potential yield increase of soybean (Glycine max L. Merrill) due to inoculation. Soybean is cultured in rotation with rice (Oryza sativa L.) in the paddy rice belt of the southern USA. Nineteen fields were sampled to determine the influence of paddy rice culture on the population of B. japonicum. Populations in fields following soybean were approximately 1 × 104 bradyrhizobia g−1 soil. Growing rice after soybean did not reduce the population of bradyrhizobia. Apparently the bradyrhizobia were able to survive the conditions in saturated soil for several months.
Susceptibility to Compression of a Clay Loam Haplaquoll
Authors: Culley J. L. B. , Larson W. E.
Published: July 2010

The objective of this study was to determine the compressibility of a poorly drained clay loam soil cropped to corn (Zea mays L.) with moldboard plowing as primary tillage (CN) or with no tillage (NT). Undisturbed cylindrical cores (100 cm3)obtained from planter‐tracked (WT) and untracked (NWT) interrows just prior to harvest, were subjected to uniaxial compression after being equilibrated at soil moisture potentials (ψ) of −5, −10, −20, and −40 kPa. The precompression (over‐consolidated) and virgin compression regions were isolated by plotting bulk weight volume (v) against the logarithm of applied pressure. The breakpoint or precompression pressures (σp), which separated the over‐ and virgin compression regions, were determined using a statistical procedure. There was no apparent σp for cores from CN‐NWT interrows with ψ at or above −10 kPa. Tracking of tilled interrows resulted in the presence of over‐consolidated regions at all moisture potentials. Virgin compression indices (slopes) decreased in the order CN‐NWT > CN‐WT > NT‐NWT > NT‐WT. A highly significant correlation (p < 0.01) was obtained between σp and the undrained strength as measured by the fall‐cone device.
Surface Charge Characterization and Soil Solution Composition of Four Soils from the Southern Piedmont in Georgia
Authors: Gillman G. P. , Sumner M. E.
Published: July 2010

Four soils (Cecil, Typic Hapludult; Davidson, Rhodic Paleudult; Dyke, Typic Rhodudult; and Townley, Typic Hapludult) from the Southern Piedmont in Georgia, which have received large applications of gypsum, as well as soils from control plots, have been characterized with respect to their surface charge properties. The soils have variable charge character to varying degrees, but added gypsum has not affected fundamental surface charge properties such as cation and anion exchange capacities. The addition of Ca via gypsum has, however, altered the proportion of exchangeable basic and acidic cations. Analysis of extracted soil solution showed that Ca from gypsum can move rapidly through the profile, causing Mg to be displaced from exchange sites and therefore to be susceptible to leaching. A distinction is made between total cation exchange capacity and basic cation exchange capacity, and their significance with respect to exchangeable cations present is discussed.
A New Technique for Assessment of Reversibly Adsorbed Phosphate
Authors: van der Zee S. E. A. T. M. , Fokkink L. G. J. , van Riemsdijk W. H.
Published: July 2010

A new desorption technique for soil phosphate is described, in which Fe oxide coated filter paper is used as an “infinite” sink for P. This technique is applied to study desorption kinetics for nine sandy soils. The desorption can be explained with a simple Lang‐muir kinetics model. The mean value of the desorption rate constants found is kd = 0.2 ± 0.08 h−1. The estimated errors that are due to re‐equilibration during the experiments are less than experimental error. The amounts of P desorbed with the new technique, Pi, are compared to the amounts that desorb if a conventional dilution technique, Pw, is used. The new technique desorbs more P than the conventional method (Pi > Pw). By comparing Pi with oxalate‐extractable P (Pox) it is evident that reversibly adsorbed P rarely exceeds one‐third of Pox. Differences between the soils can be explained in terms of the oxalate‐extractable amounts of Fe and Al.
Effects of Soil Acidification on Chemical and Mineralogical Properties of a Limed Soil
Authors: Lietzke D. A. , Peterson D. V.
Published: July 2010

Two soil acidulents were compared for their effects on soil chemical and mineralogical properties. Aluminum sulfate [Al2(SO4)3 · 18 H2O] powder was applied at rates of 0.13, 0.26, 0.52, and 1.05 kg m−3 (7.5, 15.0, 30.0, and 60.0 g per pot, respectively). Elemental S powder was added at rates of 0.03, 0.06, 0.13, and 0.26 kg m−3 (1.9, 3.8, 7.5, and 15.0 g per pot, respectively). Sawdust was incorporated into the soil at rates of 0, 20, 40, and 60 m3 m−3 (% by volume). The soil used in this experiment was a previously limed sandy loam surface from a Typic Hapludult with an initial pH of 6.2. On a mass basis, approximately eight times as much Al2(SO4)3·18 H2O as elemental S was needed to cause a two‐unit decrease in soil pH. The acidity produced by S maintained low pH longer than Al2(SO4)3·18 H2O. Extractable levels of Ca and Mg in the highest acidulent treatments were approximately double that of the controls at the conclusion of the experiment. This is a probable response to lime particles from a previous liming being dissolved by acids. Extractable K, because of destruction of illitic clay minerals, was significantly higher in the S treatments than in the Al2(SO4)3 treatments or controls. Extractable Al levels were greater than the controls only at higher rates of both acidulents. Extractable Al levels at a given pH were higher in the Al2(SO4)3‐treated soils than in those treated with S. Destruction of clay minerals, including gibbsite, kaolinite, and hydroxy interlayered vermiculite were evident in the highest S treatment, even though both the Ca/Mg and K/NH4 cation exchange capacity values increased when compared to the controls. Aluminum sulfate had little effect on clay mineral stability when compared to the controls, and may have increased the heat stability of K saturated hydroxy interlayered vermiculite.
Interactions Among Vesicular‐Arbuscular Mycorrhizae, Soil, and Landscape Position
Authors: Day L. D. , Sylvia D. M. , Collins M. E.
Published: July 2010

The interrelationships among mycorrhizae, soil, and landscape position were investigated for a bahiagrass pasture (Paspalum notatum Flugge) in northern Florida. A significant effect of landscape position was found for spore number, root colonization, root length, the ratio of Acaulospora and Glomus to Gigaspora spores, and number of spores per centimeter of colonized root. Root colonization and propagule numbers were least in the most erosive positions (shoulder and backslope) of the landscape. This implied that the population density of vesicular‐arbuscular mycorrhizae (VAM) fungi may be reduced by soil erosion even if erosion is not severe enough to affect plant cover. The pattern of soils across the landscape influenced the distribution of genera of VAM fungi; soils in footslope positions had sandier surface textures as a consequence of erosional/depositional processes and favored higher populations of Gigaspora than of Acaulospora and Glomus.
Effects of Phosphorus and Acidity on Levels of Silica Extracted from a Palouse Silt Loam
Authors: Brown T. H. , Mahler R. L.
Published: July 2010

Concentrations of Si found in soil solutions are affected both by soil pH and by P availability. Consequently, it was hypothesized that the heavy local use of NH4‐based N fertilizers and of P fertilizers could greatly affect the Si chemistry of soils from the Palouse area of northern Idaho. The objectives of this study were to evaluate the effects of P and acidity on concentrations of Si in water extracts from Palouse silt loam (fine‐silty, mixed, mesic, Pachic Ultic Haploxerolls) soils and to correlate observed effects with possible mechanisms responsible for Si solubility, Soil samples were equilibrated with acid and with P for periods of 0.2 to 150 d in 0.02 M CaCl2 solutions. Increased acidity and the presence of P were both found to increase the concentrations of Si in solution above control levels. These data appear to be additive, suggesting that the mechanisms responsible for increasing solution Si levels for the respective treatments are different. It is postulated that acidity increases Si concentrations in solution by directly affecting the solubility of compounds containing Si, and that P oxyanions compete directly with Si compounds for specific sorption sites.
A Zinc Soil Test Calibration Based upon Mehlich 3 Extractable Zinc, pH, and Cation Exchange Capacity
Authors: Junus M. A. , Cox F. R.
Published: July 2010

The soil Zn critical level generally decreases as organic matter content increases. Certain other properties, notably cation exchange capacity (CEC) and optimum soil pH, also vary with organic content. These properties and Mehlich 3 extractable Zn (M3Zn) were used to calibrate a Zn soil test from greenhouse and field data. Soils were collected from four lime treatments in field experiments conducted on six Ultisols. An Inceptisol and a Histosol were also sampled and four lime treatments established, providing a range in pH and organic matter content. Three levels of Zn as ZnSO4 · 7H2O were added to each soil. Soybeans [Glycine max (L.) Merr., cv. Centennial] and corn (Zea mays L., cv. Pioneer 3369A) were grown successively in the greenhouse, each for 5 weeks. Mehlich 3 extractable Zn decreased with an increase in soil pH on only one of the eight soils, but Zn concentration in plants grown on all soils decreased with an increase in soil pH. Mehlich 3 extractable Zn alone accounted for little of the variation in the plant Zn concentration of the two crops. Including soil pH and CEC in the model increased the R2 to 0.56 and 0.50 for soybeans and corn, respectively. When the squared and first‐order interaction terms of these variables were considered, the R2 increased to 0.76 for soybeans and 0.66 for corn. For corn grown in the field, these same variables were found to be important in Zn soil test calibration. The form of the regression equation proved to be illogical, however, because the range in soil properties was not sufficient to produce a reliable prediction equation. Regression equations from the greenhouse were then adjusted to predict the leaf Zn concentrations of crops grown in the field. For corn, an equation that gave reasonable estimates of leaf Zn concentration in the field was developed. This equation may be used to interpret the need for Zn fertilization over a continuum of extractable Zn concentration, pH, and CEC in soils.
Morphology, Mineralogy, and Genesis of a Hydrosequence of Oxisols in Brazil
Authors: Macedo J. , Bryant R. B.
Published: July 2010

Research was conducted to establish the genetic relationship between soil color patterns and natural drainage characteristics in a hydrosequence of Oxisols formed in Tertiary/Quaternary sediments of the Cerrado (Savanna) Region of the Central Plateau of Brazil. The soils classify as Acrustox and Plinthaquox in Soil Taxonomy and as Dark‐Red Latosols, Red‐Yellow Latosols, and Hydromorphic Laterite in the Brazilian classification scheme. In addition to standard soil characterization analyses, x‐ray diffraction and sodium citrate‐bicarbonate‐dithionite extractions were used to determine soil mineralogy. Precipitation was recorded and weekly positions of the water table at sampling sites were measured in observation wells for a period of 1 yr. Kaolinite, gibbsite, quartz, and Fe oxides are the dominant minerals in all sites. Relative amounts of these minerals show similar desilication trends with depth at all sites in the hydrosequence. Well‐drained soils with water tables >3 m had reddish hues (2.5YR or 5YR) indicating an oxidizing environment and a codominant hematite and goethite Fe mineralogy. The upper organic rich solum at sites with seasonally high water tables (<2 m) had yellowish hues (10YR or 7.5YR) and a dominantly goethitic Fe mineralogy. In the deeper perennially saturated zones of all profiles the matrix color has reddish hues (2.5YR or 10R) and a dominantly hematitic Fe mineralogy. Stratigraphic, geomorphic, and pedogenic evidence supports the hypothesis that soils having reddish (2.5YR or 10R) hues and codominant hematite and goethite Fe mineralogy formed in a prior environment, then underwent changes in Fe oxide mineralogy in response to changes in hydrology brought about by landscape evolution and climate change. The organic rich upper sola of soils having a seasonally high water table show color adjustment to yellowish (10YR or 7.5YR) hues and dominantly goethitic Fe mineralogy.
Virgin Hardwood Forest Soils of the Southern Appalachian Mountains: I. Soil Morphology and Geomorphology
Authors: Daniels W. L. , Everett C. J. , Zelazny L. W.
Published: July 2010

Little is known about the characteristics of undisturbed soils in the eastern USA, since few exist. Eight sites with virgin forest soils formed under southern Appalachian hardwood vegetation were studied in the Joyce Kilmer Memorial Forest, an unlogged watershed in western North Carolina. Sites ranged in elevation from 720 to 1200 m with only two on <50% slopes. Generally, soils were quite deep and highly weathered because of high rainfall (>200 cm), weatherable feldspathic parent material, and no accelerated erosion. Average solum depth was 90 cm, while depth to metasandstone bedrock was typically >1.3 m. Deeply weathered saprolites were commonly encountered. Soils on northerly aspects had thick umbric epipedons and more organic matter than soils on south‐facing slopes. Organic matter contents of A1 horizons ranged from 45 to 170 g/kg and surface horizons contained moderate coarse and medium crumb structure. Most soils had cambic horizons and clay contents that decreased with depth. Argillic horizons were present only at low elevations on south‐facing slopes. While the majority of soils were formed in colluvium, significant amounts of deep soils in residuum occurred on sideslopes and appeared stable. The present‐day land‐forms appear to be significantly influenced by periglacial activity. Windthrow appears to have mixed the surfaces of these soils. Due to their decreasing clay content with depth, oxidic mineralogy, and low CEC, these soils resemble tropical forest soils.
Virgin Hardwood Forest Soils of the Southern Appalachian Mountains: II. Weathering, Mineralogy, and Chemical Properties
Authors: Daniels W. L. , Zelazny L. W. , Everett C. J.
Published: July 2010

Eights undisturbed soils derived from feldspathic meta‐sediments in the Joyce Kilmer Memoiral Forest were studied. Gibbsite was common throughout all soils, and inceased in aboundance in the clay fraction with depth. The clay content in most soils decreased with depth, with intergrade 2:1 type minerals occurring as the dominant phyllosilicates in surface horizons. Kaolinite was low in all soils, but was more abundant in south‐facing soils. Gibbsite abundance was not aspect dependent. The silt fractions contained appreciable quantities of weathered 2:1 type minerals similar in type to the clays. The coarse sand fractions wee almost entirely quartz, while the fine sands contained quartz, weathered 2:1 minerals, and feldspars. The CEC of the mineral surfaces in these soils was extremely low. Soil CEC was almost entriely derived from organic matter, and was typeically <3 cmol/kg in subsurface horizons. Levels of exchangeable Ca and Mg, acid extractable P, and total‐N were very low below surface horizons. These soils have weathered in a wet (>200 cm precipitation) temperate environment and resemble some tropical soils. Erosion could severely damage the natural productivity of these soils. The addition of oxidic mineralogy classes to certain Inceptisol families is recommended.
Application of a Conceptual Model to Irrigation Water Requirement and Salt Tolerance of Crops
Authors: Bresler Eshel
Published: July 2010

A theoretical model describing crop yield response to water quantity and quality under irrigation conditions is generalized to obtain soil‐water‐salt regimes, water requirement, and salt tolerance curves. Theoretical results show that under continuous irrigation conditions steady water and salt regimes may be achieved only when application water quantities exceed seasonal class A pan evaporation (E0) by >50%. The effects of water quantity and soil salinity on crop yield and the shape of the response curves to electrical conductivity of saturated paste extracts are similar for measured data and simulated results. In both, salt tolerance curves of wet irrigation regimes (irrigation quantity >E0) have maximum relative yield (YR) of one, while for dry irrigation regimes (irrigation quantity <0.8. E0), YR <1.0. Explanation of salt tolerance curves is attempted.
A Cumulative Mass Coordinate to Determine Water Profile Changes in Variable Volume Soil
Authors: McGarry D. , Malafant K. W. J.
Published: July 2010

A method for calculating changes in soil water of variable volume soil using a cumulative mass coordinate is demonstrated. Water content on a mass basis is plotted against mass per unit area of soil solids rather than against depth, lines are fitted, and changes in soil water in zones of gain or loss are calculated from areas between lines. A second method is presented that assesses the need for the cumulative mass coordinate by demonstrating its relation to profile depth. Application of the methods is demonstrated through a worked example using field data taken from an experiment on a Typic Pellustert (Australia).
Significance of Potassium Chloride pH of Calcareous Soils
Authors: Moore T. J. , Loeppert R. H.
Published: July 2010

The use of high ionic‐strength media for determination of soil pH has been limited primarily to acid soils. In this study, the theoretical and practical significance of the pH of calcareous soils suspended in 1 M KCl was investigated. Solutions from suspensions of 24 soils in 1 M KCl were analyzed for pH, Ca, Mg, Na, K, and alkalinity, and equilibrium relations were evaluated. In addition, the equilibrium relations of standard calcite samples were investigated in 1 M chloride solutions at different Ca to K ratios. Suspensions of calcite were in equilibrium with respect to CaCO3; however, soil suspensions were supersaturated (Ω = 1‐3). The KCl pH values of calcareous soils were inversely related to both the Ca concentration of the KCl extract and the cation exchange capacity (CEC) of the soil. The role of K+ was to displace Ca2+ from the cation exchange complex. Increased Ca in the KCl extract resulted in a decrease in pH, as predicted from the equilibrium relations of calcite. The use of KCl pH with calcareous and acid soils is analogous in that the pH reflects CEC and the cationic composition of the exchange complex. As with acid soils, the KCl pH of calcareous soils may provide valuable precursory information concerning the chemical properties of the system.
Determination of Fe(III) and Fe(II) in Oxalate Extracts of Sediment
Authors: Phillips Elizabeth J. P. , Lovley Derek R.
Published: July 2010

A method was developed to determine the concentrations of oxalate‐extractable Fe(III) and Fe(II) in sediments. Sediment was extracted in acid ammonium oxalate under N2. Iron(II) in the extract was determined with ferrozine. Iron(III) in the extract was reduced with hydroxylamine‐hydrochloride, and total Fe in the extract was determined with ferrozine. Oxalate‐extractable Fe(III) was calculated as the difference between Fe(II) and total Fe in the extract. Iron(II) was not oxidized, and Fe(III) was not reduced during the extraction. For an accurate estimate of oxalate‐extractable Fe(III), fresh samples had to be analyzed, because air‐drying or freeze‐drying the samples oxidized Fe(II) to oxalate‐extractable Fe(III). With a minimal increase in analytical effort, the method yields far more information on Fe geochemistry than the standard aerobic oxalate extraction method.
Effects of Carbon Source on Immobilization and Chemical Distribution of Fertilizer Nitrogen in Soil
Authors: Kelley Kenneth R. , Stevenson Frank J.
Published: July 2010

Three C sources (glucose, a phenolic glycoside, and catechol) were added to soil along with 15N‐labeled (NH4)2SO4 in an incubation study to determine effects of aliphatic and phenolic substrates on transformations of fertilizer N. Microbial utilization of the C substrates resulted in a rapid depletion of available mineral N, with maximum immobilization of soil and tracer N after 6, 10, and 20 d in the glucose‐, phenolic glycoside‐, and catechol‐amended soil, respectively. A close relationship was observed between clay‐fixed nonexchangeable 15NH+4 and KCl‐extractable (exchangeable + soluble) 15NH+4 during incubation (r2 = 0.91**). The nonexchangeable 15NH+4 was readily released and immobilized during microbial utilization of the added substrates. Availability ratios indicated that the immobilized 15N at the point of maximum incorporation into the microbial biomass was from 3.5 to 8.0 times as susceptible to mineralization as the native soil N. Net mineralization of 15N was accompanied by a decrease in amino acid‐15N, an indication that synthesis and decomposition of microbial protein were closely related to the level of available mineral N. Higher levels of acid‐insoluble 15N in the phenolic glycoside‐ and catechol‐amended soil were attributed to condensation reactions involving amino compounds and substrate‐derived polyphenols. Overall, microbial transformations were more important than substrate effects in determining the distribution of immobilized 15N after 120 d of incubation.
Silica in Duric Soils: II. Mineralogy
Authors: Chadwick O. A. , Hendricks D. M. , Nettleton W. D.
Published: July 2010

Opal‐A and opal‐CT were identified by x‐ray diffraction as the primary pedogenic silica minerals in two central Nevada duric soils. Opal‐A was also present in the form of allogenic volcanic glass. Pedogenic microcrystalline quartz was not identified. Saturated paste extracts contained > 60 mg L−1 Si(OH)4 and opal‐A precipitation is likely during soil dehydration. Opal‐CT precipitates from soil solution once silica concentrations have been reduced through adsorption, precipitation, and/or increased solution ionic strength, or it may be produced by transformation from opal‐A by mineral aging processes. High concentrations of silica in soil solution favor opal formation in preference to deposition of microcrystalline quartz.
Spatial Variability of Soil Salinity in Furrow‐irrigated Torrifluvents
Authors: Miyamoto S. , Cruz I.
Published: July 2010

Distribution characteristics of salinity and sodicity in furrow‐irrigated fields have not been adequately evaluated. This study examined the pattern of salt accumulation within crop beds and its spatial variation along or across crop rows, mainly for developing sampling guides for routine salinity appraisal. Soil samples were collected at spacings ranging from 1.5 to 6 m in four furrow‐irrigated fields of the middle Rio Grande Basin and were analyzed for salinity of the saturation extract and in selected cases for the sodium adsorption ratio (SAR). Salinity varied two to sixfold within the row lengths of 110 to 190 m, and its variation generally increased with increasing sampling depth and numbers of irrigation. The analyses of autocorrelation showed that salinity readings were spatially dependent at one of the four tested fields, and the distance of dependence reached 46 m. This field showed a gradual change in soil texture (from silty clay loam to silty clay), and provided a semivariogram conforming to a generalized linear model. When samples were collected from an area consisting of a single soil type or when salinity values were stratified by soil type, the distance of dependence decreased to <15 m. The frequency distribution of both salinity and sodicity within the same soil type followed a normal distribution with the standard error of estimates of mostly <8%. The sampling sites required to obtain a mean value within 15% of the true mean ranged from 3 to 11 per test row when sampled at 0‐ to 0.20‐m depth prior to preplant irrigation, and the required number increased with increasing sampling depth and numbers of irrigation. For routine appraisal of salinity in the fields similar to examined here, soil samples can be collected on the basis of soil type, and salinity data can be analyzed by conventional statistics with a reasonable assurance that salinity values are spatially independent.
Simulating the Effects of Soil Depth and Climatic Factors on Corn Yield
Authors: Swan J. B. , Shaffer M. J. , Paulson W. H. , Peterson A. E.
Published: July 2010

Simulation models are needed to estimate crop yield responses to climate and soil water storage. Measured corn yields (Zea Mays L.) from a tillage‐residue management study on the Univ. of Wisconsin Lancaster Exp. Stn. were compared to simulated yields determined using the Nitrogen‐Tillage‐Residue Management (NTRM) simulation model. Data collected at the site from 1982 to 1985 on crop, soil, climate, and management charactertistics were utilized in the model. A significant interaction effect on corn yield was observed between climate and soil‐water‐holding capacity of individual plots. In 1983, 1984, and 1985 corn yields increased as soil depth to red clay residuum increased; in 1981 and 1982 corn yield had little relationship to soil depth to residuum. The observed differential effect of soil depth to residuum on corn yield under different years' climatic conditions necessitated the use of a simulation model to estimate corn yield accurately in a given year and to express the probability of obtaining a given yield level. Frequency distributions for grain yield were determined for specific soil depths to residuum. Grain yield was determined as a function of soil depth for specific probability levels based on simulated site‐specific daily climatic values generated for a 100‐yr period.
Relationship Between Microbial Biomass Nitrogen and a Nitrogen Availability Index
Authors: Myrold David D.
Published: July 2010

This study examined the microbiological basis for the anaerobic N mineralization assay, a technique that has been widely used in studies of N availability in forest soils. It was hypothesized that N mineralized using the anaerobic incubation method came mainly from killed microbial cells, similar to the flush of N obtained from the chloroform fumigation‐incubation method for determining microbial biomass. Soil samples, representative of a wide range of forest types in Oregon, were analyzed for the amount of NH+4 released after a 7‐d anaerobic incubation and by the standard chloroform fumigation‐incubation method. A second experiment was done using the same soils treated with 15NH4Cl, and the isotopic labeling of the NH+4 released by both methods was determined. There was a highly significant correlation between both the amount and atom % 15N of NH+4 released by the two procedures (r2 = 0.81 and 0.82, respectively). These results suggest that the anaerobic N mineralization assay measures N released primarily from the microbial biomass.
Energy and Water Balance of a Sparse Crop: Simulated and Measured Soil and Crop Evaporation
Authors: Lascano R. J. , van Bavel C. H. M. , Hatfield J. L. , Upchurch D. R.
Published: July 2010

Dryland crops grown in semiarid environments often do not completely cover the soil, leaving a portion of the soil surface exposed to a condition of rapid soil‐water evaporation. Quantitative separation of soil evaporation and crop transpiration is important if cultural practices or cultivars are to be evaluated. This study was designed to evaluate a combined energy and water balance model, ENWATBAL, to describe the concurrent heat and water fluxes in a row crop. Inputs to the model include soil and plant variables and daily weather data. Measurements were made for a period of 74 d over a cotton (Gossypium hirsutum L.) canopy during 1985 on an Olton soil (fine, mixed, thermic Aridic Paleustolls) at Lubbock, TX. Data collected included soil‐water content, soil temperature, root distribution, soil evaporation with microlysimeters, and leaf area index, for both an irrigated and a dryland plot. The values for daily evaporation and evapotranspiration calculated with the model were within 1 standard deviation of the measured values. Cumulative evaporation and evapotranspiration from the model agreed with measured values within 7% for the dryland and 8% for the irrigated plot. Estimated soil‐water and temperature profiles also agreed closely to measured values. Soil evaporation was found to be 30% of evapotranspiration, for both the irrigated and the dryland plot. The ENWATBAL model provides a reliable method of evaluating the effects of management practices and crop selection on the water‐use efficiency of crop production in a semiarid area.
Effect of Solution Composition on the Rate and Mechanism of Gibbsite Dissolution in Acid Solutions
Authors: Bloom P. R. , Erich M. S.
Published: July 2010

The rate of dissolution of gibbsite was measured as a function of H+ concentration and anion concentration. The anions examined were nitrate, sulfate, and phosphate and the pH range used was 1.5 to 4.0. Rates of gibbsite dissolution were low and comparable to reported dissolution rates for feldspars. In the presence of nitrate and sulfate the dissolution reaction was first‐order with respect to H+ below pH 2.5. In phosphate there was no dependence of the rate on H+. Above pH 3.5 in nitrate the reaction order with respect to H+ approached zero. The order of the reaction with respect to anion concentration was about 0.6, 0.4, and 0.9 for nitrate, sulfate, and phosphate, respectively. The rate dependence of gibbsite dissolution on H+ and anion concentration suggested that the mechanism of dissolution, as well as the rate, is a function of solution composition. In solutions containing ions not specifically adsorbed (e.g., NO‐3 and SO2‐4), proton attack of the surface is the rate‐determining step. In solutions containing phosphate, anion attack predominated, and the rate of the reaction is not dependent on pH.
Selenite Adsorption on Alluvial Soils: II. Solution Composition Effects
Authors: Neal Rosemary H. , Sposito Garrison , Holtzclaw K. M. , Traina S. J.
Published: July 2010

The adsorption envelope for selenite on two alluvial soils from the San Joaquin Valley, California, was investigated with respect to variations in solution composition. Sodium‐saturated soil pastes were mixed with solutions containing sulfate, phosphate, and Ca ions in a background electrolyte of 50 mol NaCl m−3. The effects of increasing chloride concentration were investigated at 100 mol NaCl m−3. No discernible change in the amount of selenite adsorbed was found as a result of increased chloride concentration or through the addition of 16 mmol Na2SO4 kg−1. In contrast, an initial concentration of phosphate comparable to that of selenite resulted in a decrease of selenite adsorbed by approximately one‐half. The addition of 100 mol CaCl2 m−3 resulted in significant increases in selenite adsorption on both soils above pH 5, which could be attributed to precipitation or an increase of surface charge through Ca adsorption.
Influence of Exchangeable Calcium on Phosphate Retention by Weakly Acid Soils
Authors: Smillie G. W. , Curtin D. , Syers J. K.
Published: July 2010

The extractability of P from two weakly acid soils that had been amended with three forms of P [KH2PO4, single superphosphate (SSP), and Chatham Rise phosphorite (CRP)] was investigated in an incubation study under field conditions. In a sequential extraction sequence with water, P release from soils incubated for 9 and 27 weeks with KH2PO4 and SSP declined with increasing extraction number. In contrast, P extracted from CRP‐treated soils increased, indicating a slow dissolution of phosphate rock. Washing with 0.1 M NaCl to remove exchangeable Ca resulted in a large increase in P extracted subsequently with water, regardless of whether sorbed P (as in KH2PO4‐ and SSP‐treated soils) or particulate Ca phosphate (as when CRP was added) was the source of the extracted P. A high proportion (up to 80%) of the added P could be recovered by water extraction when exchangeable Ca was replaced by Na. Significantly, P recovery did not decrease with time of contact between soil and P as it did before exchangeable Ca was replaced with Na. The removal of exchangeable Ca accelerates the dissolution of Ca phosphates by creating a sink for Ca. The results obtained suggest that sorbed P may enter into chemical association with Ca, possibly at metal oxide surfaces, and that this interaction with Ca constitutes an important P retention mechanism in acid soils that contain adequate exchangeable Ca.