bluuebunny/crossref_metadata_2025 huggingface dataset:
Fire Severity, Ash Deposition, and Clipping Effects on Soil Nutrients in Chaparral
Authors: Marion G. M. , Moreno J. M. , Oechel W. C.
Published: July 2010

Fire may affect soil nutrient status by direct addition of nutrients and by indirectly altering the soil environment. The objective of this study was to examine how fire severity, ash deposition, and clipping affect posttreatment soil nutrient status. There were eight experimental treatments designed to examine increasing fire severity, ash (nutrient) addition independent of fire severity, clipping to study competition for nutrients per se, and untreated controls. Fire severity affected both the quality and quantity of ash. Increasing fire severity increased the concentrations of Mg and K and decreased the concentrations of NH4‐N and NO3‐N in the ash. As fire severity increased, there was an increasing recovery of ash relative to standing biomass (10–18 g kg−1). Fire increased the availability of all nutrients (NH4‐N, NO3‐N, PO4‐P, Ca, Mg and K). This nutrient enhancement was largely restricted to the surface soil (0–5 cm); only soluble N appeared to increase in the subsurface soil (5–10 cm). The soil quantities of NH4‐N increased and NO3‐N decreased with increasing fire severity, suggesting either a direct addition of variable amounts of these N ions or an indirect effect on postfire nitrification rates. Clipping had no effect on enhancing soil nutrient availability. The apparent recovery of the basic cations in the water extracts of the ash samples was in the order: K » Mg > Ca; this was different from the subsequent recovery in the soil: Ca > K > Mg. It was hypothesized that the relative recovery of basic cations in the water extracts of the ash samples was controlled by the solubility of Ca, Mg, and K salts.
Carbon and Nitrogen Analysis of Soil Fractions Using Near‐Infrared Reflectance Spectroscopy
Authors: Morra M. J. , Hall M. H. , Freeborn L. L.
Published: July 2010

A nondestructive method to determine total C and N concentrations in soil size fractions is desirable when a limited sample is available. Near‐infrared reflectance spectroscopy (NIRS) was used to determine the total C and N concentrations in silt (50.0–2.0 µm) and coarse clay (2.0–0.2 µm), separated from 12 surface soils, by regressing the diffuse reflectance of near‐infrared radiation with constituent concentrations determined using combustion techniques. The correlation coefficients (R2) of the calibration equations were 0.93 for C and 0.89 for N, and the standard errors associated with NIRS predictions were 6.2 g kg−1 soil for total C and 0.6 g kg−1 for total N. Equation development with only silt samples improved the accuracy of NIRS calibration equations. Coefficients of variation [CV = (standard error of performance ÷ mean of the combustion procedure) × 100] for validation sample sets ranged from 14 to 19%, which is within the acceptable range for determining inorganic elements in plant tissues. We conclude that NIRS can be used to predict C and N concentrations in soil size fractions.
Probe for Measuring Soil Specific Heat Using A Heat‐Pulse Method
Authors: Campbell G. S. , Calissendorff C. , Williams J. H.
Published: July 2010

Temperature rise, measured a short distance from a line heat source, can be used to determine the volumetric specific heat of soil and other materials. Volumetric specific heat is linearly related to the inverse of the temperature rise. The purpose of this note is to describe the construction and performance of a device for measuring specific heat using the line source method. The device was constructed from two hypodermic needles, 0.813 mm in diam. and 28 mm long, and spaced 6 mm apart. One needle contained a heater and the other a thermocouple. The temperature rise from heat pulses given to the heater were measured with the thermocouple. The coefficientof variation (CV) of specific heat on replicate samples was around 1%. Since water is the main variable component of the specific heat in nonswelling soil, changes in water content might be resolved to 0.01 or better in nonswelling soils.
Field Infiltration of a Salt‐Loaded Soil: Evidence of a Permeability Hysteresis
Authors: Mitchell A. R. , Donovan T. J.
Published: July 2010

Low water‐infiltration rates may be detrimental to crop growth by reducing the water available to the plant, limiting salt leaching, and inducing ponding that may result in poor aeration during irrigation. Permeability has been shown to be a function of both the total salinity and the exchangeable sodium percentage (ESP) of the soil. Our objective was to measure the changes in water infiltration that occurred following extended salt loading on a Holtville silty clay (clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent) with permeability problems. An earlier 4‐yr salt‐tolerance experiment provided large plots (6 by 6 m) with six levels of salinity‐sodicity and three replicates. Plots were surrounded by fiberglass barriers and were adequately drained. Colorado River water, with an electrical conductivity (EC) of 0.9 dS m−1, was used to reclaim the plots in a series of small 80‐mm irrigations. Measurements of the salinity and the exchangeable cations of saturated soil extracts were taken before, midway through, and following reclamation. Infiltration rates were measured after 4 h of ponding and were found to differ significantly both during and after salt removal by leaching. The infiltration rates showed a hysteretic effect (delayed reaction) of saline and sodic treatments on soil water permeability. We attributed the effect to the slowly reversible flocculation and deflocculation of clay particles. Final soil ESP data from different treatments indicated that a traditional ESP threshold value may be of limited worth unless past salt history of the soil is considered. Models of hydraulic conductivity should account for this permeability hysteresis. Strategies of reusing saline drainage water may benefit from the hysteretic permeability by allowing high infiltration rates to persist.
New Method for Characterizing Soil Contrast
Authors: Villamayor F. P. , Huddleston J. H.
Published: July 2010

Limitations of existing definitions of similar and contrasting soils for soil survey interpretations relating to both inclusions in map units and landscape patterns of soils led to the development of a new procedure for characterizing soil contrast. Six classes, or levels of soil contrast, are defined based on differences in intrinsic soil properties. Soil texture, coarse fragments, depth of rooting, drainage, permeability, pH, salinity, slope, erosion, and flooding are used to define 12 parameters for comparing soils. The range of values for each parameter is divided into a small number of discrete classes to facilitate comparisons. Within a given parameter (e.g., surface texture), class comparisons are rated as very similar, similar, somewhat contrasting, contrasting, or very contrasting, depending on whether the property values are in the same class, an adjacent class, nearby classes, or remote classes. Repeating this procedure for each parameter generates a set of 12 parameter contrasts for the two soils being compared. The distribution of contrasts among contrast levels determines the overall degree of contrast between the two soils. Where one or two parameters have a higher contrast than any of the others, that contrast level becomes the overall degree of soil contrast. Where several parameters vary at the same level, the cumulative effect of multiple variation is expressed by increasing the overall contrast to the next higher level. Advantages of the new model include multiple classes, definition of contrasts in terms of soil properties, and a precise procedure that can be duplicated by any two people given the same set of data.
Overwinter Changes in Physical Properties of No‐Tillage Soil
Authors: Unger Paul W.
Published: July 2010

Soil physical properties often improve during winter, even without tillage. Based on observations, improvement is greater on ridged than on relatively flat soil, and it appears related to soil freezing and thawing. The objective of this study was to determine changes in bulk density, penetration resistance, aggregate‐size distribution, organic‐matter concentration, and water retention that occur during winter in a soil having low or high ridges formed by tillage. The study was conducted from 1985 to 1988 on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) at Bushland, TX. The 1985–1986 winter was coldest and had the least late‐period precipitation (19 mm). For the 0.04‐ to 0.07‐m depth increment during this winter, bulk density (Db) decreased 0.10 Mg m−3; penetration resistance (PR) decreased 0.14 and 0.20 kPa at −4.89 and −19.6 kPa matric potentials, respectively; mean weight diameter (MWD) of water‐stable aggregates increased 0.5 mm; organic matter (OM) decreased 0.7 g kg−1; and water retention at potentials from −2.44 to −19.6 kPa decreased 0.019 to 0.069 m3 m−3, all significant at P = 0.05. Changes were slight during the 1986–1987 winter. During 1987–1988. Db increased 0.07 Mg m−3, PR increased 0.06 kPa (at −19.6 kPa matric potential), OM decreased 0.4 g kg−1, MWD of water‐stable aggregates decreased 0.7 mm, MWD of dry aggregates increased 3.3 mm, and most changes in water retention were not significant. The 1987–1988 changes were opposite those for 1985–1986, apparently because of less intense freezing and more late‐period precipitation (44 mm). Late precipitation possibly reconsolidated soil that may have been loosened previously by freezing. In most cases, results for low‐ and high‐ridge treatments were similar. Freezing can improve soil physical properties, but improvements may be negated by late‐winter or early‐spring precipitation.
Specific Effect of Magnesium on Soil Erosion and Water Infiltration
Authors: Keren R.
Published: July 2010

This study was conducted to determine the effects of adsorbed Mg on erosion of soils exposed to rain. The effects of adsorbed Mg and Ca on soil erosion and infiltration rate (IR) of two soils (a Calcic Haploxeralf and a Typic Rhodoxeralf) exposed to rainfall, in the absence and presence of adsorbed Na, was studied. A drip‐type rainfall simulator and deionized water were used at water‐drop kinetic energy of 12.5 kJ m−3. The erosion rate of the soils was higher for the Mg‐soils than for the Ca‐soils. Both the steady‐state IR and the cumulative water depth required to reach a steady‐state IR were lower for Mg soils than for Ca soils. Adsorbed Mg by the montmorillonitic soil increased erosion and lowered IR, regardless of CaCO3 content. The Ca aggregates were more stable than Mg aggregates, even in the presence of Na. The specific effect of Mg on soil erosion was explained by the presence of these ions on the external surfaces of the clay tactoids, and the wider hydration shell of the Mg ion, as opposed to that of the Ca ion. It was suggested that the steady‐state infiltration and soil erosion rates are the result of two processes that occur in opposite directions: seal formation and soil detachment.
Predicting Cation‐Exchange Capacity from Soil Physical and Chemical Properties
Authors: Manrique L. A. , Jones C. A. , Dyke P. T.
Published: July 2010

Cation‐exchange capacity (CEC) is an important soil property in describing nutrient availability for plant growth. Measurements of CEC, however, are often not available or have been measured using different analytical methods. The need, therefore, exists to develop alternative procedures to predict CEC from accessory soil properties. In this study, regression analysis was used to examine the relationships between CEC and clay (CLAY), organic carbon (OC), and other soil properties. Multiple regressions indicated that CLAY, OC, and soil pH accounted for up to 51% of the variation in CEC for all soil (n = 37921). For soil orders, CLAY and OC accounted for up to 67% of the variation in CEC for Alfisols, Inceptisols, Mollisols, and Vertisols, and up to 78% of the variation in CEC for Entisols and Spodosols. The OC alone accounted for up to 73% of the variation in CEC for Spodosols. Poor predictions of CEC resulted from CLAY for Aridisols and Vertisols, indicating that factors other than CLAY interfered with accurate predictions of CEC.
Tillage and Simulated Rainfall Intensity Effect on Bromide Movement in an Argiudoll
Authors: Bicki Thomas J. , Guo Lei
Published: July 2010

Movement of Br‐ in a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) managed under five different tillage systems and subjected to three simulated rainfall intensities was documented. Under low (10 mm/h) and medium (25 mm/h) simulated rainfall intensities, movement of Br‐ in the soil profile was not significantly different between moldboard plow, chisel plow, disk plow, para‐till, and no‐till systems. When subjected to a high simulated rainfall intensity, significantly greater Br‐ movement occurred in the soil profile managed under continuous, long‐term no‐till. Greater movement of Br‐ in the no‐till soil was attributed to preferential flow.
Determination of Low Concentrations of Phosphorus in Soil Extracts Using Malachite Green
Authors: Ohno Tsutomu , Zibilske Larry M.
Published: July 2010

A sensitive method is needed to analyze soil‐water extracts that contain P at submicromolar concentrations. The proposed spectrophotometric method, based on the ionic association of malachite green with phosphomolybdate under acidic conditions, was evaluated on soil extracts. The molar absorptivity was 64641 ± 743 L mol−1 cm−1. Absorbance of the reagent blank was 0.069 ± 0.004. With 1‐cm path length cells and limiting absorbance of 0.004, the detection limit calculated from the Beer‐Lambert equation was 6.7 × 10−8 M orthophosphate P. Recovery of added P in saturated paste extracts averaged 91% with a range of 87 to 94% and averaged 101% with a range of 93 to 109% for 1:1 soil/water extract. The method was successfully applied to saturated paste extracts from soils of varied organic matter content and pH. The proposed malachite green method allows for P determination in restricted volume samples and at concentrations too low for the standard Murphy‐Riley method.
High‐Resolution Measurement of Root Water Uptake Using Automated Time‐Domain Reflectometry
Authors: Wraith J. M. , Baker J. M.
Published: July 2010

Methods for monitoring changes in soil water content with high resolution in both space and time are needed to help quantify patterns of soil‐water uptake by plant roots. We designed and tested an automated time‐domain reflectometry (TDR) system for precise, continuous measurement of such changes. A two‐dimensional root‐zone enclosure was constructed from stainless steel wire cloth, with a parallel pair waveguide centered within each of 10 rectangular compartments. The wire cloth confined the electromagnetic pulse from the TDR without restricting root growth or water movement. Digitized waveforms from the analog TDR unit were captured, analyzed, and converted to volumetric water content by a program written for a datalogger. A sorghum (Sorghum bicolor [L.] Moench) plant was grown for 84 d, during which soil water content and changes in weight were monitored at 15‐min intervals. Standard deviations in water‐content measurement were estimated to be between 0.0008 and 0.001 m3 m−3. Water‐balance computations of evapotranspiration agreed well with measurements by a precision electronic balance, with a standard deviation of 0.0012 m3 m−3 during a 6‐d period. The wire mesh supported the root system, which had grown through it, even after soil was removed by rinsing with water. This will facilitate determination of root densities corresponding to measured changes in water content. The high degree of spatial and temporal resolution afforded by the system make it a valuable tool for studying the dynamics of water flow in the root zone, and information provided by this method may allow resolution of some issues that have remained controversial due to lack of measurement ability.
Phosphate and Accompanying Cation Transport in a Calcareous Cation‐Exchange Resin System
Authors: Akinremi O. O. , Cho C. M.
Published: July 2010

Cation‐exchange interactions are known to modify the movement of the individual cations involved. It is uncertain, however, how such interactions affect the movement and immobilization of an anionic species such as phosphate. An experiment was conducted to assess the influence of cation‐exchange reactions on the transport and immobilization of phosphate ions in a system of cation‐exchange resin with CaCO3 as the buffer. A 0.2‐g amount of KH2PO4 salt was uniformly applied to the surface of columns packed with either a mixture of CaCO3 and quartz sand or a mixture of CaCO3, quartz sand, and Ca2+‐saturated exchange resin. Phosphate ions diffused to a distance of 45, 60, and >60 mm from the surface after 3, 7, and 14 d of incubation, respectively, in columns packed with the CaCO3‐sand mixture. In the columns containing both CaCO3 and Ca2+‐saturated exchange resin, phosphate ions diffused about 35, 45, and 50 mm down the column during the same periods of incubation. The reduced movement of phosphate in the presence of Ca2+‐saturated resin is explained by the magnitude of precipitated phosphate obtained. In the columns containing CaCO3 and quartz sand, the amount of precipitated phosphate in the upper 6‐mm portion ranged from 20 to 180 mmol L−1. The corresponding value for columns containing Ca2+‐saturated exchange resin ranged from 250 to 550 mmol L−1. The movement of K+ was similarly retarded by the presence of Ca2+‐saturated resin. The results showed that the influence of cation‐exchange interactions on ion mobility is not limited to the cations involved. The mobility of an anionic species can also be affected where the exchangeable cation, when liberated into solution, can form a precipitate with the anion. In soils containing exchangeable cations capable of reacting with phosphate to form a precipitate, there is a need to take cation exchange into consideration when describing the fate of applied P.
Abrasion of Crusted Soils: Influence of Abrader Flux and Soil Properties
Authors: Zobeck T. M.
Published: July 2010

Surface crusts greatly affect soil susceptibility to wind erosion. Little is known about the effects of soil properties and environmental factors on crust abrasion. In this study, the influence of abrader flux, degree of crust consolidation, and selected soil properties on soilcrust erosion was evaluated and sattistically modeled. Fourteen soils, representing a wide range of physical and chemical preperties, were evaluated. Soils were subjected to simulated rainfall rates of either 25 or 64 mm h−1, air dried, and abraded at mass fluxes of 0.010, 0.025, and 0.050 kg m−1 s−1. Crust abrasion (abrasion coefficient, AC) was defined as the slope of the linear regression of cumulative soil loss vs. cumulative abrader passage. An analysis of variance indicated that abrader flux, crust consolidation level, soil properties, and their interactions significantly affected (P < 0.05) soil loss. The AC ranged from 3.179 m−1 for an organic soil to 0.002 m−1 for silt loam and clay soils. The range of AC for unconsolidated soils was from 5 to 5000 times greater than for crusted soils. The mean AC for unconsolidated soils was 40 and 70 times greater than for crusted soils created at rainfall rates of 25 and 64 mm h−1, respectively. Regression analyses revealed that the natural logarithm of AC was positively correlated with sand content and the cation‐exchange capacity/clay ratio, and negatively correlated with abrader flux.
Geochemistry of Dissolved Organic Nutrients in Water Percolating through a Forest Ecosystem
Authors: Qualls Robert G. , Haines Bruce L.
Published: July 2010

Dissolved organic matter (DOM) is a major vehicle for the translocation and loss of N and P from forest ecosystems. The chemical properties of DOM and its interactions with soil surfaces are crucial in determining the mobility of these organic nutrients. We fractionated DOM from throughfall, all soil horizons (Ultisols and Inceptisols), and stream water from an Appalachian mountain forest ecosystem into hydrophobic or hydrophilic acids, neutrals, and bases. We analyzed each fraction for dissolved organic C (DOC), N (DON), and P (DOP). Most of the DOC was in the acid fractions, with the humic fractions (hydrophobic acids and phenols) comprising 35 to 57% of the DOC in all samples except summer throughfall. Concentrations of all fractions declined with depth in the soil. As a percent of total DOC, the humics declined with depth, whereas the hydrophilic neutrals increased. Bases, which we expected to contain cationic amino groups, were < 2.5% of the DOC. Instead, most DON was in the humic, hydrophilic acid, and hydrophilic neutral fractions. Most DOP occurred in the hydrophilic acid, humic, and hydrophilic neutral fractions. The functional groups in which N and P occur had little influence on the behavior of most of the DOM as a whole since: (i) cationic DOM was such a minor component, and (ii) P was simply too rare to influence the anionic behavior of many molecules. Nevertheless, for those molecules in which P did occur, P may have influenced their behavior since a large percentage of the DOP was in the hydrophilic acid (i.e., anionic) fraction. The carboxylic and phenolic functional groups, or in some cases the neutrality, of the DOM molecules appeared to be much more important than N‐containing groups in influencing the behavior of the N carried passively by the DOM.
Capillary‐Wick Unsaturated Zone Soil Pore Water Sampler
Authors: Holder M. , Brown K. W. , Thomas J. C. , Zabcik D. , Murray H. E.
Published: July 2010

Existing unsaturated zone soil water samplers have several deficiencies that jeopardize their utility for field sampling. Suction cups function only when a vacuum is applied, and sample from an unknown volume of soil. Pan samplers sample only saturated flow. A capillary‐wick sampler was developed to overcome these problems and was tested in both the laboratory and field to evaluate its performance. Breakthrough curves for selected inorganic ions and organic chemicals were established in the laboratory. No adsorption/desorption of these chemicals was found for the capillary‐wick sampler made entirely of glass. Banks of eight capillary‐wick samplers were installed in field plots of Padina sand (loamy, siliceous, thermic, Grossarenic Paleustalf), Weswood silt loam (fine‐silty, mixed, thermic Fluventic Ustochrept), and Lufkin clay (fine, montmorillonitic, thermic Vertic Albaqualf) soils. Saturated soil Br breakthrough curves were determined at each location and used to estimate the number of samplers required to characterize the flow of contaminants. To achieve 95% confidence in the chemical data from the three soils and plot sizes tested, 31 samplers were required for the sandy soil, six for the silt loam soil, and only two for the clay soil. The wick‐activated sampler collected soil solution samples from soils having soil water potentials ranging from 0 to −6.0 kPa. The capillary‐wick sampler collected samples continuously across this range of water potentials without the need for a continuous vacuum and is thus an improvement over existing samplers. While the capillary‐wick samplers usually collected sample volumes representative of the flux at potentials of −5 kPa, samples collected at greater and lesser potentials were not representative of the flux.
Modeling Root Water Potential and Soil‐Root Water Transport: I. Model Presentation
Authors: Lafolie F. , Bruckler L. , Tardieu F.
Published: July 2010

Plant water uptake has classically been supposed to depend on the leaf water potential (LWP) and LWP was assumed to control the stomatal conductance. A new approach to stomatal control has recently been proposed in which root water potential (RWP) determines stomatal aperture, and hence transpiration, by means of chemical messages. In such a case, models that provide precise calculations of RWP become essential for understanding soil‐root water transport. The objective of this paper is to propose a theoretical approach to calculate RWP and water uptake by roots in the X‐Y plane for any spatial root distribution. For the calculations of RWP, we assumed that the plant continuously adjusted its RWP so as to minimize the difference between the maximum evapotranspiration (MET) and the amount of water extracted by the root system. Water release from the roots in the soil was considered to be negligible, so roots in dry soil were temporarily removed from the pool of active roots. A Galerkin finite element method was used to solve Richards' equation. Examples of calculation are presented for a nonuniform root distribution under both wet and dry initial situations. Root water potential and the number of active roots varied greatly with time. Results suggested that no simple relationship existed between the plant water uptake and the root water potential. Furthermore, soil water‐potential maps showed a close relationship between water uptake and root positions, and great differences between RWP and the mean soil water potential could be calculated. A greater or lesser water redistribution toward the roots occurred during the night. Finally, the proposed approach may be validated with precise soil and plant measurements.
Equivalent Diameter of Simulated Macropore Systems during Saturated Flow
Authors: Dunn G. H. , Phillips R. E.
Published: July 2010

Under natural conditions, soil pore systems that conduct water vary in shape, cross‐sectional area, and continuity. Because of this, it is virtually impossible to predict the flow of water through these pore systems. We conducted an experiment to measure the equivalent spherical diameter, deq, of simulated nonuniform macropore systems for 11 combinations of lengths of three radii of cylindrical, straight‐walled glass tubing during saturated flow. Also, we wanted to determine if experimental data of deq of the simulated macropores are described by a derived theoretical equation where deq is a function of the total length of the three tubes, their individual lengths, and their radii. Three known, uniform‐i.‐d. tubes of differing lengths, of cylindrical, straight‐walled glass, in series configuration were used to simulate to a small degree the geometry of macropores as they occur in the field. Inside diameters were 5.08 (L), 1.88 (M), and 0.94 (S) mm. A constant length of 0.60 m was maintained for the pore system. The deq values of these non‐uniform pore systems were measured. Flux values were measured at eight hydraulic pressures. Equivalent diameters were calculated using Poiseuille's law from the measured flux. The data points of deq of the pore system were described well by the derived equation. The experimental saturated hydraulic conductivity (Ksat) was also well described by a derived function.
Phosphate‐Induced Release of Arsenic from Soils Contaminated with Lead Arsenate
Authors: Peryea Frank J.
Published: July 2010

Mixing high rates of monoammonium phosphate (MAP) or monocalcium phosphate fertilizers with orchard soil often stimulates growth of newly planted pome fruit trees. This practice may increase As solubility in soils contaminated with lead arsenate pesticide residues because of competitive PO4‐AsO4 exchange. Laboratory experiments were conducted examining As release in batch suspensions of five lead arsenate‐contaminated soils. Dissolved Pb concentrations were <5 µmol/L in all soil suspensions. Redox potential exceeded 500 mV in all suspensions, suggesting that the primary form of dissolved As was probably AsO4. Phosphate‐induced As release was dependent on soil type, occurring in four nonvolcanic soils but not in a pumiceous soil. Arsenic release was positively related to added PO4 concentration but was not significantly influenced by PO4 source. Ammonium sulfate did not enhance As release. Arsenic solubility was consistent with a mechanism of specific PO4‐AsO4 exchange, while PO4 solubility was consistent with control by metastable PO4 minerals. Phosphate‐released As was not appreciably resorbed after multiple wetting and drying cycles. These results explain enhanced As mobility, phytoavailability, and phytotoxicity observed in lead arsenate‐contaminated soils amended with MAP.
Organic Carbon Sorption in Arctic and Subalpine Spodosol B Horizons
Authors: Dahlgren R. A. , Marrett D. J.
Published: July 2010

The sorption of dissolved organic carbon (DOC) on B horizons from arctic and subalpine Spodosols was investigated at low temperatures typical of these soils. The arctic Spodosol, from northern Alaska, had an inverted horizon sequence (Bs overlying Bhs) and other properties inconsistent with the metal‐fulvate theory of podzolization. The subalpine Spodosol, from the Cascade Range of Washington state, developed in a mixture of volcanic and glacial materials and had classic Spodosol morphology. Batch studies were conducted under the following conditions: 3 °C, pH of 4.5, C/metal ratio of 59, a 10:1 solution/soil ratio, and an ionic strength of 10−3 M. Final pH, DOC, Fe, Al, and Si concentrations were determined. Between 30 and 50% of the adsorption/desorption occurred within the first 0.25 h and steady‐state DOC concentrations occurred between 4 and 12 h. Only the subalpine Bs horizon adsorbed DOC, while both Bhs horizons and the arctic Bs horizon desorbed DOC. Dispersion of fine colloids (<0.2 µm) affected desorption in arctic soils at reaction times >4 h. The results suggest that the main mechanism of DOC immobilization involved initial solubilization of metals, which lowered C/metal ratios in solution, followed by adsorption of the organo‐metal complexes. The ability of the subalpine Bs horizon to effectively adsorb DOC may be due to the large concentration of uncoated short‐range‐order materials (imogolite and ferrihydrite) present in this horizon.
Legume Mulch and Nitrogen Fertilizer Effects on Soil Water and Corn Production
Authors: Corak S. J. , Frye W. W. , Smith M. S.
Published: July 2010

Hairy vetch (Vicia villosa Roth), as a winter annual legume cover crop, can increase grain yield of no‐till corn (Zea mays L.). Optimizing management of this system depends on understanding beneficial effects. This field study examined effects of hairy vetch (HV) and N fertilizer on soil water content, crop growth, N assimilation, and water‐use efficiency. Cover‐crop treatments, each with 0 and 255 kg ha−1 of fertilizer N, were (i) winter fallow, (ii) aboveground HV removed at corn planting, (iii) HV left in place, and (iv) HV left in place and supplemented with that removed from (ii). Transpiration by HV before corn planting reduced soil water content, decreasing early growth of corn during years of low spring rainfall. By 2 to 4 wk after planting, however, soil water cotnent under HV mulch was similar to winter fallow. Soil water content was higher with HV mulch only during the second 4‐wk period following planting and only in the upper 7.5 cm of the profile. Greater soil water use associated with N fertilizer occurred after about 8 wk in 2 of the 3 yr. Hairy vetch treatments at the zero‐N fertilizer level increased corn growth, N assimilation, grain yield, and water‐use efficiency. The high‐N treatment negated these benefits of HV. Because of this and the lack of mulch effects on soil water during later stages of crop growth, we concluded that N supplied to no‐till corn was the principal, immediate benefit of HV during this study.
Freezing Effects on Aggregate Stability Affected by Texture, Mineralogy, and Organic Matter
Authors: Lehrsch G. A. , Sojka R. E. , Carter D. L. , Jolley P. M.
Published: July 2010

Aggregate stability, an important property influencing a soil's response to erosive forces, is affected by freezing. The objectives of this laboratory study were to determine how constrainment, number of freeze‐thaw cycles, and water content at freezing affect the aggregate stability of six continental USA soils differing in texture, mineralogy, and organic‐matter content. Moist aggregates, after being frozen and thawed either zero, one, three, or five times, were vapor wetted to 0.30 kg kg−1 and analyzed by wet sieving. Soils with clay contents of 17% or more and organic‐matter contents >3% were the most stable after freezing. Aggregate stability for fine‐ and medium‐textured soils generally decreased linearly with increasing water content at freezing. This linear decrease in stability was more rapid for constrained samples than for unconstrained samples. The stability of field‐moist aggregates generally increased from zero to one or three freeze‐thaw cycles. For at least one low‐organic‐matter soil, stability increased from one to three freeze‐thaw cycles, but then decreased at five cycles. After thawing, aggregates at water contents of 0.15 kg kg−1 or more that were constrained when frozen were always significantly less stable than aggregates that were unconstrained when frozen.
Forest Soil Sampling Efficiency: Matching Laboratory Analyses and Field Sampling Procedures
Authors: Mroz Glenn D. , Reed David D.
Published: July 2010

Soil characteristics can be extremely variable, both spatially and temporally, and the cost of sampling to achieve high levels of precision may be prohibitive. Researchers are often faced with the need to obtain the best possible precision within a fixed budget. We present methods of determining the optimal number of field composite samples, the number of field samples per composite, and the number of laboratory analyses per composite. Example problems illustrate methods of obtaining both a desired precision at a minimum cost and the greatest possible precision at a given cost. Calculations to compare and select among alternative laboratory procedures are also illustrated. Often, less precise but inexpensive laboratory procedures may result in greater overall precision than highly precise but expensive procedures.
Vegetation‐Soil Relationships on Thin or Shallow Range Sites in Western South Dakota
Authors: White E. M.
Published: July 2010

Little bluestem (Schizachyrium scoparium [Michx.] Nash) and/or big bluestem (Andropogon gerardii Vitman) stands often occur adjacent to western wheatgrass (Agropyron smithii Rydb.) stands on thin or shallow range sites and closely related sites. The purpose of this study was to identify soil properties that cause the nonrandom distribution of the grasses. Particle size, pH, organic matter, total N, total PO4, and available PO4‐P were determined on 17 soil profiles that supported different grass distributions. Soils with western wheatgrass had more plant‐available PO4‐P than soils with bluestem, but usually less organic matter. Western wheatgrass needs a large supply of available PO4‐P because it grows rapidly in the spring. The bluestems grow when temperatures are higher and the microbial‐chemical release of plant nutrients is greatest. The distribution of the grasses is related to soil properties that in turn, are perpetuated by bluestems supplying more organic matter to the soil surface layer that western wheatgrass. Sideoats grama (Bouteloua curtipendula [Michx.]) can grow under conditions intermediate to those suited for bluestems and western wheatgrass.
Simulation of Crop Response to Polyolefin‐Coated Urea: I. Field Dissolution
Authors: Gandeza A. T. , Shoji S. , Yamada I.
Published: July 2010

Polyolefin‐coated urea (POCU) is a controlled‐release granular fertilizer whose dissolution is primarily temperature‐dependent. The coating is made of ethylene vinyl acetate, polyolefin, and talc to control N release. Dissolution doubles for every 10 °C rise in temperature, a Q10 matching that of plants. This study was conducted to understand its N release under Andisol field conditions and show its temperature dependency. Cumulative N release (CNR) with time between 10 and 30 °C is described by a quadratic equation in the general form CNR = a + b(day) + c(day)2. The equation corresponding to the mean daily soil or air temperature was used to calculate CNR. The CNR gradually increased with time and reached about 80% of the total N content at about 126 d after application. Two‐year experiments showed that observed CNR and predicted CNR determined using either soil or air temperature expressed as functions of time were closely correlated. Using cumulative temperature (CT) as the variable, CNR is given by the relation CNR = a + b(CT) + c(CT)2. This means that N dissolution from POCU can be predicted. Such behavior of N dissolution has significant implications on N supply to plants, fertilizer efficiency, and efforts to minimize environmental pollution.
Simulation of Crop Response to Polyolefin‐Coated Urea: II. Nitrogen Uptake by Corn
Authors: Shoji S. , Gandeza A. T. , Kimura K.
Published: July 2010

Controlled‐release N fertilizers are more desirable if release characteristics are synchronized to plant uptake. This study was conducted to determine the relationship between N dissolution from polyolefin‐coated urea (POCU) and N uptake by corn (Zea mays L.) under Andisol field conditions. Cumulative N release (CNR) followed a quadratic curve as a function of either time or cumulative air temperature (CAT). Rate of N dissolution was high at the early growth stages, but gradually decreased with time. The CNR reached about 80% of the total N content of the fertilizer at around 126 d after application or when CAT had reached about 2300 °C. Nitrogen uptake from the fertilizer followed a typical sigmoid curve. Therefore, the fertilizer can supply the N requirements of corn throughout the whole growing period. Since N dissolution can be simulated, it may also be possible to simulate N uptake from POCU by crops. Nitrogen uptake by corn can be predicted in terms of the total amount of N dissolved. Actual recovery of the fertilizer was very high compared with highly soluble fertilizers like (NH4)2SO4 or urea. Since POCU releases N gradually, depending on variations in temperature when soil moisture is sufficient, recovery by crops is less likely to be influenced by variations in climate, such as the occurrence of heavy rains; hence N losses are minimized. Such characteristics of the fertilizer increases nutrient efficiency and contributes to efforts in controlling pollution.
Stability of Iron Oxides in Two Soils with Contrasting Colors
Authors: Bigham J. M. , Smeck N. E. , Heckendorn S. E. , Jaynes W. F.
Published: July 2010

Two soils formed from sedimentary rocks with contrasting colors (dark reddish brown, 2.5YR 3/4 vs. olive, 5Y 5/3) were studied to assess the origin and relative stability of their constituent Fe oxides. Field morphology and total elemental analyses of the silt fractions for Ti, Zr, and K indicated that both soils had developed in uniform residuum overlain by approximately 30 cm of late Wisconsinan loess. The residual 2Bt horizons were contrasting in color but similar in clay content (50–65%), mineralogy (smectitic), and chemistry (pH = 4.5–6.0, base saturation = 50–60%). X‐ray diffraction studies of Fe‐oxide‐enriched specimens obtained through high‐gradient magnetic separations of the soil clays showed goethite to be the only detectable Fe oxide in the pedon formed from olive (5Y 5/3) shale. Red pigmentation in the companion soil was due to the presence of lithogenic hematite associated with varying amounts of goethite and lepidocrocite. Lepidocrocite occurred only in the solum and was most abundant in the clayey argillic horizon. Hematite grains from the 2C horizon consisted of thin, pseudohexagonal crystals with diameters <0.5 µm, whereas those isolated from overlying horizons were rounded and exhibited dissolution cavities attributable to instability within the modern pedoenvironment. Ratios of dithionite‐extractable to total Fe (Fed/Fet) indicated that goethite had formed primarily by pedogenic weathering of silicate minerals in the profile developed from olive shale. In contrast, sufficient Fe was apparently mobilized by dissolution of lithogenic hematite in the red soil to suppress the release of Fe from silicates and to exceed the solubility products of associated goethite and lepidocrocite on at least a seasonal basis.
Water Infiltration into Soil in Response to Ponded‐Water Head
Authors: Swartzendruber D. , Hogarth W. L.
Published: July 2010

The pressure head of water ponded on the soil surface can increase the infiltration of water into soil, but the effect has often been complicated to describe mathematically. This study was conducted to devise a simpler mathematical description without undue sacrifice of accuracy. A new three‐parameter infiltration equation was examined for its capability in describing the effect of soil‐surface‐ponded water head, h, on the cumulative quantity of water infiltrated into the soil with time. The infiltration equation, as reduced to two‐parameter dimensionless from, was fitted by nonlinear least squares to dimensionless data generated from mathematical descriptions of infiltration that included the effect of h in somewhat complicated parametric form. The fitted two‐parameter equation gave an excellent description of all the generated data, in terms of both goodness of fit and in recovery of the dimensionless ponded head p used as an input into the generated data. From an overall perspective, recovery of h was achieved within a relative error of ±1.4% across the complete range of the generated data, thus validating the new and relatively simple equation in its description of the general effect of ponded head on the cumulative infiltration process.
Topographic Effects on Spring Wheat Yields and Water Use
Authors: Halvorson Gary A. , Doll E. C.
Published: July 2010

Water redistribution in a complex landscape needs to be quantified in order to determine field productivity. Landscape effects on water use and spring wheat (Triticum aestivum L.) yields were studied by monitoring two fields at each of two locations in North Dakota for 5 years. Four soil series at different positions within each field were monitored: the Zahl loam series (fine‐loamy, mixed Entic Haploboroll) on hilltops and shoulder positions, the Williams loam series (fine‐loamy, mixed Typic Argiboroll) on side slopes and hilltops, the Bowbells loam series (fine‐loamy, mixed Pachic Haploboroll) on footslopes and toeslopes, and the Tonka silt loam series (fine, montmorillonitic, frigid Argiaquic Argialboll) in small undrained depressional areas. Topographic factors were calculated at each site by measuring the slope in four directions, 90° apart, and adding the slopes together. If a slope was downward toward a site, it was considered positive, if a slope was upward toward a site it was considered negative. This number, if positive, would indicate that runon water would be added to the site and, if negative, water would be lost from the site due to runoff. Topographic factors were calculated 3, 6, 15, and 30 m from each site. As expected, wheat yields from the four soils were in the order Tonka > Bowbells > Williams > Zahl. Spring wheat grain yields ranged from 5.1 Mg ha−1 on Bowbells in 1985 to no yield in 1988 at the Underwood location. Spring wheat grain yields were generally correlated to total water use. When the topographic factor was added into the regression of yield vs. total water use, the coefficient of determination, R2, increased in the first 3 yr. The last 2 yr of the study were drought years and the topographic factor accurately reflected the lack of water redistribution in those years. Topographic factors measured 15 m from the site gave the highest R2 values.
Soil Productivity Index: Predictions of Site Quality for White Spruce Plantations
Authors: Gale M. R. , Grigal D. F. , Harding R. B.
Published: July 2010

Very few site‐quality models have incorporated the biological effects of multiple soil properties on optimum root growth. One such model that was originally developed for agronomic crops and has been used for naturally forested stands is the soil productivity index (PI) model. Our objectives for this study were to determine if the PI model could be used to estimate site quality for white spruce (Picea glauca [Moench] Voss) plantations and to compare the use of PI vs. site index in equations describing changes in aboveground biomass with age. The PI model includes an estimate of optimum vertical root distributions that is used to weight the relative effects of mineral‐soil characteristics (bulk density, pH, available water capacity, and aeration) on aboveground biomass. Relative topographic (percent slope) and climatic (precipitation and evaporation potential) information are also used in the model. Results indicated that site index and PI were not significantly correlated. However, PI was more highly correlated with aboveground stand biomass and mean annual biomass increment than was site index. Site index was more highly correlated with biomass estimates in older plantations (35–43 yr), whereas PI was more highly correlated to biomass estimates in younger plantations (19–34 yr). To further assess the relationships between estimates of biomass and site quality, adjusted for age, a Schumacher‐type equation was used. Comparable results were observed between stand‐biomass equations using PI vs. site index.
Soil‐Core Break Method to Estimate Pine Root Distribution
Authors: Escamilla J. A. , Comerford N. B. , Neary D. G.
Published: July 2010

Root‐distribution studies are tedious and time consuming; there‐fore, root systems of forest ecosystems are one of the least studied components. Yet they are essential in order to assess belowground effects of forest‐management activities. This study used the soil core‐break method to measure the number of roots crossing a horizontal unit area (N, expressed in no. cm−2) as an alternative to measuring the more time consuming root‐length density (Lv, expressed as cm root length cm−3 soil volume). Soil core samples were taken from the surface horizon of a 7‐yr‐old slash pine (Pinus elliottii Engelm.) stand growing on a Pomona sand (sandy, siliceous, hyperthermic Ultic Haplaquod). Soil cores, 15.2‐cm diameter by 30 cm long, were extracted from two microsite locations within the check and complete‐weed‐control plots. Root‐length density and roots per square centimeter were measured at 2‐cm depth increments. The roots‐per‐square centimeter measure was a useful predictor of root‐length density only when treatment means were used, and even then the data did not fit the theoretical relationship of Lv = 2N. An Lv/N slope of ≈1 suggested that roots have a preferential vertical orientation in the A horizon. However, depth trends of root‐length density and roots per square centimeter were similar regardless of management practices or microsite. Roots measured as roots per square centimeter was also a less variable measure of root quantity than was root‐length density. Although roots per square centimeter can only be used to calculate root‐length density on an empirical basis, the more easily obtained value of roots per square centimeter can be used to depict root response to belowground competition.