bluuebunny/crossref_metadata_2025 huggingface dataset:
Litter Decomposition Across an Air‐Pollution Gradient in the San Bernardino Mountains
Authors: Fenn Mark E. , Dunn Paul H.
Published: July 2010

Air pollution may affect forest ecosystems by altering nutrient cycling rates. The objective of this study was to compare decomposition rates of L‐layer litter of ponderosa pine (Pinus ponderosa Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) collected from across an air‐pollution gradient in the San Bernardino Mountains in southern California. Litter from the more polluted western areas decomposed at a significantly (P = 0.01) faster rate than litter from plots in areas exposed to moderate or low pollution levels. The Shannon diversity index values for litter fungi were 1.41, 1.84, and 2.25 for plots in areas exposed to low, moderate, and high pollution levels. Nitrogen content of litter was greatest in the high pollution plots and was positively correlated with litter decomposition rate. Higher N and lower Ca content of litter at the more polluted western sites suggest that litter in the western plots originates from younger foliage than litter at the less polluted sites, possibly because of ozone (O3)‐induced needle abscission. Possible factors contributing to increased decomposition and fungal diversity in the western plots include: higher litter nutrient content because litter originates from younger foliage, higher soil N levels which may result in higher foliar N content, greater input of N from air pollution, and O3 damage to needles creating favorable sites for microbial decomposers.
Nitrogen Source, Rate, and Application Method for No‐Tillage Corn
Authors: Howard Donald D. , Tyler Donald D.
Published: July 2010

Surface applying urea‐containing N fertilizers may result in greater N losses by volatilization of NH3 as urea hydrolyses than nonurea containing materials. The objective of this study was to evaluate the N efficiency of urea‐ammonium nitrate (UAN), urea and urea‐urea phosphate (UUP) at 56, 112, 168, and 224 kg ha−1 N rates applied broadcast, surface banded, and injected for no‐till corn (Zea mays L.). Yield, ear‐leaf N concentration, and N uptake were used to estimate N availability. Broadcast ammonium nitrate (AN) and injected anhydrous ammonia (AA) were used as controls for evaluating N efficiency of urea‐containing N sources and their application methods. The method of applying the urea‐containing N sources has a significant effect on apparent N fertilizer availability. Injecting UAN and urea resulted in significantly higher yield, leaf N concentration, and N uptake when compared with broadcast and surface band application methods. Surface banding UAN at 168 and 224 kg ha−1 resulted in higher yields than urea or UUP. Yield, leaf N concentration and N uptake differences among the three urea‐containing N sources were not observed when broadcast applied. Broadcasting AN at 168 and 224 kg ha−1 resulted in higher yields than UAN, urea or UUP. Injecting the N sources resulted in higher yields when compared with broadcasting AN.
Electro‐Optic Detection of Liquid in Translucent Porous Material
Authors: Cary J. W. , McBride J. F. , Simmons C. S.
Published: July 2010

The amount of light transmitted through translucent porous materials can be accurately and inexpensively measured with a phototransistor or a CdS resistance cell. The results presented here suggest that light attenuation measurements in fritted glass or fibrous filters may be more easily calibrated to soil‐water content than the electrical resistance blocks that are commercially available because of reduced sensitivity to salt concentration. Light attenuation measurement in porous polyethylene offers a practical and inexpensive way to detect an organic liquid in the vadose zone or on the surface of the groundwater table. Light attenuation measurements also correlate with changes in water content in plant leaves.
Soil Surface Salty Crusts and Water Loss by Evaporation
Authors: Galizzi Fernando A. , Peinemann Norman
Published: July 2010

Water evaporation measurements in small soil columns saturated with different salt solutions show that the surface salty crusts affect the water content as well as the water movement in the soils in the order: NaCl < Na2CO3 < Na2SO4 < MgSO4. Morphological observations suggest that these differences are due to the deposited salt crust.
Subsurface Occurrence of Mirabilite in a Mollisol of Southern Alberta, Canada: A Case Study
Authors: Beke G. J. , Palmer C. J.
Published: July 2010

An efflorescent mineral, occurring at about 1 m depth in a moderately well‐drained soil of southern Alberta, had a chemical composition which corresponded to that of mirabilite, a hydrated sodium sulfate mineral. The x‐ray diffraction analysis of dehydrated crystals identified the anhydrous sodium sulfate mineral thenardite. The mirabilite crystals occurred in unsaturated soil beneath a melting frozen layer. Saturation extracts of bulk soil samples identified two zones of high ionic concentration, at the depth of mirabilite occurrence and below the water table. The dominant ions in these zones were sulfate and sodium and, to a lesser extent, magnesium. All saturation extracts and soil solutions from below the frozen layer and the groundwater were found to be saturated with respect to calcite, dolomite, and gypsum. Only the soil solutions from the 90 to 120 cm depth showed saturation with mirabilite. Mirabilite formation was attributed to the low soil temperatures, high soil water contents, and concentration of ions below the frozen layer.
Phosphorus Behavior in Flooded‐Drained Soils. III. Phosphorus Desorption and Availability
Authors: Sah R. N. , Mikkelsen D. S. , Hafez A. A.
Published: July 2010

Four California soils that showed wide variability in soil properties and P sorptivity under flooded‐drained (FD) conditions were selected for this study. The soils were flooded for 0 to 90 d at two levels of organic matter (OM, 0 and 10 g kg−1) and two temperatures (23 and 35 °C). They were subsequently drained and used for P‐sorption studies at 0.3, 1.2, and 2.0 mM initial P concentrations. The P desorption from P‐sorbed soils were carried out in three consecutive extractions with 0.1 M NaCl. The effect of FD conditions on P availability to corn (Zea mays L.), was studied at three levels of P (0, 5, and 20 mg P kg−1 soil). Without OM treatment, FD conditions decreased P desorption in three of four soils examined. Added OM and higher temperature further decreased P desorption and the period of flooding (FP) required to reach the minimum P desorption. Organic matter markedly decreased P desorption even in Soil 3, which was unaffected by FD conditions. Under FD conditions, plant‐tissue P concentration of corn was decreased to a variable extent depending on soil type. The desorption of added fertilizer P in a given FD soil correlated well with changes in the amorphous FeA fraction under comparable conditions. Phosphorus sorption and desorption were controlled by the changes in amorphous FeA and, in some cases, amorphous FeB fractions.
Reasons for Differences among Soils in Placement of Phosphorus for Maximum Predicted Uptake
Authors: Kovar J. L. , Barber S. A.
Published: July 2010

Previous research on placement of phosphate fertilizer has shown that the fraction of the soil fertilized with P affected P uptake by the crop, and that the fraction fertilized for maximum P uptake varied among soils. Placement effects on P uptake have been successfully simulated with a mechanistic uptake model. Values of parameters in the model describing P supply to the root depend on Pli, the initial concentration of P in the soil solution, and Psi, the initial P concentration of the solid phase that rapidly equilibrates with Pli. The objective of this research was to determine the importance of differences among soils in changes in Pli and Psi with increasing rate of P added, on the effect of P placement. Previous research has shown that, as P rate in the fertilized soil increases proportionally with a reduction in the fraction of the soil fertilized, Pli increased curvilinearly and Psi increased linearly. These relations were de‐on calculated P uptake with differing P placements was examined rate of P added, a, c and h are constants and d and g are predicted values of initial Pli and Psi, respectively. The effect of varying the coefficients a and c for the Pli function and of h for the Psi function on calculated P uptake with differing P placements was examined in this study. Standard deviations for c and h of 25% of the mean for 33 diverse soils were obtained from previous research. However, these data also showed that log a was correlated negatively with c (r = −0.92). Hence, in a study of curvilinearity of Pli with P added, it was necessary to adjust log a as c was changed. When log a was decreased as c was increased, the fraction of the soil to fertilize for maximum uptake decreased and predicted P uptake with optimum placement increased. When h was increased while holding c and log a constant, there was only a small increase in predicted P uptake and no change in fraction of the soil to fertilize for maximum P uptake. Hence, changes in Pli had a greater effect on predicted P uptake with changes in P placement than changes in Psi.
Winter Legume Effects on Soil Properties and Nitrogen Fertilizer Requirements
Authors: McVay K. A. , Radcliffe D. E. , Hargrove W. L.
Published: July 2010

Winter legume cover crops have been shown to provide significant amounts of N to subsequent nonleguminous crops, but benefits beyond those directly attributed to N are rarely cited. A 3 yr field study at two Georgia locations utilizing a randomized, complete‐block, split‐plot design with four replications was begun in 1985 to measure the equivalent fertilizer N supplied by winter annual legumes and to monitor changes in soil physical and chemical properties. Corn, Zea mays L. was grown on a Rome gravelly clay loam soil (fine‐loamy, mixed, thermic Typic Hapludult) at the Limestone Valley location, and grain sorghum [Sorghum bicolor (L) Moench] on a Greenville sandy clay loam soil (clayey, kaolinitic, thermic Rhodic Paleudult) in the Coastal Plain. Main plots were cover crops of hairy vetch (Vicia villosa Roth.), crimson clover (Trifolium incarnatum L), berseem clover (Trifolium alexandrinum L), winter pea [Pisum sativum subsp. arvense (L) poir], wheat (Triticum aestivum L), and fallow. Subplots were broadcast NH4NO3 fertilizer of varying rates. Hairy vetch and crimson clover replaced the greatest amount of fertilizer N averaging 123 and 99 kg N ha−1, respectively. More water‐stable aggregates were found following cover crops than fallow in the 0‐ to 0.025‐m depth at the Coastal Plain location. Higher infiltration rates were found following cover crops than fallow at both locations and infiltration rates were greater following hairy vetch than following wheat at the Coastal Plain site. An adapted winter legume cover crop can replace all of the fertilizer N necessary for optimum rain‐fed grain sorghum and up to two‐thirds of that required for corn production, and improve soil physical properties.
Mineralogy and Micromorphology of Soils from Volcanic Tuffs in the Humid Tropics
Authors: Goenadi Didiek H. , Tan Kim H.
Published: July 2010

An investigation was conducted to study mineralogy, chemical characteristics, and micromorphology of three pedons from andesito‐dacitic volcanic tuffs in Banten, West Java, Indonesia. The soils were strongly acid, had clayey textures, argillic horizons, and base saturations <35% in the control sections. The clay distribution suggested two of the soils to be Hapludults whereas the third was a Paleudult. Kaolinite was the dominant clay mineral, though the clay fractions did not meet the definition for low activity clays because of their relatively high cation exchange capacity (CEC) values. The sand and silt fractions contained substantial amounts of weatherable minerals (>10%). Micromorphic characteristics supported pedological features in the field. The Ap horizons exhibited soil fabrics composed of skeletal grains and plasma, and granular to crumb micropedal structures. In contrast, the Bt horizons had soil fabrics showing large amounts of plasma, angular blocky microstructures, and the presence of argillans.
Carbonate Phases in Calcareous Soils of the Western United States
Authors: Bui E. N. , Loeppert R. H. , Wilding L. P.
Published: July 2010

The carbonate phases of 39 calcareous soil samples, representing 23 soil series from the western US, were studied by wet‐chemical techniques, x‐ray diffraction (XRD), and electron microscopy to determine the particle‐size distribution, chemical composition, mineralogy, particle morphology, and Mg‐substitution patterns of the carbonate phases. The multivariate relationship between carbonate mineralogy and saturated‐paste extract composition was also investigated. Soil samples were fractionated into sand, coarse‐silt (5–50 µm), fine‐silt (2–5 µm) and clay particle‐size fractions. The silt‐size fraction accounted for a median proportion of 57% of the total soil carbonate. The percentage of the total carbonate in the clay‐size fraction was variable among soils, ranging from <1 to 60%. Calcite, Mg‐substituted calcite, and dolomite were identified by XRD, and each of these phases was identified in the clay‐size fraction of selected soils. The occurrence of clay‐ and fine‐silt‐size carbonates is indicative of the presence of pedogenic secondary carbonates (including dolomite). For the clay‐size fractions, the Mg/(Ca + Mg) molar ratios of the dissolution extracts of several of the samples were considerably higher than the theoretical ratios calculated from the experimentally determined calcite and dolomite contents, indicating the possible occurrence of poorly crystalline Mg‐rich carbonate phases that were too disordered or too small in particle size to give distinct XRD reflections. Dolomite had a predominantly euhedral particle morphology, compared with calcite, which appeared as aggregates of smaller (<1 µm) particles. The mineralogy and morphology of the specific carbonate phases probably reflect the environment of precipitation and seasonal differences in soil‐solution composition.
Determining Soil Salinity from Soil Electrical Conductivity using Different Models and Estimates
Authors: Rhoades J. D. , Shouse P. J. , Alves W. J. , Manteghi Nahid A. , Lesch S. M.
Published: July 2010

The appropriateness of two versions of a model describing electrical current flow in undisturbed soil was evaluated for purposes of diagnosing and mapping soil salinity (ECe). Different methods of measuring bulk soil electrical conductivity (ECa) and different ways of obtaining the values of other parameters required by the model were also evaluated using three different sets of data. The reliability of the variously predicted salinities were evaluated by comparing them against conventionally measured salinities using linear regression analyses, ranking tests, and a procedure based on the weighted sums of squared differences. It was found that salinity‐prediction accuracy, though relatively good, was underestimated for the instrumental/model techniques because of sample‐size differences and spatial‐variability effects. Conclusions arrived at from earlier sensitivity analyses about the suitability of the parameter‐estimation procedures were borne out by these results, i.e., that soil salinity appraisal and mapping can be quite adequately made using field measurements of ECa (by any one of three methods) and estimates of soil water content, bulk density, and surface conductance determined by “feel” methods.
Measurement of Calcite Ion Activity Products in Soils
Authors: Reddy K. J. , Lindsay W. L. , Workman S. M. , Drever J. I.
Published: July 2010

Soils often show supersaturation with respect to calcite. This study was undertaken to test alternative methods of measuring Ca2+ and CO2‐3 activities to assess their effects on measured ion‐activity products (IAP) of calcite in soils. Soils were reacted with atmospheric CO2(g) and distilled H2O for 1, 3, and 7 d. The soil extracts were analyzed for pH, electrical conductivity (EC), cations, anions, and dissolved organic carbon (DOC). Carbonate activities in soil extracts were obtained by two methods. The first consisted of titrating the soil extracts with standard HCl to pH 4.0 (direct‐titration method). The second method consisted of acidifying soil extracts to pH 4.0 and trapping the evolved CO2 gas in a NaOH + BaCl2 solution (CO2 gas release method). The IAP values for calcite were calculated in two ways. First, Ca2+ activity was obtained by speciating total soluble Ca while CO2‐3 activity was obtained from the direct titration of soil extracts. This method gave mean log IAP values of calcite ranging from −7.90 to −7.78 compared with a log Ko (Ca2+)(CO2‐3) (equilibrium constant) of −8.48 for calcite. These results suggest supersaturation with respect to calcite. Secondly, when Ca2+ activity was measured with a Ca2+‐specific ion electrode and CO2‐3 activity was estimated by the CO2 gas release method, the mean log IAP values of calcite ranged from −8.45 to −8.35, which is very near equilibrium with calcite. The apparent supersaturation in the first case was probably caused by DOC, which both complexed Ca2+ and contributed to titratably alkalinity over that of carbonate and bicarbonate alone.
Aliphatics in Soil Organic Matter in Fine‐Clay Fractions
Authors: Schulten H. ‐R. , Schnitzer M.
Published: July 2010

Fine‐clay fractions were separated from three agricultural soils and extracted sequentially with n‐hexane, chloroform and supercritical n‐pentane. The resulting extracts were analyzed by field ionization (FI) and field desorption (FD) mass spectrometry (MS). The major components indentified included C11 to C94 n‐alkanes, C13 to C34 n‐fatty acids, n‐C16 and n‐C24 diols, and C38 to C67 n‐alkyl monoesters. Minor components were C22, C32, and C34 n‐alcohols, C27 and C29 sterols, C56 to C91 n‐alkyl diesters, C83 to C99 n‐alkyl triesters, and C17 to C21 unsaturated monocarboxylic acids in extracts of one clay only. The highest molecular weight compound identified was the C99 n‐alkyl triester (m/z 1478). Especially noteworthy was that: (i) similar aliphatics were extracted from the three clays, (ii) the compounds identified were typical of components of natural waxes, which appear to be present in the organic matter in fine‐clay fractions, and (iii) the soft ionization mass spectrometric methods employed were found to be eminently suitable for the identification of medium to high molecular weight aliphatics in the organic matter in fine‐clay fractions.
Long‐Term Conventional and No‐Tillage Effects on Selected Soil Physical Properties
Authors: Hill R. L.
Published: July 2010

Soil management systems can affect soil physical properties and, thus, have a direct bearing on crop performance. This study determined the effects of continuous long‐term conventional and no‐tillage management on selected soil physical properties and compared observed yield differences between these tillage systems with soil physical properties. Three Maryland locations, each having randomized complete‐block designs with three replications of continuous corn (Zea mays L.) under conventional and no‐tillage management, were used. Sites 1 and 2 were in their 12th yr of tillage and Site 3 was in its 11th yr. Soils at all three sites were silt loams (fine‐loamy, mixed, Aquic Hapludults). Tillage affected bulk density at the 0.05 level at Site 1 and the 0.10 level at Site 2. No‐tilled soils generally had higher bulk density at all soil depths for Sites 1 and 2. Tillage affected soil strength at Sites 1 and 2, but not at Site 3. Soil strength for no‐tilled soils was consistently greater than for conventionally tilled soils. Conventionally tilled soils had greater pore volume in pores with radii >15 µm at Sites 1 and 2, and, therefore, should drain more readily than no‐tilled soils. More importantly, the amount of pore space available for the storage of plant‐available water was greater for conventionally‐tilled soils at Sites 1 and 2. Although soil physical properties within the Ap horizon are not adequate to account for differences in corn yield response, tillage differences in soil physical properties were found for the soils at Sites 1 and 2, which had previously shown tillage yield differences.
Dry Aggregate Size Distribution of Sandy Soils as Influenced by Tillage and Precipitation
Authors: Zobeck T. M. , Popham T. W.
Published: July 2010

Surface soil dry aggregate size distribution (ASD) has a significant effect on the amount and intensity of wind‐induced soil erosion. The ASD of cropland varies through time primarily due to the effects of management and climatic factors. A method of predicting ASD is needed to make accurate estimates of wind erosion. The effects of tillage on ASD are described and models proposed to estimate changes in ASD after precipitation has further modified a sandy soil surface. The ASD and bulk density of the near‐surface soil were measured on four west Texas sandy soils immediately after tillage and after up to 130 mm subsequent rainfall. Tillage methods included moldboard plow, lister, chisel, and tandem disk. Results indicated that the four tillage methods tested could be separated into two groups to produce reliable estimates of ASD. Moldboard plowing produced significantly larger aggregates than a tillage‐tool group comprised of lister, chisel, and tandem disk. The combined effects of tillage and precipitation after tillage produced significant differences (P < 0.002) in ASD for each soil tested. Regression models to estimate ASD using bulk density in the near‐surface soil and cumulative precipitation as independent variables accounted for up to 80% of the variation.
Tensiometer Data Acquisition System for Hydrologic Studies Requiring High Temporal Resolution
Authors: Nyhan John W. , Drennon Barry J.
Published: July 2010

Commercially available differential pressure transducers, tensiometers, and a data acquisition system were combined to evaluate soil water tension changes with time within two landfill cover designs used for the shallow land burial of waste materials. A typical error for the differential pressure transducers in the voltage‐pressure calibration curve was estimated to be 0.14 V at a transducer output of 4 V. Tensiometer data collected simultaneously using the data‐acquisition system and a hand‐held manual pressure‐transducer system agreed well (r2 = 0.994). The utility of the tensiometer data acquisition system to collect field data was demonstrated successfully using reference tensiometers with known hydraulic heads. Diurnal fluctuations in tensiometer data collected in the field are discussed relative to future experiments to be performed with the system. In addition, tensiometers with unknown and variable hydraulic heads were used to determine tensiometer response times of approximately 50 min.
Ion Transport during Unsteady Water Flow in an Unsaturated Clay Soil
Authors: Bond W. J. , Phillips I. R.
Published: July 2010

The transport of many solutes through soils is strongly affected by their reaction with the solid constituents. One of the most common of such reactions is cation exchange. It is, therefore, important to be able to predict the effects of cation‐exchange reactions on cation transport. The purpose of this study was to examine experimentally the effects of two different types of cation exchange on the transport of cations through soil, and to compare the results with simple mathematical predictions. The experiments also permitted an examination of the effect of cation exchange on anion transport via its effect on anion exclusion. The effects of both K‐Ca and Na‐Ca exchange were studied because these have quite different isotherm shapes, Na‐Ca exchange being much less favorable than K‐Ca exchange. The spatial distributions of water, tritium, Cl, Na, K, and Ca were measured following constant‐flux horizontal infiltration of tritiated NaCl or KCl solutions into a Ca‐saturated clay soil. The concentrations of cations both in solution and in the sorbed phase were measured independently. Soil water fluxes throughout the experiments were small enough to ensure that physical and chemical equilibrium was attained. Anion exclusion caused the Cl front to move faster than the tritium front (which moved with the average pore‐water velocity), while exchange resulted in the monovalent cations moving more slowly than tritium. The position of the Cl front was independent of the cation in the invading solution, being determined by the anion‐exclusion properties of the soil in equilibrium with the cation in the initial solution. The shape of the cation profiles, the relationship between the position of the cation fronts in the solution and sorbed phases, and the average position of the cation fronts depended on the shape of the exchange isotherm and the inflowing solution concentration. The penetration of the center of mass of the combined cation fronts (total cation mass per unit soil volume) was successfully predicted using the effective distribution coefficient and a moving coordinate based on the water.
Divalent Zinc Activity in Arid‐Zone Soils Obtained by Chelation
Authors: Ma Qiying , Lindsay W. L.
Published: July 2010

Because of the low solubility of Zn in alkaline soils, it is virtually impossible to measure Zn activity directly. In the present study Zn activities in 10 arid‐zone soils were obtained by chelation. The Zn activities were extremely low, ranging from 10−7.9 to 10−10.9 M and were inversely related to pH, with a correlation coefficient of 0.94. Direct identification of solid phases controlling Zn solubility in these soils has not been achieved. The Zn activities measured in these soils can be expressed by the relationship soil Zn + 2H+ ⇌ Zn2+ with log Ko = 5.7 ± 0.38, where Ko is the equilibrium constant expressed in terms of activities. This is nearly identical to that reported earlier from this laboratory. This observed solubility relationship could be explained by the formation of ZnFe2O4 (franklinite), but that possibility awaits further study.
Modeling Magnesium Uptake from an Acid Soil: I. Nutrient Relationships at the Soil‐Root Interface
Authors: Rengel Z. , Robinson D. L.
Published: July 2010

Annual ryegrass (Lolium multiflorum Lam.), an important forage crop in the southeastern USA, is often grown on soils with potentially toxic levels of soluble Al. Effects of Al on nutrient uptake are poorly understood. Two ryegrass cultivars were grown on an acid Stough soil (a coarse‐loamy, siliceous, thermic Fragiaquic Paleudult) in a greenhouse. Lime (CaO) at three rates to give soil pH values of 3.8, 4.4, and 5.6, and Mg (as MgCl2) at rates of 0, 12, and 36 mg kg−1 were applied in factorial combination. Magnesium application increased shoot Mg concentration, especially in plants grown on unlimed soil. Net Mg influx increased with increased Mg and lime application but decreased with plant age. Liming and plant uptake each caused significant decreases in soil‐solution Mg concentrations. Calculated concentrations of Mg and Ca were higher and K concentrations lower at the root surface than were corresponding concentrations in the bulk soil solution. Concentrations of monomeric hydroxy‐Al species (Almon) at the root surface varied widely. Concentrations of Mg at the root surface were significantly related to net Mg influx only for plants grown in unlimed soil (r2 = 0.89, P < 0.005, and r2 = 0.81, P < 0.014, for 23‐ and 35‐d‐old plants, respectively). For plants grown on limed soil, the ratios of concentrations at the root surface (Mg/Ca, Mg/K, and Mg/Almon), rather than Mg concentration alone, were significantly related to net Mg influx, substantiating existence of the complementary‐ion effect.
Conservation Tillage Effects on the Potassium Status of Some Kentucky Soils
Authors: Karathanasis A. D. , Wells K. L.
Published: July 2010

Changes in the soil K status occurring as a result of shifting from conventional to no‐tillage management in selected fields were evaluated in this study. The fields were on loess‐ and limestone‐derived soils in western and central Kentucky and have been under no‐tillage management for the last 6 to 16 yr. Two‐ to three‐fold increases in exchangeable and soluble K were evident in most upper surface horizons (Ap1) of soils receiving no‐tillage management, and these increases correlated well with organic matter (OM) accumulations. Adsorption of exchangeable K appeared to be favored over that of Ca and Mg with increases in OM up to a maximum value, beyond which additional OM accumulations had a negative or no effect. Notillage management resulted in a lower overall affinity for K of the exchange sites in all soils (especially the Memphis soil) apparently due to OM accumulations. Quantity/intensity plots reflecting the tillage‐shift effect on K relationships suggested that the loessial soils could reach K‐availability equilibria sooner than the limestone soils due to mineralogical and textural differences. This could mean less fertilizer‐K use on loess‐ than on limestone‐derived soils to attain maximum crop yields under no‐till management.
Differential Chemoreductive Dissolution of Iron Oxides in a Brazilian Oxisol
Authors: Bryant R. B. , Macedo J.
Published: July 2010

Stabilities of naturally occurring hematite and goethite in the Bol horizon of a well‐drained Brazilian Oxisol, and their rate of reductive dissolution by sodium dithionite, were investigated. The soil has codominant hematitic and goethitic Fe oxide mineralogy and a reddish hue (2.5YR). There was no apparent foreign‐ion substitution in the hematite, but the goethite contained 34 mole percent of AlOOH substituting for FeOOH. Results of limited additions of sodium dithionite and measured redox‐potential (Eh) development during the reaction showed that hematite and Al goethite were metastable at Eh = 98 mV, pH = 7.3, and 25 °C. Aluminum goethite was metastable at Eh = −2 mV, pH = 7.3, and 25 °C. Hematite dissolution at low Eh occurred readily at 25 °C. Aluminum‐goethite dissolution at low Eh was imperceptible at 25 °C, but occurred readily at 75 °C.
Influence of Plant Uptake on the Performance of Bromide Tracer
Authors: Kung K.‐J. S.
Published: July 2010

Bromide has been used to study solute transport in unsaturated soils. However, no field studies have addressed the impact of plant uptake on the performance and reliability of Br as a tracer. Field experiments were conducted in a Russet Burbank potato (Solanum tuberosum L.) field on a Plainfield loamy sand soil (mixed, mesic Typic Upidsamment) at the Hancock Research Station in central Wisconsin. At emergence, a 6.8‐mm pulse of KBr solution with 15 kg m−3 concentration was banded at the center of each potato row. The application rate was equivalent to 111.2 kg ha−1 of Br. At 65 d after Br application, soil, potato canopies, tubers, and residues of dead potato leaves and vines from four vertical profiles were collected and the total mass of Br from each sample was measured. The results showed that at least 53% of applied Br mass was absorbed by potato plants. About 44% of the absorbed Br ions could be redistributed to the soil surface when the dead leaves and vines decayed. Leaching of some chemicals, which are metabolized or degraded after being taken up by the plant, can therefore be grossly overestimated by using Br breakthrough curves under certain conditions. Before using Br as a tracer in a field experiment, preliminary laboratory studies should be conducted to determine whether Br uptake and redistribution will be significant under a particular cultivar, Br‐application concentration and mode, and water‐application scheme.
Design of Soil Map Units on a Karst Area in West Central Florida
Authors: Puckett W. E. , Collins M. E. , Schellentrager G. W.
Published: July 2010

The objectives of this research were to identify soil taxa and to evaluate soil‐landscape relationships in order to design map units that accurately describe soil distribution on the Chiefland Limestone Plain (CLP) in west central Florida. A conceptual soil‐landscape model for mapping the CLP was derived based on information from similar karst areas in adjacent counties. Preliminary field observations using the model along with analysis of initial ground‐penetrating radar (GPR) data indicated intricate soil patterns and little relationship between soil occurrence and landscape position. Flexgrid surveys were conducted and 61 GPR transects were performed to design map units and to facilitate placement of map‐unit boundaries. Confidence levels of 95 and 80% were used to establish confidence intervals for named and similar soils in each map unit. A new kind of map unit termed “intriplex” was defined to bridge the gap between complexes and undifferentiated groups.
Surface Soil Acidification under Red Pine and Norway Spruce
Authors: Pallant Eric , Riha Susan J.
Published: July 2010

Near‐tree patterns of forest‐soil pH under red pine (Pinus resinosa Ait.) and Norway spruce [Picea abies (L.) Karst.] were examined in order to evaluate the role of trees in acidification processes of surface soils. Variability in soil pH was analyzed by comparing samples obtained at different distances and directions from the base of a tree, at different times within a year, under live and dead trees, trees of different sizes, and trees of the same species growing on different soil types. Accumulation of soil organic matter, pH of freshly fallen litter, and the concentration of oxalate in water extracts of Oe horizons were measured as a function of distance from the base of selected trees. A significant decrease in soil pH from the edge of the canopy to the base of the tree was found in the upper mineral soil and organic horizons beneath live trees of both species. In general, the direction of sampling, the percent organic matter within a soil sample, and the time of year for sampling did not significantly affect soil pH. Mass of organic matter above the mineral soil did not exhibit a distinct pattern with distance from a tree. Twelve years after thinning red pine trees, a significant depression in pH existed in Oi and Oe horizons near the base of a dead tree or stump. Near‐tree depression in pH of the Oi horizon, where tree roots are not present, and of the Oi and Oe horizons around previously thinned trees where no stemflow occurs, suggests that soil fungi endemic or more active in the near‐tree environment of red pine and Norway spruce could make a significant contribution to acidification of soil surface horizons.
Lysimeter and Centrifuge Soil Solutions: Seasonal Differences between Methods
Authors: Zabowski D. , Ugolini F. C.
Published: July 2010

Lysimetry and centrifugation were compared as variable‐tension (centrifugation) and low‐tension (lysimetry) soil‐solution collection methods. Low‐tension lysimetry and low‐ and high‐speed centrifugation with double‐bottom cups were used to collect soil solutions from each major horizon of a subalpine Spodosol. Solution samples were collected monthly and compared throughout a 1‐yr period. Few seasonal changes were observed in the cation, anion, pH, or C concentrations of the lysimetry solutions. Both low‐ and high‐speed centrifuge solutions showed a strong seasonal cycle for major cations, anions, and C; peaks occurred in winter and summer and were especially evident in the upper horizons. Centrifuge solution concentrations were frequently greater than those of the lysimeter solutions. Aluminum and Si were exceptions, with lysimetry solution concentrations equal to or greater than those of the centrifuge solutions. Centrifuge solution concentrations of Al and Si also showed increases in concentration during summer months only. Seasonal variations may be due to differences in soil water residence time or biological processes. Results suggest that both the methodology used for obtaining soil solutions and the time of sampling can influence solution composition.
Diffusion, Adsorption, and Predicted Longevity of Banded Phosphorus Fertilizer in Three Soils
Authors: Eghball Bahman , Sander D. H. , Skopp J.
Published: July 2010

Diffusion of banded P fertilizer influences the residual P effect, root/P‐fertilizer contact, fertilizer‐P longevity (the time after which the contribution of applied band to plant P uptake is insignificant) and the probability that the P‐affected soil will be collected during soil sampling. An experiment was conducted to determine the extent of P diffusion from banded P application, diffusion coefficients, and the longevity of banded P fertilizer. Six P rates of 15, 22.5, 30, 37.5, 45, and 60 kg P ha−1 tagged with 32P were applied in a band in three soils and allowed to diffuse under field conditions for 94 d. Phosphorus‐fertilizer movement from the injected band centers (30‐cm spacing) after 94 d ranged from 1.8‐cm radius at the 15 kg P ha−1 rate in the Sharpsburg (fine, montmorillonitic, mesic Typic Argiudoll) and Coly (fine‐silty, mixed [calcareous], mesic Typic Ustorthent) soils to 3.9 cm at the 60 kg P ha−1 rate in the Nora (fine‐silty, mixed, mesic Udic Haplustoll) soil. The diffusion distances and apparent diffusion coefficients increased in a linear manner as the P application rate increased. The calculated longevity of banded P fertilizer ranged from 2.6 yr at 15 kg P ha−1 in the Sharpsburg soil to 6.5 yr at 60 kg P ha−1 in the Coly soil. The longevity of banded P fertilizer was shortest for the Sharpsburg soil with the highest P‐adsorption capacity and was longest for the Coly soil with the lowest P‐adsorption capacity. The probability of P‐affected soil being collected during soil sampling ranged from 11.7% at 11.7% at 15 kg P ha−1 in the Sharpsburg soil to 25.9% at 60 kg P ha−1 in the Nora soil. Soil sampling and soil‐test P calibration should be altered to account for the residual nature of applied P bands.
Clay Minerals of Two Eutrandepts of Hawaii, Having Isohyperthermic Temperature and Ustic Moisture Regimes
Authors: Wada K. , Kakuto Y. , Ikawa H.
Published: July 2010

Clay minerals of two pedons of Naalehu soils from Hawaii were studied by a combination of methods. According to Soil Taxonomy, they are classified as medial, isohyperthermic Typic Eutrandept. In the Andisol proposal, Naalehu‐1 is not an Andisol because its P retention is <85%, but Naalehu‐2 is classified as an Andisol because it meets all of the definitions of andic materials. Their clay content was high (49–85%), with no significant difference between the two soils. The Naalehu‐2 soil clays, however, had higher contents of oxalate‐oxalic acid soluble aluminosilicates and Fe oxides than the Naalehu‐1 soil clays. These clays also showed halloysite (1.0 nm), concentric spherules and curled flakes, and possibly hollow spherical aluminosilicates having a close structural relation with allophane. The Naalehu‐1 soil clays, on the other hand, showed smectite, halloysite (1.0 nm), and their interstratified species. Both soils contained X‐ray‐detectable amorphous Fe oxides in the clay and poorly crystalline maghemite, olivine, and plagioclase in the silt and sand fractions. The importance of the soil‐forming factors of parent material, climate (soil moisture and soil temperature), and age was inferred from comparison of the smectite and/or halloysite mineralogy of the isohyperthermic Naalehu soils with the imogolite and/or allophane mineralogy of the isothermic and isomesic Maui soils studied earlier.
Diffusion of Soil Extracts for Nitrogen and Nitrogen‐15 Analyses by Automated Combustion/Mass Spectrometry
Authors: Burke Ingrid C. , O'Deen Louise A. , Mosier Arvin R. , Porter Lynn K.
Published: July 2010

The coupling of automated combustion instruments with mass spectrometry has streamlined total N and 15N analyses of soil and plant materials. New methods are needed for analysis of soil NH4 and NO3 15N to take advantage of the efficiency in automated combustion analysis. We have developed a method to quantitatively determine NO3, NH4, and 15N content of soil extracts by automated combustion/mass spectrometry. Soil extracts are made basic, and diffused into acid‐washed zeolite in tin combustion cups. Zeolite samples are then analyzed on the automated combustion/mass spectrometry system for N and 15N. Ammonium‐ and NO3‐N and 15N can be quantitatively recovered and analyzed during this procedure, reliably collecting 97% of the N and 15N in the extract, with a repeatability of ±2%.
Modeling Reactive Gas Uptake, Transport, and Transformation in Aggregated Soils
Authors: Rasmuson Anders , Gimmi Thomas , Flühler Hannes
Published: July 2010

Gas diffusion research in soils covers, to a large extent, the transport behavior of practically insoluble gases. We extend the mathematical description of gas transport to include reactive gaseous components that hydrolyze in water such as SO2 and CO2. The path between the free atmosphere and the microporous niches is modeled by assuming penetration through gas‐filled macropores, air‐water phase transfer, and diffusion and speciation in the liquid phase. For hydrolyzable gases, the rate of mass transfer into and the total absorption capacity of the soil solution may be high. Both the capacity and the transfer rate are influenced by the soil‐solution pH; for high pH, they become extremely high for SO2. The soil absorption of such gases is also influenced by soil structure. Well‐aerated, near‐neutral soils are a potentially important sink for SO2.
Kinetics and Mechanisms of Sulfate Adsorption/Desorption on Goethite Using Pressure‐Jump Relaxation
Authors: Zhang Peng Chu , Sparks Donald L.
Published: July 2010

Sulfate adsorption/desorption on goethite (FeOOH) in aqueous suspension was investigated thermodynamically and kinetically. The SO4‐adsorption isotherm indicated that adsorption decreased with increased pH of the goethite suspension. The triple‐layer model fit the experimental data well when adsorbed SO4 was assumed to be located at the β plane and held via outer‐sphere complexation. Pressure‐jump relaxation was used to determine the kinetics of SO4 adsorption/desorption on goethite. A single relaxation was observed due to adsorption/desorption processes. Based on the equilibrium and kinetic studies, we hypothesized and tested two reaction mechanisms for SO4 retention. The first postulated mechanism (Reaction 1) assumed that SO4 was adsorbed on a positively charged surface site through electrostatic attraction. This mechanism was rejected because of the poor conformity between the intrinsic equilibrium constant (Kinteq) determined from the static studies and that found from the ratio of forward (kint1) and backward (kint‐1) rate constants, i.e., Kint1 = kint1/kint‐1. It was found that the adsorption of SO4 on goethite occurred simultaneously with the protonation of a neutral surface site, as assumed in the second hypothesized mechanism (Reaction 2). Based on this mechanism, a linear relationship between the reciprocal relaxation time (τ−1) and various concentration terms was observed. From this relationship, kint2 and kint‐2 were calculated and were 2.02 × 108 mol−2 L2s−1 and 0.144 s−1, respectively. The intrinsic equilibrium constant from kinetic measurements (Kint2) was 109.14 mol−2L2, which was similar to the intrinsic equilibrium constant from the equilibrium studies, 109.60.
Analyses of Adsorption Kinetics Using a Stirred‐Flow Chamber: II. Potassium‐Calcium Exchange on Clay Minerals
Authors: Eick Matthew J. , Sparks Donald L. , Bar‐Tal Asher , Feigenbaum Sala
Published: July 2010

Potassium‐calcium adsorption kinetics on a Llano vermiculite and an Arizona montmorillonite were studied using a stirred‐flow technique. Various experiments were conducted to distinguish between (i) instantaneous equilibrium and time‐dependent reactions, and (ii) solution‐concentration‐dependent kinetic models vs. those that are independent of solution concentration. These experiments included varying the flow rate and influent concentration and stopping the flow for a period of time. It was found that K‐Ca exchange on montmorillonite was too rapid to be measured with the stirred‐flow technique, while exchange rates on vermiculite could be ascertained. Adsorption kinetic parameters should be included in transport models to more accurately predict the fate of ions in soils dominated by vermiculitic and micaceous clay minerals.
Potassium Supply Characteristics of Thirty‐three Soils as Influenced by Seven Rates of Potassium
Authors: Kovar J. L. , Barber S. A.
Published: July 2010

Limited information is available on the effect of applications of multielement fertilizer materials on the concurrent changes in Kl (soil‐solution K) and Ks (exchangeable K). The objectives of this research were to: (i) investigate the relative increases in both Kl and Ks after addition of graded amounts of a 3‐4‐7.5 solution fertilizer; and (ii) determine if the changes in Kl and Ks with fertilizer additions were related to some measurable physical or chemical property of the soil. Thirty‐three surface soils were equilibrated moist for 3 wk after addition of 0, 21, 42, 104, 208, 415, and 1245 mg K per kg of soil. High rates of application were used because they occur when the same total amount of K is placed in a small fraction of soil, e.g., band application. Values of Kl were determined from water‐displaced soil solution. Values of Ks were obtained from K extracted with 1.0 M NH4OAc at pH 7.0 minus θKl, where θ is the volumetric water content g−1 of sample. The increase in Kl with K addition was described by Kl = axc + d, where x is the amount of added K and a and d are regression constants. Values of c, the curvilinearity coefficient, varied from 1.00 (linear) to 1.59. The increase in Ks with K addition was described by Ks = g + hx. The value g represents the amount of exchangeable K in the untreated soil. Values of h, the slope, varied from 0.42 to 1.13. The coefficients describing the relation of both Kl and Ks to added K were not correlated with any of the measured soil properties. There was no significant correlation between c and h. Characterization of the changes in Kl and Ks after addition of K gives information useful for determining the effectiveness of K placement.
Antecedent Water Content and Rainfall Energy Influence on Soil Aggregate Breakdown
Authors: Truman C. C. , Bradford J. M. , Ferris J. E.
Published: July 2010

Stability of soil aggregates under rainfall plays an important role in determining the magnitude of soil loss from cultivated fields. Soil and environmental factors controlling aggregate breakdown have yet to be fully defined. The objective of this study was to determine the influence of soil water condition, aggregate size, and rainfall intensity and duration on aggregate breakdown. Five soils ranging in texture from sandy loam to clay were studied. Using the wet‐sieving method, median aggregate diameter values (D50) were determined on both whole‐soil samples (0–19 mm) and aggregate samples (2–4, 4–8, and 8–19 mm in diam.) at three water conditions (−0.5 kPa, −1.0 kPa, and air dried). A companion set of whole‐soil samples was subjected to 64 and 127 mm h−1 simulated rainfall for 5, 15, and 30 min, and a set of aggregate samples was exposed to 64 mm h−1 simulated rainfall for 15 min; all samples were then wet sieved. Prewetting from air dry to −1.0‐kPa matric potential provided the greatest increase in D′50 values (D50 corrected for primary particle size) for the wet‐sieved Broughton clay (0.49–1.91 mm). Prewetting the Broughton clay also decreased the difference (ΔD50) between Broughton D50 values obtained from whole‐soil samples receiving rain plus wet sieving and D50 values of only wet‐sieved samples by 1.4 mm for all rainfall energies. Changes in D′50 and ΔD50 values due to rainfall energy were greatest for the air‐dried Heiden clay. Rainfall energy (0.26 J cm−2) decreased D′50 values from 0.87 to 0.33 mm and increased ΔD50 values from 0.32 to 0.54 mm. Results of this study indicate that an increase in initial water condition increases the resistance of an aggregate to the forces of raindrops and flowing water, thereby lessening particle detachment (if other hydraulic variables are held constant).