bluuebunny/crossref_metadata_2025 huggingface dataset:
Resistant and Exploratory Techniques for Use in Semivariogram Analyses
Authors: Hamlett J. M. , Horton R. , Cressie N. A. C.
Published: July 2010

“Traditional” statistical analyses based on the assumption of independent observations are being replaced by spatial analyses that take account of correlations between neighboring observations. Geostatistics is one approach; it characterizes the spatial relationships of data via the variogram, which is in turn used for kriging (optimal, unbiased linear interpolation). Exploratory data analysis techniques, relying on resistant measures, graphical tools, and robustness ideas, can be used to help “model” the spatial structure of data. Data should fulfill certain stationarity conditions before computing and interpreting the semivariogram. Data of soil‐water pressure potential are analyzed by straight‐forward techniques that assure the data meet the implicit assumptions of stationarity (of the mean and the variance) and at least symmetry. Stem‐and‐leaf plots and plots of mean vs. variance (or for a more resistant analysis, median vs. interquartile range squared) are used to assess the variance stationarity and data distributions. Median‐based techniques (rather than polynomial modeling and generalized least‐squares fitting of drift) are used to remove drift along both grid directions. Then the spatial structure is exposed through computing and interpreting semivariograms of the modified data.
Effect of Mineral Weathering on the Response of Sodic Soils to Exchangeable Magnesium
Authors: Alperovitch N. , Shainberg I. , Rhoades J. D.
Published: July 2010

The clay dispersivity and hydraulic conductivity (HC) properties of three California soils were studied as a function of exchangeable Na and electrolyte concentration in Na/Ca and Na/Mg systems. Soils that are relatively stable chemically are concluded to be the most sensitive to low levels of exchangeable Na and to the “specific” effect of exchangeable Mg when leached with distilled water. The results agree with the hypothesis that the susceptibility of soils to HC decreases produced by exchangeable Na and exchangeable Mg depends on their rates of mineral dissolution. Exchangeable Mg reduces the dissolution rates of noncalcareous soils and increases soil susceptibility to exchangeable Na under conditions of low electrolyte concentrations.
Comparison of Inoculant and Indigenous Rhizobial Dinitrogen Fixation in Cowpeas by Direct Nitrogen‐15 Analyses
Authors: ElHassan G. A. , Focht D. D.
Published: July 2010

Soil that contained 15N enriched organic matter (0.461 % 15N) was used to determine competitiveness of six strains at different logarithmic inoculum densities against indigenous rhizobia and against a previous surviving inoculant (strain P132). Analyses of N content of plant tissues by direct 15N technique showed that cowpeas (Vigna unguiculata L. Walp.) were capable of deriving 60 to 98% of shoot N from N2 fixation. The two fast‐growing strains (176A26 and 176A28) were poorer competitors and fixed less N2 compared to the other slow‐growing strains. Inoculum density had no effect upon yield response of cowpeas, but inoculation with strains P132, 401, and 22A1 effected greater seed yield, shoot dry matter, total N, and percentage of N derived from fixation (86‐98%) than other strains and the uninoculated control (60‐73%). By contrast, N2 fixation and yield parameters in inoculated cowpeas were not significantly different from inoculated controls that contained residual P132 from a previous inoculum study. The higher hydrogen uptake (Hup) efficiency of nodules containing residual P132 (98 ± 2%) facilitated presumptive identification of P132 (100% ± 0 Hup efficiency axenically) as the surviving and infecting inoculant strain since nodules infected by indigenous rhizobia had lower Hup efficiencies (88 ± 2%).
Chloride, Soil Solution Osmotic Potential, and Soil pH Effects on Nitrification
Authors: Roseberg R. J. , Christensen N. W. , Jackson T. L.
Published: July 2010

Laboratory incubation studies designed to measure chloride (Cl‐), soil solution osmotic potential, and soil pH effects on nitrification of added NH+4 were conducted in order to help explain effects of Cl‐containing fertilizers and liming on soil NH+4 and NO‐3 concentrations measured in field experiments. Samples of an Aquultic Argixerolls (pH 5.5, 6.0, 6.4, and 6.7) and a Xeric Haplohumults (pH 4.9, 5.5, and 6.2) were amended with 100 mg NH+4‐N kg−1, maintained at −10‐kPa matric potential and incubated at 25°C. Ammonium was added as either NH4Cl or (NH4)2SO4 salt solutions with four osmotic potential levels ranging from −96 to −692 and −90 to −669 kPa, respectively. Osmotic potential gradients were obtained by adding KCl to the NH4Cl solutions and K2SO4 to the (NH4)2SO4 solutions. At 0, 3, 9, 14, and 28 d, samples were extracted with 2 M KCl and analyzed for NH+4, NO‐3, and NO‐2. At 15 d, soil solutions were recovered by centrifugation and analyzed for Al, Ca, Mg, K, Na, Mn, NH4, NO3, PO4, SO4, Cl, pH, and osmotic potential. Soil solution osmotic potential was lower in soils amended with Cl‐ than with SO2‐4 salt solutions. In both soils, nitrification was inhibited by Cl‐ and by decreasing soil solution osmotic potential. Chloride inhibition of nitrification was greatest (⋍30%) at low soil pH (4.9‐5.5) but disappeared or decreased markedly in magnitude above pH 6.0 to 6.2. Because of soil solution osmotic potential and pH by Cl‐ interaction effects, inhibition of nitrification would be expected to be greatest where Cl‐containing fertilizers are applied in a band on moderately acid (pH 5.0‐5.5) soils.
Relationships between Root Length of Soybean and Calculated Activities of Aluminum Monomers in Nutrient Solution
Authors: Alva A. K. , Edwards D. G. , Asher C. J. , Blamey F. P. C.
Published: July 2010

Aluminum species composition in solution is largely dependent on solution pH. Effects of Al on root length of soybean [Glycine max (L.) Merr.] were studied in solution culture using an incomplete factorial design comprising varying pH levels of 4.0, 4.2, 4.4, 4.6, 4.8, and 5.0 and added Al concentrations of 10, 15, 20, 25, 30 and 40 µM. These treatments caused calculated sum of activities of monomeric Al species (Σ aAl mono) in solution to vary from 4.4 to 33.8 µM. The range in calculated activities of each of the Al monomers was 0.4 to 16.1 µM for Al3+, 0.3 to 2.8 µM for Al(OH)2+, 2.5 to 19.3 µM for Al(OH)+2, 0.1 to 4.4 µM for AlSO+4, and 0.02 to 0.22 µM for Al(OH)03. At a given concentration of added Al an increase in pH was associated with a decrease in calculated Σ aAl mono in solution and an increase in root length. Relative root length of soybean was highly correlated with calculated Σ aAl mono in solution (R2 = 0.910). Among the individual Al monomers, relative root length was most highly correlated with calculated activity of Al(OH)2+ (R2 = 0.870), followed by AlSO+4 (R2 = 0.674), Al(OH)+2 (R2 = 0.621), and Al3+ (R2 = 0.590). No significant correlation was found between root length and calculated activity of Al(OH)03. Reinterpretation of data from other studies with soybean, subterranean clover (Trifolium subterraneum L.), alfalfa (Medicago sativa L.), and sunflower (Helianthus annuus L.) also revealed that root growth was most highly correlated with activity of either Al(OH)2+ or Al(OH)+2. In a majority of cases the relationship between root growth and activity of Al3+ was relatively poor.
Differentiation of Spodosols and Andepts in a Western Washington Soil Climosequence
Authors: Nettleton W. D. , Goldin A. , Engel R.
Published: July 2010

Five Spodosols were sampled on mountain slopes about 20‐km southwest of Mount Baker in the Cascade Range of western Washington. The soils have formed in colluvium derived from Darrington phyllite and an admixture of 1 to 30 dag tephra kg−1. Four of the pedons form a climosequence on steep, south‐facing slopes. The fifth is at the foot of the mountain, on an east‐facing slope, and is more weathered than one would have predicted from its low elevation. The three pedons sampled above 700 m have horizons that meet the chemical criteria for Spodosols. These three, as well as the fourth of the climosequence, have silt‐size pellets and cracked coatings. The fifth, at low elevation, has a horizon that meets both the chemical and morphological criteria for Spodosols. All of these pedons have one or more horizons that have the high NaF pH, high 15‐bar to clay and CEC to clay ratios, and the smeary feel characteristic of horizons that contain amorphous material. However, unlike Andepts these pedons have E horizons that contain crystalline silicate clays, mostly smectite, have low NaF pH, and lack the smeary feel. Except for the fourth pedon of the climosequence, the pedons meet the humic acid color criteria recently proposed for Spodosols. Some of the B horizons have >2 dag kg−1 of (NH4)2C2O4 extractable Al and ≥1.5 dag kg−1 of 4 M KOH extractable Al, but are not thick enough for the soils to be placed in the proposed Andisols.
Spatial Variability and Soil Sampling for Salinity and Sodicity Appraisal in Surface‐irrigated Orchards
Authors: Miyamoto S. , Cruz I.
Published: July 2010

Localized salt accumulation and associated crop damage are common in surface‐irrigated orchards. This study examined salinity and sodicity variation at five pecan (Carya illinoensis K.) orchards in the El Paso Valley, Texas mainly to develop soil smapling schemes for salinity appraisal. The first orchard (13.6 ha) contained three mapping units, and the other orchard blocks (0.5‐3.3 ha), single mapping units or soil types. These fields had been irrigated by border or basin methods mostly with water of 1.1 dS m−1. Soil samples were collected in a systematic grid at 68 sites to a depth of 60 cm in the 13.6‐ha field, and 15 to 28 sites at three depths in the other orchard blocks. Salinity and sodicity of the saturation extract in the 13.6‐ha field ranged from 0.7 to 6.3 dS m−1 and 2.3 to 12.5 (mmol L−1)1/2, respectively. Even in the orchard blocks of <1 ha, salinity and sodicity readings varied two‐ to threefold. The semivariogram of soil salinity and sodicity along transects or within mapping units did not reveal spatial structure. Instead, salinity readings were closely related to the saturation water contents of the soils (r = 0.79), and their variation decreased several fold when stratified by mapping unit. The frequency distribution of soil salinity along transects followed a skew distribution, but when grouped by mapping unit and averaged over a depth, both salinity and sodicity readings followed a normal distribution. For routine salinity appraisal in comparatively small surface‐irrigated orchards, soil map‐based samplings may be more efficient than those based on arbitrary transects or grid. The number of samples required to obtain a mean value in an area consisting of a single mapping unit within 15% of the true mean at the 5% level ranged from 7 to 26 ha−1 for salinity, and 3 to 14 ha−1 for sodicity at a depth of 0 to 60 cm in these alluvial soils.
Blue Grama Response to Zinc Fertilization of Claypan Soil
Authors: White E. M. , Gartner F. R.
Published: July 2010

Claypan soils with blue grama [Bouteloua gracilis (H.B.K.) Lagl plants, seeded to indigenous blue grama, or seeded to barley (Hordeum vulgare L.) if salinity might limit blue grama growth were fertilized with Hoagland's formulations in the greenhouse. The objective was to identify the micronutrient(s) that limits blue grama growth in western South Dakota. Growth was increased by the macronutrients N‐P‐K and further increased if all essential micronutrients were added. Zinc probably is the limiting element, and growth was usually reduced if other micronutrients were added with Zn to the claypan soil.
Ammonia Volatilization from Nitrogen Fertilizers Surface Applied to No‐till Corn
Authors: Keller Gary D. , Mengel David B.
Published: July 2010

Low use efficiency has frequently been observed when N fertilizers, particularly those containing urea, are applied directly on the surface residue in no‐till corn (Zea mays L.) production systems. A portion of this low use efficiency has been attributed to volatilization of NH3. Field experiments were conducted at two locations in Indiana to make direct measurements of NH3 volatilization from granular urea, cogranulated urea‐urea phosphate (UUP), urea‐ammonium nitrate solutions (UAN) and prilled ammonium nitrate (AN). The fertilizers were applied directly on corn residue at a rate of 168 kg N ha−1. On a Lyles sandy loam soil (Typic Haplaquolls) 50.9 kg of the 168 kg N ha−1 applied as granular urea was lost in 120 h, with essentially all that loss occurring in the first 50 h after application. Peak loss rates of 3.0 kg N ha−1h−1 occurred 23 h after application. No significant volatilization loss occurred with AN, while 26.0 kg N were lost through volatilization with UUP and 14.6 kg N lost from UAN. Peak loss rates at 23 h after application were 1.83 and 0.37 kg N ha−1h−1 for UUP and UAN, respectively. A 25‐mm rain shower effectively stopped volatilization approximately 50 h after application. On a Bedford silt loam soil (Typic Fragiudalfs) volatilization losses were considerably lower than those found on the lower cation exchange capacity Lyles soil. Though overall losses were lower, relative losses from the different N fertilizers were similar to those found on the Lyles soil.
Mineralogy and Stability of Soil Evaporites in North Dakota
Authors: Keller L. P. , McCarthy G. J. , Richardson J. L.
Published: July 2010

The evaporite mineralogy of 106 samples of salt efflorescence collected from throughout North Dakota was determined by x‐ray powder diffraction. The mineralogies of these efflorescences are dominated by sulfate salts of Na, Mg, and Ca. The evaporite minerals were mirabilite, thenardite, gypsum, epsomite, hexahydrite, konyaite, bloedite, burkeite, and tychite. Konyaite is the most frequently and widely occurring mineral identified. Efflorescences dominated by Na‐ and MgSO4 minerals account for >90% of the observed mineralogies. The mineral assemblages dominated by Na2SO4 minerals were evenly distributed across the state. The MgSO4‐rich efflorescences were confined to the glaciated part of the state. Many of the observed minerals are labile with respect to temperature and water vapor pressure. Dissociation vapor pressure curves from the literature are used to describe the field stability relations of epsomite/hexahydrite and mirabilite/thenardite.
Statistical and Autoregressive Analysis of Soil Physical Properties of Portsmouth Sandy Loam
Authors: Anderson S. H. , Cassel D. K.
Published: July 2010

Reliable estimates of soil physical and hydraulic properties are needed for designing drainage systems for soils with limited natural drainage. The objective of the study was to determine the autocor‐relation structure of soil physical properties in a poorly drained soil. Saturated hydraulic conductivity, soil‐water characteristic, soil‐water diffusivity, texture, and bulk density were measured on undisturbed soil cores sampled from the A, Btg, and Bg soil horizons at 150 points on two transects in a field of Portsmouth sandy loam (Typic Umbraquults). Unsaturated hydraulic conductivity for each of the 450 cores was computed using a quasi‐analytical expression utilizing measured soil‐water diffusivity data and the derivative of the inverse of the van Genuchten equation for the measured water characteristic. Hydraulic conductivity values at a given soil‐water pressure had a high coefficient of variation, ranging from 130 to 3300%, and were lognormally distributed. Evidence of significant short‐range autocorrelation, usually ≤2 m, was found for hydraulic conductivity, soil‐water characteristic, texture, and bulk density. First‐order coefficients for autoregressive equations indicated a decrease in predictability of the observed variation with increasing soil depth. The number of measurements required to estimate the mean of a soil property of the A horizon to within ±10%, ranged from four for sand content to 1985 for saturated hydraulic conductivity. The means for most soil properties in the A horizon, however, can be estimated to within ±10% with 35 observations.
Chemical Modeling of Arsenate Adsorption on Aluminum and Iron Oxide Minerals
Authors: Goldberg Sabine
Published: July 2010

The constant capacitance model was used to describe arsenate adsorption on goethite, gibbsite, and amorphous Al hydroxide. Because the model assumes a ligand exchange mechanism it is appropriate for describing the specific adsorption of arsenate anions. Arsenate surface complexation constants were fitted to the experimental data using a nonlinear least squares optimization technique. The constant capacitance model was able to represent arsenate adsorption over the pH range 4.5 to 9 on each oxide using the same set of surface complexation constants. However, the values of the surface complexation constants varied with the mineral considered. The model was able to describe arsenate‐phosphate competition on gibbsite quantitatively over the pH range 4.5 to 9 using the same set of anion surface complexation constants. A set of surface complexation constants obtained for one ternary system could be used to predict competitive phosphate and arsenate adsorption on the same material for other ternary systems containing different amounts of total anions in solution.
Response of Irrigated Soybeans to Rate and Placement of Fertilizer Phosphorus
Authors: Rehm G. W.
Published: July 2010

This study was conducted to measure the response of irrigated soybeans [Glycine max (L.) Merr.] to rate and placement of fertilizer P and to develop critical values for P in this crop. Five rates of P (0, 11, 22, 33, 44 kg ha−1) were either broadcast and incorporated before planting or applied to the side of and below the seed at planting (starter) at 10 irrigated sites over 3 yr. Tissue samples consisting of the most recently matured trifoliates (petiole excluded) were collected at early bloom and analyzed for P. Use of fertilizer P increased soybean yields at three of 10 sites and higher yields at these sites were recorded each year when the fertilizer P was broadcast and incorporated before planting. Fertilizer P increased yields when the soil test P level (0‐20 cm) measured by the Bray and Kurtz no. 1 procedure was <3.1 mg kg−1. There was no response to fertilizer P when the P level measured by this method was 9.6 mg kg−1 or higher. Soil P measured by the Na HCO3 method was as satisfactory as the Bray and Kurtz no. 1 procedure for separating responsive from nonresponsive sites when subsoil P was considered. The P concentration of leaf tissue at responsive sites was increased with application of fertilizer P. At 95% of maximum yield, P concentration in leaf tissue was 3.35 g kg−1.
Achieving Desired Moisture Conditions in Potentially Mineralizable Nitrogen Incubation Studies
Authors: Lueking M. A. , Schepers J. S.
Published: July 2010

A technique was developed to determine soil‐to‐sand mixing ratios to achieve desired soil moisture conditions during incubation in potentially mineralizable N studies. Five soils were selected to represent a range of soil textures. Segmented plastic leaching tubes were used to determine gravimetric water content, bulk density, and percent water‐filled pore space (WFP) for two portions of soils used within the incubation tubes. Vacuum leaching resulted in greater water content of soil near the bottom of the incubation tubes compared to the top of the tubes. The proportion of soil‐to‐sand used in the incubation tubes, which was necessary to attain a given WFP status, was different for each soil type and was a function of original sand and organic C contents. The technique is an inexpensive and time‐efficient means to standardize and document soil moisture conditions within incubation tubes used to determine potentially mineralizable N.
Irrigation Management for Soil Salinity Control: Theories and Tests
Authors: Bresler Eshel , Hoffman Glenn J.
Published: July 2010

The steady‐state leaching theory and related concepts regarding soil salinity control were evaluated in view of the transient‐state theories presented and recent experimental results. Data from small plot experiments to establish the leaching requirement of nine crops and from a rhizotron study on the influence of irrigation frequency on soil salinity control agreed with theoretical, transient‐state predictions that consider water flow, salt transport, and water uptake by crop roots, simultaneously. Root water uptake was assumed to depend on matric (water content) and osmotic (soil salinity) potentials, and on a critical root‐water potential of about −0.3 MPa. The assumption that the major effect of soil salinity is a reduction in plant water uptake was substantiated. Results show water balance components (for nine crops irrigated several times each day and for grass irrigated with various combinations of quantity, quality, and frequency) deviated significantly from predictions based on the steady‐state leaching fraction equation. The deviation was attributed to an increase in soil‐water content and transpiration as irrigation applications increased; or conversely, an increase in soil‐water content as transpiration decreased because of increased soil salinity. The practical limitations of salinity control in irrigated agriculture based on the steady‐state leaching equation were evident even for high frequency irrigation where steady‐state conditions should be approached. Measured commercial yields and aboveground dry matter production compared well with yields computed on the assumption that relative crop yield is equivalent to relative transpiration. Both measured and computed results indicated that irrigation water quality and quantity, rather than irrigation frequency, influenced dry matter production of grass.
Soil Acidity in Loblolly Pine Stands with Interval Burning
Authors: Binkley Dan
Published: July 2010

Prescribed burning of loblolly pine (Pinus taeda L.) stands every 2 yr for 24 yr increased soil pH by 0.3 to 0.9 units. Measurements of total acidity (titratable to pH 8.2) in the forest floor showed about a 14 to 21 kmol H+ ha−1 decrease in burned plots. Burning increased the acid neutralizing capacity per gram of forest floor material, but the reduction in forest floor biomass largely offset the difference. Titration curves indicated that the burned forest floor would require only about 0.6 kmol H+ ha−1 to lower its pH to the level of the control plots. Total acidity in the 0 to 10 cm mineral soil was more variable; one burned plot showed no decrease relative to controls, but a more intensely burned plot decreased by about 95 kmol H+ ha−1. Despite this large reduction in total acidity, titration curves indicated that only 25 kmol H+ ha−1 would lower the pH to the control level. This increase in acid neutralizing capacity is about 50 times the current annual H+ input in rain. However, other major components of the ecosystem's H+ budget would need to be quantified to assess the importance of fire in relation to acid deposition impacts.
Errors in Analyses for Ammonium and Nitrate Caused by Contamination from Filter Papers
Authors: Sparrow S. D. , Masiak Darleen T.
Published: July 2010

Filter papers were tested for NH4 and NO3 contamination by eluting them with 2 M KCl solution and analyzing the leachate. Significant amounts of NH4 or NO3‐N were found in many filters. Variability between grades and kinds of filters, among lots within a grade, and within packages was high. For cellulose papers, quantitative grades were usually relatively high in NH4 and low in NO3. The reverse was true for qualitative grades. Glass fiber filters contained low but usually significant amounts of both ions. Most of the NH4‐ and NO3‐N was removed from cellulose filters by prewashing with water or 2 M KCl solution. Water successfully removed NO‐3 but not NH+4 from glass filters.
Comparison of a Forced‐draft Technique to Nitrogen‐15 Recovery for Measuring Ammonia Volatilization Under Field Conditions
Authors: Hargrove W. L. , Bock B. R. , Raunikar R. A. , Urban W. J.
Published: July 2010

Reliable field measurements of NH3 volatilization are necessary for evaluating N‐fertilizer efficiency for sod crops and conservation crop production systems. This study was conducted to compare NH3 loss measurements under field conditions using a forced‐draft technique and recovery of urea‐15N. Measurements were made from urea solution applied at a rate of 100 kg N ha−1 to a bare or mulched Cecil sandy loam soil (Typic Hapludult). In an adjacent area, microplots were established to which urea enriched with 15N was added. Ammonia losses from the bare and mulched soil were 49 and 72% of the applied N by the forced‐draft technique, and 14 and 46% of the applied N by 15N recovery. The air flow rate with the forced‐draft technique was shown to exceed the actual wind speed near the soil surface 10 and 50% of the time for bare and mulched soil, respectively. These results raise serious questions about the validity and accuracy of the forced‐draft technique. The usefulness of the forced‐draft technique may be limited to relative comparisons of N sources, N rates, and various management practices.
The Influence of Eolian Dust on the Genesis of Alpine Soils in the Front Range, Colorado
Authors: Litaor M. Iggy
Published: July 2010

The chemical and mineralogical properties of the soils in an alpine watershed, Front Range, CO, were studied to assess the sensitivity of the soil environment to acid deposition. Field and laboratory analyses indicated that properties of surface horizons were heavily influenced by eolian dust accumulation whereas the subsurface horizons were mainly derived from local bedrock. Surface and subsurface horizons differed in texture, bulk density, pH, CEC, exchangeable cations, and clay and silt mineralogy. A discriminant analysis based on these parameters proved useful for confirming lithologic differences between the surface (alpine loess) and subsurface horizons (bedrock residua). The alpine environment in the Front Range, which is naturally acidic and therefore very susceptible to acid deposition, has been affected by wind‐blown calcite that has raised the pH of surface horizons. Such natural liming presumably increases the ability of the alpine soils to buffer acid deposition.
Estimating Air Porosity and Available Water Capacity from Soil Morphology
Authors: McKeague J. A.
Published: July 2010

Field guidelines based on soil morphology and calibrated against measured values were developed for estimating air porosity (AP, volume percent air‐filled pores at 5 kPa) and available water capacity (AWC, volume percent water retained between 5 and 1500 kPa). The guidelines were tested by estimating and subsequently measuring these properties of 24 soil horizons. The mean of the absolute differences between estimated and measured AP and AWC were 3.7 and 4.5% respectively. AP for the 24 horizons ranged from 3 to 30% and AWC from 14 to 39%. In view of the magnitude of local soil variability, the discrepancies in measured values of AP and AWC by different methods and the lack of standard methods, the estimates are shown to be useful. Estimation of air‐water regime properties of soils from well‐calibrated morphological guidelines is recommended for use in soil survey and in research on effects of management on soil physical properties.
Effects of Soybean and Corn Residue Decomposition on Soil Strength and Splash Detachment
Authors: Gantzer C. J. , Buyanovsky G. A. , Alberts E. E. , Remley P. A.
Published: July 2010

Although field experiments have documented increased soil and water losses after soybeans (Glycine max L.) as compared with corn (Zea mays L.), a “soil effect” appears to be nondetectable by regular laboratory means. Because significant differences in quantity and quality of post‐harvest residues occur between soybean and corn, a laboratory incubation experiment was designed to assess the effect of the plant materials on soil properties. Analysis shows that laboratory incubation of disturbed soil with and without corn and soybean residues at 20°C, with optimal water contents of 25% v/v, decreases splash detachment, increases shear strength and aggregate size after 7 to 14 d. Additions of corn or soybean residues increase soil strength and decrease soil splash in a log‐linear fashion. The most pronounced effects were observed after 14 d. This corresponds to peak microbiological activity, indicating changes in stability are probably related to biological processes. Corn residue at typical field rates (20 Mg/ha) reduced soil splash by about one‐third and increased strength about two times as compared to the check after 14 d of incubation. Incubation with soybean residue for a similar time caused slightly greater soil splash than incubation with the same amount of corn residue, suggesting that small changes in stability are related to residue quality. No difference in soil strength relative to residue quality was detected after 14 d of incubation, indicating a subtle difference between splash and strength as measures of surface‐soil stability. Aggregate size measurements were less sensitive to plant residue treatment and time of incubation than splash or strength.
Distribution and Recovery of Nitrogen‐15‐labeled Liquid Anhydrous Ammonia Among Various Soil Fractions
Authors: Norman R. J. , Kurtz L. T. , Stevenson F. J.
Published: July 2010

Since liquid anhydrous ammonia (LAA) is a major N fertilizer, information was sought about the proportions of LAA that enter into various combinations in soils. Liquid anhydrous NH3, labeled with 15N was injected into three soils (Drummer, Typic Haplaquoll; Blount, Aeric Ochraqualf; Cisne, Mollic Albaqualf) in the laboratory at a rate equivalent to a field application of 206 kg N ha−1 in 76.2 cm knife‐spacings. At 1, 7, 14, 28, 56, and 112 d after application, fertilizer N present in different soil fractions was determined in five concentric zones with radii of 0 to 1.5, 1.5 to 3.0, 3.0 to 4.5, 4.5 to 6.0, and 6.0 to 7.0 cm around the point of application. Depending on the soil, from 68 to 83% of the applied 15N was accounted for as (exchangeable NH+4 + NO‐3 + NO‐2)‐N by the 112th day following application, the remainder being accounted for as clay‐fixed NH+4 (1.9‐4.9%), organic matter‐fixed NH3 (4.0‐6.0%), and biologically immobilized organic N (3.9‐9.3%). From 50 to 70% of the organic matter‐fixed NH3‐N was released by hydrolysis with dilute KOH solution as compared to 10 to 15% for the immobilized N. Total recovery of 15N at 112 d ranged from 77% for the Cisne soil to about 97% for the Drummer and Blount soils. Lateral distributions and transformations of NH+4 and NO‐3 and pH trends after LAA applications were similar to those reported by previous investigators.
Evaluation of Urea‐Urea Phosphate as a Nitrogen Source for No‐tillage Production
Authors: Urban W. J. , Hargrove W. L. , Bock B.R. , Raunikar R.A.
Published: July 2010

Urea‐urea phosphate (UUP), a combination of urea and phosphoric acid, has properties which reduce the potential for NH3 volatilization but has not been evaluated extensively under field conditions. The objective of this study was to evaluate UUP (34‐17‐0) under laboratory and field conditions. All experiments were conducted on acid sandy soils typical of the predominant Ultisols found in the southeastern USA. A forced‐draft technique was used to make direct measurements of NH3 losses in a growth chamber and also in the field. In addition, UUP and six other N sources were compared for no‐till grain sorghum (Sorghum bicolor L. Moench) production. Direct measurement of NH3 losses in the growth chamber resulted in small losses from UUP on both mulched and bare soils, while NH3 losses from urea ranged from 15 to 32% of the applied N on a bare soil and 68 to 82% on a mulched soil. Direct field measurement of NH3 losses from urea, UUP, and ammonium nitrate applied at 200 kg N/ha were 19, 5, and 2% of the applied N, respectively. In the field plot studies, UUP compared favorably with ammonium nitrate and calcium nitrate with respect to crop response. The mechanism of NH3 loss prevention appears to be pH buffering by the phosphoric acid component of UUP. It is concluded that UUP is an effective N source for surface application to noncalcareous soils under no‐tillage management.
Soil Air Carbon Dioxide Concentrations in a New England Spruce‐Fir Forest
Authors: Fernandez Ivan J. , Kosian Patricia A.
Published: July 2010

Research and modeling efforts to evaluate soil‐soil solution chemical interactions must take into account solution equilibria with soil air CO2. Measurements of soil air CO2 and soil temperature were made in the major horizons of a forest soil in eastern Maine through the 1985 growing season. Soil air CO2 concentration ranged from 0.10 to 0.35%, 0.10 to 1.25%, and 0.20 to 1.20% in the O, B, and C horizons respectively. Peak soil air CO2 concentration occurred in July and early October which coincided with high points in soil temperature during the growing season.
Analytical Solution for Punctual Kriging in one Dimension
Authors: Hemyari Parichehr , Nofziger D. L.
Published: July 2010

The solution to the system of equations required for punctual kriging in one dimension was determined analytically for a linear semivariogram. The solution indicates that kriging in this situation is identical to linear interpolation between the two closest neighbors. The kriged values are independent of the coefficients in the linear semivariogram model. The estimation variance is linearly dependent upon the coefficients in the model. Although no analytical solution was obtained for the spherical and exponential semivariance models, kriged values for these models were found to be essentially the linearly interpolated values. These results provide insight into the behavior of the kriging estimator. They can be used to save substantial numerical computation and to guide the user in selecting the neighborhood of points used in one‐dimensional kriging.
Thermodynamics of Fluridone Adsorption and Desorption on Three California Soils
Authors: McCloskey William B. , Bayer David E.
Published: July 2010

The thermodynamic parameters associated with fluridone {1‐methyl‐3‐phenyl‐5‐[3‐(trifluoromethyl)phenyl]‐4(1H)‐pyridinone} adsorption and desorption on three California soils were calculated from the temperature dependence of the adsorption reaction. The standard free energy change for the adsorption reaction on all three soils was negative, signifying a spontaneous reaction. The isosteric heat of adsorption and the partial molar enthalpy change indicated that van der Waals or physical forces were involved in fluridone adsorption. The enthalpy changes also showed that fluridone adsorption became weaker as the amount adsorbed increased on Yolo sandy clay loam (Typic Xerorthents) and Hesperia fine sandy loam (Typic Xerorthents) while the reverse was true on Stockton clay (not classified). Fluridone adsorption was correlated with clay content and increased as the time of exposure to the soils increased (i.e., the desorption isotherms exhibited hysteresis). The isosteric heats of adsorption calculated from the desorption isotherms were similar to those calculated from the adsorption isotherms indicating that there was no change in adsorption mechanisms between adsorption and desorption equilibrations. Thus, the thermodynamic parameters provided evidence that fluridone adsorption on the three soils was reversible and that the hysteresis between adsorption and desorption isotherms was not due to an irreversible adsorption reaction (chemical or coulombic adsorption). The increased retention of fluridone with time was attributed to the diffusion of fluridone molecules to relatively less accessible binding sites on clay particles as the time of fluridone exposure to the soils increased.
Quantification and Compositional Characterization of Pedogenic Calcite and Dolomite in Calcic Horizons of Selected Aquolls
Authors: Sobecki T. M. , Karathanasis A. D.
Published: July 2010

A combination of thermogravimetric analysis (TGA), x‐ray diffraction (XRD), and selective dissolution analysis (SD) was used to quantify and calculate structural formulae of carbonate mineral phases in silt fractions of calcic horizons in selected Texas Coastal Prairie Aquolls. The Algoa pedon (Aeric Calciaquolls) had about 11% poorly crystalline high‐Mg calcite [(Ca.87Mg.13)CO3], 12 to 20% dolomite, and approximately 25% low‐Mg calcite [(Ca0.95Mg0.05)CO3]. The dolomite was a Ca‐rich variety that was previously interpreted to be pedogenic. The Addicks pedon (Aquic Haplustolls) lacked dolomite. The upper calcic horizon was dominated by low‐Mg calcite [(Ca0.99Mg0.01)CO3] with about 7% poorly crystalline high‐Mg calcite [(Ca0.90Mg0.10)CO3]. The presence of dolomite and high‐Mg calcite in the Algoa pedon are related to elevated soluble Mg/Ca ratios. Thermodynamic relationships based on soil solution Mg/Ca activity ratios support these findings. It is suggested that poorly crystalline Ca‐Mg carbonates, including high‐Mg calcites, may be more abundant in calcic horizons than commonly believed. Their poor crystallinity makes them difficult to detect by standard XRD methods. However, TGA coupled with quantitative XRD and SD can be useful in detecting their presence and estimating their chemical composition.
A Pedogenic Chronology for Kilbourne Hole, Southern New Mexico: I. Soils in the Tuff
Authors: Gile Leland H.
Published: July 2010

Kilbourne Hole, in southern New Mexico, was formed by steam explosions and is a maar volcano surrounded by tuff, most of which is prominently stratified. Although a few carbonate nodules are in unstratified materials of soils at stablest sites, a banded carbonate horizon is the most prominent and extensive pedogenic feature and has formed in stratified tuff. The carbonate bands are commonly about 1 to 2 mm thick, have formed along some of the primary strata of the tuff, and are separated from each other by tuff with little or no macroscopic carbonate. Development of the carbonate bands is attributed to the character of the parent materials, which are stratified, cohesive sands deposited by base surge and differing considerably in size and consistence. These factors have caused pedogenic carbonate to accumulate in banded form instead of the nodules and cylindroids that are more common in other materials which have little or no gravel. The bands consist of both laminar and nonlaminar types. The stratified tuff constitutes a special case in which the laminar horizon would form much faster than in the conventional sediments of basin floors, alluvial fans, and fan piedmonts that dominate many arid regions. Most of the studied soils are sandy Entisols that have been classified as Typic Torriorthents, sandy, mixed, thermic. They have been classified as Orthents instead of Psamments because hazards are minimal for blowing and for the support of wheeled vehicles. An exclusion for soils of stratified, cohesive sands of base surge origin is needed in the definition of Psamments. Minor areas of Typic Haplargids, coarse‐loamy, mixed, thermic, are also present.
Extraction Time Requirements for Determination of Exchangeable Bases with a Mechanical Vacuum Extractor
Authors: Hammer R. David , Lewis Russell J.
Published: July 2010

Determination of extractable bases with neutral 1 M NH4OAc is a commonly performed soil analysis. Introduction of a mechanically controlled vacuum extractor permits control of extraction time across the range of soil textures. Comparisons of organic soil materials, montmorillonitic and low cation exchange capacity (CEC) soils revealed that complete base extraction is possible with reduced extraction times. Fourteen‐hour extraction is required for base removal from organic soils, but 8‐ and 4‐h extractions removed bases from montmorillonitic and low CEC soils, respectively. Decreased extraction times permit increased capacity for laboratory soil analyses, increase the effective life of the vacuum extractor, and decrease analysis time.
Experimental and Numerical Analyses of Perched Groundwater Mounds Below Septic Systems
Authors: Wilson G. V. , Scott H. D. , Wills L. D.
Published: July 2010

For purification, effluent must move through unsaturated soil for an adequate time and distance before contacting the saturated zone. Formation of perched groundwater mounds may limit the purification processes. The dynamics of groundwater mounds associated with septic systems must be understood in order to reduce the potential for contamination from septic systems. Previous models for perched mounds have not been verified with in situ measurements. A septic tank filter field system consisting of a triple line source was installed in a Captina silt loam (Typic Fragiudult). The soil has a fragipan at the −0.7 m depth with a wavy, irregular boundary. Tensiometers were used to monitor the temporal and spatial distributions of soilwater potential. The results revealed that steady‐state soil water conditions existed during spring and fall. Soil water pressure potentials at unmeasured locations were kriged from in situ data with quadratic drift removed using universal kriging. The kriged pressure potentials were contoured resulting in equipotential lines, with the zero equipotential line representing the water table. The Laplace equation in two dimensions, including a source term, appropriate for these flow conditions, was solved using a Galerkin finite element technique. Contours of equal pressure potential predicted by the model for various flow conditions were obtained. The two‐dimensional simulation model was verified with the in situ data by overlaying the contour graphs of the kriged values with the model's predicted values. The effect of highly variable saturated hydraulic conductivity on the model's prediction was also investigated. The finite element model adequately predicted the depth of the water table as well as the range in equipotential lines and their locations when based on the mean saturated hydraulic conductivity. Therefore, the finite element model can be considered acceptable for modeling a perched water table below septic systems under steady‐state conditions.
Determination of FeEDDHA in Soils and Fertilizers by Anion Exchange Chromatography
Authors: Barak Phillip , Chen Yona
Published: July 2010

The specific conditions for the quantitative analysis of FeEDDHA (ethylenedimine di‐o‐hydroxyphenylacetic acid) by high pressure liquid chromatography (HPLC) were studied and defined. Using a 3‐cm anion exchange column and 5 mM H2SO4 + 0.01 mM Fe2(SO4)3 as an eluent, FeEDDHA was separated into the dl‐racemic and meso isomers. With the same column and 3 mM H2SO4 + 50 mM Na2SO4 + 0.01 mM Fe2(SO4)3, FeEDDHA eluted as a single peak. Standard calibration curves for FeEDDHA were obtained with regression coefficients of 0.9999 at concentrations up to 0.25 mM. The coefficient of variation is 1.5%, or 1.8 µmol L−1 using a 50‐µL sample; the detection limit was 1.2 µmol L−1. FeEDDHA was separated easily on anion exchange HPLC columns from other chelates such as CDTA, EDTA, and DTPA. The proposed method was used to determine FeEDDHA concentrations in water extracts of soils that were incubated with the compound. With variation of the eluent, separation of ferrated and unferrated EDDHA is possible.
Calcite Supersaturation in Soils as a Result of Organic Matter Mineralization
Authors: Amrhein C. , Suarez D. L.
Published: July 2010

Solutions equilibrated with soils under laboratory conditions often exhibit Ca2+ and CO2‐3 activities that exceed calcite saturation. This supersaturation has been attributed to various possibilities, none of which have been fully able to explain the phenomenon. In this study we report on the attainment of calcite supersaturation in calcite + water + organic matter systems under controlled CO2 conditions. The decomposition of alfalfa shoots (Medicago sativa L.) and soybean roots (Glycine max L. merr.) in batch reactors under CO2 pressures of 1.0, 10.0, and 99.5 kPa was found to result in HCO3 as an end product of aerobic decomposition. The rate of HCO3 production from mineralizing organic matter exceeded calcite precipitation rates and, thus, calcite supersaturation resulted. The decomposition of pure organic compounds (dextrose, inositol, glucosamine, glucuronic acid, citric acid, and sodium citrate) was studied to elucidate the mechanism of HCO3 production. It was determined that the decomposition of organic anions associated with inorganic cations always results in HCO3 as an end product. The rates of calcite dissolution and precipitation were greatly inhibited in the presence of decomposing organic matter.
Diversity within Iowa Bradyrhizobium japonicum Serogroup 123
Authors: Hickey W. J. , Loynachan T. E. , Ayanaba A. , Zablotowicz R. M.
Published: July 2010

Bradyrhizobium japonicum serogroup 123 dominate soybean [Glycine max (L.) Merr.] nodules in the midwestern USA, but the diversity within this group has been little characterized. This study examined three collections of serogroup 123: nine USDA serogroup 123 strains (representing organisms from several states), 98 isolates collected from several counties and soils across Iowa, and 78 isolates from an intensively sampled 22.8‐m2 area in central Iowa. The organisms were characterized by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis of proteins (SDS‐PAGE) and growth response to antibiotics, arginine, and succinate. Of the two methods, SDS‐PAGE was more useful for differentiating organisms. By using SDS‐PAGE, 74 strains were identified from 176 Iowa serogroup 123 isolates. No relation was evident between strain distribution and soil characteristics or geography. Strain USDA 123 was found not to be representative of the Iowa isolates.