bluuebunny/crossref_metadata_2025 huggingface dataset:
Bulk Density Values Diagnostic of Restricted Root Growth in Coarse‐textured Soils
Authors: Vepraskas M. J.
Published: July 2010

Bulk density values diagnostic of both moderate and excessive levels of soil compaction have not been conclusively identified. This study estimated diagnostic bulk density values related to conditions where root elongation was virtually stopped due to high mechanical impedance, and also to the less compact condition where root growth was occurring but where subsoiling could be used to increase root growth and yield. Undisturbed cores were collected from Ap, E‐B, and B horizons of 24 Paleudults and Hapludults. Each core was equilibrated to a soil water potential of −0.1 MPa and mechanical impedance was determined and expressed as a cone index (CI). Bulk density and particle size distribution were also measured. A model was developed to estimate CI from bulk density (ρb) and percentages of sand, clay, and very fine sand (0.125‐0.050 mm diam). Using the CI model and previously published soil, tobacco (Nicotiana tabacum L.) root, and tobacco yield data, diagnostic CI values related to zero root growth and significant subsoiling effects on both root growth and yield were estimated. The combinations of ρb and texture that produced the diagnostic CI values were then computed for four textural classes having very fine sand percentages of 0, 10, and 20%. The minimum bulk density values associated with where subsoiling increased both root number and yield over that of a moldboard plow/disk treatment were 1.66, 1.61, 1.60, and 1.58 Mg m−3 for the sand, loamy sand, sandy loam and sandy clay loam textural classes, respectively, having 10% very fine sand. It was estimated that root concentration would be zero at bulk densities of 1.85, 1.82, 1.81, and 1.80 Mg m−3 for these same textural classes.
Planting Depth and Tillage Interactions on Corn Emergence
Authors: Gupta S. C. , Swan J. B. , Schneider E. C.
Published: July 2010

Surface crop residues lower soil temperatures delaying emergence of corn (Zea mays L.) under no‐till tillage systems in the northern Corn Belt. This study evaluates the use of planting depth as a management tool to overcome the disadvantages of cool temperature under residue covered soils. Growth chamber experiments evaluated the effects of planting depths, ranges of soil temperatures, and soil matric potentials on corn emergence. The seeding medium was aggregates of Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquolls). Deep planting (75 mm) delayed emergence from 2.8 to 18 d as the soil temperatures decreased from ranges of 15 to 25 °C and 5 to 15 ° C. Seed zone growing degree days (GDD) needed to achieve 75% emergence increased with an increase in planting depth and a decrease in soil matric potential. Relationships of corn emergence vs. seed zone GDD needed to achieve 75% corn emergence at various planting depths were tested in the field for three planting depths, three tillage and three surface residue conditions during 1984 and 1985. Predicted time to 75% corn emergence was within 2 d of the field‐measured values for three planting depths, and seven tillage and surface residue conditions, over two seasons. Simulation studies were conducted to predict the effects of tillage, planting depth, and planting date on the probability of obtaining 75% corn emergence within 14 d of planting. Input data for simulation studies included 10 to 20 yr of daily maximum and minimum air temperatures from Morris, MN and Lexington, KY. Tillage treatments included moldboard plow, no surface residue, and no‐till surface residues. Reducing the planting depth from 50 to 25 mm advanced the planting date from 2 d to several weeks, depending on the weather, soil matric potential, and tillage‐surface residue conditions. When soil water is nonlimiting, the effect of cooler temperatures on corn emergence under a no‐till tillage system (with surface residues) can be compensated for by reducing the planting depth by 25 mm or less from that of average planting depth under conventional tillage systems.
Effect of the Sampling Network on Estimates of the Covariance Function of Stationary Fields
Authors: Russo David , Jury William A.
Published: July 2010

The covariance function of the stochastic component of various soil properties plays an essential role in the estimation and interpolation of spatial phenomena using kriging techniques and in the solution of transport problems in heterogeneous media using stochastic continuum transport modeling. In this study the effect of the sampling network on the estimates of covariance functions of two‐dimensional, isotropic, second‐order stationary processes, characterized by different underlying correlation scales, was analyzed. Estimates of the covariance function based on a standard systematic sampling network were compared with estimates of the covariance functions based on a modified sampling network. Results of these comparisons showed that the modified sampling network was better suited than the systematic network to resolving the statistical properties of the underlying stochastic process at small separation distances. This may result in an improvement in structure identification. Analyses of the effect of the sampling network used for estimating the covariance function on the results of conditional inference procedures such as kriging showed that the kriging estimates were essentially insensitive to the geometric configuration of the sampling network. Uncertainties about these estimates were reduced when using the modified sampling network, however. In the case of unconditional inferences, such as with stochastic analyses of transport problems in heterogeneous media, predictions of the head variance provided by using estimates of the parameters of the covariance function of the log saturated hydraulic conductivity based on the modified sampling network fit the theoretical head variance better than those based on the systematic sampling network. The effect of the sampling network used for estimating the covariance function on the predicted head variance was significant, particularly when the underlying correlation scale was relatively small, when the porous medium texture became finer, and when the hydraulic conductivity variations were treated as being three‐dimensional.
Spectroscopic Evidence for a Copper‐Picloram Complex on Cu(II)‐Saturated and Cu(II)‐Hydrous Oxide Coated Montmorillonite
Authors: Aochi Y. , Farmer W. J.
Published: July 2010

Deuteration and deconvolution techniques were applied to infrared investigations of bonding between the herbicide picloram (4‐amino‐3,5,6‐trichloropicolinic acid) and mineral surfaces. Self‐supporting clay films for infrared analysis were prepared from aqueous suspensions of picloram with Cu‐treated montmorillonite or with montmorillonite coated with Cu hydrous oxides. The spectral data show clear evidence for a coordination type bonding between picloram and the Cu‐treated mineral surfaces. Additional evidence is presented from infrared data confirming the presence of the monomeric acid on Al‐ and Fe‐treated montmorillonite. Deuteration of the picloram‐Cu‐montmorillonite and of the picloram‐Cu hydrous oxide‐montmorillonite systems were both extremely slow, requiring several weeks to complete compared to a few hours for the Al‐ and Fe‐systems.
Fluorescence Quenching and Aluminum Complexation by a Chestnut Leaf Litter Extract
Authors: Shotyk William , Sposito Garrison
Published: July 2010

Fluorescence quenching (FQ) on addition of Al (III) to aqueous solutions of chestnut (Castanea sativa L.) leaf litter extract (LLE) has been interpreted previously as a parameter directly proportional to the mole fraction of Al‐complexed organic ligands in the LLE. To provide independent confirmation of this interpretation, FQ and labile Al (defined by a 15‐s reaction with 8‐hydroxyquinoline) were measured simultaneously in mixtures of Al(ClO4)3 with the LLE. Solutions containing about 0.3 kg m−3 organic matter with total Al concentrations in the range 0 to 60 mmol m−3 were investigated at pH 4.0, 4.5, and 5.0. The total concentration of inorganic Al in the solutions (Alin) at each pH value was calculated as the sum of labile Al and the concentrations of the species Al(OH)+2 and Al(OH)−4 as estimated with thermodynamic hydrolysis constants. The independently‐measured parameters, FQ and Alin, then were used to calculate an overall stability coefficient for Al complexation by the leaf litter extract at each pH value. The values obtained were in good agreement with previous determinations of the stability coefficient based on fluorescence quenching alone. The conditional stability constant cβ0/0 for the quasiparticle species AlL (L = organic ligands) was found to have the value 108.7 ± 0.5 in agreement with a previous estimate of 108.6 ± 0.1 derived from FQ data only. These results confirmed the hypothesis that fluorescence quenching is proportional to Al complexation by the ligands in the LLE.
Boron Sorption on Composted Organic Matter
Authors: Yermiyaho U. , Keren R. , Chen Y.
Published: July 2010

Boron (B) sorption on composted organic matter at various pH levels and ionic strengths was determined. The compost contained 158 g kg−1 of humic acid and 56 g kg−1 of fulvic acid fractions, totaling 21.4% of the organic matter. At pH 8, the amount of sorbed B increased by about 57% with an ionic strength increase from 0 to 0.15 M. For solutions of CaCl2 at concentrations lower than 5 × 10−3 M, the effect of CaCl2 on B sorption was negligible. Sorption isotherms of B on organic matter were determined at pH levels of 7.0, 7.9, and 8.9. The sorption increased with increasing B concentration in solution and pH.

A comparison with literature data for clays shows that sorption of B on organic matter at similar pH levels and total B concentration is significantly higher than on clays. A modified Langmuir equation was fitted to the measured data. Based on the isotherms, sorption coefficients were derived and used to calculate the predicted dependence on pH of B sorption on organic matter at various total B levels. Desorption studies of B from organic matter at pH 8 and increasing levels of sorbed B exhibited strong hysteresis effects and the sorbed B was removed to a partial extent only. The formation of dihydroxy and/or hydroxy‐carboxy binding of borate to humic substances and/or carbohydrates is proposed to be the sorption mechanism. These bonds may explain the limited irreversibility of the process.
Evaluation of Nitrogen‐15 Tracer Techniques for Direct Measurement of Denitrification in Soil: IV. Field Studies
Authors: Mulvaney R. L. , Vanden Heuvel R. M.
Published: July 2010

Field studies were conducted to determine whether underestimation occurs in measuring evolution of nitrous oxide (N2O) using an 15N‐tracer technique based on the assumption of isotopic uniformity. Microplots of 58, 553, or 1684 cm2 in area were treated with 15N‐labeled KNO3 (68.5 atom % 15N) at the rate of 100 kg N ha−1. Isotope‐ratio analyses of the NO−3 in soil cores collected from one plot of each size showed considerable spatial variability in 15N enrichment, but measurements of N2O evolution from these plots by gas chromatography (GC) and mass spectrometry (MS) usually did not differ significantly (0.05 level), demonstrating that appreciable error does not necessarily arise in the use of 15N‐tracer methodology to measure denitrification of NO−3 that is not isotopically uniform. In a subsequent study, replicate atmospheric samples were collected from three plots of each size following rainfall or irrigation for analysis of N2O by GC and MS. The measurements differed significantly (0.05 level) for approximately 60% of the collections that were made; however, the magnitude of the difference was usually small compared to spatial variability in N2O evolution. Significant differences occurred more often with medium or large plots than with small plots, and the greater value was usually obtained by GC. The extent of the difference was not affected by increasing the period of enclosure used in collection of atmospheric samples, but it was affected by subsequent application of fertilizer (25 kg N ha−1), which led to serious underestimation by MS of N2O evolved from most of the medium and large plots.
Microbial Release and Degradation of Catechol and Chlorophenols Bound to Synthetic Humic Acid
Authors: Dec Jerzy , Bollag Jean‐Marc
Published: July 2010

The binding of xenobiotics of humus occurs continuously in nature, and it is possible that this reaction can also be used for decontamination of the environment. It is not yet clear, however, to what extent the release of xenobiotics from humus may cause a delayed pollution problem. To evaluate this question, 14C‐labeled catechol (o‐dihydroxybenzene), 4‐chlorophenol, 2,4‐dichlorophenol, 2,4,5‐trichlorophenol, and pentachlorophenol bound to synthetic humic acid polymer were incubated with microbial soil populations, and the evolution of 14CO2 and release of radioactive compounds into the medium was monitored. The quantity of 14CO2 evolved varied with the source of the inocula and the chemical structure of the compound under investigation. After 13 wk of incubation, 14CO2 evolution ranged from 1.2 to 10.0% of the initially bound radioactivity. Radioactive substances, which were released into the media mostly in the form of the unchanged compound, varied from 0.4 to 12.4% of the initially bound radioactivity. Most radioactivity (54.7–88.9%) remained bound to the synthetic humic acid, suggesting that once chlorophenols are incorporated into humus their release is very slow and unlikely to adversely affect the environment.
Sulfur Transformations in Forest Litter and Soil: Results of Laboratory and Field Incubations
Authors: Watwood M. E. , Fitzgerald J. W.
Published: July 2010

Field incubations of litter (01 and 02 layers) and A horizon soil utilizing 35S‐labeled inorganic sulfate were conducted during July 1985 in an eastern white pine (Pinus strobus L.) and a hardwood forest. Samples were assayed for the capacity to form 35S‐labeled organic S, and in most cases these capacities were very similar to those determined in corresponding laboratory incubations. The A horizon soils from both watersheds formed approximately 3.0 nmol of organic S g−1 dry weight of sample during 2‐d field or laboratory incubations. No substantial increase in this amount was observed after 7‐d field incubations. Intrinsic S fractions of samples were quantified prior to and following field incubations, and organic S represented the majority of the total S in all cases. Total S ranged from 260 to 1180 and from 150 to 270 mg kg−1 in the litter layers and the A horizon, respectively. Sulfonate S (13–74% of total S) and nonphosphate extractable ester sulfate (16–82% of total S) were the largest organic S pools. Water soluble and phosphate extractable S pools were comprised of both inorganic sulfate and ester sulfate, and the latter was found to represent up to 8.1% of total S. The distribution of 35S following field incubations was determined, and organic 35S fractions in a variety of linkage groups were again found to predominate. Total C, moisture content, and throughfall sulfate concentrations during the field incubations were also determined.
Simulated Transport of Multiple Cations in Soil Using Variable Selectivity Coefficients
Authors: Mansell R. S. , Bloom S. A. , Selim H. M. , Rhue R. D.
Published: July 2010

A chromatographic model for describing the transport of multiple cations in soil was modified to include both mobile‐immobile flow regions and variable ion exchange selectivity coefficients Kij for each binary combination of cation species in a ternary soil‐water system. The model was evaluated by comparing simulated results with published breakthrough curves (BTC) for Na+ and Mg2+ concentrations in effluent from columns of Yolo loam soil initially saturated with Ca2+ ions. Experimental BTC for the relatively uncompetitive Na+ species were adequately described when either constant or variable values of Kij were used in the model. For the more competitive Mg2+ species however, simulations using constant Kij coefficients described the relative location for maximum concentration but underestimated tailing for the BTC. When all of the soil solution was assumed to be mobile, description of tailing for Mg2+ BTC was improved by the use of variable Kij values in simulations, but retardation for Mg2+ transport tended to be overestimated. The combined use of mobile‐immobile liquid regions and of variable selectivity coefficients provided the observed tailing in Mg2+ BTC but minimized overestimation of retardation.
Disjunctive Kriging as an Approach to Management Decision Making
Authors: Yates S. R. , Yates Marylynn V.
Published: July 2010

Disjunctive kriging is a nonlinear estimation technique that allows the conditional probability that the value of a spatially variable management parameter is greater than a cutoff level to be calculated. The method can be used in management decision making to help determine when some reclamation action is necessary. Two input parameters are required to use the technique: a cutoff level and the critical probability level. The use of disjunctive kriging as a decision making tool is illustrated using the regulation of septic tank setback distance as a means for minimizing the contamination of groundwater by viruses. Two examples are described: given a setback distance, the spatial distribution of the conditional probability that the virus concentration will be greater than acceptable levels is calculated; and given a critical probability level, calculating the spatial distribution of setback distances which satisfy that probability level. The study showed that, to be 90% confident that virus concentrations would be within acceptable limits, in many areas the setback distance would have to be severalfold higher than prescribed by current regulations.
Electrophoretic Mobility of Hydroxy‐Aluminum and Sodium‐Hectorite in Aqueous Solutions
Authors: Harsh James B. , Doner H. E. , Fuerstenau D. W.
Published: July 2010

The electrokinetic behavior of colloids titrated with acid or base in the presence of hydrolyzable metal cations is often modeled by assuming the substrate surface is partially or completely coated with the metal hydroxide. In aged OH‐Al‐clays much of the Al(OH)3 surface precipitate resides in the interlayer, but it is not known if the external surfaces of aged OH‐Al clays contain Al(OH)3. We precipitated Al(OH)3 on hectorite and measured electrophoretic mobility (µ), which is a function of the electric potential at the shear plane of the substrate, with varying pH, time, and ionic strength. The behavior was compared to that of Na‐hectorite in the presence and absence of AlCl3. We found that (i) the OH‐Al‐hectorite had a more positive µ than the Na‐hectorite between pH 3 and 5.5, but had a more negative µ between pH 5.5 and 7; (ii) µ became more negative with increasing NaCl concentration; and (iii) neither clay equilibrated rapidly with time. Ion exchange experiments showed that Na displaced exchangeable Al and Mg that originated from dissolution of the hectorite and Al(OH)3. There was no evidence for significant Al(OH)3 coating external surfaces, because this would have resulted in a more positive µ for the clay at all pH values below the point of zero charge of Al(OH)3 (pH = 9). Exchangeable cations on external surfaces primarily determined the shear plane potential in this system.
Acid Phosphatase Activity in Soils of the Appalachian Region
Authors: Baligar V. C. , Wright R. J. , Smedley M. D.
Published: July 2010

Acid phosphatase (AP) activity was determined in 14 hill land soils of the Appalachian region. Soil samples were obtained from surface (A or Ap) and subsurface (E, BA, Bt, or Bw) horizons during spring, and subsamples were stored field‐moist at 4 °C and air‐dry (AD) for 36 wk prior to determination of AP activity. The average AP activities of surface and subsurface horizons stored field‐moist at 4 °C were 1.7 to 1.9 times higher than those of AD samples. The average AP activity of air‐dry surface horizons was 3.3 times higher than that of subsurface horizons. Significant positive relationships were found between the AP activities of AD and 4 °C samples, and total C and N content of soils. Positive relationships were observed between AP activities and various forms of soil P. The original soil moisture content by weight or volume and percent water‐filler pores (% WFP) were significantly related to AP activities of surface soil horizons. Each soil type has its own inherent level of phosphatase activity.
Denitrification in Soil Aggregates of Different Sizes
Authors: Seech A. G. , Beauchamp E. G.
Published: July 2010

The denitrification potential in different size aggregates of a silt loam soil was studied to explain spatial variability of denitrification. Seven aggregate size ranges (<0.25, 0.25–0.5, 0.5–1, 1–2, 2–5, 5–10, and 10–20‐mm diam.) were obtained by gentle dry sieving of the sampled soil. The denitrification rate was determined by the acetylene block method following imposition of several different treatments. It was observed that the denitrification rate was much larger with the smaller aggregates and generally decreased as aggregate size increased. Crushing of the aggregates to <0.25‐mm diam. resulted in some diminishment of this relationship. The supply of NO−3 was not limiting in the different size aggregates but the addition of glucose suggested that C substrate supply in larger aggregates was limiting denitrifier activity. Carbon dioxide production during aerobic incubation was greatest in microaggregates (<0.25 mm) and decreased with increasing aggregate size, further substantiating the deficiency in C substrate in large macroaggregates. It was found also that biomass C was greatest in microaggregates and decreased with increasing aggregate size when determined for both aerobic and anaerobic incubation conditions. The results of this study may be interpreted to suggest that considerable variability of available substrate C occurs in association with different size aggregates and could partly explain the large spatial variability of denitrification that occurs over relatively short distances in field soil
Calcium‐Aluminum Balance and the Growth of Soybean Roots in Nutrient Solutions
Authors: Noble A. D. , Fey M. V. , Sumner M. E.
Published: July 2010

The effect of varying two parameters having contrasting effects has been largely overlooked when describing Al phytotoxicity. Consequently the effects of varying pH (4.2, 4.5, and 4.8), Al (0, 20, 40, 80, and 160 µM Al) and CaSO4 (625, 1250, 2500, 5000, and 10 000 µM Ca) levels on root length of soybeans (Glycine max (L.) Merr.) were evaluated in a solution culture experiment. At a given pH and Al concentration, an increase in the level of CaSO4 resulted in a decrease in the activities of Al3+, AlOH2+ and Al(OH)+2 while the activity of AlSO+4 increased. Among the individual Al monomers, relative root length was most highly correlated with the calculated activity of Al3+ (R2 = 0.811) followed by AlOH2+ (R2 = 0.687), while AlSO+4 (R2 = 0.338) gave the poorest correlation. Thus, the AlSO+4 species appears to be less phytotoxic. Relative tap root length was poorly correlated with the concentration of monomeric Al determined by the modified Aluminon method, which also assays the less phytotoxic AlSO+4 species under the prevailing conditions. An expression termed CAB , enabled the most precise assessment to be made of the effects of soluble Ca and Al, together, on root growth (R2 = 0.900). The coefficients in the CAB expression were introduced as a weighing to accommodate the assumed importance of valence in ion interactions at the plant root surface. The CAB was also found to be a better index of the solution conditions affecting root growth when applied to data from other published studies.
Using Texture and Other Soil Properties to Predict the Unsaturated Soil Hydraulic Functions
Authors: Wösten J. H. M. , van Genuchten M. Th.
Published: July 2010

The unsaturated hydraulic properties of soils are important but difficult to measure. Rather than measuring the hydraulic properties directly, we followed a different approach by fitting analytical expressions for the soil water retention and hydraulic conductivity functions to experimental data for a wide range of soils in the Netherlands. Analysis of the data shows the flexibility of the analytical expressions and also gives insight into how the different model parameters affect the calculated unsaturated hydraulic functions. Regression analyses are used to relate the estimated model parameters to more easily measured soil properties, such as bulk density and percentages silt, clay and organic matter. After calibration, the relations are used to predict the hydraulic functions of soils for which only the more easily measured soil properties are available. Accuracy of the predictions is analyzed in terms of functional criteria which are relevant to practical management problems. The predictive regression models are useful for estimating the unsaturated soil hydraulic properties of large areas of land, but need improvement for application to specific sites.
Transformation and Losses of Applied Nitrogen‐15 Labeled Ammonium in a Flooded Organic Soil
Authors: Meyer Michael L. , Bloom Paul R. , Grava John
Published: July 2010

Ammonia volatilization, denitrification, and mineralization‐immobilization turnover rates (MIT) in a flooded organic soil were estimated using 15N‐labeled NH4Cl fertilizer. The soil was placed in 15‐cm columns either under dark or illuminated conditions. Volatilization of NH3‐15N was 8 and 4% of the initial fertilizer N added to the dark and illuminated columns, respectively. The rates of fertilizer N and total N denitrification in the dark columns were constant over the experiment at 1.2 and 2.1 mg N kg−1 d−1, respectively. After 74 d 22% of the initial amended fertilizer N had been denitrified. The rate of net mineralization of N in the anoxic zone was constant with time at 1.5 mg N kg−1 d−1. Mineralization and immobilization turnover fit the model y = ymax (1 − e‐kt), where y is the quantity of N mineralized or immobilized and k is the rate coefficient. For gross mineralization ymax = 480 mg N kg−1 d−1 and k = 0.00914 d−1. For immobilization ymax = 160 mg N kg−1 d−1 and k = 0.025 d−1. Mineralization and immobilization were not affected by the concentration of extractable NH4‐N. Algae increased immobilization in illuminated columns. No priming effect of added NH+4 on N mineralization was found. The impact of MIT on calculation of fertilizer efficiency is illustrated.
Effect of Saline Irrigation Waters on Soil Manganese Leaching and Bioavailability to Sugar Beet
Authors: Khattak Riaz A. , Jarrell Wesley M.
Published: July 2010

Use of saline water for irrigation has shown considerable promise. However, its effect on the solubility and bioavailability of native soil nutrients is not well understood. This study was conducted to evaluate the extent of the salt‐induced Mn solubility and phytotoxicity to sugar beet [Beta vulgaris (L.) USH 11] under a soil‐plant‐leachate system. Sugar beet grown in the glasshouse on four diverse California soils was irrigated with either deionized water or 22.5 and 45.0 mol m−3 NaCl‐CaCl2 solution. Saline irrigation waters significantly (P < 0.001) increased (27 to 97%) the Mn concentration ([Mn]) and total Mn accumulation (48 to 130%) in sugar beet tops in all soils. The [Mn] in the soil solution leachate increased significantly with net increases of 55.3, 35.5, and 2.6 mg Mn kg−1 in Maymen, Aiken‐Tehama, and Aiken‐ElDorado soil, respectively, for the highest salinity, but only traces of Mn were detected in leachate of a high pH (8.23) Mojave soil. Diethylenetriamine pentaacetic acid (DTPA)‐extractable soil Mn significantly increased with salinity levels in irrigation waters in Maymen (92%), Aiken‐ElDorado (68%), and Mojave (47%) soils, but decreased (37%) in Aiken‐Tehama soil of low pH (5.10) and low C (3.60 g kg−1). The multiple regression analyses produced R2 = 0.864*** (P < 0.001) when shoot [Mn] was regressed on ECe, soil solution [Mn], soil pH, and DTPA‐extractable soil Mn. Since sugar beet tops contained in excess of 1000 mg Mn kg−1 top tissue, it was concluded that salt‐induced Mn accumulation under saline irrigation can be potentially toxic.
Infuence of Micaceous Minerals on Mineralogy Class Placement of Loamy and Sandy Soils
Authors: Rebertus R. A. , Buol S. W.
Published: July 2010

In Soil Taxonomy, mineralogy classes of pedons that have a fragmental, sandy, sandy‐skeletal, loamy, or loamy‐skeletal particle‐size class are defined by weight percent minerals in the coarse silt and larger fractions of the control section. However, a footnote to the key to mineralogy classes states that percentages by weight are estimated from grain counts of one or two of the dominant separates from a conventional mechanical analysis. The relationship of grain count number to volumetric percentage depends upon grain shape, size and cleavage, and the counting method used, making weight estimations, or even volumetric estimations impracticable. Revisions in the key to mineralogy classes are suggested because presently the key requires determination of grain size and shape relationships as well as the identification of minerals and their densities where often there is a gradation of mineral compositions and properties. According to the estimates used in this study, a line count of 80 to 85% micaceous minerals is needed to classify a pedon as micaceous; however, field classification of micaceous occurred at around 70% line count micaceous grains. This paper discusses limitations of grain counts for quantitative mineralogical analysis of the coarser fine‐earth fractions, presents a case for the revision of the key to mineralogy classes through use of actual mineralogic data, and recommends adoption of the line count method of determining composition for the purpose of mineralogy class placement.
Changes in Infiltration Under Alfalfa as Influenced by Time and Wheel Traffic
Authors: Meek B. D. , Rechel E. A. , Carter L. M. , DeTar W. R.
Published: July 2010

Infiltration rates were measured for alfalfa, (Medicago sativa L., cv. WL514) subjected to treatments where wheel traffic was varied in terms of area covered and time of application on a Wasco sandy loam (coarse‐loamy, mixed, nonacid thermic Xeric Torriorthent). Traffic treatments were (i) No‐traffic, (ii) Preplant, (iii) Repeated, and (iv) traffic similar to what a grower would apply. Infiltration rates increased for all treatments, with increases being 240% for treatments without harvest traffic and 140% for treatments with harvest traffic. Increases in infiltration were related to decreases in stand density. Slight packing (traffic) applied before the soil was flood‐irrigated in 1983 increased infiltration rates 20% compared to flooding loosened soil (no traffic). Harvest traffic resulted in slower water movement in the soil.
Distance and Distribution Effects of Phosphorus Fertilizer on Corn
Authors: Eghball B. , Sander D. H.
Published: July 2010

Fertilizer P distribution and distance of application from the plant can affect fertilizer P efficiency. Ammonium polyphosphate solution tagged with 32P was injected into Sharpsburg sicl (Typic Argiudoll) 10‐cm deep on circle located 16, 32, 48, and 64 cm from five corn seeds (Zea mays L.) planted in the center. The P fertilizer for each plot was divided into 10 equal parts and was injected into 10 spots on the circle's circumference at five different spacings. To study the movement of P in the soil, seven concentrations of P fertilizer were injected into the soil 5‐cm deep. Results indicate that after 90 d P fertilizer moves outward from the injected point to form a near perfect sphere whose volume was related in a quadratic manner to the P application rate. At early stages of growth, seed placement of P fertilizer and placement up to 16 cm resulted in greater plant P from fertilizer than other P distances. At maturity little or no effect of P application distance was observed. Plant P from fertilizer increased as the surface area of the fertilizer P‐effected soil increased, indicating surface area is an important factor involved in determining the probability of root‐fertilizer contact. Plant P from fertilizer increased as the spacing between injection points increased because surface area of the fertilizer P‐effected soil was increasing. Plant P from fertilizer decreased with time indicating that a greater proportion of plant P was from soil P late in the growing season.
Transport of Inorganic and Natural Organic Tracers Through an Isolated Pedon in a Forest Watershed
Authors: Jardine P. M. , Wilson G. V. , Luxmoore R. J. , McCarthy J. F.
Published: July 2010

The transport of several inorganic ions (Mg2+, NH+4, Br‐, and NO‐3) and natural dissolved organic C (DOC) through the upper 1.2 m of an isolated in‐situ forest pedon was investigated. The purpose of the study was to investigate the spatial heterogeneity and the rate of nutrient transport in a forest soil. The tracers were added as a pulse to the soil surface during saturated flow in three separate experiments sequentially involving MgBr2, NH4NO3, and DOC, respectively. The temporal patterns of NO‐3 and Br‐ concentration observed at selected profile locations in the pedon were described by the convective‐dispersive (CD) equation using flux‐type boundary conditions with effluent concentrations treated as flux‐averaged concentrations. Skewed breakthrough curves (BTC) indicative of preferential flow were obtained at all measurement positions. Modelfitted velocities (v) agreed well with saturated infiltration rates established in‐situ for soils of the adjacent forest watershed. Although the CD equation could describe the temporal mobility of the nonreactive Br‐ and NO‐3 tracers at any given point in the pedon, it could not adequately describe the tracer concentration profiles with depth at selected times after tracer addition. Observed BTCs for Mg2+, NH+4, and DOC indicated that these tracers were reactive with the soil but also demonstrated that a significant quantity of these tracers moved through the soil via preferential flow. The temporal patterns for reactive tracer movement through the pedon could be modeled with the CD equation when adsorption was reversible.
A Comparison of Batch‐ and Flow‐Generated Anion Adsorption Isotherms
Authors: Miller D. M. , Sumner M. E. , Miller W. P.
Published: July 2010

Solute transport models often use batch‐generated adsorption isotherms to partition solute between the aqueous and adsorbed phases, but the relationship at equilibrium between aqueous and adsorbed solute concentrations may be different in closed (batch) and open (flow) systems. Adsorption isotherms were generated for orthophosphate/goethite, silicate/goethite, orthophosphate/soil clay and orthophosphate/arsenated‐goethite systems using batch and flow (miscible displacement) techniques. The contact times were 168 and 96 h in the batch and flow experiments, respectively. The shapes of the isotherms generated by the two methods were very similar in all cases, although the flow‐generated isotherms were displaced slightly upward relative to the batch isotherms. Simple Langmuir plots of both batch and flow data were nonlinear for all systems, while in all systems containing phosphate, flow‐generated distribution coefficients were greater than the corresponding batch‐generated values, particularly at low surface coverage. In addition, adsorption maxima and values of the two‐surface Langmuir parameter b1 were consistently greater in the flow systems. The results indicate that provided transport processes do not keep the flow system far from chemical equilibrium, batch‐generated anion adsorption isotherms are likely to underestimate the extent of adsorption in the corresponding flow system, particularly at relatively low aqueous phase sorbate concentrations. This appears to be due, in part, to the removal of competitive antecedent species in the flow system effluent. It is suggested that flow systems are thermodynamically equivalent to batch systems having very wide solid/solution ratios.
Molybdate Adsorption on Kaolinite, Montmorillonite, and Illite: Constant Capacitance Modeling
Authors: Motta M. Manuela , Miranda C. F.
Published: July 2010

The adsorption of molybdate by kaolinite, montmorillonite, and illite was investigated at 25 and 40 °C, in a 0.01 M NaCl background medium, for equilibrium Mo concentrations ranging from 0.1 to 100 mg L−1. The constant capacitance model was shown to be able to describe molybdate adsorption on the three minerals and for the two temperatures used. The model comprises five adjustable parameters for each mineral: two surface protonation‐deprotonation constants, two molybdate surface complexation constants, and a capacitance density parameter. However, for montmorillonite and illite the number of adjustable parameters was reduced to four since adsorption data could be fitted using only one molybdate complexation constant. The protonation‐deprotonation constants were obtained from potentiometric titration data and the molybdate complexation constants from adsorption data. The capacitance density was chosen on the basis of a literature compilation of values used in previous applications of the constant capacitance model to the adsorption of several ions on oxide minerals. Tentative estimations of thermodynamic functions of molybdate adsorption are presented.
Adsorption of Chromate by Subsurface Soil Horizons
Authors: Zachara J. M. , Ainsworth C. C. , Cowan C. E. , Resch C. T.
Published: July 2010

Chromate adsorption was measured with and without reactive cosolutes on four subsurface soil horizons differing in pH and mineralogy, and on clay fractions from two of the oxide‐containing subsoils. Chromate adsorption was greatest in lower pH materials enriched in kaolinite and crystalline iron oxides. Over a range in pH, chromate adsorption to subsoil was similar to that observed for pure‐phase oxides. Chromate binding was reversible to pH and was depressed in the presence of SO2‐4 and dissolved inorganic C, which compete for adsorption sites. A surface site density for crystalline Al‐substituted iron oxides in the subsoils was estimated from chromate adsorption on the clay fractions using the model FITEQL and outer sphere surface coordination constants from Al‐goethite. The estimated site density for soil crystalline iron oxides was well below that of clean oxides, suggesting surface saturation by indigenous soil ions. The calculated site density and surface binding constants for Al‐goethite were used in the Triple Layer Model to calculate the effect of ionic strength, cosolutes, solids concentration, and sorbate concentration on CrO2‐4 adsorption. Model calculations were in good qualitative agreement with experimental results.
Simulation by NCSOIL of Net Mineralization in Soils from the Deherain and 36 Parcelles Fields at Grignon
Authors: Houot Sabine , Molina J.A.E. , Chaussod R. , Clapp C.E.
Published: July 2010

Soil N and C mineralization was measured from the Deherain and 36 Parcelles fields at the experimental station of Grignon, France. In the Deherain plots, manure and inorganic N effects have been compared on a wheat‐sugarbeet rotation since 1875. In the 36 Parcelles field, the effect of composted straw and inorganic N on the soil organic matter have been studied since 1959 on bare plots. Control plots without any organic or inorganic additions were maintained in both fields. In cultivated and bare plots, rates of C mineralization were similar when soils had been organically amended (farm manure or composted straw). The addition of inorganic N increased the soil total organic N and C content in comparison to the respective control plots, but it did not change the rates of N and C mineralization. Net N mineralization was linear and the determination of potentially net mineralizable N (No) as the asymptotic value of an exponential kinetic gave aberrant values. A new approach to measure No was proposed using the model NCSOIL which simultaneously simulates N and C dynamics in soil. The No was quantified as the initial N content of the model's pool I plus pool II which represent the soil active organic matter involved in N and C turnover.
Evaluation of Factors Affecting Emergence of Winter Wheat Planted with Seed‐Banded Nitrogen Fertilizers
Authors: Mahler R. L. , Lutcher L. K. , Everson D. O.
Published: July 2010

Nitrogen use efficiency by cereal crops may be increased by the placement of fertilizer with the seed; however, high N concentrations often cause injury and reduce both germination and emergence. Two studies were conducted under controlled greenhouse conditions to evaluate factors affecting emergence of winter wheat (Triticum aestivum L.) planted with seed‐banded N fertilizers. Soil from the Ap horizon of a Palouse silt loam (fine‐silty, mixed, mesic Pachic Ultic Haploxeroll) was used in both studies. Two N materials (ammonium nitrate and urea) were banded with the winter wheat seed (‘Stephens’) at N rates of 0, 11, 22, 33, 44, 55, and 66 kg ha−1, and placed in soils at soil matric potentials of −0.15, −0.25, and −0.35 MPa. The tolerance of five winter wheat cultivars ‘Daws’, ‘Hill 81’, ‘Nugaines’, ‘Peck’, and Stephens to sulfur‐coated urea (SCU) materials SCU‐10, SCU‐20, and SCU‐30 was evaluated in a separate study. Nitrogen rates of 0, 50, 100, and 150 kg ha−1 were used at a soil matric potential of −0.20 MPa. In the first study significant N source × water potential (P < 0.0003) and water potential × N rate (P < 0.0001) interactions were observed. In the second study, significant N source × N rate × cultivar (P < 0.0001), N source × N rate (P < 0.0001), and N source × cultivar (P < 0.0001) interactions were found. The N source, N application rate, soil‐water potential, and winter wheat cultivar main effects were all significant for winter wheat emergence. Ammonium nitrate reduced winter wheat emergence 5 to 26% less than urea when comparable quantities of N were placed with the seed. Winter wheat emergence decreased as soil‐water potential decreased (became more negative). These studies demonstrated how the evaluated factors are interrelated with regard to winter wheat emergence. Consequently, guidelines routinely used for seed‐banded N fertilization that only consider N application rate should be modified to also consider N source and soil moisture.
Mechanism of Native Manganese Release in Salt‐Treated Soils
Authors: Khattak Riaz A. , Page A. L. , Jarrell Wesley M.
Published: July 2010

The release of native soil Mn was evaluated under laboratory conditions in Aiken (fine, kaolinitic, thermic Abruptic Durixeralfs) and Redding (fine, kaolinitic, thermic Abruptic Durixeralfs) clay loam soils saturated with either deionized water, or 75 and 150 mmol L−1 NaCl‐CaCl2 solution. As the NaCl‐CaCl2 concentrations increased, soil solution Mn increased and exchangeable Mn decreased proportionately. The regression of the net increases (Δ) in soluble Mn vs. the corresponding decreases (Δ) in exchangeable Mn produced the relationship, Δ exchangeable Mn (mg kg−1) = 0.788 + 0.868 Δ soluble Mn (mg kg−1), R2 = 0.63** (P < 0.01). This suggested that in these salt‐treated soils Mn was released into solution by a cation exchange reaction involving Ca and Na. The increases (122 to 252%) in exchangeable Mn after 5 d incubation, as compared to untreated air‐dried soils, and the favorable pH (4.44 to 6.01) and Eh (redox potential) values (+202 to 254 mV) suggested that Mn(III,IV) was reduced to Mn(II). The Mn(II) primarily accumulated on the exchange phase and was subsequently displaced from the exchange sites by added Na+ and Ca2+. At equal equivalent concentrations, almost twice as much Mn entered the soil solution with Ca2+‐salts (Cl, ClO4, and NO‐3) as with Na+‐salts. The sum of soluble + exchangeable Mn did not increase (rather decreased significantly at the highest salt treatments). It was concluded that salinity had no effect on the extent to which Mn(III,IV) were reduced to Mn(II). These results indicated that management practices that increase soil solution salinity on soils high in native Mn could elevate soil solution Mn to concentrations potentially toxic to Mn‐sensitive crops.
Organic Matter and Natural Carbon‐13 Distribution in Forested and Cultivated Oxisols
Authors: Vitorello V. A. , Cerri C. C. , Andreux F. , Feller C. , Victória R. L.
Published: July 2010

Soil carbon (C) distribution, natural 13C abundances and their changes as a consequence of cropping were studied in three neighboring areas on an Oxisol from Brazil. One site (T0) was under forest, while the two other sites (T12 and T50) had been deforested, then cultivated with sugar cane for 12 and 50 yr, respectively. Soil morphological, chemical and mineralogical characteristics in all three sites were very similar. Total C content of the 0.06‐m layer of T0 was twice that of T12 and T50, then decreased sharply with depth, to values similar to the other profiles. Delta 13C had practically constant values of −25.1, −22.8, and −20.4‰, throughout the 0 to 0.30‐m layer of T0, T12, and T50 respectively. These values increased in deeper layers, to about −17‰, due to increased humification and possibly to deposition of organic matter from a former 13C‐rich vegetation. The 0.10‐ to 0.20‐m layer was separated into particle‐size fractions and alkaline extract. Carbon contents decreased from T0 to T50 in the sand‐size fractions and alkaline extracts, but did not change in the clay‐size fractions. Delta 13C values were used to estimate the proportions of C derived from forest (Cdff) and from sugar cane (Cdfc). Carbon derived from sugar cane represented 17.3 ± 3.2% and 40.5 ± 2.2% of total C in T12 and T50, respectively. It reached its maximum value (67 ± 3.7%) in the coarse sand fraction of T12 and T50 and decreased with decreasing fraction size, to 13.8 ± 9.4% and 30.5 ± 6.5% in the fine clay fractions of T12 and T50, respectively. Thus, Cdff persisted mainly in the clay‐size fraction.
Dynamics of Evaporite Distribution in Soils on a Fan‐Playa Transect in the Carrizo Plain, California
Authors: Eghbal M. K. , Southard R. J. , Whittig L. D.
Published: July 2010

Investigation of the distribution and dynamics of evaporites along an alluvial fan‐playa transect in the Carrizo Plain, CA, shows that the overall salt concentration increases toward the center of the playa. Within profiles along the transect, the highest salt concentrations are found in the lower part of profiles. Sodium, K, Mg, Cl, and SO4 concentrations increase along the transect toward Soda Lake. Calcium concentration, in the form of gypsum, is generally higher in profiles in the middle of the transect. Concentrations of Na, Ca, Mg, Cl, and SO4 increase with depth in profiles away from Soda Lake as a function of a greater degree of leaching; higher concentrations of these ions are found toward the surface in profiles closer to Soda Lake due to capillary movement from the groundwater. Halite is the only mineral in the surface horizons. Gypsum is more common in lower horizons, closer to ground water, and is the common salt in soils farther away from Soda Lake. Other soluble evaporites, including halite, loeweite [Na12Mg7(SO4)13 · 15H2O], and bloedite [Na2Mg(SO4)2 · 4H2O], together with gypsum, are found in extracts of soils near Soda Lake. A seasonal influence on the anion and cation distribution generally is noticeable only in soils with intermediate salt concentrations. Higher concentrations of anions and cations are found following the dry season. The orderly differences in anion and cation concentrations within most of the profiles and along the transect reflect the well established differences in solubility of the different salts.