bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relationships Between Soil Urease Activity and Other Soil Properties
Authors: Zantua M. I. , Dumenil L. C. , Bremner J. M. 
Published: July 2010

AbstractSurface samples of 21 diverse Iowa soils representing a wide range in pH, texture, and organic matter content were studied to determine the relationships between soil urease activity and other soil properties.Simple correlation analyses showed that urease activity was correlated very highly significantly with organic C (r = 0.72***), total N (r = 0.71***), and cation‐exchange capacity (r = 0.67***). Urease activity also was significantly correlated with clay (0.53*), sand (−0.47*), and surface area (0.45*), but was not significantly correlated with pH, silt, or CaCO3 equivalent. Multiple regression analyses showed that organic matter content accounted for most of the variation in urease activity.
Fragipan Horizons in Soils of the Memphis‐Loring‐Grenada Sequence in West Tennessee
Authors: Buntley G. J. , Daniels R. B. , Gamble E. E. , Brown W. T. 
Published: July 2010

AbstractThe distribution of soils on the loess‐mantled landscapes of west Tennessee does not fit the traditional concept that the older, more strongly developed soils occur on the more stable positions in the landscape. The objective of this study was to attempt to ascertain whether the development and distribution of these soils were related to weathering associated with the modern landscape or whether they were in part relict from the earlier period of weathering. Power augers were used along west to east transects to determine the characteristics and thickness of the three identifiable loess sheets involved and to explore their relationship to the distribution of soils within landscapes at different points along the loess thickness sequence. The top of the Roxana loess was everywhere marked by a distinctly brittle zone 1 to 2 m thick. Evidence that the brittle zone in the top of the Roxana is a product of pre‐Peorian weathering is the fact that it occurs under calcareous loess near the bluff and can be traced eastward under the thinning Peoria loess until it grades into the fragipan horizons within the sola of the Loring and Grenada soils. The stratigraphic, geomorphic, and morphologic evidence leads to the conclusion that the fragipan horizon of the Loring and Grenada soils is a relic of pre‐Peorian weathering that has undergone subsequent modification by processes related to the modern surface.
Water Movement Through Pedal Soils: I. Saturated Flow
Authors: Anderson J. L. , Bouma J. 
Published: July 2010

AbstractApparent dispersion coefficients were determined with a chloride tracer in 55‐cm long undisturbed columns from four pedal soil horizons of three pedons. Five medium subangular blocky structures were compared with five coarse prismatic structures, all with a silty clay loam texture. Dispersion coefficients (D), which could not always be calculated due to “nonideal” behavior of the flow system, were significantly different for the two types of structures. Application of an unlimited quantity of traced water to drained columns resulted in very high dispersion particularly for the subangular blocky structures. Some practical implications of the occurrence of hydrodynamic dispersion are discussed.
Water Movement Through Pedal Soils II. Unsaturated Flow
Authors: Anderson J. L. , Bouma J. 
Published: July 2010

AbstractVery high hydrodynamic dispersion, occurring during application of an unlimited dose of chloride‐traced water to 10 drained 55‐cm long columns with undisturbed pedal soils, was strongly reduced by a daily application of 1 cm of water. Dispersion in five columns with subangular blocky structures remained significantly higher than that measured in five columns with prismatic structures. Differences are explained by a hypothetical analysis of flow patterns in both types of structure. Application of a surface crust strongly reduced dispersion in the subangular blocky structures, even though the flow rate remained approximately 1 cm/day. This was attributed to lack of flow into the larger vertical pores extending through the columns. Pronounced differences in terms of hydrodynamic dispersion were found among two types of structures from three soil series, all with a silty clay loam texture. This demonstrates the potential usefulness of routine soil structure descriptions as a correlative tool for predicting certain aspects of physical behavior.
A Comparison of In Situ Extractors for Sampling Soil Water
Authors: Levin M. J. , Jackson D. R. 
Published: July 2010

AbstractComparisons were made of two in situ extractors for collection of soil water samples: Amicon hollow fibers and porous ceramic cup lysimeters. Intact soil cores removed from a fescue pasture were fitted with lysimeters and fibers at 10 and 20 cm depth. Cores were leached by adding increments of water in excess of field capacity weekly. After drainage, soil solutions were extracted using lysimeters and fibers. Concentrations of Ca and Mg in soil solutions were greater at 10‐cm than at 20‐cm soil depths. Neither extractor altered the concentrations of Ca, Mg, or PO4‐P during collection.These studies suggest that lysimeters and hollow fibers are viable devices for extracting of soil water samples. Porous ceramic cup lysimeters are preferable for field plots, while hollow fibers are advantageous for intact soil cores. A major advantage of the hollow fiber technique is the small soil displacement required for installation.
Nitrogen Fertilization I. Nitrate Accumulation and Losses Under Continuous Corn Cropping
Authors: Hahne H. C. H. , Kroontje Wybe , Lutz J. A. 
Published: July 2010

AbstractSelected treatments were chosen from three field experiments with corn (Zea mays L.) to determine effects of N rates on the vertical distribution of nitrates in the soil. The experiments were located on three different soil types and corn was grown for 5 consecutive years. Irrigation was a variable in two of the experiments.Appreciable amounts of NO3‐N accumulated in the soils when the optimum rate of 140 kg N/ha at Blacksburg and Charlotte Courthouse and 168 kg N/ha at Orange had been exceeded. Amounts of vertical distributions of NO3‐N accumulations were highly dependent on soil type, and on amounts of irrigation and rainfall. Lowest NO3‐N accumulations and highest NO3‐N losses were encountered in the Cecil fsl. An increase in NO3‐N was found in the Davidson clay loam whereas no loss or gain was observed in the Groseclose silt loam.Irrigation markedly reduced the maximum NO3‐N accumulation in the Davidson clay loam especially in the 120 to 195‐cm depth. Irrigation on the Cecil fine sandy loam had less influence on NO3‐N and hardly affected the spread of the accumulation zone. The data indicated that proper irrigation of soils with high internal drainage can markedly reduce NO3‐N loss through leaching; the reduction in NO3‐N loss in the Cecil fine sandy loam was from 48 to 5% at near optimum N rate of application.
Nitrogen Fertilization: II. Effect on the Soil Solution Composition, Acidity, and Nitrate Adsorption
Authors: Lutz J. A. , Kroontje Wybe , Hahne H. C. H. 
Published: July 2010

AbstractAnalyses were performed on soil solution extracts of samples obtained from depths where nitrate accumulation occurred due to ammonium nitrate applications on three different soils, i.e., Cecil fine sandy loam (Typic, Hapludult; clayey, kaolinitic, thermic), Groseclose silt loam (Typic, Hapludult; clayey, mixed, mesic), and Davidson clay loam (Rhodic, Paleudult; clayey, kaolinitic, thermic). Comparisons were made between treatments of moderate and high N applications in all three soils and between irrigated and nonirrigated conditions on the Cecil and Davidson soils.Nitrate movement and accumulation resulted in markedly different effects on the soil solution composition in the various soils. In the Groseclose silt loam, which has a subsurface layer of low permeability, high nitrate and electrolyte concentrations accompanied by lower pH values and higher amounts of Zn, Mn, and Al in the soil solution were encountered. In the Cecil fine sandy loam and Davidson clay loam, substantial amounts of nitrate were in an adsorbed state which resulted in lower electrolyte concentrations in soil solution. The degree of adsorption was dependent on pH conditions which were affected by movement of acidity. The high NO3‐N adsorbed/NO3‐N solution ratios in the Cecil and Davidson soils indicate that denitrification was not predominant at lower depths in these soils.The fact that applications of acid‐forming N fertilizers may affect the plant root environment mardedly in some soils and result in increased Mn and Al concentrations in the soil solution also suggest that toxic levels for some plants and crops may occur.
Hydraulic and Thermal Properties of a Sandy Soil as Influenced by Incorporation of Sewage Sludge
Authors: Gupta S. C. , Dowdy R. H. , Larson W. E. 
Published: July 2010

AbstractSoil‐water retention was increased by incorporation of sewage sludge into a sandy soil. Most of this increase resulted from water adsorbed by organic matter (15‐bar water). At any given water content, unsaturated hydraulic conductivity and soil‐water diffusivity decreased as rates of sludge addition increased. However, saturated hydraulic conductivity increased as rates of sludge addition increased.Thermal conductivity decreased with increasing rates of sludge application. However, the heat capacity of all oven‐dried sludge‐soil mixtures was the same as that of the control treatment. The combination of a lower thermal conductivity and a higher specific heat (due to higher water content) buffered sludge‐amended soil against sudden temperature changes. Thus, maximum and minimum daily temperatures on plots receiving sludge were a few degrees lower and higher, respectively, than those on the control treatment.
Use of a Versatile Experimental System for Soil Erosion Studies
Authors: Walker P. H. , Hutka J. , Moss A. J. , Kinnell P. I. A. 
Published: July 2010

AbstractA laboratory facility for the study of soil erosion is described. Rainfall from a modular system supplied raindrops at near terminal velocity to prepared soil beds set in a flume with slope adjustable up to 30%. A comparison was made of erosion under overland flow alone and storm rains of the same intensity (discharge), but different energy levels. Raindrop impact in runoff flow was a powerful agency in promoting soil transport and inhibiting rill formation. Bed‐load movement was important in the transport of sand grains, even where the runoff was disturbed by raindrops.
Solute Transfer, with Exchange between Mobile and Stagnant Water, through Unsaturated Sand
Authors: Gaudet J. P. , Jégat H. , Vachaud G. , Wierenga P. J. 
Published: July 2010

AbstractChanges in salt concentration with time were measured at several depths inside and at the exit of a 94‐cm uniform unsaturated sand column which was leached at steady rates with solutions of calcium chloride. Observed salt distributions were compared with salt distributions calculated with a numerical procedure which was based on the dead‐end pore model of Coats and Smith (1964).Values for the dispersion coefficient, the diffusional mass transfer coefficient, and the fraction mobile water used in the model were obtained at different water contents by curve fitting observed and calculated concentrations at one depth. These same values were then used to calculate salt distributions at other depths and at the exit of the column and compared with measured salt distributions. Excellent agreement was obtained. The model presented a good description of the extensive tailing of the salt concentration distributions observed inside and at the exit of the column. The amount of stagnant water was found to increase with decreasing water content from 4% of the total water content of 0.256 cm3/cm3 to 40% of the total water content at a water content of 0.200 cm3/cm3. The apparent dispersion coefficient decreased from 6 cm2/hour to 1 cm2/hour at water contents of 0.256 and 0.200 cm3/cm3, respectively.
Steady Infiltration from a Ditch: Theory and Experiment
Authors: Batu Vedat 
Published: July 2010

AbstractThe two‐dimensional, steady‐state water flow equation, which is based on the assumption that the hydraulic conductivity is an exponential function of the soil water pressure, is solved for a ditch on the soil surface. The results include expressions describing the distributions of matric flux potential and water content. Measured water contents were compared with this mathematical model and also with the models given by Lomen and Warrick (1974) for a line source, and Warrick and Lomen (1976) for a strip source.
Adsorption of Zn by Fe and Al Hydrous Oxides as Influenced by Aging and pH
Authors: Shuman L. M. 
Published: July 2010

AbstractZinc solutions were equilibrated with both fresh and aged Fe and Al hydrous oxides to measure Zn adsorption. The data conformed to the Langmuir isotherm, and the Langmuir coefficients for Zn adsorption capacities and bonding energies were determined. The adsorption capacities for the aged Fe oxide (goethite) and the aged Al oxide (gibbsite) were the same. The adsorption capacities for both of the fresh oxides (amorphous) were about 10 times those for the aged oxides which corresponded to a 10‐fold difference between their respective CEC's and surface areas. The bonding energies for Zn for the fresh Al oxide were three times that for the fresh Fe oxide, but the bonding energies for the two aged oxides were the same. Bonding energies were directly related to adsorption capacities. The inflection points on the Zn adsorption vs. pH curves were between pH 5 and 6 for both oxides.
Kinetics of Salt Release from a Saline Soil
Authors: Jurinak J. J. , Whitmore J. C. , Wagenet R. J. 
Published: July 2010

AbstractThe kinetics of salt release from simulated saline sediments was studied to ascertain the potential of sediments as a diffuse source of salinity. Two rate equations were derived, both based on the premise that dissolution was a diffusion controlled process. The equations were ln (1 − C/Cs) = ‐kt and C = k′t1/2, where c is the concentration at any point in the bulk solution, cs is the equilibrium concentration of the soluble soil minerals, t is time, k is the first‐order rate constant, and k′ a proportionality constant. Kinetic data were obtained from a saline typic torriorthent soil derived from Mancos shale in the Price river Basin, Utah. During the initial 72 hours of reaction, dissolution can be described by three, diffusion controlled, reactions. Increasing particle size decreased the rate of reaction. Both derived equations were equally effective in describing salt release.
Efficient and Inefficient Use of Phosphorus by Sorghum
Authors: Brown J. C. , Clark R. B. , Jones W. E. 
Published: July 2010

AbstractTwelve (Sorghum bicolor L. Moench) genotypes were grown on acid‐Bladen soil (pH 4.3, P stressed or Al toxic), on limed‐Bladen soil (pH 5.2, Cu stressed), and on alkaline Quinlan soil (pH 7.5, Fe stressed) to determine the effect of P efficiency on use of these clements by the plants. Under P‐stress or Al‐toxicity conditions, the most P‐efficient sorghum genotypes absorbed more 32P than the most P‐inefficient lines and grew normally, while the P‐inefficient plants developed P‐deficiency symptoms. Under Fe‐stress conditions, the most P‐efficient genotypes developed Fe chlorosis, while the most P‐inefficient plants remained green. Under Cu‐stress conditions, one of six genotypes developed severe Cu‐deficiency symptoms, characterized by the accumulation of higher P in the lower leaves, and by lower Fe and Ca in upper leaves of Cu‐stressed plants as compared with Cu‐sufficient plants. Thus, P efficiency in plants may be an asset when P availability limits growth, but it may be a liability when these same plants are subjected to Fe or Cu stress.
The Use of COLE Values for Soil Engineering Evaluation
Authors: Hallberg George R. 
Published: July 2010

AbstractThe coefficient of linear extensibility (COLE) measures soil swelling of natural soil clods and was designed for use in soil genesis and characterization studies. In an attempt to quantify engineering ratings of shrink‐swell potential and to enhance nonagricultural use of soil survey data COLE has been statistically related to arbitrary PVC values. However, the data used to calculate COLE can also be used to directly calculate standard engineering parameters: shrinkage limit (SL), shrinkage ratio (SR), and percentage of volumetric change (VC). These values are more widely understood by the potential user as well. COLE is being measured in standard characterization studies by the National Soil Survey Laboratory and forms an immediate data base for quantification of shrinkage factors for soil survey interpretation. SL, SR, and VC can also be calculated from some pedon characterization data measured before the COLE techniques were put into use.
A Light Interception Method for Measuring Row Crop Ground Cover
Authors: Adams J. E. , Arkin G. F. 
Published: July 2010

AbstractGround cover determined by light interception is the percentage of the soil surface shaded by the plant canopy; i.e., it is a measure of the shadow projected by the plant canopy. The best time to measure ground cover is near solar noon when changes in solar angle result in the least change in ground cover. Measurements of ground covered by canopy foliage are used to evaluate the effectiveness of sunlight interception in photosynthesis and evapotranspiration studies. Ground cover measurements are also useful indicators of the ability of various row crops and cropping systems to intercept rainfall and reduce runoff and erosion.Ground cover of grain sorghum [Sorghum bicolor (L.) Moench], cotton [Gossipium hirsutum L.], sunflower [Helianthus annus (L.)], soybean [Glycine max (L.) Merr.], and corn [Zea mays (L.)] were determined using a meter stick, overhead photography, and photosensitive light sensors.The meter‐stick method is as accurate, faster, simpler, and more economical than any of the other methods used to determine ground cover. There were no significant differences in ground cover determinations using the meter‐stick method, overhead photographs, spatial quantum sensor, or traversing quantum cell. Ground cover was not linearly related to Leaf area index (LAI). A single measurement of ground cover across the plant row (perpendicular) was as accurate as the average of 21 inter‐row measurements parallel to the plant rows.
Oxidation‐reduction Mechanism for Structural Iron in Nontronite
Authors: Stucki J. W. , Roth C. B. 
Published: July 2010

AbstractChemical and physical properties of the clay mineral nontronite were studied as the oxidation state of structural iron was altered. Magnesium exchange capacities (CEC) were determined for different nontronite samples that were unaltered, dithionite‐reduced, and reduced‐reoxidized, and were compared to predicted values calculated from the molecular formula. Observed CEC increased from 125 meq/100 g as predicted with increasing Fe2+ content until the Fe2+ content reached about 53 mmoles/100 g then the CEC remained constant at 142 meq/100 g even though the Fe2+ content was increased further to 139 mmoles/100 g. A two‐step mechanism is proposed that involves first, an initial reduction of Fe3+ to a Fe2+ content of 53 mmoles/100 g with an accompanying increase in layer charge and no structural changes; and second, further reduction to a Fe2+ content of 139 mmoles/100 g during which a constant layer charge is maintained by elimination of structural OH and the coordination number of iron in the octahedral sheet is decreased. The mechanism explains changes in oxidation state and electronic environments monitored by Electron Spectroscopy for Chemical Analysis (ESCA) and Mossbauer spectroscopy. The Fe3+(2p3/2) electron binding energy for oxidized nontronite was observed at 711.8 eV, the Mossbauer isomer shift (I.S.) at +0.44 mm/sec and quadrupole splitting (Q.S.) was zero. Hydrazine‐reduced nontronite showed a binding energy at 711.8 eV for Fe3+ and 708.6 eV for Fe2+. Dithionite‐reduced nontronite shifted the binding energy for Fe3+ to 711.0 eV, and Fe2+ remained at 708.6 eV. Mossbauer I.S. moved down to +0.10 mm/sec for Fe3+ and the Q.S. increased to 1.11 mm/sec, and for Fe2+ the I.S. was centered at 1.17 mm/sec with Q.S. near 2.77 mm/sec. The proposed mechanism also accounts for shifts in infrared vibrational energies for the O‐H stretching mode, the FeO‐H deformation, and the Fe‐OH octahedral vibrational modes.
Correcting Turbidity Interference in the Determination of Phosphorus
Authors: Folsom B. L. , Sunderman H. D. , Hossner L. R. 
Published: July 2010

AbstractTurbidity caused severe interference in the presence of excess ammonium when determining phosphorus by the method of Murphy and Riley. The precipitated complex was isolated and found to be composed of NH4+, antimony, P, and molybdenum in a ratio of 115.8:1.5:1.0:11.6. The combination of Sb and NH4+ in solution during color development caused the turbidity interference. The turbidity could be eliminated by raising the pH above 8.2 with NaOH and boiling to drive off NH4+ as NH3 gas prior to color development or by substituting heat for Sb to develop the characteristic molybdenum blue color.
Tracing the Transformations of Urea Fertilizer during Leaching
Authors: Wagenet R. J. , Biggar J. W. , Nielsen D. R. 
Published: July 2010

AbstractThe transport and transformation of urea, NH4+, and NO3‐ in soil were mathematically described as functions of depth and time, subject to either steady feed or pulse application of N, using relationships derived by assuming diffusion and mass transfer as transport processes and first‐order kinetics as a transformational mechanism. The mathematical model was used to study the enzymatic hydrolysis of urea, nitrification, and denitrification in laboratory soil columns. Urea hydrolysis was found to be independent of initial urea concentration and the O2 concentration of the soil atmosphere. The rate of nitrification under transient N conditions was found to be one order of magnitude greater than the rate of denitrification when there was 20% O2 in the soil atmosphere. Populations of nitrifiers were found to increase in response to successive applications of N.
Erodibility of Selected Clay Subsoils in Relation to Physical and Chemical Properties
Authors: Römkens M. J. M. , Roth C. B. , Nelson D. W. 
Published: July 2010

AbstractPredictions of soil erodibility factors for selected clay subsoils were studied in relation to physical and chemical properties. Erodibility factors were determined from soil erosion rates on scalped surfaces during a series of simulated rainstorms. Subsoils were analyzed for their textural, chemical, and mineralogical composition. A predictive model, derived from previously gathered data of 46 surface soils, was used to determined the significance of soil properties in predicting subsoil erodibility. Weighted linear regression analysis using data from surface soils of the test model and seven selected subsoils indicated that a textural parameter and the percent of iron plus aluminum extractable with citrate‐dithionite‐bicarbonate (CDB) were significant prediction properties of erodibility for these clay subsoils. Multiple linear regression yielded a prediction equation with a coefficient of multiple determination of R2 = 0.90.