bluuebunny/crossref_metadata_2025 huggingface dataset:
A Core Sampler for Puddled Soils
Authors: Sharma P. K. , De Datta S. K.
Published: July 2010

A core sampler was designed to collect undisturbed samples of known volume from the 0‐ to 10‐cm depth in soft‐puddled soils. The instrument is simple, inexpensive to construct, and easy to operate. With practice, the operator can routinely collect a sample from flooded, puddled soils in < 2 min.
Evaluation of the Hot Air Method for Measuring Soil Water Diffusivity
Authors: van Grinsven J. J. M. , Dirksen C. , Bouten W.
Published: July 2010

The Hot Air Method (HAM) is a fairly new and simple method for measuring soil water diffusivity. However, with the introduction of temperatures much higher than originally proposed by Arya et al. (1975), the validity of the underlying assumptions must be questioned. Philip's iterative solution was adapted for desorption out of a semi‐infinite column at constant surface water content to evaluate effects of soil type and boundary water contents on the experimental results. Errors due to deviations from assumed isothermal conditions were evaluated with the Philip and de Vries (1957) theory for the large temperature increases that occur in soil columns during execution of HAM. Evaporation losses and water redistribution during sampling of the soil column were evaluated by simulation. Error analysis indicates that, with the present usage of air temperatures up to 250°C and sampling times of several minutes, HAM does not satisfy the prerequisite assumptions. Reports of favorable results from HAM are probably due to mutual compensation of different errors and to considerable smoothing of experimental results. In spite of its great experimental advantages one should be dissuaded from using HAM unless the experimental errors are minimized and the calculation technique is made objective and reproducible. In this paper some improvements for the experimental procedure are proposed.
Estimating Soil Water Characteristics from Simpler Properties or Limited Data
Authors: Ahuja L. R. , Naney J. W. , Williams R. D.
Published: July 2010

Broad‐based regression equations of Rawls and associates were investigated for estimating the spatially variable soil water content‐matric potential relationships in a 1.6‐ha watershed (Udertic Paleustolls) from soil textural and structural properties, with and without one or two known values of the relationships. Also examined were a simple log‐log line based on two known values and estimates obtained from one known value for each relationship and a complete relationship for one case using the similar‐media scaling concept. The results were compared with measurements on 189 soil cores representing different sites and horizons. With the equations based on soil texture, bulk density and organic matter content, the soil water contents calculated at different matric potentials were generally larger than the measured values. The mean relative error ranged from 8 to 29%, with the standard deviation of errors ranging from 17 to 36%. The model which incorporated one measured soil water content (at −1500 kPa potential) as an additional independent variable, did not improve the results much. The model which incorporated two measured soil water contents (at −33 and −1500 kPa potentials) as additional variables reduced the errors in calculated values considerably. A simple log‐log line drawn through the two known points gave nearly the same accuracy. The estimates from the method of scaling were better than those from the model based on textural and structural variables alone; the mean relative error in the calculated water contents ranged from −0.96 to 9.10%, and the standard deviation of errors was also reduced.
Potassium Fixation Characteristics of Five Southern California Soils
Authors: Shaviv A. , Mohsin M. , Pratt P. F. , Mattigod S. V.
Published: July 2010

Potassium fixation in five southern California soils, sampled at 15‐cm depth increments down to a depth of 105 cm, is reported. The objective was to develop quantitative relationships between K fixation and other soil and solution properties. The experiments were conducted under wet conditions only and the exchangeable cation removal done by BaCl2. Potassium fixation, Kf, was calculated by the difference between total initial K and total final exchangeable plus soluble K in a given system and compared to ΔCEC, the decreases in the initial cation exchange capacity (CECin). The difference between Kf and ΔCEC appeared small, inferring that under wet field conditions, fixation mainly occurred via the mechanism of K entrapment between clay plates. Linear increases of Kf with EP (the ratio of adsorbed K to adsorbed Ca and Mg) and with PAR = {(K+)/[(Ca2+)+(Mg2+)]1/2} were found for each depth for each soil. Potassium fixation also increased with increasing depth. Relating the fractional fixation FKf = (Kf/CECin) to EP and PAR, a more general representation of K fixation was obtained. Fractional fixation and EP showed a linear relationship as FKf = A2 + B2 × EP. Such a correlation resulted in one or two regression lines representative of fixation through a given soil profile to the 105‐cm depth.
Effect of Tillage on the Distribution of Manganese, Copper, Iron, and Zinc in Soil Fractions
Authors: Shuman L. M. , Hargrove W. L.
Published: July 2010

The availability of micronutrients is affected by soil properties such as pH, organic matter content, and clay mineralogy. Some of these properties can be altered by tillage. Therefore, a study was conducted to determine the influence of tillage on the distribution of Mn, Cu, Fe, and Zn among soil fractions. Soil samples were taken at the 0 to 2 cm depth from a long‐term (8 yr) tillage experiment. The treatments were no‐tillage, minimum tillage (fall tillage only), and conventional tillage (spring and fall tillage). Soil samples were fractionated sequentially to determine Mn, Cu, Fe, and Zn in the following fractions: exchangeable, organic, Mn oxide, amorphous Fe oxide, crystalline Fe oxide, and residual. Double acid‐extractable P and Zn, organic matter content, and cation exchange capacity were higher in no‐tillage treatments than in the other tillage treatments. Tillage had more effect on the distribution of Mn and Fe among fractions than on the distribution of Zn and Cu. No‐tillage lowered the Mn in the exchangeable and amorphous Fe oxide fractions and raised Mn in the organic fraction compared to minimum tillage or conventional tillage. Iron in the exchangeable and organic fractions was higher for no‐tillage, while amorphous oxide Fe and residual Fe were lower for no‐tillage compared to conventional tillage. Both Mn and Fe appeared to be shifted by no‐tillage from the oxide and residual forms into the more plant‐available exchangeable or organic forms.
Solubility Relationships of Fluorine Minerals in Soils
Authors: Elrashidi M. A. , Lindsay W. L.
Published: July 2010

Predictive models for the solubility of F minerals were developed and compared to the F solubility measurements made on 109 soils. The experimental findings indicate that AlF3(c) may be the solid phase controlling F solubility in strongly acid soils, CaF2 (fluorite) in slightly acid soils, and KMg3AlSi3O10F2 (fluorophlogopite) in neutral and alkaline soils. Although Ca5(PO4)3F (fluorapatite) alone or in combination with hydroxyapatite is theoretically able to lower F activity in soils below that controlled by any of the aforementioned minerals, solubility measurements on all soils indicate supersaturation with respect to these apatite minerals.
Effect of Aluminum Substitution in Goethite on Phosphorus Adsorption: I. Adsorption and Isotopic Exchange
Authors: Ainsworth C. C. , Sumner M. E. , Hurst V. J.
Published: July 2010

Three sets of goethite samples, pure (α‐FeOOH) and aluminum substituted (α‐[Fe,Al]OOH), were made using different synthesis techniques. Specific surface area ranged from 6.8 to 28.4 × 104 m2 kg−1. Adsorption isotherms were carried out on a surface area basis at pH values ranging from 2.6 to 7.6 for up to 120 h. The specific surface area (determined by Brunauer, Emmett, and Teller N2 adsorption [BET]) depended on the method of synthesis. Phosphate adsorption and isotopic exchange rates were dependent upon mode of synthesis, aluminum substitution, and pH. These results and the accompanying transmission electron micrographs indicate that the chemico‐physical environment during synthesis is a prime determinant of goethite's phosphate adsorption capacity. Aluminum substitution affects specific surface area and extent of phosphate adsorption as greatly as does the synthesis process. The Al samples had faster isotopic exchange rates than their pure counterparts. The rate of exchange increased with increasing surface area (smaller crystal size).
Effect of Aluminum Substitution in Goethite on Phosphorus Adsorption: II. Rate of Adsorption
Authors: Ainsworth C. C. , Sumner M. E.
Published: July 2010

The effects of initial pH, P concentration, Al substitution and method of synthesis on the rate of phosphate adsorption by a series of α‐FeOOH samples containing up to 30 mol % Al were investigated. The results, plotted as first‐order reactions with respect to phosphate disappearance, were characterized by an initial fast phase followed by a pseudo‐first‐order reaction. An approximation of the magnitude of the fast phase was made by extrapolating the first‐order line back to zero time. The difference between the initial and zero time first‐order concentration was then considered to be the magnitude of the rapid phase of the reaction. Phosphate concentration, initial pH, and method of synthesis influenced this parameter. Al substitution had little effect. However, Al substitution did affect the pseudo‐first‐order rate constant at all pH levels and lower P concentrations. It is postulated that Al substitution may sterically hinder the sorption of phosphate. The various synthesis methods affected the magnitude of the fast phase and the pseudo‐first‐order rate. This may be due to the apparent change in the number of active sites related to changes in synthesis as discussed in part 1.
High Humidity‐induced Increase in Water Repellency in Some Sandy Soils
Authors: Jex G. W. , Bleakley B. H. , Hubbell D. H. , Munro L. L.
Published: July 2010

The degree of resistance to water penetration of diverse water repellent soils was found to be controlled by their moisture states. Repellency was found to increase sharply when samples were incubated at 100% relative humidity and to decline when wetted or when incubated at humidities < 90%. A soil which was nonwater‐repellent in the field did not become repellent at 100% relative humidity. A Florida soil (St. Lucie series, hyperthermic, uncoated Typic Quartzipsamments) was used for detailed study. Repellency increase in this sand was temperature dependent and could be eliminated by gamma irradiation, indicating the biological nature of the process. Application of antibiotics prior to incubation suggested that prokaryotic organisms were essential to repellency increase. A dilution study of the St. Lucie soil incubated at 100% relative humidity for various periods revealed that the actinomycete population correlated best with the repellency increase. When incubated St. Lucie sand was investigated by electron microscopy, actinomycetes were found to dominate the visual field. A model for repellency increase and decline, based on soil humidity, is offered.
Scanning Electron Microscopy of Humic Matter as Influenced by Methods of Preparation
Authors: Tan K. H.
Published: July 2010

Scanning electron microscopy (SEM) has recently been used to study the macromolecular structure of fulvic (FA) and humic acids (HA). Differences in soils and sample preparations are believed to produce different results, but little is known to confirm the latter. This investigation was initiated to study the effect of different sample preparations on SEM of humic matter extracted from Omega, Mascotte, Onaway, and Cecil soil series. Using air dry specimens, SEM showed massive sheets of FA and HA with granular surfaces observable at high magnification, similar to those obtained by transmission electron microscopy (TEM). The individual spheres of FA and HA reported in earlier TEM studies appeared in the present SEM analysis only after the samples had been frozen at 0°C in a freezer. Use of a modified liquid‐N procedure, to provide a simpler and faster method, yielded similar tissue‐like structures for FA and HA as with the freon‐liquid‐N method on mica strips. Fulvic acid (pH 3.0) was composed of fiber‐like tissue, whereas HA (pH 7.0) had the appearance of shredded sheets. In both FA and HA, the sheets became prevalent at higher pH values. No effect was noticed by differences in concentration, but differences in soils had a definite influence on the SEM of the humic fractions. The fibers of FA from the Omega soil were coarse and thick, compared to those of the Mascotte soil where they were very fine. In the Onaway series, the FA fibers were medium in size. Fulvic acid from the Cecil soil, on the other hand, had the appearance of shredded or perforated sheets. Six types of structures were distinguished, e.g., fibrous, spheroids connected by fibers, sheets interwoven by fibers, perforated sheets, bladed, and shredded sheets. They were believed to be the result of the method of freezing.
Factors Affecting Oxidation‐reduction Processes in an Oxisol with a Seasonal Water Table
Authors: Couto W. , Sanzonowicz C. , Barcellos A. de O.
Published: July 2010

The weekly fluctuation of the water table was recorded for a period of 2 yr at five sites along a transect of a high plateau area in the Cerrados of Brazil characterized by minimal variation in soil morphology, color, and texture. The soil studied was a Red‐Yellow Latosol, a member of the clayey, oxidic, isohyperthermic family of Typic Acrustoxes. The soil profile to a depth of 200 cm did not show mottling or color chromas of 2 or less at any site. However, the water table was within 0.4 to 2.0 m of the soil surface at some sites for more than 90 d yr−1. Bright platinum electrodes installed at three sites showed only a moderate range of Eh values (700‐500 mV) indicating that no reduction took place in the soil at any depth, in spite of the standing water table. Soil samples taken at the 0‐ to 20‐, 20‐ to 40‐, 40‐ to 60‐ and 60‐ to 80‐cm depth, and subjected to different treatments, were incubated for 90 d at approximately 30 kPa water tension or under waterlogged conditions. Treatments consisted of nutrients, nutrients plus lime, and sucrose at two rates, 0 and 10 g kg−1 of soil. The Fe (II) content measured in moist samples at the end of the incubation period showed that intensive reduction took place under all treatments in soil samples taken from the 0‐ to 20‐ and 20‐ to 40‐cm depths. Samples taken below 40 cm contained a high Fe (II) content only when sucrose was applied. These data suggest that reduction does not occur in the field in the lower part of the soil profile even when a high water table is present due to the lack of a source of energy for microbial activity. It is suggested that the organic matter present in the lower part of the soil profile is too stable and/or too low in available nutrients for the reduction process to take place during the water logging period.
Biotite Kaolinization in Virginia Piedmont Soils: I. Extent, Profile Trends, and Grain Morphological Effects
Authors: Harris W. G. , Zelazny L. W. , Baker J. C. , Martens D. C.
Published: July 2010

Biotite kaolinization was examined for acidic, well‐drained Virginia Piedmont soils with respect to extent, profile trends, and grain morphological effects. Fifty‐eight samples from 16 profiles were treated to remove Fe‐oxides, fractionated by particle size, and examined mineralogically using optical microscopy and x‐ray diffraction (XRD). Selected samples were examined by infrared (IR) spectroscopy, differential scanning calorimetric (DSC), scanning electron microscopy (SEM), and Hg‐intrusion porosimetry. All profiles contained kaolinized biotite sand grains and had kaolinite‐dominated clay fractions. Vermiculite was a minor component of most samples. Kaolinization increased with decreasing particle size and, for some profiles, with decreasing depth. Individual sand‐sized grains commonly contained both biotite and kaolinite. Kaolinized grains had lighter colored, duller (001) cleavage surfaces, and more pores than unaltered biotite grains. Pores extended from the edges inward, exposing new surfaces to soil solution thereby fostering continued kaolinite encroachment. The pore volume difference between kaolinite and biotite specimens was only slightly greater than the calculated difference based on a 1:1 layer‐for‐layer replacement of biotite by kaolinite.
Weathering Assessment of Quartz Grains: A Semiquantitative Approach
Authors: Darmody R. G.
Published: July 2010

This paper details the development of a technique to assess the relative weathering state of quartz grains as revealed by scanning electron microscopy (SEM). This approach considers the criticisms leveled against environmental assessments based on SEM observations. The method uses only one size fraction of grains to eliminate size dependent surface texture variability. Operator bias is removed by coding specimens. A semiquantitative approach is used: five grain surface features indicative of “weathering” and five indicative of “freshness” are observed on each grain. A binary scoring system is used where a negative point is assigned for the presence of a weathering feature and a positive point is assigned for the presence of a freshness feature. A zero is assigned for each absent indicator feature. Summing the points gives the weathering class (WC) for a grain. The mean WC for 15 to 30 grains is the weathering classification for a sample. This systematic approach is an improvement over qualitative assessments and allows for statistical analysis of the data.
Determining Soil Hydraulic Properties from One‐step Outflow Experiments by Parameter Estimation: II. Experimental Studies
Authors: Parker J. C. , Kool J. B. , van Genuchten M. Th.
Published: July 2010

Unsaturated hydraulic properties of four soils of varying particle size distributions were evaluated by determining values of the five parameters in van Genuchten's (1980) hydraulic model. Saturated conductivities (Ks) and saturated water contents (θs) were directly measured and values of residual water content (θr) and the parameters α and n were evaluated by a nonlinear inversion method to minimize various objective functions. Method I uses an objective function involving sums of squared deviations between measured cumulative outflow with time Q(t) for one‐step pressure desorption and numerically simulated outflow from saturation to a final pressure head h = − 10 m. Method II supplements Q(t) data with the measured equilibrium water content θ at h = − 150 m, while Method III employs equilibrium θ(h) data only. Method I yields the most accurate description of Q(t) and the independently determined hydraulic diffusivity D(θ). A fair description of θ(h) is obtained within the range of the one‐step experiment but at lower θ predictions are less reliable especially for finer‐textured soil. Method II extends the range of validity of the predicted θ(h) to lower θ with generally small effects on predicted D(θ) and Q(t). Method III gives the best description of θ(h) but at the expense of accuracy in Q(t) and D(θ). Implications for routine evaluation of soil hydraulic properties are discussed.
Effects of Drying Treatments on Porosity of Soil Materials
Authors: Thompson Michael L. , McBride John F. , Horton Robert
Published: July 2010

The effects of three drying techniques on total porosity and pore size distribution of soil materials were studied by Hg intrusion porosimetry. The three soils investigated had different clay contents (21%, 35%, and 44%), but the clay fraction of each was dominated by montmorillonite. Some samples were dried in an oven at 40°C for 7 d; some samples were quick‐frozen in liquid N and lyophilized; some samples were dried by acetone vapor exchange and immersion, followed by evaporation of the acetone. Both undisturbed and compacted samples were investigated. The three drying techniques caused a reduction in sample total porosity ranging from 3 to 52%. Freeze drying usually caused the least change in total porosity. Although materials highest in clay shrank the most, there was no other discernible relationship between shrinkage and clay content. Freeze‐dried samples had the greatest volume of porosity in the 0.2‐ to 2‐ µm equivalent pore radius (epr) range, whereas acetone‐dried samples had the greatest volume of porosity in the 0.02‐ to 0.2‐ and 0.2‐ to 2‐µm epr ranges. Pore size distributions of oven‐dried samples varied from soil to soil. The consistency of pore size distributions in freeze‐dried materials strongly suggests that pores were deformed by ice crystals either during or after freezing of the samples. In the epr range of 0.002 to 0.02 µm, acetone‐dried samples had porosities similar to oven‐dried samples.
Boron Adsorption on Aluminum and Iron Oxide Minerals
Authors: Goldberg Sabine , Glaubig R. A.
Published: July 2010

Boron adsorption behavior was investigated on various crystalline and x‐ray amorphous Al and Fe oxide minerals. Adsorption increased at low pH, exhibited a peak in the pH range 7 to 8, and decreased at high pH. The magnitude of B adsorption was much greater for the x‐ray amorphous materials. Since B adsorbs specifically on Al and Fe oxide minerals, the constant capacitance model containing a ligand exchange mechanism was used to describe its adsorption behavior. The constant capacitance model was able to represent B adsorption on all minerals over the entire pH range studied (3–12) using the same set of surface complexation constants. With the exception of amorphous Al oxide, B adsorption on these oxide minerals could be successfully described by optimizing only the B surface complexation constant. Other nonexperimental parameters were held fixed at values identical to those previously used in modeling phosphate, silicate, and selenite adsorption on Al and Fe oxide minerals.
Ethylene Biosynthesis in Soil: II. Kinetics and Thermodynamics in the Conversion of 1‐aminocyclopropane‐1‐carboxylic Acid to Ethylene
Authors: Frankenberger W. T. , Phelan Patrick J.
Published: July 2010

Kinetic analyses were performed to characterize the conversion of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) to ethylene (C2H4) in soils. Application of three linear transformations of the Michaelis‐Menten equation indicated that the Km values varied slightly among soils, but were similar in magnitude. By using the Lineweaver‐Burk plot, the Km values in three soils ranged from 2.7 to 6.1 (avg = 4.8) mM and Vmax values ranged from 3.9 to 16.5 mmol of C2H4 released kg−1 soil 48 h−1. The activation energy (Ea) and enthalpy of activation (ΔH*) values, expressed in kJ mol−1, ranged from 35.4 to 70.5 (avg = 49.4) and 32.8 to 67.9 (avg = 46.8), respectively. The Q10 values within a temperature range of 5 to 50°C ranged from 1.52 to 2.60. A direct relationship was established between soil pH of 20 unbuffered surface soils and ACC enhanced‐C2H4 production, but no such relationship was found with any other soil parameter tested including organic C, total N, CEC, and texture. Antibiotic treatments of soils revealed that both fungistatic and bacteriostatic agents were effective in inhibiting (25–82%) ACC derived‐C2H4 production in soils indicating that both major groups are active C2H4 producers.
Puddling Influence on Soil, Rice Development, and Yield
Authors: Sharma P. K. , De Datta S. K.
Published: July 2010

The effects of puddling on soil physical properties, percolation losses of water and nutrients, and nutrient uptake and grain yield of IR36 rice (Oryza sativa L.) in an Andaqueptic Haplaquoll and a Lithic Hapludoll were evaluated in a field experiment. Puddling decreased the bulk densities of both soils in the top 0.1‐m layer by about 30%, but the differences in bulk density between puddled and nonpuddled soil narrowed with time. In the first soil, mechanical strength at 1 d after transplanting (DT) and at 60 DT was the same for both puddled and nonpuddled soils and was <0.3 MPa in the top 0.15‐m layer. In the second soil, it was significantly lower in puddled plots at 1 DT, but the differences between puddled and nonpuddled plots were not significant at 60 DT. Puddling decreased percolation rate by > 70% in the second soil but its effect on percolation rate was negligible in the first. It decreased seasonal water losses by percolation by about 0.03 m in the first soil and by 0.48 m in the second. Puddling decreased significantly the saturated hydraulic conductivities (Ks) of the surface layer in the second soil. In the top 0.15‐m layer, puddling decreased maximum temperatures and diurnal temperature amplitudes in the second soil, but caused no measurable differences in the first. Puddling decreased the redox potential (Eh) of both soils and increased Fe and Mn solubilities. In puddled soil, at the 0.3‐m depth, soil‐solution concentrations of Mn and Fe were higher and those of NH+4‐N, P, K, and Zn comparable to those in nonpuddled soil. The concentration of NO‐3‐N in puddled soil was either comparable to or lower than that in nonpuddled soil. In the first soil, puddling significantly decreased leaching losses of NO‐3‐N; in the second, it decreased leaching losses of NO‐3‐N, NH+4‐N, P, K, and Zn. Puddling significantly increased grain yield in both soils. Total nutrient uptake by rice increased significantly with puddling in both soils. Higher percolation rates did not improve soil productivity, but increased leaching losses of water and plant nutrients. Bulk density and soil strength were the main factors affecting grain yield.
Comparative Effects of an Organic and Inorganic Nitrogen Source in Flooded Soils
Authors: Westcott M. P. , Mikkelsen D. S.
Published: July 2010

The availability of N from organic and inorganic sources in soils is controlled by contrasting microbiological processes. Nitrogen from an added organic source is made gradually available through mineralization whereas immobilization and N loss mechanisms act to decrease inorganic‐N availability with time. To define these initial processes, it is necessary to trace the availability of N from both added and native sources and to measure biological activity while varying a controlling factor such as temperature. A laboratory incubation study was designed to compare (NH4)2SO4 and vetch as added N sources in a flooded soil (Clear Lake clay, Typic Pelloxererts, fine, montmorillonitic, thermic). Nitrogen‐15 labeled materials were added at rates of 0, 50, or 100 µg N/g in factorial combination to 50 g samples of soil and placed in vessels forming columns 10‐ to 12‐cm deep. Temperature regimes of 20, 25, and 30°C were utilized. Available (soluble and exchangeable) NH+4‐N and CO2 production were periodically measured over a 30‐d incubation time. Vetch‐N underwent a gradual mineralization paralleling that of soil‐N. Levels of total NH+4‐N in the vetch treatments were positively affected by temperature and showed a highly significant correlation with CO2 production. Levels of total (labeled + unlabeled) NH+4‐N were consistently higher throughout the incubation period in the (NH4)2SO4 treatments as compared to vetch treatments at equal rates of addition. Labeled (NH4)2SO4‐N rapidly disappeared from the available form, however, and a simultaneous “priming effect” on soil—N mineralization occurred. These two events were quantitatively correlated. The priming effect was not correlated with CO2 production. These findings support the concept that the priming effect of labeled fertilizer‐N on soil‐N mineralization is an apparent effect due to the interchange of labeled available‐N with unlabeled organic‐N with no net effect on N mineralization.
Geophysical Techniques for Reconnaissance Investigations of Soils and Surficial Deposits in Mountainous Terrain
Authors: Olson C. G. , Doolittle J. A.
Published: July 2010

Two geophysical techniques—ground‐penetrating radar (GPR) and seismic refraction—were assessed for their capabilities in reconnaissance studies of soil characteristics, depth to the water table, and depth to bedrock beneath surficial deposits in mountainous terrain. Ground‐penetrating radar had the best near‐surface resolution in the upper 2 m of the profile and provided continuous interpretable imagery of soil profiles and bedrock surfaces. Where thick colluvium blankets side slopes, the GPR could not consistently define the bedrock interface. In areas with clayey or shaley sediments, the GPR is also more limited in defining depth and is less reliable. Seismic refraction proved useful in determining the elevation of the water table and depth to bedrock, regardless of thickness of overlying material, but could not distinguish soil‐profile characteristics. Although both techniques provide adequate information for reconnaissance purposes, these techniques have a greater probability of success in areas where there is some subsurface information. Independent use of any one method is advised only where ground control is well documented.
Effects of Tillage and Rainfall Simulation Date on Water and Soil Losses
Authors: Andraski B. J. , Mueller D. H. , Daniel T. C.
Published: July 2010

Time of data collection relative to recent tillage may influence results of studies comparing water and soil losses among tillage systems. In this study a rainfall simulator was used at various times during the growing season over a 4‐yr period: (i) to compare water and soil losses from conventional (moldboard plow; CN) and three conservation tillage (CT) treatments: chisel plow (CH), till‐plant (TP), and no‐till (NT) and (ii) to observe major trends in runoff volumes as a function of rainfall simulation date. Above‐ground portions of corn (Zea mays L.) plants were removed prior to rainfall simulation. Trials were conducted in September 1980, June and July 1981, October 1982, and June and July 1983. Runoff volumes for CT treatments were consistently less than those observed for CN. For CT treatments, the volume of runoff (per unit rainfall) averaged 11, 20, and 52% lower than that observed for CN for the June 1983, July 1981 and 1983, and October 1982 sampling periods, respectively. Only the CH treatment significantly reduced runoff relative to CN soon after planting. Among CT treatments, CH was significantly more effective in reducing runoff in September 1980. For the remaining sampling periods, differences among CT treatments were not significant. An increase in residue cover consistently resulted in a decrease in sediment concentrations and, most often, a decrease in soil loss. Across all sampling periods, the NT treatment consistently decreased soil loss by 80 to 90% relative to CN, while soil losses for the CH and TP treatments varied, ranging from about 45 to 90% less than those for CN. Only in September 1980 did low runoff for CH result in soil loss which was less than that observed for NT.
The Selection Erosion of Plant Nutrients in Runoff
Authors: Sharpley A. N.
Published: July 2010

The enrichment of several P forms (Bray I, labile, inorganic, and organic), N, C, and K in runoff sediment was investigated for six soils of varying physical and chemical composition, using simulated rainfall (60 and 120 mm h−1). Differing enrichment ratios (ER) for C, N, and organic P (2.00, 1.61, and 1.47 avg for the six soils) indicate that erosion may reduce the C/N/organic P ratio of the remaining surface soil. Average ERs, for Bray I (2.45) and labile P (2.89) were significantly greater than for the other P forms (1.48). This was attributed to less aggregation of sediment compared to source soil for the major proportion (70%) of the runoff events studied. Phosphorus desorption‐sorption characteristics, buffer capacity (1.49), sorption index (1.56), equilibrium P concentration (1.80), and exchangeable K (2.46) were also enriched in runoff sediment compared to source soil. The logarithm of ER for each P form, N, C, and K was related to the logarithm of soil loss, which ranged from 10 to 800 kg ha−1. Statistically significant differences between regression equations for each nutrient indicate that more than one equation is needed to estimate different nutrient ERs. Nutrient ER was related to clay and specific surface area ER of the sediment. This is to be expected as the nutrients described are chemically associated with clay‐sized particles. The potential use of ERs in estimating the effect of erosion on soil fertility is discussed.
Recording Cone Penetrometer Developed in Reclamation Research
Authors: Hooks C. L. , Jansen I. J.
Published: July 2010

A constant rate cone penetrometer has been developed for use in a strip mine reclamation project at the Univ. of Illinois. The device is capable of recording soil strength profiles to a depth of 112 cm. (44 in.). It utilizes a tractor‐mounted hydraulic coring machine as a source of movement. A chart recorder and data acquisition system are operated by 12 V DC electrical power. The penetrometer is effective in detecting soil layers where compaction is likely to inhibit root system development. It is useful in measuring soil strength in mine soils where the amount and depth of compaction may vary due to reclamation methods. Differences in soil strength may prove to be a clue to crop performance on reclaimed land.
Effect of Organic Acids on Aluminum Toxicity in Subsoils
Authors: Hue N. V. , Craddock G. R. , Adams Fred
Published: July 2010

Aluminum has long been recognized as a major limiting factor for root growth in acid subsoils, but little has been done to delineate toxic and nontoxic forms of soil‐solution Al. In an effort to determine if the presence of organic acids in soil solutions affected Al phytotoxicity, short‐term, split‐root experiments were conducted with cotton (Gossypium hirsutum L.) taproots as the growth indicator. Based on pure solution experiments, short‐chain, carboxylic acids can be divided into three groups as Al detoxifiers: (i) strong (citric, oxalic, tartaric), (ii) moderate (malic, malonic, salicylic), and (iii) weak (succinic, lactic, formic, acetic, phthalic). The Al detoxifying capacities of these acids were positively correlated with the relative position of OH/COOH groups on their main C chain, positions that favored the formation of stable 5‐ or 6‐bond ring structures with Al. In addition, analyses of soil solutions from several eluviated acid horizons (E, EB, BE) revealed the presence of several organic acids whose concentrations were generally higher in forested than in cultivated soils. Based on these concentrations, total solution Al (as measured by ICAP) was partitioned into monomeric Al (Al3+ + hydroxy‐Al species) and complexed Al (Al‐organic acid complexes). The latter accounted for 93 and 76% of the total solution Al concentrations of the two acid subsoils into which elongation rate of cotton taproot was studied. Root growth was significantly correlated with monomeric Al but not with total Al in soil solutions.
The Spatial Variability of Nitrogen‐15 and its Relation to the Variability of Other Soil Properties
Authors: Selles F. , Karamanos R. E. , Kachanoski R. G.
Published: July 2010

The spatial variability of natural 15N abundance of a cultivated Chernozemic soil and its native prairie counterpart were smaller than that of total N, organic C, and the C/N ratio. Further, the number of samples required to estimate the true mean of total N with a given precision at various probability levels were twofold those required to determine the mean 15N abundance in both soils. The variability of organic C was > 10 times that observed for total N. The results of this study indicate that the spatial variability of the natural 15N abundance of total soil N in the surface horizons may reflect the isotopic composition of the nitrogenous substances entering the soil system or changes in the isotopic composition of soil N due to humification processes, probably induced by variations in topographic and microrelief features of the soil.
Simultaneous Determination of Moisture, Organic Carbon, and Total Nitrogen by Near Infrared Reflectance Spectrophotometry
Authors: Dalal R. C. , Henry R. J.
Published: July 2010

Near infrared diffuse reflectance spectrophotometry, within the wavelength range 1100 to 2500 nm, was investigated for use in the simultaneous prediction of the moisture, organic C, and total N contents of air‐dried soils. An infraAlyzer 500 C (Technicon Instruments Corp.) scanning spectrophotometer was used to obtain near infrared reflectance of soils at 2‐nm intervals. Calibration equations for each of the soil constituents studied were based upon selection of the best combination of three wavelengths in a multiple regression analysis. The wavelengths selected for moisture, organic C, and total N, respectively, were 1926, 1954, and 2150 nm, 1744, 1870 and 2052 nm, and 1702, 1870 and 2052 nm. The standard errors of prediction for finely ground samples (<0.25 mm) from the top layers (0‐0.1, 0.1‐0.2, 0.2‐0.3, 0.3‐0.6 m) were 0.58, 0.16, and 0.014% for moisture, organic C, and total N, respectively. The standard errors of prediction, however, were much larger for coarsely ground soils (<2 mm), soils containing low amounts of organic C (<0.3%) and total N (<0.03%), and for those with a wide range in colors. Within a narrow range in soil color and at moderate amounts of organic matter (0.3–2.5%C), the near infrared reflectance technique provides a rapid, nondestructive, and simultaneous measurement of moisture, organic C and total N in soils
Use of Boundary Lines in Establishing Diagnostic Norms
Authors: Walworth J. L. , Letzsch W. S. , Sumner M. E.
Published: July 2010

Whether utilizing a critical value or a nutrient balance system such as the Diagnosis and Recommendation Integrated System (DRIS) for interpreting plant tissue composition, determination of accurate optima is of paramount importance. Two procedures for determining such optima, one using the mean of a high yielding population, the second establishing yield maxima at all nutrient values (henceforth termed the boundary line approach) were contrasted. Ear leaf nutrient composition and associated yield information were collected on over 8000 maize (Zea mays L.) samples from around the world. Values of N/DM, P/DM, K/DM (DM = dry matter), P/N, N/K, and K/P as well as the DRIS indices for N, P, and K were plotted against grain yields. Boundary lines confining the resultant scatters of points were then mathematically described. The boundary lines define yields that may occur under a given set of conditions and can be used to determine plant tissue optima, or as a yield specific alternative to the conventional critical value system. In addition, the maximum yield possible at any given compositional value may be predicted from boundary lines. A comparison of the optima determined via the boundary line approach and those estimated by the mean of the high yielding population revealed extremely small differences indicating that either method is acceptable for estimating these parameters.
Effect of Fertilizer Phosphorus Placement Depth on Winter Wheat Yield
Authors: McConnell S. G. , Sander D. H. , Peterson G. A.
Published: July 2010

Field studies were conducted with winter wheat (Triticum aestivum L. ‘Centurk 78’) at nine locations in southwestern, central, and eastern Nebraska in 1982 and 1983 to determine the effect of phosphorus (P) placement depth (0, 5, 10, and 15 cm). As a comparison to these depths, seed placed P, soil surface placed P, and no P treatments were used. A rate of 11 kg P ha−1 was applied. Soil great groups were either Argiustolls or Argiudolls with surface soil Bray and Kurtz no. 1 P levels ranging from 4 to 9 mg kg−1 and pH values ranging from 5.5 to 7.5. Grain yield was increased by added P in both years though magnitude of response varied at different locations. A linear and quadratic response to depth was evident in both years, though variation occurred between locations. Optium depths of P placement for maximum grain yield occurred at 11.9 cm in 1982 and 10.4 cm in 1983. No differences between either the best depth (10 cm) and seed treatments or the surface and seed treatments were found, indicating that, depending on management situations, these methods of P application could be used interchangeably. Total P uptake was increased by P applications in a manner similar to grain yield. Phosphorus uptake of the seed treatment and the best depth treatment at several growth stages (Feekes' stages 2.0, 6.0, 10.0, 10.5, and 11.4) was compared. An early advantage (stage 2.0) of the seed treatment was not evident at harvest, indicating that early P uptake is not necessary for maximum yield. The number of heads and seed weight were both increased due to applied P in both years and seed weight responded linearly to depth in 1982. No effect on the seed number per head was found.
Earthworms as a Factor in the Reduction of Soil Crusting
Authors: Kladivko Eileen J. , Mackay Alec D. , Bradford Joe M.
Published: July 2010

Surface soil crusting after heavy rainfall is a problem on many cultivated soils. The objective of this study was to investigate the effect of earthworms (Lumbricus rubellus) on the aggregate stability and infiltration rate of a soil and then assess the susceptibility of this soil to surface crusting. The effect of 0, 15 (250 m−2), or 30 (500 m−2) earthworms pot−1 on a Raub silt loam (Aquic Argiudolls) to which no, soybean [Glycine max (L.) Merr.] or corn (Zea mays L.) residue had been added was studied in 16‐L pots over a 54‐d period in the greenhouse. Earthworms increased both mean weight diameters (MWD) and water‐stable aggregates > 2mm when determined on initially moist soil. In the absence of earthworms, steady‐state infiltration rates on the Raub soil were 22 µm s−1 (8 cm h−1). Addition of 15 and 30 earthworms pot−1 to soil containing crop residues, increased infiltration rates to 181 and 328 µm s−1 (65 and 118 cm h−1), respectively. The susceptibility of the undisturbed soil in the 16‐L pots and of sieved, repacked soil to surface crusting under simulated rainfall was evaluated by measuring corn seedling emergence. Ten days after planting and simulated rainfall (6.25 cm h−1), 85 to 100% of corn seedlings had emerged in the undisturbed soil in which earthworms were active, whereas in the absence of earthworms only 50 to 52% of seedlings had emerged. When the sieved soil that had received residues and earthworms was exposed to simulated rainfall, 40 to 73% of seedlings had emerged at 10 d, and by 16 d 80 to 88% had emerged. This compares with only 38% emergence in soil to which neither residue nor earthworms was added. Through their feeding, casting, and burrowing activity, earthworms are an important factor in the reduction of surface crusting.
Binding of Ionic and Neutral Herbicides by Soil Humic Acid
Authors: Madhun Yousef A. , Freed V. H. , Young J. L.
Published: July 2010

The gel filtration method of Hummel and Dreyer has been used for the study of binding of bromacil (5‐bromo‐3‐sec‐butyl‐6‐methy‐luracil), diuron [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea], chlortoluron [3‐(3‐chloro‐4‐methylphenyl)‐1,1‐dimethylurea], simazine (2‐ chloro‐4,6‐bis‐ethylamino‐s‐triazine), glyphosate [N‐(phosphonomethyl) glycine], and diquat (1,1‐ethylene‐2,2‐bipyridylium ion) by humic acid. The chromatographic method was found germane for the study of the ionic, as well as the nonionic herbicides. The results expressed as the number of moles of herbicide complexed per unit weight humic acid indicated the utility and reliability of the procedure for the quantitative evaluation of binding. Valid quantitative data on the interaction of herbicides with humic acid would be indispensable for the assessment of these chemicals mobility and transport in soil and water environments.
Analysis of Humic Acids by Solution and Solid‐state Carbon‐13 Nuclear Magnetic Resonance
Authors: Schnitzer M. , Preston C. M.
Published: July 2010

Eighteen humic acids (HA's) were characterized by chemical analyses, infrared (IR) and electron spin resonance spectra, and by solution and solid‐state cross polarization magic‐angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR). The main objectives of this investigation were: (i) to compare the solution and solid‐state 13C NMR spectra of the HA's; (ii) to examine effects of different delay times (D1) on the solution spectra; and (iii) to find reasons for the failure of 13C NMR to detect the presence of significant concentrations of phenolic C in unmethylated HA's. Compared to solution spectra, CPMAS spectra consisted of relatively few, broad bands, indicative of considerable overlapping of individual signals, especially in the aliphatic regions. Proportions of aliphatic C determined by solution 13C NMR at D1 = 0.74 s were greater than those obtained at D1 = 1.90 s and by CPMAS 13C NMR (where D1 = relaxation delay). By contrast, proportions of aromatic C and aromaticities were greatest at D1 = 1.90 s. The highest values for CO2H groups were obtained by CPMAS 13C NMR and approached total acidities; values measured by solution 13C NMR at D1 = 1.90 s were intermediate, while those determined by solution 13C NMR with D1 = 0.74 s were the lowest and closest to CO2H concentrations determined chemically. Because the presence in HA's of significant concentrations of phenolic OH groups has been confirmed by several independent methods, it is possible that in 13C NMR spectra of HA's, signals arising from phenolic C are shifted downfield so that they overlap with resonances of C in CO2H groups. The net result is that CO2H groups are overestimated and phenolic OH groups underestimated.
Equations for Determination of Nitrogen‐15 Labeled Dinitrogen and Nitrous Oxide by Mass Spectrometry
Authors: Mulvaney R. L. , Boast C. W.
Published: July 2010

In mass spectrometric procedures recently developed for determination of 15N‐labeled dinitrogen (N2) and nitrous oxide (N2O) evolved from soils, calculations are performed to determine the mole fraction of 15N in the N pool from which this N2 or N2O was derived (15XN), and a fraction proportional to the amount evolved (d). The equations originally derived for these calculations are based on several approximations and are so simple that they can easily be performed using a handheld calculator. Modern ratio mass spectrometers are usually equipped with an on‐line programmable calculator or computer to process the digital output from the integrating ratiometer, which has made it practical to calculate 15XN and d using equations based on fewer approximations than the equations previously derived. Refined versions of the equations are derived in this paper. The refined equations are much more complicated than the original equations, but they are more accurate and permit the use of fertilizers containing <20 atom % 15N in studies of denitrification.