bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Factors Controlling Soil Organic Matter Levels in Great Plains Grasslands
Authors: Parton W. J. , Schimel D. S. , Cole C. V. , Ojima D. S.
Published: July 2010

We analyzed climatic and textural controls of soil organic C and N for soils of the U.S. Great Plains. We used a model of soil organic matter (SOM) quantity and composition to simulate steady‐state organic matter levels for 24 grassland locations in the Great Plains. The model was able to simulate the effects of climatic gradients on SOM and productivity. Soil texture was also a major control over organic matter dynamics. The model adequately predicted aboveground plant production and soil C and N levels across soil textures (sandy, medium, and fine); however, the model tended to overestimate soil C and N levels for fine textured soil by 10 to 15%. The impact of grazing on the system was simulated and showed that steady‐state soil C and N levels were sensitive to the grazing intensity, with soil C and N levels decreasing with increased grazing rates. Regional trends in SOM can be predicted using four site‐specific variables, temperature, moisture, soil texture, and plant lignin content. Nitrogen inputs must also be known. Grazing intensity during soil development is also a significant control over steady‐state levels of SOM, and since few data are available on presettlement grazing, some uncertainty is inherent in the model predictions.
Variability of Infiltration in a Field with Surface‐sealed Soil
Authors: Ben‐Hur M. , Shainberg I. , Morin J.
Published: July 2010

The infiltration rates (IR) for water were measured at 30 random sites within a 1‐ha field by sprinkler and flood infiltrometers. A portable rainfall infiltrometer was used to measure the infiltration rate under water‐drop impact conditions, and double‐ring infiltrometers were used to measure IR in flooded conditions. No spatial dependence of the steady‐state IR values measured with the two methods was found. The mean steady‐state IR measured with the flood infiltrometer was 57.8 mm h−1 with a coefficient of variation (CV) of 41.8%. The mean steady‐state IR measured with the sprinkler infiltrometer was 8.6 mm h−1 with a CV of 14.7%. This difference was due to the formation of a soil surface seal from the impact of falling drops. The seal's hydraulic conductivity was much lower and less variable than that of bulk soil. Frequency distributions of the steady‐state IRs measured with the two methods were different; that from the double‐ring infiltrometer had a small deviation to the left, while that of the sprinkler infiltrometer had a large deviation to the right. The distribution of steady‐state sprinkler IR values corresponds with the distribution in the cation exchange capacity (CEC) and exchangeable sodium percentage (ESP) in the field, verifying the known dependence between surface seal formation and the soil CEC and ESP relationship. This dependence was not found for the IR values measured by flooding. No correlation was found between the IR values measured by the two methods. Thus, for soils that seal, it is impossible to predict IR under water drops from measurements under flooding conditions.
Measurement of Waterdrop Impact Pressures on Soil Surfaces
Authors: Nearing M. A. , Bradford J. M. , Holtz R. D.
Published: July 2010

Limited data on pressures induced by waterdrop impact on soil surfaces restricts our understanding the mechanism of soil detachment due to raindrop impact. Impact pressures on rigid surfaces are known but their application to soil surfaces is questionable. This study was undertaken to measure vertical pressures of waterdrop impact on soil surfaces. A 1‐mm diam piezoelectric transducer was developed and measurements of impact pressures as a function of radial distance from drop center were made. Dickinson loam (coarse‐loamy, mixed, mesic Typic Hapludoll) and Ida silt loam (fine‐silty, mixed [calcareous] mesic Typic Udorthent) with bulk densities of 1.0 and 1.2 Mg/m3 and with matric potentials of −0.5 and −2.5 kPa were used. The waterdrop had a diameter of 5.6 mm and a fall height of 14 m. Average peak impact pressures were greatest at a distance of 1.8 to 2.3 mm from center of impact and of the order of 190 to 290 kPa. These stress levels are almost two orders of magnitude less than those for impact on a rigid surface. Much of the difference between soil and rigid cases was due to nonrigid, nonhomogeneous nature of the soil material. The remainder of the difference in stress levels was thought to be due to the effect of soil granularity or to the presence of surface and shear waves generated by impact.
Field Procedure for Estimating Soil Thermal Environments
Authors: Flint Alan L. , Childs Stuart W.
Published: July 2010

Intensive measurements are required to precisely define soil temperature, heat flux, and thermal properties of heterogeneous forest soils. Fifty detailed profiles of temperature, density, and water content were used with the conduction heat flow equation to estimate soil thermal properties for a clearcut harvest area in a mixed conifer forest in southwest Oregon. These profiles were used to determine the accuracy with which soil temperatures could be modeled and the number of soil layers required to characterize a given field site. The soil was modeled as a profile of between 1 and 21 layers of known (measured) volumetric heat capacity and measured initial and boundary conditions. Soil thermal conductivity for each layer was determined for each of 50 datasets using an iterative numerical procedure. The accuracy of the various models was assessed by comparing the error between measured and modeled profiles. For the skeletal soil studied, a numerical model and field measurements of four soil layers proved to be the best combination of accuracy and simplicity. The assumption of a homogeneous (1‐layer) profile was satisfactory in several cases. The need for detailed field measurements was assessed by comparing modeled and measured soil temperature: minimum and maximum temperature, duration of high temperature and low temperature events, and positive and negative heat flux. Models based on measurements from four or more soil layers predicted soil temperature within ±0.3°C of measured values. Models based on two or more measured soil layers were within ± 0.006 MJ m−2 of measured daily positive heat flux.
Determination of the Combined Nitrogen‐15 Content of Dinitrogen and Nitrous Oxide in Air
Authors: Strong W. M. , Austin E. R. , Holt L. S. , Buresh R. J.
Published: July 2010

A method for measuring the total 15N content of an air sample containing 15N‐N2O and 15N‐N2 has been developed. A high voltage arcing process is used to rapidly decompose N2O into N2 and NOx, to randomly distribute the N isotopes between the N2 and NOx pools, and to fix a sample of N2 as NOx. A routine mass spectrometric 15N analysis based on the 29:28 ion signal ratio of either the N2 pool or the NOx sample after conversion to N2 will be equivalent to the 15N content of the original sample. Two methods of 15N analysis were shown to be equally accurate and precise. The air sample may be arced and the N2 analyzed by direct inlet into the mass spectrometer while cryogenically trapping the NOx, or the NOx may be reduced to an NH+4‐N salt that can be stored and analyzed later. If only a small air sample is available, 10 mL of air (at ambient pressure and temperature) can be mixed with ultrapure O2 to a N2/O2 ratio of 9:91 in a 90‐mL arc vessel and arced at atmospheric pressure for at least 150 s to produce sufficient NOx to yield 1 mg of fixed N for mass spectrometric analysis. The arc method measures the combined 15N content of the major gas species produced by denitrification by a single analysis and may be applicable for field studies.
Layer Charge Properties of Smectites and Vermiculites: Tetrahedral vs. Octahedral
Authors: Malla P. B. , Douglas Lowell A.
Published: July 2010

Total layer charge and charge of octahedral sheets of 2:1 soil clays were estimated by combining alkylammonium ion exchange technique and the Hofmann and Klemen effect. The estimation of charge before and after Hofmann and Klemen effect (Li‐saturation and heat treatment) gave the total layer and tetrahedral charge, respectively. The difference of total and tetrahedral charge provided the charge contribution of octahedral sheets, assuming that a complete neutralization of octahedral charge was achieved by Li+ migration during the heat treatment. As much as 50% of the charge was found to be located in the octahedral sheets in soil smectites and soil vermiculites. Clays with total layer charge in the vermiculitic range that accommodated both double (1.8 nm) and single (1.4 nm) interlayers of glycerol in the interlayer spaces formed only double‐layer complexes after Li+ treatment, indicating a reduction in total layer charge, plus a random distribution of charge in both octahedral and tetrahedral sheets of each 2:1 layer. Trioctahedral vermiculites with a total layer charge comparable to the total layer charge of dioctahedral soil vermiculites gave only single layer complexes with glycerol after Mg‐saturation. These sorption characteristics can be explained in terms of Coulomb's law and the higher concentration of negative charge of trioctahedral vermiculites in the tetrahedral sheet compared with dioctahedral soil vermiculites.
Improved Performance of Zero‐Tension Lysimeters
Authors: Radulovich R. , Sollins P.
Published: July 2010

Published collection efficiencies (volume of water collected divided by percolating volume calculated from a water balance) of zero‐tension lysimeters are <10%, suggesting that samples collected by such lysimeters may not be representative of the water percolating downward. By increasing catchment area to 2500 cm2, and by pushing the lysimeter rim upward into the soil, collection efficiency was increased to 36% under grass and 17% under forest; failure rate (proportion of lysimeters yielding <50 mL) was decreased from 60 to 6% under grass and to 23% under forest.
Upper and Lower Bounds of the Ponding Time for Near Constant Surface Flux
Authors: Boulier J. F. , Parlange J.‐Y. , Vauclin M. , Lockington D. A. , Haverkamp R.
Published: July 2010

Upper and lower bounds on the relation between the time course of cumulated infiltration into soil and water content at the soil surface are derived. These estimates can be used specifically to predict upper and lower bounds of the ponding time. The analytical results are derived for mildly varying surface flux. However, the accuracy of the limits is illustrated and discussed for Granoble sand with constant rainfall rates only. A numerical solution is also obtained that yields results outside the range of the more accurate analytical results. This confirms that errors are introduced in the numerical scheme during the early stages of infiltration. Less accurate, but easier to apply, analytical limits are also presented and discussed.
A Mechanism by which Organic Liquids Increase the Hydraulic Conductivity of Compacted Clay Materials
Authors: Brown K. W. , Thomas J. C.
Published: July 2010

The ability of concentrated organic chemicals, with low dielectric constants (E) to increase the hydraulic conductivity of compacted soils has been well documented. This study was undertaken to evaluate a mechanism by which these increases occur. Theory predicts that the spacing between adjacent clay particles diminishes as the E value decreases. Hydraulic conductivity measurements were made in fixed wall permeameters with a range of concentration of organic liquids in water. Marked increases in hydraulic conductivity occurred at concentrations above which the clay flocculated. Smectite d spacings increased when the clay was equilibrated with acetone and ethanol solutions having E values ranging from 65 to 77, but decreased when equilibrated with solutions having E values <35 to 50 as compared to that in water. All three clays tested exhibited reductions in electrophoretic mobility (µ) and the absolute value of the zeta potential|ζ| which would be associated with flocculation at low E values. Relative clay content measurements indicated that all three soils flocculated in solutions with low E values. At E values >49, all clays remained dispersed. When bulk samples were exposed to organic liquids, the volume changes were proportional to the E values of the permeant. The results indicate that when organic liquids or salts are sufficiently concentrated, soil particles will be drawn closer together until the clays flocculate. Thus, changes in the surface electrical properties of the clays cause shrinkage, resulting in cracking and increases in hydraulic conductivity. Flocculation tests and E values may be used as tools to predict the influence of a solution on the hydraulic conductivity of compacted soils.
Adsorption and Oxidation of Phenolic Compounds by Iron and Manganese Oxides
Authors: McBride M. B.
Published: July 2010

The adsorption and oxidation of catechol and hydroquinone by Fe and Mn oxides has been investigated by Fourier transform infrared spectroscopic (FTIR) analysis of the adsorbed molecules and by the measurement of O2 consumption by aqueous suspensions of these oxides. Evidence for direct coordination of catechol and salicylate to surface Fe3+ on iron oxides was obtained by FTIR. The promotion of catechol and hydroquinone oxidation by Fe and Mn oxides was confirmed by measured rates of O2 consumption and by the appearance of Fe2+ and Mn2+ in the solutions. However, only trace levels of soluble Fe2+ were detected, suggesting that oxidation by Fe(III) oxides was catalytic in that electron transfer between the phenols and Fe3+ generated Fe2+, which was rapidly reoxidized by O2. Other adsorbates introduced into these oxide/phenol systems, such as acetate, phosphate, and Cu2+, diminished O2 consumption rates, but the effect was generally attributable to a Iowered pH that inhibited oxidation. A model of surface oxidation by Mn and Fe is presented in which coordination of the organic at the surface is a prerequisite to electron transfer. Oxidation of organics can proceed with or without the uptake of O2, depending largely on pH, which determines the rate of reoxidation of the reduced metal ions by O2. The results emphasize the difficulty in interpreting the effects that chemical buffers have on oxidation reactions at oxide surfaces.
The Effect of Time and Temperature on Nitrogen Mineralization in Arctic Tundra Soils
Authors: Marion G. M. , Black C. H.
Published: July 2010

The objective of this work was to evaluate several mathematical models for describing N mineralization in three arctic tundra soils (Histic Pergelic Cryaquepts) as functions of time and temperature. Intact soil cores were collected in the field and incubated in a laboratory at 5, 15, 25, and 35 °C for 11 weeks. The exponential equation fit the data well at 35 °C but was generally unsuited for describing N mineralization at lower temperatures. The parabolic equation better fit the N mineralization data than the exponential equation except in a few cases where the data appeared to be approaching an asymptote. The parameters of the parabolic equation did not follow simple trends with respect to temperature, however, which made interpolating between experimental temperatures difficult. A second‐order polynomial equation with respect to both time and temperature was evaluated. This empirical equation gave R2 >0.98 in all but one case. The major advantages of the empirical, polynomial equation are that it assumes little about the nature of the N mineralization process, it is flexible, and it is accurate. The temperature data did not follow the Arrhenius relationship nor have a simple overall Q10 value because the mineralization rates at different temperatures did not follow similar trends with respect to time. Only a small fraction of the N that is potentially mineralizable is likely to be mineralized under the prevailing cold temperatures of these arctic soils.
Seasonal Variation of Potentially Mineralizable Nitrogen in Four Cropping Systems
Authors: Bonde Torben A. , Rosswall Thomas
Published: July 2010

The concept of potentially mineralizable N is discussed and data that support the identification of N0 as an active fraction of soil organic N are presented. Aerobic medium‐term incubations (13 weeks) were used to measure the potentially mineralizable nitrogen (N0) in four cropping systems on four different occasions from early spring to late autumn. The cropping systems consisted of barley (Hordeum distichum L.) with no N fertilizers (B0), barley receiving 120 kg N ha−1 yr−1 (B120), meadow fescue (Festuca pratensis Hudson) ley receiving 120 + 80 kg N ha−1 yr−1 (GL), and lucerne (Medicago sativa L.) ley with no N additions (LL). The amounts of N mineralized during the 13‐week incubations (37°C) ranged from 188 to 483 kg N ha−1, and the cropping systems ranked in the order GL > LL > B120 > B0 and showed a steady decline in all systems from spring to harvest and a subsequent increase from harvest to autumn. The seasonal differences were as large as the differences between systems. Three related models were employed to describe the kinetics of N mineralization during the incubations: (i) first‐order, (ii) two‐component (sum of two first‐order models), and (iii) a simplified special case of the two‐component model. In all cases, the special case of the two‐component model offered the best description of the curves of accumulated mineral N. Based on the mineralization course and an observed relationship between literature values of N0 and the rate constant (k), it is hypothesized that the mineralization is mediated by two distinct populations: an opportunistic, mainly immobile, population (bacteria) and a generalistic, mobile one (fungi), and that the k value is influenced both by the amount of substrate and its quality. The fact that the amount of mineralizable N decreases during the growing season and increases in autumn as a result of organic matter input provides evidence for the existence of an active fraction of soil organic matter.
Basin Properties and Postglacial Erosion Rates of Minor Moraines in Iowa
Authors: Burras C. L. , Scholtes W. H.
Published: July 2010

Two minor moraine basins in Story County, Iowa, were examined to determine the extent and effect of postglacial erosion on the present landscape and stratigraphy. Minor moraines are subtle repeating ridge and valley landforms with relief of approximately 2 m. The stratigraphy was examined in this study using grid and transect borings. A mantle of locally derived postglacial sediment blanketed the Late Wisconsinan till in both basins. In places, a strata of coarse diamicton separated the till and sediment. The postglacial sediment was identified primarily on particle size distribution and bulk density. After determining the extent and thickness of sediment in each basin, the sediment volume and mass were calculated. Previously, the Late Wisconsinan till in central Iowa was dated as being deposited 14 000 RCYBP (radio carbon years before present). This age was used to calculate a gross annual rate of postglacial erosion. The basin with modern relief of 2.7 m had a 0.9 Mg ha−1 yr−1 erosion rate and the basin with modern relief of 1 m had a 0.7 Mg ha−1 yr−1 erosion rate.
Landscape Position and Particle‐size Effects on Soil Phosphorus Distributions
Authors: Day L. D. , Collins M. E. , Washer N. E.
Published: July 2010

The objectives of this study were to investigate the effects of pedogenesis and landscape position on (i) the association of total P with particle‐size content and with various particle‐size separates, (ii) relative abundance of different forms of P, and (iii) P distributions between horizons and soils representing five landscape positions on an Ultisol hillslope in northwest Florida. Total‐P content in soil seemed to be directly associated with the amount of clay in the lower landscape positions. This association may be the result of the activity of the mineralogy dominant in the clay fraction. Total P in the clay and P‐fraction values indicated that some P had been redistributed between horizons and possibly between soils on the landscape. Coarser sands commonly had more total P than finer sand fractions. The sand fractions were composed primarily of quartz and ironstone. The amount of ironstone in the sand fraction was probably responsible for the amount of total P. Among P fractions, a large portion of P was in the residual form, especially in lower horizons, implying that the soils are intensely weathered or developed from parent materials that contained considerable residual‐P, which was occluded in sesquioxides prior to deposition of the sediments. The P forms were present in the order of decreasing abundance as residual‐P, Fe‐P, Al‐P, and Ca‐P. Water‐soluble P was not detected in any of the soils.
Phosphorus Redistribution from Cultivated Fields into Riparian Areas
Authors: Cooper J. R. , Gilliam J. W.
Published: July 2010

The accumulation of P in sediments deposited within riparian areas was measured to study the role of these areas as P sinks. The sediments originated from the cultivated fields and forests of the uplands and were deposited during the last 20 to 25 years. The riparian areas were studied in the Atlantic Coastal Plain and consisted of four field‐forest edges, four ephemeral streams and four flood plains of intermittent streams that flowed into a flood plain swamp. Selective sorting and deposition of sand and silt near the field‐forest edge (0–20 m) and clay deposition downstream (1–4 km) on the flood plains and swamps explained much of the total P distribution in the riparian areas. The P in the sediments increased with percent clay, R2 = 0.80. Laboratory measurements of the equilibrium phosphorus concentration (EPC) in flood plain swamp sediments were two to three times higher than P concentrations in the overlying water (1.0 vs. 0.4 µmol P L−1) during high flow stages of winter and spring. During summer and fall the ortho‐P concentrations of isolated pools and base flow ranged from 1.0 to 1.3 µmol P L−1. Approximately 260 kmol of P were deposited in the riparian areas of the 1850 ha watershed during the past 20 to 25 years. The amount of P deposited was equal to the amount estimated to have been removed from the watershed in the drainage water. Thus about 50% of the P leaving agricultural fields appeared to be removed from the runoff water in the riparian areas. Riparian areas between the field edge and a perennial stream were sinks for P because of the continual deposition of fresh sediment from upland areas.
Soil‐water Regimes of a Typic Haplaquoll under Conventional and No‐tillage
Authors: Culley J. L. B. , Larson W. E. , Allmaras R. R. , Shaffer M. J.
Published: July 2010

Computer simulation models are needed to help describe the dynamic nature of soil‐water regimes. A simple water budget and an integrated soil‐plant‐atmosphere simulation model (NTRM) were each evaluated for predicting water regimes under no‐till (NT) and conventional tillage (CN) of a well‐structured soil. Estimates of soil physical properties related to the retention and movement of water, which were required as input for the models, were obtained from laboratory measurements on undisturbed soil cores. An in situ drainage experiment, using Br‐ labeled water, also provided information on field capacity water retention properties. Ponded water containing Br‐ moved rapidly through the surface 0.5‐m profiles of both tillage treatments. Redistribution of the added water was effectively completed within about 8 h. Field capacity matric potentials of both profiles were above −6 kPa. Chromatography theory indicated that the labeled water may have mixed with only 43 and 25% of the initial soil water in the CN and NT profiles, respectively. Despite these observations, both models, which assumed complete mixing within each soil layer, were reasonably satisfactory at predicting soil‐water contents under corn (Zea mays L.) through the 1984 growing season at a southern Minnesota location. Output from the NTRM model agreed better with experimental data showing water contents lower under CN than NT.
Effects of Combinations of Triple Superphosphate and a Reactive Phosphate Rock on Yield and Phosphorus Uptake by Corn
Authors: Chien S. H. , Adams F. , Khasawneh F. E. , Henao J.
Published: July 2010

A combination of finely ground phosphate rock (PR) and triple superphosphate (TSP) represents a method that can improve the agronomic value of PR at a lower cost than would be required to manufacture the conventional, fully acidulated fertilizers from that same rock. A reactive PR from North Carolina was evaluated for its effectiveness as a P source when used in conjunction with TSP at P rates up to 266 mg P kg−1 in a short‐term (6‐week) greenhouse experiment. The soil used was a limed Mountview silt loam (Typic Paleudult) with pH 6.2. As measured by dry‐matter yield and P uptake, P availability from PR appeared to increase with increases in the proportions of TSP to PR in the TSP‐PR mixtures. Although PR alone was less effective than TSP, PR was just as effective as TSP when mixed with TSP at a P ratio of at least 1:1. Because plants responded to both TSP and PR, and because there was an interaction between TSP and PR in the soil, neither water solubility nor total citrate solubility could be used to predict the effectiveness of TSP‐PR mixtures with different P ratios.
Apparatus for Extraction of Undisturbed Samples on Noncohesive Subsoils
Authors: Schuh W. M.
Published: July 2010

A sampler was designed and tested for extracting 60‐ by 53‐mm (length by depth) undisturbed core samples from subsoils. The sampler consists of a sample cylinder “barrel,” and an “adaptor block” for fitting the barrel to the end of a 76.1‐mm o.d. hydraulic probe tube. Samples are taken by augering to the desired depth, and using the tube and sampler assembly to extract the sample. The tube and sampler assembly can also be used with a protective steel anvil to remove samples in shallow subsoils without a hydraulic probe. Samples on sands have been taken as deep as 2.5 m using the hydraulic probe, and as deep as 0.61 m using the anvil and maul method.
Determining Unsaturated Hydraulic Conductivity from Tensiometric Data Alone
Authors: Ahuja L. R. , Ross J. D. , Bruce R. R. , Cassel D. K.
Published: July 2010

A simplified functions approach, presented earlier, for determining the unsaturated hydraulic conductivity of soil from only the field tensiometric data taken during steady infiltration and draining, along with steady infiltration rate, is evaluated further. The assumptions concerning the form of soil‐water characteristics used in the operational equations of the method are recast in an integral form. These assumptions, as well as the intermediate steps in the computation, are tested on the experimental data for shallow as well as deeper depths of two new soil types. One of these soil types has a complex layered profile with texture varying from sandy to clayey, and the other a relatively uniform sandy profile. The final hydraulic conductivities obtained are compared with the values determined by the more rigorous Darcian analysis of the data for three sites. The results show that the assumptions made in the simplified method approximately hold for these soils at the depths tested, as deep as 1.9 and 1.35 m, respectively. The unsaturated hydraulic conductivity values determined by the proposed method are reasonably close to those values obtained by the detailed Darcian analysis for all depths. Large fluctuations in the tensiometric data for certain depths resulted in a large scatter in the conductivity values obtained by the detailed Darcian method, as well as greater discrepancy between the two methods. Practical validity of the basic assumptions of the method and the final results, for shallow as well as depper depths of the new contrasting soil profiles, constitutes significant information that provides confidence in the simplified approach.
Rapid Nondestructive Bulk Density and Soil‐Water Content Determination by Computed Tomography
Authors: Anderson S. H. , Gantzer C. J. , Boone J. M. , Tully R. J.
Published: July 2010

Computed tomography (Ct) is a promising tool that may help provide measurements needed to obtain finer resolution in soil‐water content and bulk density for water uptake studies or detailed investigation of root‐soil interactions. A need exists for a unified method to accurately predict soil bulk density and water content using output from CT. Research was conducted on soil collected from the A horizon of Mexico silt loam (Udollic Ochraqualfs) and the B2t horizon of Crider silt loam (Typic Paleudalfs) to evaluate the relationship between linear attenuation coefficients and volume fraction of soil solids and water. Air‐dry soil (<2 mm) was packed into polyvinyl chloride cylinders at densities between 1.2 and 1.6 Mg/m3 and CT slices or tomographs were taken before and after water was added. The relationship between attenuation coefficients and volume fraction of soil solids was linear for both of the soils evaluated. Parameter values for the Mexico soil compared favorably with those determined on previous data collected from Metea fine sandy loam (Arenic Hapludalfs). Differences in the parameter values for the Mexico and Crider soils were attributed to differences in Fe content. An experiment with Fe added to the Mexico soil was conducted that verified the effect of Fe content on the attenuation coefficients. Approximately 98% of the variation between the attenuation coefficients and volume fraction of soil water was accounted for by using linear regression relationships after correction for swelling. Results from this study indicate that it may be possible to develop a universal relationship for computed tomography data vs. soil bulk density and water content; however, more research is needed to characterize the influence of sample size on the calibration relationship.
Spatial Variability of Remotely Sensed Surface Temperatures at Field Scale
Authors: Yates S. R. , Warrick A. W. , Matthias A. D. , Musil S.
Published: July 2010

Bare soil surface temperatures (BST) and crop canopy temperatures (CCT) were collected from a 1‐ha field in central Arizona using an infrared thermometer to determine whether they were spatially correlated. The measurements were taken from a two‐dimensional random sampling pattern for selected dates and times to investigate the spatial and temporal distribution. Three measures of the correlation distance including two integral scales were calculated. Kriging, which produces the best linear unbiased estimator, was used to show the spatial pattern of the BST and CCT in the field on selected dates. The results indicate that the BST and CCT are spatially dependent random functions with integral scales that varied from 2 to 15 m for wet and dry conditions, respectively. The autocorrelation as the lagged distance approaches zero was greater than 0.4 except under wet soil conditions, where the autocorrelation for the CCT was found to be lower. The results are important because, to date, no geostatistical study has shown that the CCT is a spatially dependent random function.
Temperature Effects on Urea Diffusion Coefficients and Urea Movement in Soil
Authors: Sadeghi A. M. , Kissel D. E. , Cabrera M. L.
Published: July 2010

Urea fertilizer is often applied at the soil surface, where it hydrolyzes and can form NH3. To quantify the volatilization of NH3, the molecular diffusion of urea into the soil must be described. The diffusion coefficient of urea in soil is related to its diffusion coefficient in water, which varies with temperature. We initially regressed the value of the urea diffusion coefficient in water from the international critical tables (ICT) on temperature for the range of 10 to 20 °C. Since surface soil temperatures often fall outside this range, additional values for the urea diffusion coefficients were needed. The capillary tube method of Phillips and Ellis was used to measure the diffusion coefficient of urea in water at temperatures ranging from 0 to 50 °C. The laboratory values obtained for the diffusion coefficient of urea in water were higher, by a factor of 1.5, than the ICT values. A comparison was made between measured values of urea concentration in columns of Richfield and Haynie soils and simulated values using regression equations based on laboratory results (new) and ICT data (old). The new regression equation allowed a better agreement between actual and simulated urea concentrations in soil.
Stimulated Denitrification in the Microenvironment of a Biodegradable Organic Waste Injected into Soil
Authors: Rice Charles W. , Sierzega Philip E. , Tiedje James M. , Jacobs Lee W.
Published: July 2010

Denitrification and the associated processes of nitrification, mineralization, and respiration were studied in the zone around the injection slit in which two fermentation wastes were injected into soil. All processes were stimulated apparently due to the greater availability of N and C and the increased anaerobiosis caused by the greatly enhanced respiration. Under field conditions, denitrification rates as high as 4.9 and 2.3 µg cm−2 h−1 were measured from the cell waste and the spent growth medium, respectively. If extrapolated over the 73‐d period after application, the accelerated denitrification would remove over one‐half of the added N. The rate of CO2 production explained 31.4 to 46.8% of the variation in denitrification, whereas soil moisture explained only 3.6 to 18.9% of the variation. This suggests that respiratory activity created an anaerobic microenvironment making conditions favorable for denitrification. Under laboratory conditions, the loss of N due to denitrification of the cell waste could be reduced by 68% with surface incorporation rather than injection. This was probably due to the cell waste material being applied to a greater volume of soil, thus reducing both the temporal and spatial zones of anaerobiosis. Samples 5 cm away from the injection slit did not have enhanced denitrification rates nor NO‐3 concentrations, suggesting little lateral movement of the applied waste material. The enhanced denitrification response to cell waste C addition emphasizes the importance of respiratory O2 consumption by heterotrophs on denitrification. These results are expected to hold for any waste that is reasonably biodegradable and has a medium to low C/N ratio.
Phosphorus Supply Characteristics of 33 Soils as Influenced by Seven Rates of Phosphorus Addition
Authors: Kovar John L. , Barber Stanley A.
Published: July 2010

Soil P supply to plant roots increases after addition of P fertilizer due to both the increase in soil solution P (Pl) and adsorbed P (Ps) that equilibrates rapidly with Pl. Little information is available on the effect of added P on the concurrent increase in Pl and Ps. The objective of this research was to investigate the relation between P added and increase in Pl and Ps of 33 soils. Surface soils collected from the U. S. and Canada were equilibrated moist for three weeks with seven rates of P ranging from 0 to 655 mg P kg−1. High rates of application occur where P is placed in a small fraction of the soil. Values for Pl were obtained from P analysis of displaced soil solution and values for Ps from a 24‐h extraction with anion exchange resin. For all soils relation of Pl, curvilinear with P addition, x, was described by Pl = axc + d. Values for c, the curvilinearity, varied from 1.03 to 3.15. There was a negative correlation between c and exchangeable Ca (r = −0.65*, significant at the 0.05 probability level) and soil solution P concentration before P addition, Pli, (r = −0.61*). Adsorbed P increased linearly with P addition for all soils, the slope of the relation varying from 0.35 to 0.86. The slope indicates the fraction of added P extracted with the anion‐exchange resin. There was a positive correlation between the slopes and the effective diffusion coefficients, De, for P in the soils (r = 0.47*). There was no significant correlation between c and the adsorption line slope. Development of methods for predicting the effect of added P on Pl and Ps will be useful in quantifying their increase in soil resulting from P addition.
Computer Simulation of Soil Sensitivity to Acid Rain
Authors: Levine Elissa R. , Ciolkosz Edward J.
Published: July 2010

A two‐horizon (A and B) simulation model was used to determine the sensitivity of Pennsylvania soils to acid deposition. The model simulated changes in the soild phase of soils in humid, temperate climates undergoing acidification and cation leaching. The Pennsylvania State Univ. Soils Data Base, and precipitation data provided input to the model. Soils were grouped into sensitivity classes based on the amount of time required for bare, uncultivated, and unlimed soils to reach critical threshold values. Simulation results showed most Pennsylvania soils were either very sensitive or nonsensitive. Sensitive soils were already at the threshold values at the beginning of the simulation run. Nonsensitive soils contained sufficient buffer capacity to withstand present inputs of acid deposition for at least 90 yr. According to the model, changes in soil properties occur in the upper horizons first, and after a lag period, occur in the lower horizons. The number of exchangeable bases was the soil parameter most highly correlated with soil sensitivity due to the acid buffering ability of exchangeable cations. Adding CaCO3 to the simulation of slightly sensitive and very sensitive soils changed them to nonsensitive status by increasing the number of exchangeable bases available for buffering.
Soil Engaging Tool Effects on Surface Residue and Roughness with Chisel‐type Implements
Authors: Johnson Richard R.
Published: July 2010

The site specific nature of optimum tillage systems makes it desirable to provide versatility in tillage performance at a minimal cost. Chisel‐type implements are among the most flexible primary tillage machines, largely due to the range in options for soil‐engaging tools. The objective of this study was to evaluate surface residue and roughness from a full range of shovels, points, and sweeps on both a disk chisel and a chisel plow operated during fall tillage in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] stubble. Effects of operating speed and depth were also examined. Changing soilengaging tools caused remaining spring residue to range from 44 to 59% in corn and from 22 to 54% in soybean stubble. Residue remaining generally ranked from high to low as follows: low crown sweep ≥ medium crown sweep > chisel point > high crown sweep > concave twisted shovels. Sweep and shovel width had only minor effects on surface cover, but similar soil engaging tools on a chisel plow left about 10% more surface cover than on a disk chisel. Soil engaging tools had less effect on roughness than residue. Twisted shovels left the roughest soil surface and sweeps left the smoothest surface. The chisel point left surface conditions smoother than twisted shovels but often not significantly rougher than sweeps. Shovel and sweep width as well as machine type (chisel plow vs. disk chisel) did not greatly affect surface roughness. Operating speeds of 5 to 9 km/h did not affect surface roughness, but reducing speed to 2.5 km/h increased residue and decreased roughness. Increasing operating depth of a disk chisel decreased surface residue, but had little effect on surface roughness.
Modeling the Losses of Soil‐applied Chemicals in Runoff: Lateral Irrigation versus Precipitation
Authors: Wallach Rony , Jury William A. , Spencer William F.
Published: July 2010

The differences between rainfall‐ and surface irrigation‐induced runoff are described in relation to the transfer of the surface‐applied chemicals from soil solution to surface runoff water in the absence of infiltration. The different processes inducing runoff are characterized by the residence time distribution (RTD) of the water in the system. The time‐dependent chemical concentration at the field outlet is affected by the RTD, even for the case of instantaneous equilibrium between chemicals in runoff water and soil solution. In this approach the water and chemical transport process in the field is represented by linear well‐stirred mixing cells in series, for which a general solution for the effluent concentration is available. The rainfall‐ and the lateral irrigation‐induced runoff processes, which are represented by complete mixing and plug flow models, respectively, form the two limiting cases for the actual chemical transport process by runoff. For each of these two extremes, mixing in the system is characterized by the parameter n, which is the number of cells in the series chosen to represent the actual transport process over the field.
Transfer of Chemicals from Soil solution to Surface Runoff: A Diffusion‐based Soil Model
Authors: Wallach Rony , Jury William A. , Spencer William F.
Published: July 2010

A physically‐based diffusion and transport model is developed to describe chemical outflow concentrations during chemical removal from soil to overlying runoff water induced by continuous rainfall over the soil surface. In contrast to earlier models, movement from the soil to the runoff water is described as a liquid diffusion process to the surface, coupled to the runoff zone through a laminar boundary layer at the runoff interface with the soil surface. Within the soil, diffusion is moderated by equilibrium adsorption to solid surfaces characterized by a partition coefficient. The runoff concentration at the outlet is derived by treating the runoff zone as a wellmixed reactor, characterized by a residence time. The model was used to predict the results obtained in the experimental study of L.R. Ahuja and O.R. Lehman (1983) where infiltration was suppressed, with good agreement obtained between predicted and measured outflow concentrations when the model parameters were estimated independently using standard engineering equations from channel flow hydraulics. The model also predicted the final soil concentrations satisfactorily after runoff ceased.
Changes in Water‐extractability of Soil Inorganic Phosphate Induced by Sodium Saturation
Authors: Sharpley A. N. , Curtin D. , Syers J. K.
Published: July 2010

The effect of replacing indigenous exchangeable cations with Na on the subsequent release of inorganic phosphate (P) from 34 USDA‐SCS benchmark soils representing nine soil orders was investigated by sequential extraction with distilled water. Sodium saturation substantially increased the water extractability of P regardless of whether Ca‐P or sorbed P was the predominant form of inorganic P in the soil. On average, Na‐saturated soils released about 2.5 times more P than the untreated soils. Sequential chemical extractions were used to identify the sources of P extracted. In soils that had not been Na saturated, water‐extractable P appeared to originate largely from the NaHCO3‐extractable fraction. The additional P released following Na saturation was accounted for by a disappearance of Ca‐P compounds (HCl‐extractable) in soils where such entities were present or a decrease in the sorbed‐P fraction extracted by NaOH. The results indicate that the distribution of P between solid and solution phases is strongly dependent on the nature of the exchangeable cation population. These results have important implications to soil fertility and P availability in irrigated soils influenced by Na.
Potentiometric Determination of Potassium Q/I Relationships
Authors: Wang Jian , Farrell R. E. , Scott A. D.
Published: July 2010

Methods of determining potassium quantity‐intensity (Q/I) relationships with ion‐selective electrodes (ISEs) were developed and evaluated with three Iowa soils. In doing so, soil suspensions and their filtrates were characterized with single‐ISE [ISE(S)] and dual‐ISE [ISE(D)] procedures, the ISEs were calibrated in terms of ion concentrations to obtain Q/I relationships based on concentration ratios (CR), and the results were compared with those obtained by conventional analyses of the filtrates by atomic absorption spectrometry (AAS). By using ISEs with filtrates from soil suspensions that were equilibrated for 18 h, it was established that the ISE(S) and ISE(D) methods yield essentially the same Q/I curves and related parameters as the reference AAS method. The potentiometrically determined CR values agreed particularly well with the AAS values that were based on Ca2+ plus Mg2+ because of the response of the Ca‐ISE to Mg2+. Subsequent experiments on the feasibility of using the ISE(D) procedure with the soil suspensions (to eliminate the filtration step) also yielded results that were in excellent agreement (no significant difference at α = 0.05) with those obtained by analyzing the filtrates. The time required for Q/I determinations was further reduced by using the ISEs with soil suspensions to which successive increments of KCl were added. This procedure, however, altered the shape and critical parameters of the Q/I curves. Clearly more information about the relevance of the different Q/I results is needed. The ISE methods provide a simple and rapid means of obtaining the necessary data.
Overwinter Transformations of Nitrate Derived from Soil and 15N‐Labeled Potassium Nitrate
Authors: Heaney D. J. , Nyborg M.
Published: July 2010

Transformations of NO3‐N from fall through spring were examined in a Typic Cryoboralf and a Typic Argialboll in northcentral Alberta. Nitrogen‐15 labeled KNO3 (96% atom abundance) was applied at the rate of 2.4 kg N ha−1 to fallow and stubble plots in October and incorporated to a depth of 0.13 m. Isotopic analyses of NH4‐N, NO3‐N, and total‐N were performed on soil samples taken to a depth 0.60 m in November, January, March, and May. Analysis of November samples indicated apparent denitrification, immobilization, and release of 15N as NH4‐N occurred in both soils. Losses of NO3‐N occurred simultaneously with additions between November and January in 3 of 4 fallow‐stubble/soil combinations. Migration of soil water towards ice lenses in the surface 0.30 m suggested upward movement of NO3‐N took place as the soil froze. Between January and March, NO3‐N levels increased an average of 6.4 mg N kg−1 in the Cryoboralf while recovery of 15N was unchanged. In the Argialboll, NO3‐N levels remained constant from January to March. Lower recovery of 15N under fallow indicated that the NO3‐N pool remained active and losses were balanced by gains. In may recovery as NO3‐N accounted for only 1 to 24% of labeled N added in October. Immobilization accounted for 4 to 30%. Trace amounts of 15N were detectable in the 0.13 to 0.30‐m depth, but not in the 0.30 to 0.60‐m depth. Overwinter loss of labeled N from 0 to 0.60 m ranged from 55 to 86%. Processes affecting NO3‐N remained active between October and May, including periods during which soils were frozen throughout the 0 to 0.60‐m depth.
Early Stages of Mine Soil Genesis in a Southwest Virginia Spoil Lithosequence
Authors: Roberts J. A. , Daniels W. L. , Burger J. A. , Bell J. C.
Published: July 2010

Natural topsoils in the Appalachian surface mining region are often more difficult to use and less desirable than alternative spoil materials. Parent material effects and initial pedogenic changes over 3 yr were observed in 5 mixes of sandstone (SS) and siltstone (SiS) spoils under grass vegetation. Spoil type controlled initial soil texture, but significant decreases in sand contents and increases in silt contents occurred in several spoil mixes within 2 yr. All mine soils studied were high (≥65%) in coarse fragments. Mine soils derived from spoils high in siltstone content were higher in coarse fragments, pH, extractable cations and iron, fine earth (<2 mm) water holding capacity, and electrical conductivity than sandstone mine soils. Dissolution and leaching, oxidation, and organic matter incorporation were dominant pedogenic processes influencing mine soil properties over the period of this experiment. Distinct surface A horizons formed within 3 yr. Water retention in the <2‐mm fraction increased over time in the surface (0 to 5 cm) of all spoil types except pure sandstone. Extractable Fe and total N increased between 1982 and 1984, while pH, and extractable Ca, Mg and P decreased in most spoil types. These changes reflect rapid pedogenesis in fresh unweathered parent materials in a humid environment.