bluuebunny/crossref_metadata_2025 huggingface dataset:
Converting Root Numbers Observed at Minirhizotrons to Equivalent Root Length Density
Authors: Merrill S. D. , Upchurch D. R.
Published: July 2010

Root length density (RLD) is the measure of plant root growth having greatest general utility. The use of clear material observation tubes, known as minirhizotrons (MR), in field soil has proved to be an effective method for measurement of root growth dynamics. To convert numbers of roots observed at MRs to equivalent bulk soil RLD, workers have used empirical and time‐costly calibrations with soil sample‐derived RLD. A modified version of an earlier theory for converting MR observations to soil RLD is presented. The theory is based on calculation of the mean root length that would occur inside a MR if it were not present and if all possible root growth orientations at a root interception by the MR are considered. The theory indicates that a dimensionless factor ranging in value from 3.0 to 3.8 will convert MR interceptions per incremental observation area to equivalent soil RLD for MR tubes ranging in diameter from 9.6 to 2.5 cm. An experimental test with cotton (Gossypium hirsutum L.), presented here, and one from the literature using wheat (Triticum aestivum L.), both give numerical support to the theory. Another test from the literature using cotton appeared to indicate that the theory numerically overpredicted RLD. In contrast, a test in corn (Zea mays L.) presented here showed the theory underpredicting RLD. Methodological factors appeared to weaken the significance of the latter test. Inaccuracies in RLD determination from soil sampling may affect the accuracy of empirical calibrations of MR tubes to an extent comparable to uncertainties about the predictive accuracy of the theory.
Effect of pH and Ionic Strength on Boron Adsorption by Pyrophyllite
Authors: Keren R. , Sparks D. L.
Published: July 2010

The negative electrical field around clay particles whose edge thickness is small relative to the Debye length of the diffuse double layer associated with the planar surfaces may spill over into the edge region. Such a spillover may affect B adsorption by the clay. This study was conducted to determine the effect of edge surface properties of 2:1 clay on B adsorption. Pyrophyllite, which shows little deviation from the ideal formula of dioctahedral structure of 2:1 clay type, was used for that purpose. Boron adsorption by pyrophyllite was studied at 25.0 ± 0.5°C at ionic strengths of 0.005, 0.01, and 0.1 mol L−1 for pH 7 and 9 and ionic strengths of 0.01 and 0.1 mol L−1 for pH 5. It was suggested that B is specifically adsorbed via ligand exchange to the structural Al located on the edge surfaces. Boron adsorption increased with increasing ionic strength. The effect of ionic strength on B adsorption was smaller at pH 7 than at pH 9, consistent with the decrease in B(OH)−4 activity fraction in equilibrium solution at pH 7 and the low affinity of the clay to B(OH)3. The effect of ionic strength on B adsorption was small at pH 5, attributable to the weak electrical field at this pH (electrical potential, ψo = −47 mV) together with the low B(OH)−4 concentration and the low affinity of the clay for B(OH)03. The higher capacity of pyrophyllite, in comparison to montmorillonite, to adsorb B at pH 9 where the ψo at the edge surfaces of the clay is ‐285 mV, supports the hypothesis that the negative electrical field associated with this planar surfaces affects B adsorption.
Equilibrium and Kinetics of Borate Adsorption‐Desorption on Pyrophyllite in Aqueous Suspensions
Authors: Keren R. , Grossl P. R. , Sparks D. L.
Published: July 2010

This study was conducted to elucidate the dynamic aspects of the adsorption‐desorption of borate ions on edge surfaces of 2:1 clay minerals. A pressurve‐jump relaxation method was used to evaluate the elementary processes involved in the adsorption‐desorption of borate ions by pyrophyllite in aqueous media at pH 9 and ionic strength of 0.01 (NaNO3). This clay was selected because of the small deviation from the ideal structural formula of the dioctahedral 2:1 clay minerals. At pH 9, 37% of the total B in solution is in the B(OH)−4 form, whereas of the total adsorbed B, the fraction of the adsorbed B(OH)−4 is assumed to be ≈ 0.99 at all levels of adsorbed B studied. This high fraction is probably due to the absence of repulsive forces associated with the planar surfaces. A linear correlation (R2 = 0.94) between the reciprocal value of the relaxation time, τ−1, and the sum of concentrations of the free adsorption sites and borate ions in solution at equilibrium was determined. The forward rate constant, k1, for the adsorption was 104.26 L mol−1 and the backward rate constant, k‐1, for the desorption was 101.11 s−1. The desorption rate constant was three orders of magnitudes smaller than the adsorption rate constant. The intrinsic equilibrium constant obtained from the kinetic measurements (log10 Kkinetic = 3.15) agreed relatively well with that calculated from the static studies (log10 Kstatic = 3.51). The suggested reaction scheme for the B‐pyrophyllite interaction is:
urn:x-wiley:03615995:saj2sssaj199403615995005800040016x:equation:saj2sssaj199403615995005800040016x-math-0001 or
urn:x-wiley:03615995:saj2sssaj199403615995005800040016x:equation:saj2sssaj199403615995005800040016x-math-0002
An Infiltration Equation to Assess Cropping Effects on Soil Water Infiltration
Authors: Ali A.‐S. I. , Swartzendruber D.
Published: July 2010

The effect of crop plants on the infiltration of water into soil has been difficult to characterize. This study was conducted to determine whether a new three‐parameter infiltration equation, obtained from a recent infiltration quasi solution, could be validated and used for improved characterization of infiltration. For field plots under different cropping conditions of corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], soybean [Glycine max (L.) Merr.], and fallow, water‐infiltration data from ponded double‐ring infiltrometers were fitted by nonlinear least squares to the new equation, and, for comparison, to the two‐parameter Philip form and to the strictly empirical Lewis equation. Physically problematic negative values of the sated (near‐saturated) hydraulic conductivity K were yielded by the Philip form in well over half of the data sets, but all were superseded with positive K values by use of the new equation which, of the three, also gave the best fit to the data, in keeping with the additional fitted parameter. Statistically, by using orthogonal‐contrast analysis of the several equation parameters, the new equation also produced the largest number of significant differences between crops and crop sequences (rotations). Grain sorghum created the largest sorptivity S, whereas corn decreased it. Soybean produced the smallest K, but corn and grain sorghum caused moderate and equal increases in K. The new equation and these findings offer promise for improved characterization and understanding of plant effects on water infiltration.
Neutron Probe Calibration in Unsaturated Tuff
Authors: Elder A. N. , Rasmussen Todd C.
Published: July 2010

The measurement of water content in unsaturated media using neutron moisture probes requires a calibration relationship between neutron counts and water contents. Techniques for obtaining the relationship in unconsolidated geologic media may be unsuitable for consolidated media due to the difficulty of extracting undisturbed samples for water content analysis. The calibration relationship, θ = α0 + (α1 + α2ρb)C = α3ρb, with C = neutron counts, and ρb = dry bulk density, provided a good predictor of volumetric water content, θ, for consolidated media at the Apache Leap Tuff Site. Four techniques were employed to obtain data necessary to construct this relationship. Two methods employed a neutron transport code to predict neutron counts from scattering and absorption neutron cross sections. The first method calculated cross sections from elemental compositions, while the second used cross sections obtained from rock samples placed in a graphite pile containing a neutron source. The third method used in situ neutron counts measured in two access holes constructed in unsaturated rock with known water contents estimated from rock fragments excavated surrounding the access holes using a pneumatic hammer. The fourth technique used neutron counts from crushed rock packed into containers and maintained at prescribed water contents. Neutron cross sections obtained from elemental analyses were smaller than graphite‐pile values, although the differences were insignificant at the 95% confidence level and the difference in rock water content predictions was small. The neutron transport model provided neutron count estimates consistent with in situ counts and counts from saturated crushed rock in containers.
Infiltration Characteristics under No‐Till and Clean‐Till Furrow Irrigation
Authors: Christensen N. B. , Jones T. L. , Kauta G. J.
Published: July 2010

Tillage or the lack of tillage affects infiltration and its variability across the field. To quantify infiltration characteristics of soil under no‐till and clean‐till furrow irrigated systems, a 3‐yr rotation of wheat (Tritium aestivum L.)‐sorghum [Sorghum bicolor (L.) Moench]‐fallow on a Pullman sandy clay loam soil (fine, mixed, thermic Torrentic Paleustoll) was initiated. Treatments were no‐till and clean‐till with or without wheel traffic. Soil water contents, water advance times down the furrow, wetted cross‐sectional area of flow, and cumulative furrow infiltration during three irrigations for each cropping event were determined. No‐till treatments conserved significantly more soil water (3.0 cm) during the fallow periods than clean‐till. Average water advance times to the end of the field were 301 and 175 min for no‐till and clean‐till, respectively. Wheel traffic significantly decreased advance times, by a factor of 1.98, during the initial irrigations at planting with no effect on subsequent irrigations. Wetted cross‐sectional area in no‐till furrows was significantly greater than in clean‐till during sorghum irrigations, averaging 0.0206 and 0.0093 m2, respectively. However, these factors did not contribute to a consistent increase in infiltration in the no‐till treatments. Grain yields for sorghum were significantly greater in no‐till than clean‐till: 4147 and 3584 kg ha−1, respectively, but clean‐till wheat yields (5414 kg ha−1) were significantly greater than no‐till yields (4657 kg ha−1). No‐till conserved more water during the fallow periods, but surface characteristics of planting wheat no‐till in sorghum residue may decrease uniformity over long furrows.
Cover‐Crop‐Enhanced Water Infiltration of a Slowly Permeable Fine Sandy Loam
Authors: Gulick S. H. , Grimes D. W. , Munk D. S. , Goldhamer D. A.
Published: July 2010

Infiltration improvement in many sandy to medium textured soils of California's Central Valley is often hampered by unfavorable soil properties, unfavorable management practices, and the need to protect perennial crop roots. Minimum‐tillage practices using chemical sprays, mulches, and cover crops avoid soil structure deterioration due to high traffic, but some properties of these methods are not universally acceptable. Furrow irrigation water infiltration, water use, and ‘Thompson Seedless’ grape production were evaluated on a Hanford fine sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Xerorthent) for three management systems for 2 yr to develop a useful system. The compared systems were (i) continuous cover crop [winter ‘Blando’ bromegrass (Bromus mollis L.) followed by summer resident vegetation] (CC); (ii) winter bromegrass, herbicide treated to form a summer mulch (CHT); and (iii) bare soil, herbicide treated as needed (BHT). Cumulative infiltration for 8‐h irrigation periods, averaged for five irrigations, was 177 mm for CC, 125 mm for CHT, and 74 mm for BHT during the second season. Eight‐hour cumulative infiltration was unchanged from the first year to the second for BHT but increased with CC from 107 mm to 202 mm at the first irrigation of each year; the increase for CHT was intermediate. Cover cropping between vineyard rows increased soil water depletion in the between‐row zone profile by an average of 14 mm for CHT and 27 mm for CC for each drying cycle between irrigations. Soil water depletion beneath vine rows was unchanged by treatment.
Applications of X‐ray Absorption Fine Structure Spectroscopy to Soils
Authors: Fendorf S. E. , Sparks D. L. , Lamble G. M. , Kelley M. J.
Published: July 2010

Determining the local chemical environment of a species is often a necessity for evaluating its reactivity in the environment. However, obtaining direct molecular‐level information is often problematic and may only be possible with severely invasive techniques. We discuss the physical and chemical aspects of x‐ray absorption fine structure spectroscopy (XAFS) and its application in soils. This technique can determine the local chemical and structural surroundings of a particular elemental species in soil and water or other natural systems, without the need to subject the sample to a foreign atmosphere. Electronic information and a fingerprint of the x‐ray absorbing element's local environment is provided with XAFS and can be used to determine the speciation of an element in media like soils. Precise structural information (bond distances within 0.02 Å) can also be ascertained with this method, although this precision is often difficult to obtain in heterogeneous materials. Nevertheless, XAFS is a method that can contribute significantly to our knowledge of soils and soil reactions.
Efficacy of Dicyandiamide as a Soil Nitrification Inhibitor in Citrus Production
Authors: Serna M. D. , Legaz F. , Primo‐Millo E.
Published: July 2010

Nitrification inhibitors such as dicyandiamide (DCD) help reduce leaching losses by retaining applied N in the ammoniacal form. Research objectives were to evaluate dicyandiamide added to ammonium sulphate nitrate (ASN) as a nitrification inhibitor in cultivated soils (Xeropsamments) and its effect on N uptake by citrus (Citrus sinensis (L.) Osbeck). In a greenhouse experiment, 10 g N as ASN either with or without 2% of DCD‐N were applied to plants grown in 50‐L pots filled with peat and sand (2:1). Addition of DCD to ASN resulted in significantly higher levels of NH+4‐N in the substrate than the ASN treatment, for at least 100 d. Drainage water from the ASN‐DCD treated pots was lower in NO−3‐N concentration during the first 60 d. Inclusion of DCD with ASN resulted in greater uptake of the fertilizer N by citrus plants. Under field conditions, fertilization of adult trees with ASN (600 g N tree−1) either with or without DCD (2% DCD‐N) was compared. In the ASN‐amended soil, nitrification was much more rapid than when DCD was added to the ASN. Fertilization with ASN + DCD maintained relatively high levels of NO−3‐N in soil longer than ASN alone. In another experiment, 60 g N as ASN either with or without DCD (2% DCD‐N) were applied to 3‐yr‐old citrus plants grown individually outdoors in containers and the distribution of NH+4‐N and NO−3‐N in the soil profile after consecutive flood irrigations was monitored. After the third irrigation, 68% of applied N was leached below 0.45 m in ASN amended soils, whereas only a very small amount of the applied N was retained above this depth. When DCD was added, only 20% of the applied N was lost by leaching at this time. The DCD nitrification inhibitor improved the N fertilizer efficiency and decreased NO−3 losses so as to minimize the economic and environmental risks that are inherent in irrigated production of citrus.
Methane Emissions and Growth of Spartina patens in Response to Soil Redox Intensity
Authors: Kludze H. K. , DeLaune R. D.
Published: July 2010

Laboratory experiments were conducted to determine the influence of soil redox intensity (Eh) on the growth, root porosity (POR), radial O2 loss, and CH4 production, oxidation, and emission in Spartina patens (Aiton) Muhlenb. (salt meadow cordgrass). Plants were grown for 50 d in a Mississippi alluvial soil (silty‐clay loam, Typic Fluvaquent) under controlled Eh values of 200, −200, and −300 mV. Plant growth decreased with increase in Eh intensity. Root dry weights decreased by 37% and shoot dry weights by 25% between the soil redox intensity treatments of 200 and −300 mV. Root air space formation was enhanced by a decrease in Eh up to about 30 d when further development appeared to cease and levelled off in all the redox treatments. Methane production was generally enhanced by the intensity of reduction. Plant‐mediated emissions were commensurate with production levels but were influenced by plant related factors, especially POR. No differences (P < 0.05) existed between emissions in light and in the dark, which suggests a lack of stomatal influence on CH4 emissions from S. patens. Plant‐mediated CH4 oxidation was higher at −200 mV than at −300 mV by a factor of 16%. Results of this study demonstrate how soil redox intensity initiates physiological changes in S. patens, which in turn modulates the gas transport in the plant. Although the experimental conditions do not represent the natural environment, the results provide a theoretical understanding of the influence of soil redox intensity on the growth, CH4 production, and gas exchange in S. patens.
Transport of Reactive Solutes in Soils: A Modified Two‐Region Approach
Authors: Selim H. M. , Ma Liwang
Published: July 2010

A modified two‐region approach that accounts for chemical and physical nonequilibrium of solute behavior in soils was developed. Chemical nonequilibrium was described by a second‐order two‐site model, while physical nonequilibrium was represented by a two‐region (mobile‐immobile) approach. Model validity was based on predictions of atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino‐s‐triazine] miscible displacement experiments in a Sharkey clay soil (very fine, montmorillonitic, nonacid, thermic Vertic Haplaquept) for different aggregate sizes, flow velocities, column lengths, and flow interruption. Independently measured model parameters from kinetic batch experiments were used in model validation. Two model formulations were evaluated. Model I was based on the classical two‐region approach where the soil matrix was divided into two fractions. In Model II, we assumed that the rate of reaction within each soil region was a function of the total number of vacant sites in the soil. Thus, the partitioning coefficient f of the two‐region concept, which is difficult to measure, need not be specified and the amounts retained by each soil region is solely a function of reaction rate coefficients. Model I with f = F (F = θm/θ, mobile/total water contents) provided the worst atrazine predictions. Moreover, based on Model I predictions with f = 1 and f = 0, the significance of physical nonequilibrium was dependent on experimental constraints such as aggregate size and flow velocity. Based on root mean squares, however, the best overall predictions were obtained using Model II. We concluded that Model II, which requires fewer parameters, is superior to Model I in its prediction capability for transport results.
The Philosophical Basis of Soil Classification and Its Evolution
Authors: Haskett Jonathan D.
Published: July 2010

The system of soil classification used in the U.S. system of soil taxonomy has been criticized as being based on the flawed 19th century logic of John Stuart Mill. Mill postulated that objects have self‐evident properties that will be apparent to any observer. Further, these properties reflect inherent differences between objects. However, language shapes perception to a great extent, and knowledge of external reality can be obtained only by observation. It cannot be assumed that all observers, particularly those using different languages, will find the same things important. Therefore, different observers are likely to categorize in different ways. In order to avoid arbitrary classifications, an inductive method is used based on tests of predictive ability. This allows the creation of a classification system that follows the regularities of nature, within the constraints on perception imposed by any linguistic division. Classification in natural history as well as in soil science has moved from a noncontextual naming of independent objects to a bounded self‐consistent system in which each entity is defined in relation to all others in the system. This represents an evolutionary process that proceeds through the adoption of the inductive method and ultimately leads to the creation of a classification system consistent with the underlying principles of the discipline. The current system of soil classification is consistent with the progressive nature of this process and is not in need of fundamental modification.
Models and Modeling of Hydrogeologic Processes
Authors: Narasimhan T. N.
Published: July 2010

J.R. Philip recently articulated a concern of many earth scientists that computer‐based mathematical models are impacting soil science practice and soil science education in an undesirable way. Unrealistic faith in the ability of these models to predict the future has encouraged overzealous use of models at the expense of the observational enterprise. These real concerns draw attention to the fact that much needs to be learned about the proper use of models in general and computer‐based models in particular in the earth sciences. I was impressed by Philip's thoughts, and here reflect on the current status and the role of models of hydrogeologic processes. While agreeing with Philip's concerns about the improper use of models, I advance a perspective that models (analytical or numerical) are tools with inherent limitations. Despite their overenthusiastic use, computer‐based models are potentially capable of helping us advance our knowledge of earth processes in unprecedented ways. As we seek to exploit this tool to its full potential, we may be challenged to reexamine and refine our conceptual foundations so that hydrologic processes are described more precisely than has hitherto been possible.
Developments in the Physics of Infiltration
Authors: Youngs E. G.
Published: July 2010

Developments in the physics of infiltration, particularly the many theoretical contributions of John Philip, have been based on solutions of Richards' equation for flow in unsaturated soils. Solutions for constant surface soil‐water pressure and constant surface flux into soils initially at a uniform water content have given the physical basis for infiltration that generally takes place in conditions described by more complex initial and boundary conditions. The Green and Ampt step function and Gardner's exponential function models for the relationship between hydraulic conductivity and soil‐water pressure head are often employed to facilitate solutions. However, Richards' equation makes assumptions in the physics of the flow that do not take account of many complicating factors that may vitiate theories based on it. These factors include the influence of the air phase on the soil‐water movement, the effects of soil heterogeneity, soil swelling, soil aggregation and soil instability, deviations from Darcy's law, thermal effects and the hysteresis in soil‐water relationships. These factors need to be addressed in order to provide a better physical understanding of infiltration behavior in the field, first by understanding simple systems, as with much of John Philip's work, and then by progressing to more complex situations.
Liquid Flow in Swelling Soils
Authors: Smiles D. E.
Published: July 2010

Theory of flow of water in media that change volume with water content change owes much to the insights of John Philip. In particular, his development and explanation of a one‐dimensional model in Eulerian space that correctly accounts for the statics and dynamics of the phases in a two‐phase swelling system is a paradigm of the combination of the models of mathematics with clear physical insights. In addition, transformation of the approach from Eulerian to Lagrangian space permits use, for swelling systems, of all the methods of analysis developed in soil physics to describe water flow in nonswelling soils. The approach has been used to describe important practical problems of filtration, sedimentation, centrifugation, and consolidation of colloidal and soil systems in chemical, civil, and mine tailings engineering. Regrettably, material coordinates, rather than the more familiar spatial coordinates, continue to present conceptual difficulties for many engineers and soil scientists, as does the effect of volume change on the potential of the water. Furthermore, the approach has yet to be satisfactorily extended to unsaturated systems and to multidimensional ones. Its use in agriculture thus remains uncertain despite the great importance of water management in swelling and cracking soils. This review discusses some of these issues and specifically identifies the energetics and mechanics of cracking, overburden effects in unsaturated porous materials, and structural effects of the equilibrium ambient solution type and concentration in swelling systems as practically important areas for further study.
The Role of Edge Surfaces in Flocculation of 2:1 Clay Minerals
Authors: Keren R. , Sparks D. L.
Published: July 2010

The effect of pH on the flocculation, settling rate, and gel volume of pyrophyllite in dilute suspension was studied in solutions of various NaNO3 concentrations to evaluate the role of the edge surfaces in particle‐particle interaction. The critical flocculation concentration (CFC) increased with increasing pH, being 1.6 × 10−4, 4 × 10−4, 1.5 × 10−3, 9.5 × 10−3, 1.6 × 10−2, and 0.1 molc L−1 at pH 3.2, 4.4, 5.3, 6.0, 7.4, 8.5, and 10.2, respectively. The CFC increased significantly in the presence of small amounts of sodium hexametaphosphate in the suspension. The changes in CFC from low values in the absence of the polymer to higher values in the presence of it support the hypothesis that the edge surfaces are involved in particle‐particle interactions. The settling rate of the clay particles at pH 8.5 increased as the electrolyte concentration was decreased. The effect of electrolyte concentration on settling rate was explained by the presence of an electrical field associated with the edge surfaces. The gel volume, after reaching a stable volume, increased with the increasing of electrolyte concentration. This increase in water content, indicating an open structure of clay platelets, also supports the hypothesis that edge surfaces are associated with clay flocculation. The electrical field associated with the edge surface also has an effect on the gel volume.
On the Rothmund‐Kornfeld Description of Cation Exchange
Authors: Bond W. J.
Published: July 2010

Simple descriptions of cation‐exchange isotherms are required to permit interpolation and extrapolation from a limited data set. Conventional thermodynamic approaches do not result in simple expressions in terms of a small number of measurable constants. The empirical Rothmund‐Kornfeld power function approach has been found to be applicable to a large number of data sets. It permits description of an entire exchange isotherm with two parameters obtained directly from measured points on the isotherm. It is shown here that these parameters can be used to derive the true exchange equilibrium constant for the exchange reaction, as well as the exchange‐phase activity coefficients used in thermodynamic approaches based on the Vanselow‐Argersinger (mole fraction) and Gaines‐Thomas (equivalent fraction) conventions. Values of the exchange equilibrium constant and the exchange‐phase activity coefficients calculated from fitted Rothmund‐Kornfeld parameters compare favorably with those calculated using conventional thermodynamic approaches. The method based on the Rothmund‐Kornfeld approach is potentially more accurate because it avoids subjective extrapolation of the data required for the thermodynamic approach.
Influence of Sample Size on Chemical and Physical Soil Measurements
Authors: Starr J. L. , Meisinger J. J. , Parkin T. B.
Published: July 2010

Understanding the distribution of soil properties with respect to sample size is essential for designing efficient soil sampling strategies. This study was conducted to evaluate the influence of the size of soil samples on the distribution of estimated soil physical (bulk density and water content), chemical (pH and orthophosphate P), and biological (NO3‐N and denitrification rates) properties. The experiment was conducted at Beltsville, MD, on a Beltsville silt loam soil (fine‐loamy, mixed, mesic Typic Fragiudult). Soil samples were collected from the surface layer (0–16 cm) using five different sized soil coring tubes, 1.7 to 5.4 cm in diameter, and one 20 by 30 cm block. Thirty‐six samples of each sample size were collected twice before and twice after planting corn (Zea mays L.). Frequency distributions of denitrification rates, NO3‐N, and orthophosphate P values were approximately lognormal, while the values for bulk density, water content, and pH were approximately Gaussian. All soil parameters except bulk density exhibited spatially dependent results. The effect of sample size varied with the soil property. The most consistent size effect was that smaller diameter samples gave smaller means, greater skewness, and higher variances compared with the large‐block sample statistics.
Straw Application Effects on Methane and Oxygen Exchange and Growth in Rice
Authors: Kludze H. K. , DeLaune R. D.
Published: July 2010

Currently, there is a paucity of information on plant‐soil interactive effects and plant‐related factors that control CH4 production and its emission from rice (Oryza sativa L.) paddies. Laboratory studies were conducted to evaluate the effects of rice straw application rates on growth, root porosity (POR), and gas (O2 and CH4) exchange in rice under continuously flooded conditions. Three rice cultivars were grown in Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf) amended with two levels (11 and 22 t ha−1) of rice straw. Plants were harvested for growth, POR, and radial oxygen loss (ROL) estimates at 40 d after transplanting. Methane measurements were made at 20, 30, and 40 d after transplanting. Plant growth and straw application rates were negatively correlated. Variations existed among cultivars in parameters studied. Although POR was enhanced by the higher application rate (22 t ha−1), reductions in shoot and root growth consequently resulted in reduced ROL. Two of the cultivars exhibited significant POR‐ROL correlations. Highest CH4 emissions occurred at the 11 t ha−1 application rate. At the 22 t ha−1 application rate, CH4 emissions were significantly reduced in all vegetated treatments, although emissions from unvegetated treatments were enhanced. Results indicated that reductions in CH4 emissions at the higher straw application rate resulted from reduction in the total diffusive pathway of the gas and were not due to the mitigation of methanogenesis.
Methyl Bromide Soil Fumigation Alters Plant Element Concentrations
Authors: Ellis J. R. , Varvel G. E. , Watson D. M. H. , Jawson M. D.
Published: July 2010

Soil fumigation is used to eliminate plant pathogens and weeds in commercial practice and to eliminate organisms in controlled experiments, e.g., vesicular arbuscular mycorrhizal fungi (VAMF). This study was conducted to study the effect of methyl bromide fumigation on plant accumulation of 14 elements and assess plant colonization by VAMF after fumigation. Field experiments were conducted near Mead, NE, on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll). Corn (Zea mays L.) sorghum [Sorghum bicolor (L.) Moench], and soybean [Glycine max (L.) Merr.] were used in the experiments. Fumigation increased Al, Br, Ca, Fe, Mg, Mn, and Si and decreased Cu, K, P, and Zn shoot concentrations in all three plants. Three weeks after germination, shoot Al was sevenfold greater in sorghum and soybean and 16‐fold greater in corn from fumigated plots than in shoots from nonfumigated plots. Shoot bromide concentrations from fumigated plots were sixfold greater in sorghum and 17‐ to 18‐fold greater in corn and soybean than shoots from nonfumigated plots. Lower P and Zn shoot concentrations from fumigated plots were attributed to fumigation‐induced suppression of VAMF root colonization or an ion balance problem resulting from the enhanced uptake of Al, Br, and other ions after soil fumigation. At harvest, Al was still three‐ to 10‐fold and Br eight‐ to 20‐fold greater in fumigated plot stover compared with nonfumigated plots. This study shows that methyl bromide fumigation alteration of plant uptake of Al, Br, Ca, Fe, Mg, Mn, and Si should be considered when interpreting experiments using methyl bromide soil fumigation.
Improving the Iron Oxide Sink Method for Extracting Soil Phosphorus
Authors: Myers R. G. , Pierzynski G. M. , Thien S. J.
Published: July 2010

Iron oxide coated filter paper can estimate labile P in soil by acting as a P sink. Variations in procedures and contamination from soil adhering to the sinks limit effective data interpretation, however. We evaluated two papers with pores <5.0 µm and one with pores 20 to 25 µm. Iron oxide coatings were formed by exposing FeCl3‐treated papers to NH3 vapor or 2.7 M NH4OH. Coated papers were either fixed in a screen assembly or allowed to move freely during shaking. The screen assembly eliminated abrasion loss of the FeO coating. Paper circles (5.5 cm) proved satisfactory and eliminated the need to cut 2 by 10 cm strips from coated papers. Fixed, small‐pore circles had less soil contamination (0.8–1.9 mg) than fixed, large‐pore circles (4.7–8.1 mg), a condition confirmed by x‐ray diffraction. Similarly, free, small‐pore circles retained less soil contamination (3.5–9.0 mg) than free, large‐pore circles (16.1–21.7 mg). Two sources of acid‐extractable P inflated the labile P pool. First, acid‐extractable P from soil adhering to papers increased sink‐extractable P by 7.5 to 24.1 mg P kg−1, an error of 28 to 65%. Also, paper prepared in NH3 vapor acidified the extracting solution with Kahola (fine‐silty, mixed, mesic Cumulic Hapludoll) and Haynie (coarse‐silty, mixed [calcareous], mesic Typic Udifluvent) soils and increased their extractable P an average of 13 mg P kg−1, or 56%. To eliminate some analytical problems associated with the FeO‐sink extraction of soil P, we recommend preparing small‐pore circles (<5 µm) in NH4OH solution and securing them during shaking.
Influence of Treethrow on Soil Properties in Northern Wisconsin
Authors: Meyers N. L. , McSweeney K.
Published: July 2010

The uprooting of trees (treethrow) creates major changes in some soil properties. This study was conducted to document both the extent of treethrow activity and its influence on soil properties in northern Wisconsin. We determined the extent of treethrow at 12 localities and studied 10 of those localities in detail. We determined bulk density, particle‐size distribution, P, K, pH, and moisture status of knolls, cradles, and linear areas where recent disturbance was not obvious. The terms knoll and cradle refer to the mound and depression or pit created by treethrow disturbance. We use the term linear area to identify portions of the landscape not identified as knoll or cradle. Knolls have significantly lower bulk densities throughout the upper 90 cm, compared with adjacent cradles and linear areas. Differences in particle‐size distribution are evident to a depth of 90 cm. Potassium contents are significantly higher in cradles than knolls or linear areas. No differences in P levels or pH are evident. Monthly determinations of moisture content during two growing seasons show knolls are drier than cradles or the linear areas. In light of these sizable significant differences, it seems appropriate that disturbance in these landscapes should be identified within map units and considered in both interpretations for use and taxonomic classification.
New Mexican Locust and Parent Material: Influence on Availability of Soil Macronutrients
Authors: Klemmedson James O.
Published: July 2010

The effect of New Mexican locust (Robinia neomexicana Gray) on availability of soil N, P, K, and S in ponderosa pine (Pinus ponderosa Laws.) forests in central Arizona was studied in stands with either basalt or limestone parent material. Samples of the 0‐ to 15‐cm layer of mineral soil were collected from seven pairs (with and without locust) of randomly located stands (sites), three on limestone and four on basalt. Availability of N, P, K, and S in these soils was determined in a greenhouse pot experiment with barley (Hordeum vulgare L. var. gustoe) grown for 42 d. Supply of N and P also was measured in a similar test with ponderosa pine seedlings grown for 270 d. Dry mass yield of test plants was used as the expression of nutrient availability. Barley and pine tests yielded similar results. A significant locust × parent material interaction showed opposite responses to locust presence by soils derived from limestone (positive) and basalt (negative). A highly significant parent material × nutrient interaction reflected low availability of N in limestone soils and low availability of P in basaltic soils. Low supply of P in basaltic soils, probably the result of P fixation, largely explained the locust × parent material interaction.
Sodium/Calcium‐Montmorillonite Suspension and Light Scattering
Authors: Keren R. , Klein Eva
Published: July 2010

Light scattering method was used to determine clay concentration in aqueous suspensions. Because light scattering of nonabsorbing solid particles in suspension depends on particle size and shape in addition to the particles' concentration, these two factors should be considered in determination of clay concentration in suspension. this study was conducted to determine the effect of adsorbed ion composition and clay particle size and shape on light scattering of montmorillonite suspensions. Light scattering of montmorillonite suspensions at various particle size, clay concentrations, and equivalent fraction of exchangeable sodium (EFES) was determined at a wavelength of 550 nm. Light scattering of montmorillonite suspensions depended strongly on particle size and EFES. The scattered light intensity decreased as the particle size of the clay platelets decreased and dropped sharply with increasing EFES in the range below 0.2. The relative number of particles in a given volume of suspension at any given EFES value was smaller than predicted by the theory. This deviation indicated that Rayleigh's theory is not valid for such systems. Clay concentration, therefore, cannot be adequately determined by light scattering when changes in ionic composition and electrolyte concentration alter the particle size and shape of montmorillonite in aqueous suspension.
Nitrogen Turnover by Sequential Immobilization and Mineralization during Residue Decomposition in Soils
Authors: Blackmer A. M. , Green C. J.
Published: July 2010

Additions of 15N‐labeled fertilizers to soils often induce mineralization of nonlabeled N, and such mineralization poses problems when interpreting the results of isotopic analyses. We studied the effects of added 15NO−3 on turnover of N during the decomposition of corn (Zea mays L.) residues in soils. Samples of a Galva silty clay loam (fine‐silty, mixed, mesic Typic Hapludoll) were treated with various levels of corn stover and various levels of 15N‐labeled NO−3 and were incubated for 90 d. Evolution of CO2 and concentrations and isotopic composition of NO−3 were monitored. Increases in rates of NO−3 addition increased initial rates of immobilization of labeled N and subsequent rates of mineralization of nonlabeled N. The sequential immobilization of labeled N and mineralization of nonlabeled N resulted in substantial replacement of labeled NO−3 by nonlabeled NO−3. Early added‐N‐induced immobilization of labeled N often was offset by subsequent added‐N‐induced mineralization of nonlabeled N before the end of the study. Sequential immobilization and mineralization should be recognized as a potential source of error in 15N‐tracer studies because sequential processes violate the commonly held assumptions that mineralization and immobilization occur simultaneously. This error could be avoided by recognizing that sequential immobilization and mineralization can occur and that the sequential processes result in a different distribution of isotopes than does simultaneous mineralization‐immobilization turnover.
Metabolism of Carbamothioate Herbicide, EPTC, by Rhodococcus Strain JE1 Isolated from Soil
Authors: Ankumah R. O. , Dick W. A. , McClung G.
Published: July 2010

Biodegradation of the her bicide EPTC (s‐ethyl dipropylcarbamothioate) at greatly enhanced rates, which may lead to poor weed control, can occur in soil after successive annual applications. The mechanisms of EPTC degradation by a strain of Rhodococcus sp. (designated JE1) previously isolated from soil were evaluated. Degradation of 14C‐labeled (at the 1‐propyl position) and unlabeled EPTC was followed by thin layer chromatogaphy and gas chromatography‐mass spectrometry. The N‐depropyl EPTC and EPTC sulfoxide were identified as initial metabolites formed, apparently via hydroxylation of the α‐propyl C and oxidation of the S atom of EPTC, respectively. Other products of EPTC degradation identified were propionaldehyde, s‐ethyl carbonothioic acid, s‐methyl carbonothioic acid, and traces of propylamine. It is proposed that the soil isolate Rhodococcus JE1 degrades EPTC via either an initial hydroxylation or sulfoxidation reaction, producing metabolites that can be further mineralized to form CO2. The α‐propyl hydroxylation reaction, however, is thought to be the dominant pathway whereby degradation of EPTC occurs in soil at enhanced rates.
Efficiency of an Incomplete Block Design Based on Geostatistics for Tillage Experiments
Authors: López María V. , Arrúe José L.
Published: July 2010

Spatial dependence of soil properties often reduces the power of conventional statistical methods to detect treatment differences. Control of adverse effects of soil variability is of special interest in long‐term experiments when small and slowly developing treatment effects are generally expected to occur, as in tillage research. The main objective of this study was to evaluate the ability of an incomplete block design based on geostatistical concepts to improve the precision of a conservation tillage experiment conducted at four sites in Aragón, northeast Spain. A preliminary geostatistical characterization of plow layer variability at these sites showed that, in most instances, soil water content and silt plus clay content were spatially dependent. Maps of kriged estimates of these properties were used to locate the tillage plots according to the proposed design. Using incomplete blocks of Size 2, the method estimates treatment effects by making short‐distance comparisons and ensures spatially balanced treatment contrasts through fixed comparison distances. This design was compared with a complete block design using soil and crop data obtained during the first two growing seasons of the tillage experiment. The results of a total of 1050 analysis of variance comparisons revealed that the incomplete block design was, on average, 24% more efficient than the complete block design. The use of incomplete blocks reduced the average error mean square by 33% and increased the number of cases with significant tillage treatment differences by 25% compared with the use of complete blocks.
Bioavailability of Citrate‐Insoluble Phosphorus in Monoammonium Phosphate and Triple Superphosphate Fertilizers
Authors: Sikora F. J. , Mullins G. L.
Published: July 2010

The Association of Official Analytical Chemists (AOAC) method for determining bioavailable P was rigorously tested in agronomic studies during the 1930s when the principle constituents of the citrate‐insoluble (CI) fraction were Ca phosphates. The presence of Fe, Al, and Mg phosphate compounds in the CI fraction in today's fertilizers requires a reassessment of the AOAC method. A greenhouse study was conducted to determine if the CI‐P fractions of five monoammonium phosphate (MAP) and five triple superphosphate (TSP) fertilizers were unavailable to sorghum‐sudangrass [Sorghum bicolor (L.) Moench]. Plant shoot weight (SW) and P uptake from fertilizer applied at 15 mg total P kg−1 soil was compared with the same indices obtained from reagent‐grade MAP and monocalcium phosphate (MCP) applied at rates of 13.8, 14.2, 14.6, and 15 mg P kg−1 soil (corresponding to 8, 5.3, 2.7, and 0% reduction in P supply). With a few exceptions, there was good agreement in SW and P uptake among fertilizer and reagent‐grade materials in regard to the percentage of CI‐P in the fertilizer, which lead to the conclusion that the AOAC method correctly determined unavailable P as CI‐P for short‐term plant growth. Residual availability is discussed with reference to the solubility of suspected P‐impurity compounds in the CI fraction.
Reduction of Potassium Fixation by Two Humic Acid Fractions in Vermiculitic Soils
Authors: Olk D. C. , Cassman K. G.
Published: July 2010

The capacity of soil organic matter (SOM) to reduce K fixation was investigated in calcareous vermiculitic soils. Humic acid fractions were extracted with the use of a modification of the standard NaOH extraction procedure. The mobile humic acid pool (MHA) was extracted without initial decalcification. Addition of MHA to the vermiculitic soils reduced K fixation and resulted in greater total extractable K and highly labile K, as well as greater plant K uptake. The Ca humate pool (CaHA) was extracted after decalcification, and it had little effect on K availability. An increase in extractable and highly labile K occurred within 4 h of MHA addition and thus appears to result from a rapid exchange reaction and not from mineral dissolution; the latter was confirmed in separate experiments with organic acids. This rapid effect could be reproduced by addition of dodecylammonium chloride. We speculate that the enriched amino acid content and increased solubility of MHA, compared with the more humified CaHA, contribute to the greater influence of MHA on K equilibria. The less soluble, more condensed CaHA is more likely to precipitate with Ca2+. The capacity of solubilized MHA to hold K+ against soil adsorption was also apparent when soil was separated from MHA by a dialysis membrane. These results provide further evidence that young N‐rich SOM fractions such as MHA play an important role in governing K availability in soils with high K fixation potential.