bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Cover Crop and Wheel Traffic on Soil Physical Properties in Continuous No‐Till Corn
Authors: Wagger M. G. , Denton H. P.
Published: July 2010

Conservation tillage systems utilizing winter annual cover crops represent a different soil physical environment compared to conventional tillage systems. A field experiment was conducted for 3 yr on a Goldsboro fine sandy loam (fine‐loamy, siliceous, thermic Aquic Paleudults) in the North Carolina Coastal Plain to assess effects of cover crop type and row position on soil physical properties under no‐tillage corn (Zea mays L.) management. Bulk density (ρb), soil porosity, and hydraulic conductivity (Ksat) were measured in fallow, winter wheat (Triticum aestivum L.), and hairy vetch (Vicia villosa Roth.) systems with respect to three row positions (trafficked, untrafficked, and plant row). All traffic was controlled such that each corn row was bordered by a trafficked and untrafficked interrow. In general, soil physical properties were unaffected by cover crop type but strongly influenced by position. Bulk density was significantly higher in the trafficked vs. untrafficked position (1.74 vs. 1.52 Mg m−3) after 3 yr and tended to increase with time in the trafficked interrow. Associated with higher ρb values in the trafficked interrow were significantly lower values for soil porosity and Ksat. Total porosity in the trafficked position, averaged over cover crop type and 3 yr, decreased 21% below that of the untrafficked position. After 3 yr, Ksat was 0.019 and 0.002 mm s−1 in untrafficked and trafficked interrows, respectively. These results suggest that controlled traffic patterns may be an important component in the management of continuous, conservation tillage systems.
Comparison of the Glover Solution with the Simultaneous‐Equations Approach for Measuring Hydraulic Conductivity
Authors: Amoozegar A.
Published: July 2010

The Glover solution and the simultaneous‐equations approach have been suggested for determining the saturated hydraulic conductivity (Ks) of the vadose zone by the constant‐head well permeameter technique. The objective of this paper is to examine the two procedures and discuss the uncertainty associated with calculating Ks by the simultaneous‐equations approach (referred to as Kfs) as compared with using the Glover solution. Two flow regions are identified with the constant heights of water, H1 and H2 (H2 > H1), at the bottom of an auger hole of radius r during measurements of steady state flow rates, Q1 and Q2. The Ks's over the distances H1 (lower region), H2 – H1 (upper region), and H2 (entire wetted zone) at the bottom of the hole are designated as Ksl, Ksu, and Ksc, respectively. Using the Glover solution for calculating Ksl and Ksc for a homogeneous and isotropic medium, an equation is developed for calculating Ksu based on Q1, H1, Q2, H2, and r. This equation is found to be very similar to the equation for calculating Kfs by simultaneous‐equations approach. It is shown that Ksl > Ksc whenever the Kfs value is negative. Conversely, the matric flux potential calculated by the simultaneous‐equations approach (φm) is negative only when Ksc > Ksl. This is significant because, in the simultaneous‐equations approach, the Kfs value will not be acceptable when φm is negative. The Glover solution (i.e., equation to calculate Ksc or Ksl) is applicable to both homogeneous and heterogeneous soils and does not yield a negative value, whereas the simultaneous‐equations approach can only yield reliable results for homogeneous and isotropic media.
Field Evaluation of Soil Hydraulic Property Changes Caused by Surge Water Application
Authors: Saleh A. , Hanks R. J.
Published: July 2010

Surge flow irrigation was developed, in part, to take advantage of the property of some soils whereby irrigation water is more evenly distributed along the field by applying the water in “surges” (on and off cycles) instead of continuously. Thus, if water advances more during the second on‐time of irrigation than the first, there must be some change in soil properties during the previous off‐time. Three soils were used in this study: Nibley silty clay loam (a fine, mixed, mesic Aquic Argiustoll), Millville silt loam (a coarse‐silty, carbonatic, mesic Typic Haploxeroll), and Kidman sandy loam (a coarse‐loamy, mixed, mesic Calcic Haploxeroll). It was demonstrated by field experiments that the soil surface of the coarse and medium‐textured soils consolidated markedly (soil surface elevation decreased about 3 mm) with surge compared to continuous water application for the first irrigation following spring tillage. The saturated hydraulic conductivity (Ksat) of these soils decreased about 45% from the first to the second on‐time. The surge effect was more pronounced during the first than the second irrigation. Most of the effect measured occurred during the first 10 to 20 min of the first off‐time. Consolidation and Ksat of the fine‐textured soil was not changed significantly by the same treatment. Two simple and practical field methods to evaluate this surge effect on soil hydraulic properties were developed: (i) measurement of soil‐surface consolidation by measuring the soil‐surface elevation changes, and (ii) measurement of Ksat by the dripper method. The soil surface level decreased by more than 1 mm and Ksat changed by about 25% when the surge effect was significant. An infiltration model developed during this study showed that simulated cumulative infiltration for surge water application was similar to measured results for the three soils studied.
Effects of Overland Flow on Plant Water Relations, Erosion, and Soil Water Percolation on a Mojave Desert Landscape
Authors: Schlesinger William H. , Fonteyn Paul J. , Reiners William A.
Published: July 2010

Previous work in the Mojave Desert of California has shown that diversion of overland flow from alluvial piedmonts results in lower shrub density and biomass compared to that in adjacent areas that receive overland flow. In this study, measurements of predawn xylem pressure potential of creosotebush (Larrea tridentata) on three areas that were deprived of overland flow and three adjacent areas indicated that shrubs in areas of drainage‐diversion maintained higher water potentials during midsummer drought, suggesting a greater availability of soil moisture in those areas. There were no differences in the distribution of 137Cs between these areas, suggesting that drainage‐diversion has not affected erosion of surficial deposits. Mean depth of wetting of the soil profile, as indicated by the depth distribution of mobile ions (Na+, Cl−, and SO2−4) in the soil, was not significantly different between areas, although the depth to the first peak in concentration of these ions was consistently shallower in areas of drainage‐diversion, suggesting reduced percolation of soil moisture. We conclude that the higher water potential of shrubs in areas of drainage‐diversion is due to lower competitive exploitation of soil moisture than is found among the high biomass of shrubs in undisturbed areas. In contrast, soil properties have not been greatly affected by the diversion of overland flow for the past 50 yr.
Environmental Influences on Soil Chemistry in Central Semiarid Tanzania
Authors: Jones Julia Allen
Published: July 2010

This study assessed the effectiveness of landscape features for predicting the variation in a set of chemical properties from 81 soil profiles sampled in a 236‐km2 site in central Tanzania. Soil samples were treated as points and coded by horizon and by groups, including landform, parent material, vegetation type, vegetation percent cover, and presence or absence of hypogeal termites. The variation captured by these groups in eight soil chemical properties (organic C, total N, acid‐extractable P, exchangeable cations, and extractable Al) was assessed using analysis of variance, Duncan's multiple range test, and discriminant analysis. Soil development fits the catena model along hillslope transects, but lateral subsurface transport of dissolved Fe and cations has produced plinthite and highly base‐saturated horizons just above the lithic or paralithic contact downslope of transitions between ferruginous sediments and granitic sediments. Nevertheless, biotic factors (vegetation type and density of termites) captured more variation than other groups at the regional level. Vegetation species composition and the density and type of termites in central Tanzania reflect soil depth, texture, clay mineralogy, and drainage characteristics influenced by landform and parent material. Root symbioses of native miombo and Acacia spp. woodlands may also modify local soil chemistry via selective uptake of C and exchangeable cations. Termites contribute to the depletion of organic C, total N, and associated nutrients throughout the soils they occupy in this region.
Weathering and Mineralogical Classification of Selected Soils in the Blue Ridge Mountains of South Carolina
Authors: Norfleet M. L. , Smith B. R.
Published: July 2010

Four pedons in the Blue Ridge Mountains of South Carolina were studied to determine the mineralogy and weathering in soils in the southern Appalachians. These soils formed in weathered gniess or schist and receive as much as 2160 mm of annual precipitation. Gibbsite increased with increasing slope, elevation, and rainfall, and ranged from 60 to 670 g kg−1 of the clay fraction (<2.0 µm) and was as high as 140 g kg−1 of the whole soil (<2.0 mm). Gibbsite is thought to form from weathering of feldspars. Kaolinite ranged from 0 to 470 g kg−1 in clay fractions and was as high as 380 g kg−1 of the whole soil. Kaolinite appears to be the product of biotite kaolinization. Hydroxy‐Al interlayered vermiculite (HIV) was the dominant clay mineral in surface horizons, with randomly interstratified mica‐vermiculite and mica increasing with depth. All four soils met the requirements of the oxidic mineralogy class. Release of Fe from kaolinization of biotite, abundance of gibbsite, and fine‐loamy particle‐size class of these soils cause them to have quite high oxidic ratios. However, the high weatherable mineral content of these soils is not consistent with the oxidic mineralogy concept that is supposed to represent soils in an advanced weathering stage. If the oxidic class is to separate out intensely weathered soils, then some amendments must be made to exclude less‐weathered soils similar to the ones of this study. A maximum of 10% weatherable minerals is proposed as an additional criterion for the oxidic class.
Pyrite and Trace Metals in Glauconitic Parent Materials of Maryland
Authors: Rabenhorst M. C. , Fanning D. S.
Published: July 2010

Samples were collected from the oxidized and reduced zones of three glauconitic sediment columns from the Nanjemoy (Eocene) and Aquia (Paleocene) formations on the Maryland Atlantic Coastal Plain. While absent from the oxidized zone, pyrite in the reduced zone ranged from 6 to 8 g kg−1. A portion of this pyrite was shown in thin section to be intimately associated with the glauconite. As shown by scanning electron microscopy, this pyrite occurred as euhedral octahedral crystals and clusters of crystals (up to 15 µm in size) within the matrix and in fissures of glauconite grains. Pyrite not within glauconite grains occurred as framboids, as well as euhedral crystals and clusters. Chemical analyses of magnetically separated fractions suggest enrichment of Zn, Ni, and Cu in the glauconite phase and Zn and possibly Ni in the pyrite phase. Interpretations of Cd and Pb data are less clear. With the exception of Cu, the two sites from the Aquia formation were higher in trace metals than those from the Nanjemoy site.
An Improved Method for Measuring Aggregate Stability of a Weakly Aggregated Loessial Soil
Authors: Pierson Frederick B. , Mulla David J.
Published: July 2010

The original high energy moisture characteristic (HEMC) technique for measuring aggregate stability is shown to have limitations for use with weakly aggregated soils. Improvements were made to expand the applicability of the technique to weakly aggregated soils and reduce its subjectivity to operator bias. The destructive force used to break down the aggregates was controlled by wetting aggregates 1.0 to 0.5 mm in diameter under suction on a sintered glass plate. The moisture characteristic curve for the aggregates was fit using a modified van Genuchten S‐shaped equation, and the specific water capacity curve was analytically calculated. The modal suction and the area under the specific water capacity curve were then computed and used to calculate a structural index value for aggregate stability at a fast and a slow wetting rate. Surface samples of weakly aggregated loessial soil were collected from adjacent long‐term organic and conventional farms in the Palouse region of Washington State. The coefficient of variation for replicate determination of structural indices from a slow wetting treatment using the original HEMC method on samples from both farms was 15%, whereas it was 7% using the improved method. Using the original HEMC technique, there was no difference in the stability ratio of either farm due to complete breakdown of aggregates dropped into standing water. With the improved HEMC method, the aggregate stability ratio and structural index for fast wetting were both significantly higher for soil on the traditional farm than on the organic farm. Thus, the improved method facilitates the measurement of differences in stability of weakly aggregated soils subject to long‐term differences in cropping and management history. In contrast, the original method was inappropriate for these weakly aggregated soils due to improper wetting rates and high variability resulting from operator subjectivity.
Modeling Wheat Seedling Growth and Emergence: I. Seedling Growth Affected by Soil Water Potential
Authors: Bouaziz A. , Bruckler L.
Published: July 2010

To improve the prediction of wheat (Triticum aestivum L.) emergence, an empirical model of wheat root and shoot growth, which takes into account the soil water potential effects, is proposed. Pregerminated seeds from a Moroccan wheat cultivar, Nesma 149, were used for laboratory experiments at a constant 22 °C temperature. Seminal root and shoot lengths were measured vs. time using a completely randomized design, for a clay loam soil (33.6% clay, 57.0% loam and 19.4% sand) at five water potentials: −0.02; −0.17; −0.39; −1.0; −1.31 MPa. Soil dry bulk density of aggregates ≤3 mm was 1000 kg m−3 and thus, soil mechanical resistance to root growth was regarded as a nonlimiting factor. Data were used to select satisfactory growth functions for seminal root axes and shoots and to estimate their empirical parameters. The monomolecular and Gompertz functions were retained for roots and aerial parts, respectively. Considering that the soil water potential in the root zone controlled the root elongation rate, we took into account the average soil water potential along the root axes for calculations. Furthermore, the effects of soil water potential on the estimated parameters of the models involved in the growth models were studied. Results showed that roots and shoots responded differently to soil water stress. After 17 d, total root lengths varied from approximately 600 mm to 300 mm for the −0.02 MPa and −1.31 MPa treatments, respectively, whereas shoot lengths were similar. Finally, the growth curves calculated with soil water potential as input were compared with observed results. The correlation coefficients between predicted and observed data varied from 0.77 to 1.00.
Influence of Fertilizer Application Nonuniformity on Crop Response
Authors: Ndiaye J. P. , Yost R. S.
Published: July 2010

Levels of nonuniformity in K fertilizer application were established in a field experiment on a K deficient soil. Measures of uniformity of fertilizer distribution (UCF) were calculated from the coefficient of variation (CV) of K application (UCF = 1 − CV/100). The structure of spatial dependence of exchangeable soil K was used to estimate the proportion of a given experimental plot which should be below a specified threshold of exchangeable K. Fertilizer requirements were estimated on the basis of the proportion of the region that was deficient. If deficient areas were identified in the field, then variable rates of fertilization could be applied. The response of chinese cabbage (Brassica oleracea L. Chinensis) to K application was strongly affected by the uniformity of fertilizer distribution. Maximum yield decreased 9.5% with nonuniformity of fertilizer distribution. Amounts of K associated with 95% maximum yield were 97, 113, and 444 kg K ha−1 for UCF values of 1.0, 0.42, and −0.02, respectively. Corresponding tissue K concentrations associated with 95% maximum yield were 3.5, 3.8, and 4.0%. Increased variation in exchangeable K from CV = 44.1% to CV = 96.6% resulted in critical levels of soil K of 0.28 and 0.73 cmolc ha−1, respectively.
Application of an Infiltration Model to Experimental Data
Authors: Hogarth W.L. , Parlange J.‐Y. , Haverkamp R. , Davidoff B. , Selim H.M.
Published: July 2010

Infiltration models are often fitted to experimental data in soils, but few actually take ponded depth into account. In this study, the effect of ponded depth is considered by using a model which actually incorporates ponded depth. This is achieved by fitting the model to the experimental cumulative infiltration data and comparing the resultant sorptivity values with two other models where ponded depth is assumed to be zero. The results indicate that there is a 10 to 15% difference, depending on the crop treatment, in the sorptivity when ponded depth is taken into account. It is concluded that the model gives an excellent fit to the experimental data and provides a reliable way of obtaining the physical sorptivity with different ponded depths.
Decomposition of Carbon‐14 Labeled Ryegrass and Maize under Tropical Conditions
Authors: Ayanaba A. , Jenkinson D. S.
Published: July 2010

This work is an extension of earlier studies on the rate of decay of plant material in the forest zone of Nigeria. Maize (Zea mays L.) leaves, uniformly labeled with 14C, were allowed to decompose for 2 yr under field conditions in an Alfisol (pH 7.0) or an Ultisol (pH 4.7). After two years, 15% of the original plant C still remained in the Alfisol. Decomposition was slower in the Ultisol, particularly during the first 26 wk. Maize leaves incorporated in soil at the beginning of the dry season initially decomposed more slowly than leaves incorporated during the wet season, but by the end of 2 yr the difference was small. Earlier experiments in Nigeria with labeled ryegrass (Lolium multiflorum Lam.) tops were continued: after 5 yr, 8% of the original ryegrass C remained in an Alfisol. After adjustment for differences in climate and soil texture, the current Rothamsted model for turnover of organic C in soil gave a close fit to the Nigerian data.
Corn Yield Response to Water Stress, Heat Units, and Management: Model Development and Calibration
Authors: Swan J. B. , Staricka J. A. , Shaffer M. J. , Paulson W. H. , Peterson A. E.
Published: July 2010

A crop model for corn is presented that uses readily available soil, crop, meteorological, and management data as inputs to integrate the effects on grain yield of water stress, plant density, deficit of growing degree days, and planting date. The model can be run on an IBM‐PC, was developed for use in the deep loessial lands of the Upper Mississippi Valley in Major Land Resource Area (MLRA) 105 and associated soil areas, and was calibrated using data for 1972 through 1984 from tillage‐residue management experiments at Lancaster, WI. Estimated water stress, deficit in air‐temperature growing degree days (GDD), and plant density accounted for 77% of the 79% of yield variation explained by the model. The standard error of estimate for predicted yield was 0.67 Mg ha−1. Presence in the data set of interactions between water stress and GDD, and also water stress with plant density, allowed their incorporation into the model. Tillage and residue management had the principal effects of modifying plant density, soil water storage, and rate of phenologic development to the six‐leaf stage.
Erosion‐Induced Changes in the Properties of a Fragipan Soil
Authors: Rhoton F. E. , Tyler D. D.
Published: July 2010

Accelerated erosion of fragipan soils results in a relatively fast decline in productivity, compared with soils without root‐restricting layers. This study was conducted to determine how the characteristics of fragipan soils change with an increase in degree of erosion, as indicated by a decrease in depth to fragipan. Samples were collected at 130 points from the A horizon at five sites on a Grenada silt loam (fine silty, mixed, thermic Glossic Fragiudalf) with depth to fragipan ranging from 15 to 112 cm. Laboratory analyses included a range of chemical and physical properties that influence soil productivity. The data were separated into eight groups on the basis of difference in depth to fragipan and analyzed by regression techniques. Several significant changes occurred as the depth to fragipan decreased. The amount of organic matter, extractable Mn, and silt decreased, whereas increases were observed in exchangeable Na, extractable Fe, percent sand, percent clay, modulus of rupture, color value, and chroma. A minimum of 82% of the variability in these parameters was explained by depth to fragipan. As the degree of erosion increases on fragipan soils several management problems, related to modification of the chemical and physical properties of the plow layer, can be expected. These include greater susceptibility to erosion, reduced seedling emergence and plant vigor, and less drought tolerance.
Relating Sulfate Adsorption to Soil Properties in Michigan Forest Soils
Authors: MacDonald Neil W. , Hart James B.
Published: July 2010

Six Michigan forest soil series comprising several gradients in soil physical and chemical properties were studied to relate SO4 adsorption to soil properties. The series studied were Grayling (mixed, frigid Typic Udipsamments), Rubicon (sandy, mixed, frigid Entic Haplorthods), Kalkaska (sandy, mixed, frigid Typic Haplorthods), Montcalm (coarse‐loamy, mixed Eutric Glossoboralfs), Spinks (sandy, mixed, mesic Psammentic Hapludalfs), and Oshtemo (coarse‐loamy, mixed, mesic Typic Hapludalfs). Six randomly located map units of each series were sampled in the lower peninsula of Michigan. An index of SO4 adsorption potential was determined by shaking samples in solutions containing 0.312 mmol SO4‐S L−1 and measuring the loss of SO4 from solution. The highest SO4‐adsorption potentials were found in Bw, Bs, and Bhs horizons of the Grayling, Rubicon, Kalkaska, and Montcalm series (7.0 to 14.1 mg S kg−1) and in E and Bt horizons of the Spinks and Oshtemo series (4.3 to 10.1 mg S kg−1). Significant differences in adsorption among series were present when comparing the upper 50 cm or the 100‐ to 150‐cm depths in subsurface horizons, related to differences in Al, Fe, and clay concentrations. Sulfate adsorption was positively correlated with dithionite‐citrate and ammonium oxalate extractable Al concentrations in subsurface horizons of the soils studied (r = 0.69–0.90). Regression analyses indicated that SO4 adsorption could be predicted using variables derived from commonly measured soil properties (Al, Fe, pH, organic C, extractable P), with maximum R2 values ranging from 0.83 to 0.89.
Isolation and Characterization of an Iron‐rich Chlorite‐like Mineral from Soil Clays
Authors: Ghabru S. K. , Mermut A. R. , St. Arnaud R. J.
Published: July 2010

This study reports on the isolation and characterization of a naturally occurring Fe‐rich, 1.4‐nm nonexpanding chlorite‐like interphase from soil clays. The mineral was isolated from the coarse clay (2‐1 µm) fraction of a Boralf (Gray Luvisol) from Saskatchewan, by using a high‐gradient magnetic separation (HGMS) at 0.20‐T level of magnetic flux density (MFD). While most chlorites contain Fe2+, analyses showed that all the Fe in this mineral was in the Fe3+ form. High‐resolution transmission electron microscopic (HRTEM) examination confirmed a 1.4‐nm spacing throughout isolated particles. Iron was extracted from the interlayer of the mineral by repeated dithionite‐citrate‐bicarbonate (DCB) plus citrate‐dithionite (Tamura‐CD) extractions. These treatments resulted in the collapse of the mineral from 1.4 nm to 1.0 nm following K‐saturation and 105 or 300 °C heating. Extractions of several Fe‐rich chlorites with the same DCB and Tamura‐CD treatments showed that, although some Fe was extracted from them, they retained their characteristic 1.4‐nm spacing after the K‐saturation and heat treatments. The DCB and Tamura‐CD extractions resulted in a marked increase in cation‐exchange capacity (from 27 to 150 cmolc kg−1), and a layer charge of 0.75 per half unit cell. The high initial cation‐exchange capacity (CEC) values and the rapid acquisition of a micaceous (1.0‐nm) characteristic are atypical of the normal chlorites also included in this study. It is suggested that the mineral isolated is an Fe‐hydroxy interlayered vermiculite rather than a true chlorite. Regarding the genesis of the isolated mineral, two possibilities exist: the Fe lost from the octahedral layer of an original mica could have been responsible for the formation of an Fe‐hydroxy interlayer, thus producing a chlorite‐like mineral, or the interphase may have resulted from weathering of an original chlorite since chlorites were detected in the soil parent material.
Competitive Adsorption of Aqueous Carbonic and Acetic Acids by an Aluminum Oxide
Authors: Schulthess C. P. , McCarthy J. F.
Published: July 2010

The prominence of carbonates in nature and their potential competitiveness with organic acids for sorption sites in soils may be underestimated by researchers who study the mobility of natural organic matter. The pH‐dependent adsorption envelopes of Na salts of acetic acid (AcOH) and carbonates (H2CO3, HCO−3, CO2−3) on an Al oxide were studied to elucidate the effect of carbonates on the adsorption behavior of organic acids. Using 10−3.48 and 10−3 M concentrations of the carbonate salt reduced the amount of acetate adsorbed by 29 and 48%, respectively. Using 10−3.48 M concentrations of acetate, however, did not affect the carbonate adsorption at equimolar concentrations. The relative affinity of the aqueous compounds for adsorption by the Al oxide was determined based on the pH value of their adsorption edges (i.e., based on their adsorption competitiveness relative to the aqueous OH anions). The relative affinity for adsorption by the Al oxide was OH > carbonate > acetate > Cl. The amount of both the acetate and carbonate adsorbed by Al oxide are reduced in the presence of competitive OH anions at high pH and high concentrations of Cl anions at low pH. The adsorption mechanisms of the carbonate and acetate compounds are suspected to be similar based on the chemical structure of these compounds. Batch adsorption studies, however, cannot unequivocally identify a bonding mechanism, which may include ligand exchange or H bonding. We additionally stress that both the affinities and concentrations of the aqueous compounds play an important role in competitive adsorption behavior.
Exchange Capacity and Adsorbed‐Cation Charge as Affected by Chloride and Perchlorate
Authors: Rhue R. Dean , Reve W. H.
Published: July 2010

Previous reports in the literature have indicated that apparent differences in adsorbed‐cation charge can be obtained with Cl and ClO4 media as a result of the adsorption of the bivalent cation complex CaCl. Since the original studies dealt only with smectite clay, it was of interest to determine whether these differences could be observed for other soil and clay materials. Both cation‐exchange capacity (CEC) and adsorbed‐cation charge were measured in Cl and ClO4 media using Na or Ca as the exchangeable cations. In no case was there an effect of the anion on either CEC or adsorbed‐cation charge when Ca was the predominant exchangeable cation. Furthermore, CEC and adsorbed‐cation charge were not significantly different. Studies with SAz‐1 clay showed that, when Na was the only exchangeable cation in the system, the adsorbed‐cation charge was significantly less than the CEC. This difference was attributed to negative adsorption of the anion and its contribution to the total adsorbed charge. Greater adsorbed‐cation charge in Ca‐saturated systems, compared with Na‐saturated systems, was observed for SAz‐1 clay in both Cl and ClO4 systems.
Sorbed Ortho‐ and Pyrophosphate Effects on Zinc Reactions Compared in Three Autoclaved Soils
Authors: Xie R. J. , MacKenzie A. F.
Published: July 2010

Information on interactions between ortho‐ (OP) or pyrophosphate (PP) and Zn in soils are fragmentary. Evaluating the relative effects of the two phosphates on Zn reaction in the soil requires autoclaving the soil in order to minimize biological hydrolysis of PP to OP. Sequential reactions between OP or PP and Zn in three autoclaved soil samples were compared using Zn sorption, desorption and fractionation at an initial pH 6.0 and ionic strength 0.03 M as KClO4. Soil materials were surface samples of a Typic Haplorthod, Typic Eutrochrept, and Typic Humaquept. One mmol sorbed P as OP resulted in greater increases in cation‐exchange capacity (CEC) than 1 mmol sorbed P as PP. At the same rate of P addition, the absolute increase in CEC was greater with PP than OP, because of greater P sorption as PP than as OP. Both sorbed OP and PP increased Zn sorption and decreased Zn desorption. The sorption of Zn was described best by Freundlich sorption isotherms, rather than Gunary, Langmuir, or Temkin isotherms. Results suggested that complexes of OP‐ or PP‐Zn‐soil materials have formed, particularly in the coarser textured materials, with PP being more effective in complexing Zn than OP.
Particle Density of Volcanic Soils as Measured with a Gas Pycnometer
Authors: Bielders C. L. , De Backer L. W. , Delvaux B.
Published: July 2010

In the absence of actual data, the particle density of soil is often assumed to be 2.65 Mg/m3. In this study, we will discuss whether this hypothesis applies with reasonable accuracy to various types of soils from Martinique. Thirty‐nine samples taken from seven different subgroups of soils derived from volcanic materials were considered: Andeptic Troporthent, Typic Hydrandept, Typic Dystrandept, Andic Humitropept, Typic and Oxic Dystropept, and Entic Pellustert. Particle density was measured in triplicate on undisturbed, oven‐dried samples by means of a gas pycnometer. The measurements were performed using air and He. Values found in He pycnometry ranged from 2.38 to 2.72 Mg/m3. The organic‐matter content was a major factor in explaining low particle densities, but other soil constituents may be significantly involved also. Reproductibility of He pycnometry was found to be good. Air‐pycnometry measurements revealed strongly distorted values for many soil materials when compared with He‐pycnometry results. This was assigned to a gas adsorption phenomenon and found to be linearly related to the surface area of the soil samples as measured by ethylene glycol monoethyl ether.
Functional Sensitivity Analysis of Four Methods to Generate Soil Hydraulic Functions
Authors: Wösten J. H. M. , Schuren C. H. J. E. , Bouma J. , Stein A.
Published: July 2010

Rapid advances in model building have led to the understanding that applicability of future simulations depends, to a great extent, on the availability of accurate soil hydraulic functions obtained with efficient methods rather than on new models. In this study, four different methods were used to generate hydraulic functions: Method A, direct on‐site measurement; Method B, use of measured hydraulic functions averaged on a regional scale; Method C, use of measured hydraulic functions averaged on a national scale; and Method D, use of van Genuchten parameters correlated with soil texture and organic‐matter content. Accuracy of these methods was tested by comparing the simulated water storage with the measured water storage of the upper 0.5 m of three soil profiles over a period of 7 yr. Differences in performance of the four methods were not significant. Agreement between measured and simulated water storage was best, however, when directly measured hydraulic functions (Method A) were used. Next best agreement was obtained when continuous (Method D) and two types of class pedotransfer functions (Methods B and C) were used, which relate textures and soil horizons to physical characteristics. Costs involved in obtaining directly measured soil hydraulic functions are prohibitively high, compared with costs for the other methods. With regard to both accuracy and costs, the development of a data base of measured soil hydraulic functions and use of this information to derive continuous and class pedotransfer functions assures, in many cases, optimal spending of limited available resources.
Fly Ash Use as a Time Marker in Sedimentation Studies
Authors: Jones Robert L. , Olson Kenneth R.
Published: July 2010

Fly ash from coal burning often takes the form of magnetic spherules, making it easy to separate and identify. Illinois soils near to and remote from known sources of fly ash were studied to evaluate ash incidence and accumulation of ash‐bearing sediments in the profile. Soils from both types of areas contained magnetic fly‐ash spherules. Concentrations >75% occurred in the magnetic fraction of the surface horizon (mostly in the top 12.5 cm) of a soil on an uncultivated, stable ridgetop near Springfield, IL. On the nearby Sangamon River floodplain, fly ash occurred in large numbers to the 25‐cm depth, and in lesser numbers to 45 cm, the top of a buried, organic‐C‐rich layer. This buried layer may represent the surface in the 1850s, when railroads and perhaps also industrial boilers were introduced. In depositional horizons of soils from remote sites, fly ash occurred at levels of <1%; it probably came from steam locomotives and, perhaps, steam‐powered farm machinery. From the 1850s to the late 1920s, railroads in Illinois increased to about 16 000 km of track; consequently, fly ash is ubiquitous in surface soils and is easily assayed. Steam‐powered farm machinery (although not always fueled by coal) was common from 1880 until about 1920. At depositional sites, the buried A horizon contained fly ash, but subjacent horizons did not. This pattern indicates that fly ash occurrence is useful in distinguishing the presettlement surface, thereby making possible the determination of rates of sedimentation at a particular site.
Crop Yield Variation Associated with Coastal Plain Soil Map Units
Authors: Karlen D. L. , Sadler E. J. , Busscher W. J.
Published: July 2010

Variation among soil map units needs to be quantified so farmers can implement more economically and environmentally acceptable production practices. We conducted a 4‐yr field study at an 8‐ha research site near Florence, SC, to quantify yield variation for a southeastern Coastal Plain field. Nineteen soil map units, classified as Ultisols and representing seven soil series were identified by Soil Conservation Service cooperators. Corn (Zea mays L.) was grown in 1985, 1986, and 1988, while in 1987 wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] were double‐cropped. All soils received conventional disk tillage, fertilization based on soil‐test recommendations, and uniform planting rates. Crop yield was measured by harvesting transects throughout the field and subsequently identifying soil map units for each plot. Average corn yield among soil map units ranged from 3.7 to 8.0 Mg ha−1 in 1985, 0.1 to 2.8 Mg ha−1 in 1986, and 1.1 to 5.0 Mg ha−1 in 1988. Yields were lower in 1986 because of severe drought. Wheat yield ranged from 3.5 to 6.2 Mg ha−1, while sorghum yield ranged from 1.7 to 5.2 Mg ha−1 in 1987. Extractable P, K, Ca, Mg, Mn, and Zn; soil organic matter and pH; and depth to an argillic horizon (Bt) were measured to identify causes for yield variation among soil map units. Depth to Bt had the best statistical relationship between crop yield and soil map unit, but yield variation within an individual map unit was almost as large as variation between map units. Our results demonstrate how measurements of crop yield by soil map unit can be determined and used to study soil variation. They also provide a data base that can be used to evaluate plant growth and soil management models for individual soil map units.
Relationship between Diagnosis and Recommendation Integrated System (DRIS) Optima and Foliar Nutrient Critical Levels
Authors: Needham Ted D. , Burger James A. , Oderwald Richard G.
Published: July 2010

Optimum nutrient levels for loblolly pine (Pinus taeda L.) were estimated by applying DRIS techniques to 504 randomly selected trees from loblolly pine plantations in Georgia and South Carolina. Levels of 12.0 g/kg N, 1.1 g/kg P, and 0.8 g/kg Mg were determined through this method. These values were slightly higher than the generally accepted critical levels of 11.0, 1.0, and 0.7 g/kg for these nutrients, which illustrates the theoretical relationship between critical levels and DRIS optima. This study shows that DRIS methods applied to field survey data can be used to estimate optimum foliar nutrient levels while circumventing many problems associated with traditional critical‐level derivations.
Simulation Model of Banded Ammonia in Soils
Authors: Izaurralde R. C. , Kissel D. E. , Cabrera M. L.
Published: July 2010

The efficient use of anhydrous NH3 as a fertilizer depends on factors such as N rate, knife spacing, depth of application, and soil properties like NH3‐retention capacity. We developed a computer model that predicts some characteristics of an NH3‐retention zone in soil. Soil titratable acidity to pH 9 using NH4OH as the base was an input to the model used to estimate the NH4‐N (NH3 and NH4) concentration at the line of injection 24 h after NH3 application. Data for the model were collected using a laboratory apparatus that applies anhydrous NH3 in a band. Ammoniacal‐N concentration with distance away and normal to the line of injection was predicted using a nonlinear equation and values of N rate, band spacing, and soil bulk density. Soil pH was calculated as a linear function of the ammoniacal‐N concentration in soil with ammoniacal N at pH 9 equal to titratable acidity. Direct losses of NH3 by volatilization were assumed to occur because of insufficient depth of application or rates of N application that were too high. Concentrations of NH4 and NH3 in solution were calculated using the Gapon cation‐exchange and Henderson‐Hasselbach equations, respectively. Observed vs. predicted ammoniacal N and pH at different distances from the injection line for seven soils and 13 rates (1.6–8.4 g N m−1) correlated at P < 0.01 (r2 = 0.85 and 0.84, respectively). The model provided reasonable estimates of direct NH3 loss and concentration of ammoniacal species in solution. This tool could help to better understand the behavior of NH3 in soil and, therefore, to manage its application to reduce N losses. Information on ammoniacal‐N distribution and on soil pH in an NH3 band could also be used for simulating transformations of banded N.
Soil pH and Phosphorus and Potassium Uptake by Maize Evaluated with an Uptake Model
Authors: Chen Jen‐Hshuan , Barber S. A.
Published: July 2010

Plant growth and nutrient uptake by plants have been shown to be affected by soil pH. However, the effects have not been evaluated with a mechanistic uptake model that can evaluate the relative influence of soil pH changes on changes in soil supply parameters that influence predicted P uptake. The objectives of this research were to verify the Barber‐Cushman nutrient‐uptake model under a range of soil pH conditions and to use the model to evaluate the influence of soil pH on the model parameters supplying P and K to maize (Zea mays L.) roots. A pot experiment was conducted to evaluate the accuracy of the model for predicting P and K uptake at soil pH levels of 3.8, 4.7, 5.7, 6.5, 7.6, and 8.3 in Chalmers silt loam (fine‐silty, mixed, mesic Typic Haplaquoll). This study showed that the nutrient‐uptake model accurately predicted the effect of the soil pH on P uptake (Y = 0.44 + 0.93X, r2 = 0.99) when the change of P from H2PO4 to HPO4 at the higher pH values was accounted for, and predicted K uptake (Y = 67 + 0.94X, r2 = 0.99) without modification for pH.
Soil Nitrogen Mineralization in a Clearcutting Chronosequence in a Northern California Conifer Forest
Authors: Frazer D. W. , McColl J. G. , Powers R. F.
Published: July 2010

Soil ammonification, nitrification, and N mobility were studied for 1 yr in three Sierra Nevada (USA) mixed‐conifer stands to examine the long‐term influence of timber harvesting on soil N dynamics. Clearcutting had a persistent effect on soil N mineralization, detectable by in situ incubation but not by conventional low‐tension lysimetry. Mineralization rates were greater in 5‐ and 17‐yr‐old regenerated clearcuts than in an adjacent 100‐yr‐old uncut forest. Annual rates of N mineralization averaged 12 kg ha−1 for the uncut forest, and 49 and 31 kg ha−1 for the 5‐ and 17‐yr‐old clearcuts, respectively. Mineralization continued throughout the summer, even when soil matric potentials were <‐1500 kPa. Soil solution NO3 concentrations were much higher in the younger clearcut than in either the older clearcut or the uncut forest. Sustained effects of clearcutting seem due largely to higher substrate availability and to moisture and temperature conditions favoring microbial activity. Chemical inhibition of nitrification may become important as the forest floor develops.
Adsorption of Humic Substances by Hydroxyaluminum‐ and Hydroxyaluminosilicate‐Montmorillonite Complexes
Authors: Inoue K. , Zhao L. P. , Huang P. M.
Published: July 2010

The interaction between humic substances purified from an Andisol and montmorillonite (Mt) complexed with hydroxyaluminosilicate (HAS) or hydroxyaluminum (HyA) ions was studied. The HAS ions were formed from solutions containing HyA ions and orthosilicic acid at an Al concentration of 4 mM; Si/Al atomic ratios of 0, 0.25, 0.5, 0.75, and 1.0; and a NaOH/Al molar ratio of 2.0. The adsorption of humic substances by HAS‐Mt and HyA‐Mt complexes increased as pH decreased in the adsorption systems. At concentrations of 10 to 1000 mg humic substance L−1 and pH 5.5, the adsorption of humic acid by these complexes decreased with an increase in the Si/Al atomic ratio of hydroxy materials fixed in interlamellar spaces of Mt, whereas the adsorption of fulvic acid followed almost the opposite trend. When the adsorption data of humic substances by these complexes were evaluated using the Eadie‐Hofstee plot of the Langmuir adsorption equation, multiple linear relationships were obtained, indicating the presence of multiple populations of sites that have a differing affinity for humic substances. A ligand exchange reaction, in which humic substances displaced OH or OH2 groups from the coordination shells of structural Al on the edges and HAS or HyA polymers fixed on the edges, external planar surfaces, and/or the interlamellar spaces of Mt, may be involved in the adsorption processes. The results indicate that besides HyA ions, the reactivity of HAS ions in humus accumulation and the pedogenic implication in soil environments merit attention.
Critical Evaluation of Methods for Determining Total Organic Phosphorus in Tropical Soils
Authors: Condron L. M. , Moir J. O. , Tiessen H. , Stewart J. W. B.
Published: July 2010

The determination of total organic phosphorus (TOP) in soils presents several methodological problems, particularly on strongly weathered and tropical soils. We reviewed the application of several methods for TOP determination to soils from different zones of the globe and evaluated the applicability of one ignition and two extraction methods to tropical soils from Brazil and Ghana. Reproducibility (coefficients of variation) was within 6% for the ignition method, and 13% for the extraction methods, due to the simplicity of the former. The two extraction methods produced results similar to each other, while the ignition method generally gave higher TOP contents. Unusually low C to organic P ratios indicate that the ignition method overestimated TOP in several soils. The Bowman extraction method, developed on weakly weathered soils, appeared also suitable for a variety of tropical soils.
Phosphate Sorption‐Desorption Characteristics by Magnetically Separated Soil Fractions
Authors: Saying M. , Mermut A. R. , Tiessen H.
Published: July 2010

A soil sample from the surface horizon of a Paleustollic Torrert from southeastern Turkey was size fractionated, then subfractionated further by magnetic separation to study P sorption and desorption behavior of these separates. Citrate‐dithionite (CD) extractable Fe constituents (Fed) were found effective P sorbers in silt‐size particles, especially in the coarse‐silt fraction (50–20 µm). A five‐fold increase in P sorption was noted with an 8.5‐times increase in Fed content, suggesting that, in this fraction, P sorption is largely controlled by Fe oxyhydroxides. Carbonates in sand and coarse‐silt fractions as well as CD‐extractable Al and Si, and oxalate‐soluble Al and Si in all fractions had no significant effect on P sorption. In the coarse‐clay fraction, besides the Fed content, clay minerals also affected P sorption. Desorption of P was, in general, lower in the highly magnetic fractions, and decreased with decreasing particle size. Fluctuations in P desorption among different concentrations of added P in each particular fraction cannot be explained clearly. This may suggest the possibility of P precipitation in a 24‐hr experimental time period. Removal of about 2.9% Fed from the fine clay (<0.2 µm) resulted in a 22% decrease in sorption, and an increase in desorption, from 32 to 44% to 62 to 80%. The results suggest that Fe oxyhydroxides and other Fe‐bearing constituents are important P sorbents not only in tropical soils, but also in soils of the temperate semiarid regions.
Effect of pH on Permeability of Clay‐Sand Mixture Containing Hydroxy Polymers
Authors: Keren R. , Singer M. J.
Published: July 2010

This study was conducted to determine if the effectiveness of hydroxy‐Al and ‐Fe polymers in stabilizing the hydraulic conductivity of smectite‐sand mixture increases with their charge density. The effect of pH 5.5 and 7.5 on the saturated hydraulic conductivity (HC) of Na/Ca‐smectite‐sand mixtures (5% clay and 95% sand) and in the presence of hydroxy‐Al and ‐Fe polymers was studied by leaching with NaCl‐CaCl2 solutions at sodium adsorption ratios (SAR) of 10 and 20 of electrolyte concentrations of 500, 100, 50, 10, 5, 3, 2, and 1 molc m−3 and deionized water. The HC of the mixtures essentially remained unchanged as long as the electrolyte concentration of the leachate was ≥50 molc m−3. A further decrease of the solution concentration produced a drop in HC for both the untreated and treated systems at pH 7.5. No HC reduction occurred at pH 5.5 when hydroxy‐Al polymers were present. The HC of both treated and untreated systems at pH 5.5 was higher than that at pH 7.5. The HC reduction was two and three orders of magnitude smaller for the treated systems than for the systems without hydroxy polymers. Hydroxy‐Fe polymers also reduced the effect of electrolyte concentration in the leaching solution on the HC of the clay‐sand mixture, but to a lesser extent. The effect of pH on the charge density of the hydroxy polymers explained their effectiveness in stabilizing the system at the lower pH. The lower HC of the clay‐sand mixture in the presence of hydroxy‐Fe polymers suggests that the aggregates with this polymer are weaker than those with hydroxy‐Al polymers. This difference in stability is due to the higher point of zero charge (PZC) for the hydroxy‐Al polymers.