bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationships between Sesquioxides, Kaolinite, and Phosphate Sorption in a Catena of Oxisols in Malawi
Authors: Karim May I. , Adams W. A.
Published: July 2010

A catenary sequence of Oxisols was examined to determine the phosphate sorption capacity of the oxic horizon and to identify the minerals responsible for this property. The phosphate sorption capacity of the six soil samples taken along the sequence was found to increase downslope as far as the midslope, then to decrease towards the valley bottom. All samples contained quartz, kaolinite, goethite, and hematite; gibbsite was identified in one sample. Aluminium‐substituted goethite was found to be the mineral mainly responsible for phosphate sorption capacity and the one that caused variations in this property along the slope sequence. Significant correlations between phosphate sorption capacity and both Fe and Al extracted by citrate‐dithionite are explained by their occurrence in this oxide. Amounts of noncrystalline oxides were low and there was no correlation between phosphate sorption capacity and amounts of either Fe or Al extracted by oxalate. Kaolinite was calculated to account for 12 to 29% of the phosphate sorption capacities of the soils but there was no significant correlation between the two. Hematite, which showed a progressive decrease in content downslope, had no measurable influence on phosphate sorption capacity. The distribution of Fe oxides along the sequence suggests rather slow pedogenetic change in the horizons sampled with goethite, the main oxide product of contemporary soil‐forming processes.
Trace Metal Profiles in the Forest Floor of New England
Authors: Friedland A. J. , Johnson A. H. , Siccama T. G. , Mader D. L.
Published: July 2010

Previous studies in New England have revealed high levels of trace metals in the forest floor of remote regions and evidence of increases in trace metal concentrations and amounts over time. In this study, forest floor profiles collected from a boreal forest in Vermont, a northern hardwood forest in New Hampshire and white pine (Pinus strobus L.) stands in Massachusetts were analyzed for Pb, Cu, Zn, Ni, Cd, and organic matter. Concentrations of Pb, Cu, Zn, Ni, and percent organic matter showed similar trends with depth in all three forests. Cadmium occurrence differed according to site. Concentrations of Pb, Cu, Zn, and Ni were greatest 2 to 4 cm below the surface of the forest floor in all three forests. As expected, percent organic matter decreased with depth in the profile. Concentration and accumulation of trace metals appear to occur in the Oe horizon.
Optimal Prediction of Saturation and Wetting Fronts during Trickle Irrigation
Authors: Lockington D. , Parlange J.‐Y. , Surin A.
Published: July 2010

The nonlinear diffusion equation in spherical geometry describes water movement from a point source into a porous medium. This situation occurs, for example, in the early stages of trickle irrigation. Prediction of the saturation and wetting front positions during irrigation is of obvious practical importance. In the present paper, a general formula which predicts the positions of the two fronts is found by optimization. For particular soil properties the exact numerical solution of the diffusion equation can be easily found and is used to check the accuracy of the optimization formula. This formula proves to be extremely accurate. A simple asymptotic solution is also obtained which compares favorably with the above results in the long‐time limit. The maximum error associated with neglecting gravity is quantified using this solution and proves to be quite acceptable for most practical applications. In those few cases when this error is too large to be neglected and gravity needs to be included in the theory, other effects, e.g., instability, should also be considered.
Optimal Analysis of the Effect of a Surface Crust
Authors: Parlange J.‐Y. , Hogarth W. L. , Parlange M. B.
Published: July 2010

Recently, experiments have been presented for the horizontal flow of water by soil with a surface crust and compared to an analytical model. It was found that the water content at the surface was consistently less than predicted by about a 1% water content. Such a small discrepancy may seem to be more of theoretical rather than practical interest. In fact, due to the rapid variation of soil properties near saturation, a very small error in water content at the surface implies that the model is unreliable to predict the relationship between cumulative absorption and soil water content at the soil surface, especially in the early stages of infiltration. A new model is developed here, based on an optimal principle. The results from this model are closer to the experimental observations, but some discrepancy remains. To eliminate the possibility of experimental error a simple theoretical example is also considered, where an exact solution exists, which illustrates in detail the accuracy of the optimal model.
Anisotropy of Unsaturated Soils
Authors: Mualem Yechezkel
Published: July 2010

A conceptual model is applied for quantitative evaluation of the anisotropy factor during desaturation. The soil is assumed to consist of many thin parallel layers having different hydraulic properties. A uniform density distribution function is used to represent the saturated hydraulic conductivity probability of the various layers. A power function relationship is assumed between the hydraulic conductivity and the capillary head. The exponent in the hydraulic conductivity‐capillary head relationship and the air entry value are allowed to be variables. The model indicates that the degree of anisotropy of unsaturated soil may vary considerably from its value at saturation. Reducing the capillary head gradually from zero, the anisotropy factor first decreases to a minimum and then increases rapidly as the soil dries. In some cases, the anisotropy factor can reach values several orders of magnitude higher than at saturation. Soil layers with very low permeability tend to diminish anisotropy on desaturation. Conversely, large variation of the hydraulic properties of the layers would enhance anisotropy in the unsaturated state.
Ion Activities: An Historical and Theoretical Overview
Authors: Sparks D. L.
Published: July 2010

A knowledge of ion activities in soil‐water systems is essential to a proper understanding of the physicochemical behavior of soils and to the environment of plant roots in the soil. However, with the notable exception of soil acidity, perhaps no other topic in soil chemistry has provoked such fierce arguments as the meaning of ionic activities as they apply to the soil solution. The purpose of this paper is to present an historical and theoretical overview of the use of ion activities in soil chemistry. Attempting to incorporate ionic species into a thermodynamic analysis of the soil solution is a convenient mathematical device, since an ionic species cannot be described in thermodynamic terms. Ionic species are strictly molecular or microscopic concepts. It is demonstrated in this paper that when ionic equilibria between aqueous solutions and solid phases are investigated, the division of the electrochemical potential into a term in electrical potential (φ) and a term in chemical potential (µ) is entirely arbitrary. Additionally, the early 1950s arguments of Jenny, Marshall, Peech, Coleman, Overbeek, and Babcock dealing with junction potentials, suspension effects, and mobilities of ions is reviewed. The importance of soil solution activities in relation to nutrient uptake and plant growth is also presented.
The Future of an Illusion: Ion Activities in Soil Solutions
Authors: Sposito Garrison
Published: July 2010

The thermodynamic significance of the single‐ion activity is limited to its use, through a self‐consistent set of conventions, to predict accurately the activities of electrolytes. Despite this fact, single‐ion activities appear to be of increasing importance in the study of soil‐plant relationships and in the surface chemistry of soils. Thus it is worthwhile to suggest a practical algorithm for the estimation of single‐ion activities in soil solutions: (i) Extraction and determination of the composition of the soil solution. (ii) Speciation of the extracted solution with an ion‐association computer model. (iii) Calculation of ion activities based on species concentrations and the Davies equation. This self‐consistent approach can be tested successfully with the performance criteria of: (i) adherence to Debye‐Hückel theory and Young's rules and (ii) accurate prediction of both conditional equilibrium constants and electrolyte activities that are important in soil chemistry.
Phosphate Sorption by Soils: I. A Model for Phosphate Reaction with Metal‐Oxides in Soil
Authors: van Riemsdijk W. H. , Boumans L. J. M. , de Haan F. A. M.
Published: July 2010

A model for P sorption is described which is based on previous studies concerning the interaction of phosphate with gibbsite and with a sandy soil. Formation of coatings of metal phosphate on metal oxide particles constitutes the presumed mechanism of the sorption process. Diffusion of phosphate ions through the surface coating is taken as the rate‐limiting step. The relating diffusion equation is first solved with the condition of constant concentration for reactive particles of well defined geometry. Then it is shown that for any assembly of reactive particles the sorption as a function of the concentration‐time product should yield one curve, irrespective of the reaction pathway. The form of this curve can only be predicted for very specific cases. The above curve, however, can be determined experimentally, allowing the calculation of the phosphate sorption rate for any combination of concentration and sorption values. This is very useful in modeling the transport of P through soil systems. Experimental evidence is given which supports the model theory.
Ammonia Volatilization from Surface‐Applied Urea: Effect of Hydrogen Ion Buffering Capacity
Authors: Ferguson R. B. , Kissel D. E. , Koelliker J. K. , Basel Wes
Published: July 2010

The influence of soil pH and soil cation exchange capacity on ammonia volatilization from surface applied ammoniacal nitrogen has been reported in previous studies. Since the hydrolysis of ureacontaining N fertilizers causes an increase in alkalinity, a soil's inherent H+ buffering capacity (defined as the soil's total acidity, comprised of exchangeable acidity plus non‐exchangeable, titratable acidity), should exert a dominant influence on the maximum soil pH at the site of urea fertilizer application. The objective of this study was to demonstrate the importance of a soil's H+ buffering capacity in affecting NH3 volatilization from surface‐applied urea. The H+ buffering capacity of two soils was increased by adding hydroxy‐Al polymers to one soil, and weak and strong acid cation exchange resins to the other soil. Care was taken to keep cation exchange capacity and initial pH close to the same on amended and unamended (control) soils. Urea was surface‐applied to amended and unamended soils and ammonia volatilization and soil surface pH were measured. The increase of H+ buffering capacity of soils was found to reduce soil surface pH and NH3 volatilization after application of urea. It is concluded from this work that H+ buffering capacity of a soil is a better indicator of NH3 loss potential than a soil's initial pH.
Soil Structure and Associated Rooting Behavior in Minesoils
Authors: McSweeney K. , Jansen I. J.
Published: July 2010

The objective of this study was to identify and describe soil structural patterns and rooting behavior in reclaimed minesoils. The soil chosen for this study consists of approximately 0.4 m of topsoil (A horizon) material placed on approximately 1.5 m of a blend of B horizon, mixed paleoloesses, Sangamon paleosol, and Illinoian till. Four soil pits were excavated, exposing root systems of the corn test crop. Detailed soil and root pattern descriptions were made in each pit. Root patterns were depicted using the profile wall method. An outline of soil structural pattern was superimposed over the root pattern to provide a pictorial relationship between the two. Differences in the physical condition of subsoils were distinguished on the basis of the soil descriptions and statistical analysis of the root length determinations. An artificial soil structure was characterized and attributed to particular mining and reclamation practices. The structural arrangement consists of rounded aggregates loosely compressed together, that fall within the size classes currently used for blocklike and polyhedral aggregates. Plant rooting was distinctly more profuse where this structure was present than where the soil material was massive and compact. It is proposed that structural differences among newly constructed soils are of such significance that they should be carefully characterized and described, and where appropriate used for series level separations. Operations using a mining wheel in combination with belt transportation favor the formation of the more desirable fritted structure, whereas operations using scrapers exclusively favor the formation of the less desirable massive physical condition.
Micropedological Study of Termite Mounds of Three Species of Macrotermes in Kenya
Authors: Mermut A. R. , Arshad M. A. , St. Arnaud R. J.
Published: July 2010

Seven termite mounds built by three Macrotermes species (M. michaelseni, M. subhyalinus, and M. herus) at five different sites were studied micropedologically. Construction units and void patterns were considered as integral parts of mound construction covering specific termite habitats in different eco‐climatic regions of Kenya. Regardless of the species of termites, it was found that the micro construction units recognized in the undisturbed samples taken from different parts of the nests were entirely dependent on the nature of the material form which the mounds were built. Building behavior of different termite species in the same environment appears to be very similar. Different construction units were found to occur in different parts of a mound. The fabric and micromorphological features established in this study consist of pellets, compound pellets, lenticular fabric, mesh fabric, lamellar fabric, organic laminae, cross‐hatched arrangement of ground mass, and mammillated metavughs. The fabrics of the studied mounds were made from transported and repacked soil particles with addition of insect saliva and/or excreta.
Airborne Dusts in the Edwards Plateau Region of Texas
Authors: Rabenhorst M. C. , Wilding L. P. , Girdner C. L.
Published: July 2010

As part of a larger study to estimate the impact of airborne dust on pedogenesis, seven dust traps were installed across a 100 000 km2 region in central and western Texas. Contents of the traps were collected and analyzed at 120‐d intervals. Total annual infall was approximately 12 g/m2 with significant seasonal variations occurring. The average clay content is near 60% and is primarily mica and quartz with lesser amounts of smectite and kaolinite. The medium silt (5–20 µm) comprises approximately 25% of the dust and is dominantly quartz with moderate amounts of alkali feldspars. Particulate carbonates were not observed and Ca values for water from the dust traps indicate that if present, carbonates constitute only a small portion of the total infall. Analyses of medium silt grains using SEM and microprobe indicate that quartz and feldspar grains have both smooth conchoidally fractured surfaces and rough pitted morphologies. Grain surface morphology is not adequate for mineralogical identification. Although some materials from local soils may be collected as dust, analyses indicate that the primary source is external to the study area. Grain morphologies suggest multiple source areas for the dust. Substantial uniformity in total infall, particle size distribution, mineralogy, and silt grain morphology was observed across the study area, indicating that the dust depositions are regional in character.
Influence of Long‐Term Tillage and Crop Rotation on Water Erosion
Authors: Van Doren D. M. , Moldenhauer W. C. , Triplett G. B.
Published: July 2010

Soybeans (Glycine max. L.) apparently predispose a field to greater erosion by water than does corn (Zea mays L.) at equal residue cover. Most of the available data have been obtained from locations with 5 years or less history of a specific management. This study measured soil loss during simulated rainfall from plots having an 18‐yr history of management to ascertain deviations, if any, from current expectations. The soil was a fine‐loamy, mixed mesic, Typic Fragiudalfs having an average slope of 3%. Tillage variables included no‐tillage, spring plow 20 cm deep, and spring plow 20 cm deep followed by 10 cm deep disking or equivalent. Rotations were continuous corn or corn‐soybeans. Kinetic energy of applied water was about 70% of natural rainfall at 63 mm/h rate. Runoff and soil loss were measured at 60‐s intervals during the 30‐ to 60‐min runs. Soil loss per unit of rainfall following either crop in the corn‐soybeans rotation was 45% greater than from continuous corn, after accounting for differences in residue cover by use of the Universal Soil Loss Equation (USLE). Soil loss per unit of rainfall for land not tilled for 1 or over 20 years was 90% less than expected according to the current version of the USLE.
Crop Residue Removal and Soil Productivity with No‐Till Corn, Sorghum, and Soybean
Authors: Doran J. W. , Wilhelm W. W. , Power J. F.
Published: July 2010

Crop residues have been considered during the past decade as alternate energy sources to supplement dwindling fossil fuel sources and enhance energy independence in the United States. Agricultural scientists have demonstrated the importance of crop residues in reducing soil erosion, enhancing the soil physical environment for plant growth, and as a reserve for major crop nutrients. In eastern Nebraska, we evaluated the effects of various amounts of surface crop residues (aboveground dry matter remaining after harvest) on dry‐land production of no‐till corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and soybean [Glycine max (L.) Merrill] over a 3‐yr period. Where crop residues were completely removed after harvest, average grain and residue yields of corn and soybean were 22 and 24% lower, respectively, than where residues were not removed. Removal of 50% or addition of 50% (150%) surface crop residues had little or no effect on crop yields compared to no removal (100%).

Sorghum yields were unaffected by residue removal, but stands were significantly less at the 150% residue rate. Yield reductions for corn and soybean resulted primarily from decreased soil water storage and excessive surface soil temperatures where residues were completely removed. Sorghum tolerated conditions of temperature and water stress better than other crops. Removal of surface crop residues can seriously reduce corn and soybean yields in climates where stressful conditions occur during the growing season. Considerations for using crop residues as alternate energy sources should include these potential reductions in grain and residue yields, as well as increased nutrient removal and greater potential for soil erosion.
Analysis of Solute Transport in Column Tracer Studies
Authors: Parker J. C.
Published: July 2010

To pose mathematically tractable boundary conditions for finite porous media it is necessary to regard the representative elementary volume (REV) as infinitesimal. In so doing, continuity of macroscopic concentrations across boundaries is in general sacrificed to maintain flux continuity. The macroscopic concentration discontinuity can be rationalized by regarding influent and effluent concentrations as flux‐weighted mean values relative to the volume‐averaged resident concentrations (Cr) in the porous medium near the boundaries. This concept leads logically to the definition of a flux concentration (Cf) defined macroscopically as the ratio of the solute flux density to the fluid flux density. Flux concentrations obey a convection‐dispersion equation of identical form to that for resident concentrations and transformation of boundary conditions allows direct solution for Cr or Cf. Solutions are presented for Cr and Cf for one‐dimensional steady flow which assume back‐mixing at outflow boundaries to be negligible. The solutions are checked against measured effluent curves and resident concentration distributions of Br in a high dispersivity porous medium contrived to have an REV diam (l) of about 25 mm. The solution for Cf accurately describes the breakthrough curve for a 190 mm long column and the solution for Cr matches measured resident concentrations at locations further than l/2 from the boundaries. Solutions which assume equality of Cr and Cf at exit boundaries fail to describe the experimental data. The results indicate that fractured or aggregated porous media having continuous relatively large pores may be treated as simple continua if the flow region is several times larger than the REV.
Steady Infiltration from Spherical Cavities
Authors: Philip J. R.
Published: July 2010

The problem of quasilinearized steady infiltration from spherical cavities, with the moisture potential fixed at the cavity surface, is solved exactly. Solutions are presented numerically and graphically for values of the dimensionless cavity radius R0 in the range 0 to 10. The dependence on R0 of total cavity flow, of the variation of infiltration rate around the cavity surface, and of the distributions of moisture content and potential, are examined. As R0 increases, gravity increasingly distorts the moisture distribution from the symmetry produced by capillarity alone. This distortion, although marked, is less than one‐hundredth that for infiltration from circular cylindrical cavities: a vivid illustration of the stronger dominance of gravity over capillarity in two‐dimensional systems than in three‐dimensional ones. An earlier approximate solution of this problem proves accurate only for R0 ⩽ 0.27. The cavity flow, evaluated by the present analysis, may be combined with the point source solution to give approximate results useful for the region deeper than 20 radii below the cavity.
Curve‐fit Errors in Langmuir Adsorption Maxima
Authors: Harter Robert D.
Published: July 2010

Although the Langmuir equation does not always adequately estimate “adsorption” maxima, it remains useful for empirical description of data. The test of data fit to the equation has usually been by linearity of the “Langmuir plot,” viz. concentration/adsorption plotted as a function of concentration. This test, however, is inadequate because the plotting of concentration against itself reduces data variability and always provides a statistically significant correlation coefficient. A better test of fit is to ascertain whether the adsorption isotherm has the shape of the equation model. When isotherms do not have the correct shape and only low concentration data is used, the equation can provide estimates of the adsorption maximum that are in error by 50% or more.
A Chemical Model of Phosphate Adsorption by Soils: II. Noncalcareous Soils
Authors: Goldberg Sabine , Sposito Garrison
Published: July 2010

The Constant Capacitance model provided a quantitative description of o‐phosphate adsorption by 44 noncalcareous soils whose pH values ranged from 4.9 to 7.6. The intrinsic surface protonation‐dissociation constants, capacitance density, and phosphate packing area parameters required by the model were adopted from model calculations on reference hydrous oxide minerals. The intrinsic phosphate surface complexation constants were calculated through the application of a nonlinear least squares fitting program to the soil o‐phosphate adsorption data. Two of these intrinsic constants were found to be independent of pH over the range investigated, as required by the model. However, the intrinsic constant for the formation of the neutral o‐phosphate surface species exhibited a statistically significant dependence on pH. The Constant Capacitance model was best able to describe o‐phosphate adsorption by noncalcareous soils, including pH effects, if a soil‐specific set of intrinsic phosphate surface complexation constants was employed.
Soil Gases and Temperatures: A Beef Cattle Feedlot Compared to Alfalfa
Authors: Norstadt Fred A. , Porter Lynn K.
Published: July 2010

Dry wells or caissons were used in an alfalfa field and at two locations in a feedlot pen to insert instrumentation and sampling devices to characterize the soil profiles. Soil gas compositions and temperatures studied for a 9‐yr period were strikingly dissimilar among the three sampling sites, yet each location had certain consistent properties unique to it. Two distinct areal‐wise soil‐zones had developed in the feedlot pen—one anaerobic and one aerobic. Only the anaerobic, feedbunk site produced methane (CH4). High soil carbon dioxide (CO2) and low oxygen (O2) contents were found there and at the pen center. Dinitrogen (N2) content at the feedbunk site was consistently less than in air which was attributed to a positive CO2 and CH4 pressure from biological sources. The main effects of location and year interacted with either depth or season for the common gases O2, N2, and CO2 at the three caisson sites. The main effects of depth, season, and year on O2 and CO2 were separated at the feedbunk site by excluding the other locations from data analysis. A first order interaction of season by year for N2 and CH4 showed the dependence of those gases on seasonal temperature change modified by years. A significant influence of the caissons on nearby soil temperature gradients was not detected. There were significant positive correlations between soil gas compositions and temperatures for CO2 at all locations and for CH4 at the feedbunk site. Soil N2 content was negatively correlated with soil temperature at both the feedbunk and center sites. These and other complementary results indicate that anaerobic soil conditions beneath a continuously‐maintained, intact, moist manure pack would minimize possible nitrate nitrogen (NO‐3‐N) formation and contamination of soil and groundwater.
A Simplified Soil and Plant Phosphorus Model: II. Prediction of Labile, Organic, and Sorbed Phosphorus
Authors: Sharpley A. N. , Jones C. A. , Gray Carl , Cole C. V.
Published: July 2010

Surface samples and soil chemical, physical and taxonomic data for 78 soils from the continental U.S. and Puerto Rico were obtained from the U.S. Soil Conservation Service National Soil Survey Lab. Phosphorus was extracted with the following: NH4F + HCl (Bray 1 P), NaHCO3 (Olsen P), HCl + H2SO4 (North Carolina P), and anion exchange resin (labile P). Organic P and an index of fertilizer P sorption were also measured. Soils were divided into three groups based on soil taxonomy and weathering. Regression analysis was used to obtain equations to predict labile P, organic P, and a P sorption index from soil chemical and physical properties. Labile P was related to extractable P; organic P to total N and pH; and P sorption to clay, CaCO3, labile P, and base saturation. These parameters accounted for up to 84% of labile P variation, 64% of organic P variation, and up to 78% of P sorption variation. Although the equations are empirical, independent variables chosen in the stepwide regression were consistent with P mineralization and sorption relationships previously reported. These relationships were tested using independent data sets. They can be used to generate inputs for the soil P component of the Erosion‐Productivity Impact Calculator crop management model from soil test P and data available in U.S. Soil Conservation Service/State Agricultural Experiment Station Soil Survey Investigation Reports.
Salinity, Sodium, and Potassium in an Irrigated Soil Treated with Bovine Manure
Authors: Pratt P. F.
Published: July 2010

Results of a 4‐yr field experiment with liquid feedlot and solid dairy manures and two irrigation rates on a Hanford soil (Typic Xerorthents) are reported. Objectives were to measure the effects of manures on yields of barley and sudangrass forages, the accumulation of salts in the root zone, and the leaching of salts to groundwater. The leaching fraction (LF) calculated from chloride (Cl‐) balances ranged from 0.21 to 0.37. Salinity in the root zone, as measured by the electrical conductivity of the saturation extract (ECe), decreased with increase in LF and was related to the rate and type of manure. Salinity appeared to have no negative effects on yields at manure rates up to 79 Mg ha−1 yr−1. The solid manure at 158 Mg ha−1 yr−1 reduced yields of sudangrass and the ECe for this treatment was in the range of values reported to reduce yields. Manures did not increase the sodium adsorption ratio (SAR). The calculated SAR agreed well with measured SAR values. The potassium adsorption ratio (PAR) increased with increase in rate of manure, but the measured PAR was consistently less than the calculated PAR. There was no effect of irrigation on potassium (K) concentration in the saturation extract or on measured PAR. The data indicated that the soil profile still had considerable capacity to fix K in nonexchangeable forms. The amount of sodium (Na) leached from the root zone exceeded the Na input in water and in manures. The ratio of leached Na to input Na was correlated with LF. The long‐term hazard of the use of manures on well leached irrigated lands appears to be more from K than from Na accumulation.
A Proposed Land Suitability Classification for Potato: I. Methodology
Authors: Manrique L. A. , Uehara G.
Published: July 2010

The principle of matching the biological requirements of a crop to the characteristics of the land was used as a basis for developing a land suitability classification for potato (Solanum tuberosum L.). Land characteristics needed to assess land suitability for potato production were obtained from soil surveys based on Soil Taxonomy. Soil Taxonomy provides readily available information to characterize a few important land qualities for potato production. To predict responses to soil and crop management, land suitability assessments for three levels of input, zero, low, and high, were developed for potato. Because Soil Taxonomy is used as a basis to assess land suitability, the proposed classification system is independent of national boundaries, and can be used to obtain estimates of capabilites of land wherever a soil survey based on Soil Taxonomy is available.
Loess‐Derived Soils, Mississippi Valley Region: II. Soil‐Climate System
Authors: Ruhe Robert V.
Published: July 2010

In Typic Hapludalfs formed in Peoria loess along the Mississippi River Valley from Mississippi to Minnesota, the base status distinctly and abruptly differs at 37° to 38°N latitude. The Memphis soils to the south are more intensively and deeply leached of bases than Alford and Fayette soils to the north. This change coincides with an abrupt historic climatic difference in precipitation (normal and effective). Paleoclimatic reconstruction shows that the climatic boundary could have persisted throughout the Holocene and its changing environments. The constancy of climatic difference through time can account for the soil differences at the critical latitude.
Crop Residue Removal Effects on Corn Yield and Fertility of a Norfolk Sandy Loam
Authors: Karlen D. L. , Hunt P. G. , Campbell R. B.
Published: July 2010

To meet future demands, alternative energy sources will be needed because long‐term energy problems have not been solved. Crop residue may provide a readily available on‐farm bioenergy source, but effects of removing residue on soil fertility, water conservation, and crop production need further investigation. A 4‐yr field experiment was conducted on a Norfolk sandy loam (Typic Paleudults) to determine the effects of removing crop residues on soil pH, extractable nutrient concentrations, and yield of corn (Zea mays L.). Four stover management treatments evaluated between 1979 and 1982 included conventional tillage with stover incorporated, and conservation tillage with 0, 66, or 90% of the stover removed. Treatments were split and evaluated with and without supplemental irrigation. Extractable nutrient concentrations were evaluated by comparing values obtained from an initial soil sampling with those of samples collected each fall thereafter. Ear leaf analyses were used to monitor treatment effects on plant nutrient status. Annual corn stover yields of 3 to 7 Mg ha−1 provided 5 to 11 × 107 kJ ha−1 of potential bioenergy without reducing winter surface cover below 80%. Harvesting corn residues increased annual N, P, and K removal by 26 to 57, 6 to 14, and 49 to 124 kg ha−1, respectively. Soil extractable and plant nutrient concentrations indicated fertilization rates were adequate to compensate for nutrients removed with crop residues. Annual soil analyses showed that surface‐applied lime and fertilizer were rapidly leached through low exchange capacity surface horizons, but accumulated in subsoil horizons even when conservation tillage practices were utilized. Irrigation, tillage, and residue management treatments resulted in few significant differences indicating that in this physiographic region, some crop residues could be utilized for bioenergy production. However, plant nutrients contained in those residues would have to be replaced by increased fertilization.
Soil Structure as Influenced by Simulated Tillage
Authors: Powers D. H. , Skidmore E. L.
Published: July 2010

Soil is often intensively manipulated by tillage, equipment traffic, and preparation for laboratory analysis. Realizing that manipulated and reconstituted soils have been and are being used in soil structure research, we used surface‐soil samples of cultivated and noncultivated Reading silt loam (fine, mixed, mesic, Typic Argiudolls) to evaluate the effects of simulated tillage on soil structure and to determine how well the structures of disturbed soils represent the structures of nondisturbed soils of similar composition. Soil cores 86 by 60 mm were formed after the following treatments had been applied: ultrasonically dispersed and freeze‐dried, crushed and passed through a 2‐mm sieve, and nondisturbed. The soil structural differences were evaluated by soil‐water‐characteristic curves, saturated‐hydraulic conductivities, compression indices, bulk densities, wet‐ and dry‐aggregate stabilities, and scanning‐electron‐microscopy. The results show that the soil structures of reconstituted, intensively or even mildly manipulated soils differ considerably from the nondisturbed soils of the same makeup. The greater the disturbance, the greater the differences between the nondisturbed and disturbed soils. The main differences were caused by the destruction of cements and bridges between individual aggregates, which create large, compound‐unit (ped) structures.
Soil Cohesion as Affected by Time and Water Content
Authors: Kemper W. D. , Rosenau R. C.
Published: July 2010

Cohesion increased for several months after disruption in moist soils. Rate at which cohesion increased was slower in airdry soil, but continued for years. Moduli of rupture of soils also increased with time. Effects of water content on the rate at which cohesion increases are compatible with an explanation of the bonding mechanism in terms of slightly soluble components diffusing to and cementing points of contact between particles. Cohesional forces due to water are estimated and found to be large enough to provide a major portion of the cohesion measured in soils. These estimates are supported by decreased cohesion of a silty soil when dried. However, cohesion of soils with larger amounts of clay generally increases when they are dried, indicating that other bonding mechanisms predominate.
Effects of pH and Phosphate on Cadmium Sorption by a Hydrous Ferric Oxide
Authors: Kuo S. , McNeal B. L.
Published: July 2010

Sorption of cadmium by phosphate‐free and phosphate‐enriched hydrous iron oxides was investigated in 0.1M NaNO3 solution. Significant Cd sorption by the phosphate‐free oxide sample occurred at pH levels below the oxide zero point of charge (pHZPC), indicating that the sorption was sufficiently energetic to over come some electrostatic repulsion. Phosphate enrichment of the oxide enhanced its capability to retain Cd, and lowered the average pH of the sorption edge. The Langmuir sorption constant for Cd was increased by such enrichment. Such results could be attributed to reduction of the pHZPC and surface potential with phosphate enrichment, and were described satisfactorily by simplified electrostatic theory. Calculated activities of soluble Cd in the pH range of 4 to 7 were well below those calculated from the solubilities of Cd(OH)2 or Cd3(PO4)2. This suggests that precipitation of these two compounds was not a likely mechanism controlling the concentrations of soluble Cd for these systems.
Fractionation of Metal‐Organic Components Extracted from a Sludge‐Amended Soil
Authors: Keefer R. F. , Codling E. E. , Singh R. N.
Published: July 2010

A sandy loam soil was amended insitu with three sewage sludges and after 3 yr extracted with N,N‐dimethylformamide (DMF) or sodium pyrophosphate (SP) to determine which organic fractions are associated with metals. A separate portion of the soil was pretreated by acid dialysis followed by DMF extraction. The DMF extracts and fulvic acid from the SP extract were fractionated on nonpolar, nonionic macroreticular and ion exchange resins into acidic, neutral, and basic hydrophobic organic solute fractions and acidic, neutral, and basic hydrophilic organic solute fractions. The amounts of metals associated with the hydrophilic and hydrophobic fractions depended on the metal examined, extractant used, the pretreatment, and the kind of sludge added to the soil. Cadmium was not detected in any of the organic fractions. Copper, Zn, and Ni were generally recovered least efficiently from the soil treated with a sludge highest in these metals. Most of the metals were generally associated with the hydrophobic portion following dialysis, but Cu was most often associated with the hydrophilic base fraction. This fractionation method has been demonstrated to be effective in separating metal/organic components in extracts from a soil to which three sludges were added. The data indicate that there were several mechanisms operative in combining metals with organic fractions—at least two for Cu and four each for Zn, Ni, and Pb.
Spatial Variability for One Type of Phosphate Mine Land in Central Florida
Authors: Bos J. , Collins M. E. , Gensheimer G. J. , Brown R. B.
Published: July 2010

Soil‐plant interaction problems are frequently encountered in the reclaimed phosphate minelands of central Florida. To solve some of these problems, a knowledge of the soil properties and their spatial variability must be acquired. An optimum sampling design for reclaimed mine lands can only be constructed after this information is known. Therefore, selected soil properties of one type of reclaimed phosphate mine land (overburden over sandtailings) in central Florida were investigated. A 6 × 21 sampling grid with 10‐m interval sampling points was constructed and soil samples (0–25 cm) were taken in four directions along selected transects. The results indicated that mean values were very high for total P (8.3 g/kg), extractable P (0.9 g/kg), and extractable Ca (2.3 g/kg) by the double acid method. The double acid method of extracting Ca, Mg, K, and Na yielded higher mean contents than the procedure using NH4OAc at pH 7. Correlation coefficients were highly significant between both extractable Ca and Mg and total extractable bases. Higher r values were obtained using KCl‐pH than H2O‐pH in studying the relationships of pH to the other soil properties except for total P. Semivariograms were calculated for the different soil properties studied in the four sampling directions. A composite semivariogram of all four directions was also constructed. Except for CEC and relative elevation, spatial correlation of all properties was encountered at sampling distances < 2.6 to 7.1 m. At a lag distance of six peak values occurred in several sampling directions for many of the soil properties studied. This indicates similar optimum sampling distances for the soil properties of interest.
Scanning Electron Microscope Studies of Surface Crusts Formed by Simulated Rainfall
Authors: Onofiok Otu , Singer Michael J.
Published: July 2010

The micromorphology of the surface layer of three California soils, Columbia fine sandy loam, Wyo clay loam, and Yolo silt loam, undergoing crust formation by simulated rainfall was studied using the scanning electron microscope (SEM). Crusts formed at the time of ponding (early crust) and after 60 min rainfall were examined. At the early crust stage, crusts on all soils comprised a very thin compact surficial layer, about 0.05 mm thick, and a more open underlying layer of uniform pore and particle size distributions comparable to those of the undisturbed soil. At a later stage, the crusts on Yolo and Wyo soils consisted of an upper layer (about 0.1 mm thick) of high porosity, composed predominantly of individual sand grains and a lower layer of considerably reduced porosity, composed of a higher concentration of clay and silt sized particles. The lower layer, called the “washed‐in” zone, results from the accumulation of fine materials washed out in the upper layer. Columbia late crust also comprised an upper compact surface layer (about 0.05 mm thick) of well oriented platy particles, and a lower more open layer with particles uniformly reduced in size. Decreased apparent porosity at 0.3‐ to 0.8‐mm depth, measured directly on the SEM photomontages, indicated the presence of the “washed‐in” zone in the Yolo and Wyo late crusts and its absence in the Columbia. Mean pore size of the late crust Yolo sample was significantly reduced compared to the no‐crust treatment. Small changes in mean pore size were also observed for the other two soils.
Long‐Term Availability of Applied Phosphorus to Loblolly Pine on a Piedmont Soil
Authors: Torbert J. L. , Burger J. A.
Published: July 2010

A loblolly pine (Pinus taeda L.) phosphorus (P) fertilization trial was evaluated 20 years after establishment on a Tatum silt loam (clayey, mixed, thermic, Typic Hapludults), in the Virginia Piedmont. Triple superphoshate (TSP) was applied at 160 kg P/ha and ground rock phosphate (GRP) at both 160 kg P/ha and 670 kg P/ha. Lime was applied (4.48 Mg/ha) with and without TSP. Tree growth was not significantly affected by treatment and foliar P levels were above 0.10% on control plots indicating that a deficiency was not the immediate growth‐limiting factor. Soil and foliar P levels were highest where GRP was applied at 670 kg P/ha. Foliar P levels and double acid (0.05M HCl + 0.0125M H2SO4) extractable soil P were highest when 160 kg P/ha was applied as GRP vs. TSP. Liming caused a pH increase which persisted even after 20 years, but had no direct effect on P availability.
Ion Exchange Resin Bags: Factors Affecting Estimates of Nitrogen Availability
Authors: Binkley Dan
Published: July 2010

Soil ion concentration, water regime, and microbial competition for N were examined for their importance in regulating the adsorption of ammonium and nitrate by ion‐exchange resin bags. Resin nitrate values were largely dependent on soil nitrate contents, whereas resin ammonium values were strongly affected by soil water regime. Increasing microbial competition for N by additions of cellulose markedly decreased N accumulation in the resin bags. Recovery of 15NH4 added to resin bags prior to incubation in the soil showed no indication of removal or transformation of N once adsorbed in the resin bags. Resin bags should be appropriate for field estimation of N availability when both mineralization and transport are of interest.
Effects of Rhizobial Extracellular Polysaccharide on pH and Aluminum Activity
Authors: Cunningham Scott D. , Munns Donald N.
Published: July 2010

A positive correlation has been demonstrated between the ability of Rhizobium strains to colonize acidic agar surfaces and their production of extracellular polysaccharide (EPS) in solution culture at pH 7.0. This set of experiments examined the effects of EPS on solution pH levels and Al activity, two common growth‐limiting factors in acid soils. Samples of EPS from each of 20 previously acid‐screened Rhizobium phaseoli isolates were titrated under controlled conditions and a buffering capacity was calculated. In addition, EPS from all strains were compared for ability to chelate aluminum by sodium saturation followed by equilibration against an aluminum‐phosphate solid phase. Total aluminum of the digested samples was measured by atomic adsorption spectrophotometry. The buffering ability of the EPS varied considerably between strains but was not correlated with the acid tolerance of the strain from which each was isolated. Similarly, while there were significant differences in the ability of the EPS to chelate aluminum, these were not correlated with acid tolerance. Acid tolerance did not correlate with EPS production weighted for either buffering capacity of the EPS or its ability to chelate Al. Thus, while the amount of ethanol‐precipitatable EPS from different rhizobial strains varied significantly in these two capacities, rhizobial EPS does not appear to confer acid tolerance on a strain by means of buffering pH or aluminum levels. Other possible causes of the observed relationship between acid tolerance and EPS production should be examined. These could include a role in increasing solution phosphate levels and/or the necessity of increased EPS for binding to plant lectins in an acidic environment.
Phosphorus and Potassium Effects on Yield and Nutrient Uptake in Arrowleaf Clover
Authors: Westerman R. L. , Silvertooth J. C. , Barreto H. J. , Minter D. L.
Published: July 2010

Arrowleaf clover (Trifolium vesiculosum Savi ‘Yuchi’) is a winter annual legume that can be used to extend the grazing of warm‐season perennial grasses in forage production systems. Stand establishment from overseeding often fails because of unfavorable climatic conditions and nutrient deficiencies in soils. The objectives of this research were to determine the effects of P and K fertilization on yield and nutrient uptake of arrowleaf clover and accumulation of soil P and K. Arrowleaf clover was seeded in field plots in the fall of 1978. Fertilizer treatments consisted of an incomplete factorial arrangement of multiple rates of P, K, and P plus K. Rates of P and K included a control that did not receive fertilizer; 20, 40, and 80 kg P ha−1; 37, 74, and 148 kg K ha−1; and P‐K combinations of 20:37, 40:74, and 80:148 kg ha−1. The soil type was a Taloka silt loam (Mollic Albaqualfs). Yield and N, P, and K uptake in forage were determined in four consecutive years starting in 1979. Soil test indices were measured prior to seeding in 1977, in the fall of 1978, and after four annual fertilizations in 1982. Regression equations with linear, quadratic, and interaction terms were calculated to describe dependent variable response surfaces for each year and the average over years. Phosphorus fertilization increased yield each year. Yield was not increased with K fertilization alone, but there was a positive P × K interaction in the 1982 season indicating soil K levels were decreasing. Predicted maximum yields were 6561, 6490, 6516, and 6860 kg ha−1 due to applications of 50.8, 52.4, 54.0 and 57.2 kg P ha−1, respectively, at fixed rates of 0, 37, 74, and 148 kg K ha−1. Phosphorus increased N, P, and K uptake and when applied in combinations with K, some interactions occurred. The soil test index for P increased slowly (0.5 kg ha−1 yr−1) with P rates of 20 kg ha−1 annually; however, a rapid accumulation of soil P occurred with four annual applications of 80 kg P ha−1 (16.5 kg ha−1 yr−1). Approximately 107, 16, 6, and 3 annual applications of 20, 40, 60, and 80 kg P ha−1, respectively, would be required to increase soil test values for P to a sufficient level. Soil test values for K were increased from 133 to 308 kg ha−1 with four annual applications of 148 kg K ha−1. However, after four annual applications of 80 kg P ha−1 in combination with 148 kg K ha−1, the soil test value for K was only increased to 192 kg ha−1 due to the marked response from P fertilization and subsequent increase of K removal in forage.