bluuebunny/crossref_metadata_2025_split huggingface dataset:
Soil Structure as Influenced by Simulated Tillage
Authors: Powers D. H. , Skidmore E. L. 
Published: July 2010

AbstractSoil 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

AbstractCohesion 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

AbstractSorption 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

AbstractA 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

AbstractSoil‐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

AbstractThe 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

AbstractA 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

AbstractSoil 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

AbstractA 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

AbstractArrowleaf 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.
Aluminum Toxicity and Calcium Deficiency in Acid Subsoil Horizons of Two Coastal Plains Soil Series
Authors: Adams Fred , Hathcock P. J. 
Published: July 2010

AbstractInadequate root proliferation in acid subsoil horizons of the Coastal Plain of the southeastern United States limits yields of many crops. The recognized root‐limiting chemical factors in these soils are Al toxicity and Ca deficiency, but it is not known if these properties can be predicted from soil series descriptions. In an effort to delineate Al toxicity and Ca deficiency by horizon and by soil series, six representative profiles from each of two major soil series of Alabama's Coastal Plain were sampled by horizon to a depth of 1 m. Three profiles from each of two major soil series were obtained from cultivated fields; the other three were obtained from adjacent woodlands. Horizon samples were subdivided and treated with one of the following: (i) check, or no treatment, (ii) CaSO4, (iii) MgO, and (iv) Ca(OH)2. Growth rate of cotton (Gossypium hirsutum L.) taproots into each treated soil material was measured, and visual symptoms of Al toxicity and Ca deficiency on roots were noted. Six of seven Bt horizons in the Orangeburg series were Al toxic; four of 12 in the Dothan series were Al toxic. None of the five BE horizons were Al toxic. Seven Dothan horizons and four Orangeburg horizons were Ca deficient. No Ca‐deficient horizon occurred in cultivated fields and no Al‐toxic horizon occurred in woodlands. Aluminum toxicity occurred in some Bt horizons (but not all) of cultivated fields when soil‐solution Al was only 0.4µM, but not in BE horizons of woodlands where solution Al ranged up to 11.5µM by the 8‐hydroxyquinoline method. Neither was Al saturation a satisfactory predictor of Al toxicity. Nondeficient Ca levels (both soil solution and exchangeable) were lower in cultivated fields than in woodlands. There was no apparent difference between soil series relative to Ca deficiency and Al toxicity, making it seem unlikely that soil classification will be helpful in predicting Ca deficiency and Al toxicity in subsoil horizons.
Detecting Soils under Cultural Vegetation Using Digital Landsat Thematic Mapper Data
Authors: Thompson D. R. , Henderson K. E. 
Published: July 2010

AbstractAircraft thematic mapper simulator (TMS) and Landsat‐4 Thematic Mapper (TM) data from the same site were examined for their relative accuracy in separating soils of an intensely cultivated agricultural area. Data from five different dates throughout the 1982 growing season of corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.] were used in this study. Soils under corn canopy were separated at the soil mapping unit level with an accuracy of 55.5% and soils under soybeans at an accuracy of 46% on the 23 June date. As these soils are similar in their physical and taxonomic classifications, frequent errors could be expected at the mapping unit level. As the vegetative cover increased, the errors also increased, which could be expected. At the subgroup level, however, and at the great group level, the classification accuracy of soil groups increased. The great group level was separable with greater than 60% accuracy throughout the growing season. The TMS data on 23 June had the highest accuracy (92.9 for corn and 75.6 for soybeans). The 3 September TM data, even with > 90% ground cover, separated the great group level with 72.5% accuracy for corn and 68% accuracy for soybeans. The results of this study indicate that the improved spectral and spatial resolution of TM offers the potential to separate important soil properties even in a region with similar soils and under a dense vegetation canopy.
The Influence of Aluminum on Iron Oxides: XI. Aluminum‐Substituted Maghemite in Soils and Its Formation
Authors: Schwertmann U. , Fechter H. 
Published: July 2010

AbstractMaghemites (γ‐Fe2O3) from highly weathered soils had unit cell parameters significantly lower than pure maghemites. This was due to Al for Fe substitution in the cubic structure. Al‐substituted maghemites were synthesized by heating soil and synthetic Al‐substituted goethites with sucrose and synthetic Al‐substituted magnetites. Formation of Al‐substituted maghemites in soils by fire is, therefore, postulated.
Evaluation of Closed‐Form Analytical Models to Calculate Conductivity in a Fine Sand
Authors: Stephens Daniel B. , Rehfeldt Kenneth R. 
Published: July 2010

AbstractThe soil‐water characteristic curve, θ—ψ, was determined for an undisturbed core of fine sand over a range of negative pressure heads observed in the field, 0 to 150 cm, below about the 30 cm depth. These data were used to predict relative hydraulic conductivity in a computer code of closed‐form analytical solutions developed by van Genuchten for the theoretical models of Burdine and Mualem. The equations to predict conductivity are based upon two parameters fit to observed θ—ψ data by a non‐linear least squares procedure. The two parameters are influenced by the choice of residual water content, θr, and unsaturated water content, θs. If θr is unknown, it is estimated in the program from observed data. A sensitivity analysis was performed to evaluate the reliability of the models. For this soil, calculated conductivities appear to be sensitive to θr. If θ—ψ data are available over only a limited range, or if θs is too large, model‐predicted θr‐values may be near zero, whereas θ at large ψ may actually be about 0.06 to 0.08 cm3/cm3. Predicted conductivities may differ by more than one order of magnitude at about ψ = 150 cm, depending on the choice of θr.
Measurement of Soil Water Content using Time‐domain Reflectrometry (TDR): A Field Evaluation
Authors: Topp G. C. , Davis J. L. 
Published: July 2010

AbstractFor measurement of water content using TDR, parallel wire transmission lines varying in length from 0.125 to 1 m were installed vertically at planting time at three sites in a corn field. At one of the sites horizontal lines and additional vertical transmission lines with electrical impedance discontinuities were installed for comparison. Measurements of water content using a portable TDR cable tester were made periodically during the growing season. Comparisons of water contents by TDR with those from gravimetric samples showed that generally both were the same values. Standard deviations of differences between TDR and gravimetric values were ± 0.02 m3m−3 when measured locations were the same but increased to ± 0.06 m3m−3 when measured locations were different. Repeated measurements at the same location were highly correlated, one with another, over the season. Analysis of variance showed that all transmission line types were yielding equivalent values and that the horizontal transmission lines gave the minimum standard error of the mean. Data from transmission lines with impedance discontinuities gave water content profiles from a single measurement but the analyses of the TDR data curves were more complex than for the lines without impedance discontinuities. The variety of transmission line configurations for use in TDR measurement allows considerable flexibility of choice in relation to one's application.
Gas Displacement and Aggregate Stability of Soils
Authors: Kemper W. D. , Rosenau Russell , Nelson Sheldon 
Published: July 2010

AbstractWhen surface soils are dry, O2 and N2 are adsorbed on the external mineral surfaces. In the process of wetting the soil, water molecules displace the adsorbed O2 and N2 molecules to the gas phase where they can be measured, as was done in this study. These gases, released from the adsorbed phase, join entrapped air in the gaseous phase as the primary factor disintegrating aggregates when soils are wet quickly. Adsorption of N2 and O2 occurs on surface soils during hot dry afternoons as the water molecules leave the surface. During cool nights, relative humidities commonly rise above 50%, allowing more strongly adsorbed H2O molecules to displace adsorbed O2 and N2. Release of this adsorbed N2 and O2 causes aggregates wetted by immersion during hot afternoons to be less stable than aggregates of the same soil wetted in the morning.