bluuebunny/crossref_metadata_2025 huggingface dataset:
A Solenoid‐Operated, Variable Intensity Rainfall Simulator
Authors: Miller W. P.
Published: July 2010

A portable, variable‐intensity, low‐cost rainfall simulator is described for use in small pan runoff‐erosion studies, and which can be adapted to larger plot studies for field use. Intensity is controlled by electrically operated solenoid valves into which wide square spray nozzles are fitted. The opening and closing of the solenoid valves, controlled via switches operated by a rotating cam or microcomputer, varies the intensity of rainfall from 0.0004 mm s−1 to approximately 0.024 mm s−1, at 29 kPa water pressure. Coefficients of uniformity for 1 m2 plots under a single nozzle are 90 to 95%, and 85 to 90% for 1‐ by 3‐m field plots using a three nozzle system. Kinetic energy of the rainfall, determined from drop size distributions, is about 23 J m−2 mm−1, which is within the range for natural rainfall.
Soil Surface Roughness Effects on Radiation Reflectance and Soil Heat Flux
Authors: Potter K. N. , Horton R. , Cruse R. M.
Published: July 2010

Soil surface roughness provides a mechanism to alter soil reflectance and the surface energy balance. A field study was conducted to determine the effect of surface roughness on energy absorption and energy partitioning at the soil surface. A range of surface roughness conditions was created by varying the intensity of secondary tillage after moldboard plowing. Parameters measured included spectral reflectance, net radiation, soil temperature, and soil heat flux. Reflectance of solar radiation decreased with increasing surface roughness, with the greatest differences occurring among radiation wavelengths of 850 and 1350 nm. Reflectance was similar between 400 and 850 nm. Reflectance from a visibly dry surface was increased up to 25% in some wavelengths 5 d after a 47‐mm rainfall event, possibly because of decreased surface roughness. Although net radiation increased with increased surface roughness, soil heat flux at 0.01‐m was similar for all roughness conditions. This indicates that the latent and/or sensible heat flux was increased by increasing surface roughness. Theoretical considerations indicate that increasing surface roughness results in greater transport of energy from the soil surface to the atmosphere. Relationships between the change in net radiation due to surface roughness and the partitioning of net radiation among the surface energy balance components are developed and presented graphically.
Cohesion Development in Disrupted Soils as Affected by Clay and Organic Matter Content and Temperature
Authors: Kemper W. D. , Rosenau R. C. , Dexter A. R.
Published: July 2010

Soils were dispersed and separated into sand, silt, and clay fractions that were reconstituted to give mixtures of each soil with 5 to 40% clay. In the range from 0 to 35% clay, higher clay contents resulted in greater stability. Rate of cohesion recovery was over 10 times as fast at 90°C as it was at 23°C, showing that the processes involved are physical‐chemical rather than biological. Maximum rates of cohesion recovery occurred at moderate soil water tensions, probably because some tension is needed to pull the particles into direct contact, but a continuous water phase is also essential to allow diffusion of bonding agents to the contact points. Since diffusion rates in water increase 300%, while rate of cohesion recovery increased 1000% when temperature was raised from 23 to 90°C, other factors, such as higher solubilities at higher temperatures of compounds contributing bonding ions to the solution, probably play a role in the rate of cohesion recovery. Recovery of cohesion was more rapid in the soil with organic C contents of 0.004 kg/kg than in the soil with 0.012 kg/kg. When the organic matter was removed with H2O2 from the soil with 0.012 kg C/kg, its rate of cohesion recovery increased. Rate of cohesion recovery of this high organic matter soil was also increased by aging it at 0.1 kg H2O/kg soil compared to 0.2 kg/kg. A possible explanation is that organic coatings, tending to prevent direct contact and bonding of adjacent projections of mineral surfaces, are forced away from contact points by extremely strong forces that pull the adjacent minerals together when soil water tensions are high. When the higher organic matter soil had been consolidated by air‐drying and rehydrated, its rate of cohesion recovery was just as rapid as that of the soil with low organic matter.
Estimating Transport Parameters in Soils by a Maximum Likelihood Approach
Authors: Bresler Eshel , Naor Amos
Published: July 2010

A maximum likelihood procedure that provides a powerful, convenient, and asymptotically unbiased means of estimating various salt transport parameters is briefly described. Details of estimating the dispersion coefficient or dispersivity and the volume of exclusion (per unit volume of soil) are specifically discussed. Data from laboratory column experiments are employed to illustrate the practical application of the estimation method and to compare with the least squares method. The uncertainty of estimating the parameters is incorporated in a systematic manner in the process of inference. The procedure can be expanded to implement additional solute transport parameters.
Transport and Ion Exchange of Calcium and Magnesium in an Aggregated Soil
Authors: Selim H. M. , Schulin R. , Flühler H.
Published: July 2010

The objective of this study was to describe the retention of Ca and Mg in an aggregated soil. Batch and transport experiments were carried out on two aggregate sizes (1–2 and 4–5 mm). These aggregates were separated by sieving an air‐dried Abist loam soil which was previously saturated with Ca ions. In the batch experiments, 0.005 M solutions containing various proportions of MgCl2 and CaCl2 were mixed with the soil for several time intervals up to 66 h. The dependence of ion retention on the time of reaction was not significant. For the transport experiments, a pulse of MgCl2 was introduced to soil columns which were saturated with a 0.005 M CaCl2 solution at a constant flux. The concentration of the pulse was either constant (0.005 M) or variable (from 0.005–0.05 M). Using independently measured parameters, we obtained good model descriptions of the transport of Ca and Mg in the soil. The model is based on ion‐exchange as the governing retention process with a measured cation exchange capacity (CEC) and selectivity coefficients using our batch data. Improvements in our predictions were achieved when the model was extended to the two‐region (mobile‐immobile) concept.
Influence of Organic Anions on the Speciation of Mononuclear and Polynuclear Aluminum by Ferron
Authors: Jardine P. M. , Zelazny L. W.
Published: July 2010

The kinetic reactions of ferron (8‐hydroxy‐7‐iodo‐5‐quinoline‐sulfonic acid) with unneutralized and partially neutralized Al solutions in the presence of various organic anions were investigated with the intent of distinguishing mononuclear and polynuclear Al. Mononuclear Al solutions containing malate, glutarate, succinate, salicylate, formate, malonate, and fulvate with ligand/Al molar ratios ranging from 0.4 to 7.5, reacted rapidly with ferron and were modeled using a single second‐order equation. Similarily, mononuclear Al solutions containing citrate, tartarate, and oxalate with ligand/Al molar ratios ⩽ 0.13, 0.08, and 0.38, respectively, also reacted rapidly with ferron and were modeled using a single second‐order expression. Model fitted ka values (rate of Al‐monomer reactions with ferron) for these organic‐Al solutions were similar to ka values determined for uncomplexed mononuclear Al solutions without added organic ligands. Increasing concentrations of citrate, tartarate, and oxalate that cause the ligand/Al molar ratios to exceed the critical values of 0.13, 0.08, and 0.38, respectively, form complexes with Al that are not easily degraded by ferron, thus limiting the credibility of accurate distinction between monomeric and polymeric Al. The interaction of ferron with Al‐polymers was not significantly affected by concentrations of organic anions whose ligand/Al molar ratio did not exceed these critical values. These conditions allowed the accurate distinction of mononuclear and polynuclear Al.
Chemical Modeling of Anion Competition on Oxides Using the Constant Capacitance Model‐Mixed‐ligand Approach
Authors: Goldberg Sabine , Traina Samuel J.
Published: July 2010

The constant capacitance model was used to describe selenite‐o‐phosphate and silicate‐o‐phosphate competition on synthetic goethite (α‐FeOOH) and synthetic gibbsite (Al(OH)3) by direct optimization of mixed‐ligand adsorption data. The model assumes ligand exchange mechanisms for selenite, o‐phosphate, and silicate adsorption on oxide surfaces. The computer program, FITEQL, was used to fit intrinsic surface complexation constants to the competitive adsorption data. Values for the intrinsic protonation‐dissociation constants, surface capacitance density, surface site density, and specific surface area had been determined previously. The constant capacitance model was able to represent competitive anion adsorption for selenite‐o‐phosphate over the pH range of 4 to 10 and for silicate‐o‐phosphate from pH 5.5 to 9.5. The fit to the experimental data using the mixed‐ligand approach was much better than that obtained by prediction from single anion systems. The intrinsic surface complexation constants for o‐phosphate adsorption were found to be dependent upon the surface composition of the adsorbent oxide. We suggest that this composition dependence is due to heterogeneity of surface adsorption sites. Our findings suggest the utility of mixed‐ligand modeling for describing anion competition reactions using direct optimization of competitive adsorption data.
The Solodic Subgroup: A Proposed Amendment to Soil Taxonomy
Authors: McQuaid B. F. , Schumacher B. A. , Miller B. J.
Published: July 2010

Results of characterization and field studies in Louisiana have shown that some soils have ≧ 15% exchangeable Na (ESP) at depths greater than those defined for the natric horizons in Soil Taxonomy (Soil Survey Staff, 1975). In these soils, horizons meet all criteria for the natric horizon with the exception of depth which ranges from 40 to more than 125 cm below the top of the argillic horizon. In many areas, reduction in crop yields of deep rooting annual or perennial plants growing in these soils is attributed to large quantities of exchangeable Na. It is proposed that a Solodic subgroup be included as an amendment to Soil Taxonomy to accommodate soils having an ESP of ≧15 (SAR ≧ 13) in some subhorizon within 1.25 m of the surface or an ESP ≧ 6 (SAR ≧ 5) and <15 (SAR < 13) within the upper 40 cm of the argillic horizon. The proposed subgroup does not affect the classification of soils with natric horizons.
Soil Temperature Profiles of Two Alaskan Soils
Authors: Ping C. L.
Published: July 2010

Soil temperatures of a thawed phase of a Pergelic Cryaquept were measured with copper‐constantin thermocouples at 20, 50, 100, 150, 210, 240, and 300 cm under a fallow plot for 5 yr in Fairbanks, AK. Soil temperatures of a Typic Cryorthent were measured the same way at 5, 10, 20, 50, 100, 150, and 300 cm under both grass and fallow plots for 22 yr in Palmer, AK. Fairbanks has a wider amplitude in annual air temperature variation and colder mean annual air temperature than Palmer. The mean annual soil temperature at 50 cm in Fairbanks is slightly lower (2.1°C) than in Palmer (3.0°C) under fallow plots. The difference between mean annual air temperature (MAAT) and mean annual soil temperature (MAST) is greater in Fairbanks (4.7°C) than in Palmer (1.7°C). The mean summer soil temperature is 9.5°C in Fairbanks and 13.1°C in Palmer, and the mean winter soil temperatures are −3.1 and −3.2°C, respectively. These data suggest that soil temperatures in both locations generally reflect the fluctuations in air temperature during summer and autumn. In winter, Fairbanks experiences colder air temperature than Palmer, yet mean winter soil temperatures are nearly the same. Evidently soils in Fairbanks are protected by snow cover against further cooling throughout the winter while soils in Palmer lack such protection due to the “glacier” wind and the freezethaw cycles that reduce the snow cover. The records showed that snow on the ground rather than total snowfall is accountable for the difference in temperature profiles between the soils. Both soils have forest as native vegetation. The removal of forest cover caused warming up of the soils based on elevated MAST on fallow plots. The classification of a Typic Cryorthent is not affected by such an increase in MAST. The MAST of a Pergelic Cryaquept rose above O°C, and thus changed from the pergelic to cryic temperature regime. The drainage of the Pergelic Cryaquept has also been improved, from poorly to moderately well‐drained. Perennial grass cover resulted in higher mean annual soil temperatures. The data suggest that the pergelic soil temperature regime needs to be redefined and also a new pergelic great group be established to facilitate soil surveys and interpretations in permafrost areas.
Comparison of Soil Tests for Assessing Boron Toxicity to Alfalfa
Authors: Gestring W. D. , Soltanpour P.N.
Published: July 2010

Three soils from Colorado that varied in texture and organic matter (OM) content were treated with sodium borate (Na2B4O7·10H2O) at rates of 0, 10, 20, and 40 mg B kg−1 soil. Alfalfa (Medicago sativa, ‘Ladak’, ‘Rambler’, ‘Riley’, and ‘Agate’) was planted in the soils in the greenhouse and cut twice at the 30% bloom stage. Plant tissue digests and soil extracts (ammonium bicarbonate‐diethylenetriaminepentaacetic acid [AB‐DTPA], saturation, hot water, and mannitol‐CaCl2) were analyzed for B using inductively coupled plasma atomic emission spectroscopy (ICP‐AES). Alfalfa yield was significantly (α = 0.01) reduced with increased B application rate in the Ascalon sandy loam and Ulysses loam soils, whereas no yield reduction was observed in the Keith silt loam soil (Aridic Argiustoll, Haplustoll, and Argiustoll, respectively). Yield response for the pooled soils were poorly correlated (r2 from 0.23–0.58) to the four soil extractants; however, yield reduction due to B toxicity corresponded to critical plant B levels of 850 mg B kg−1 and 975 mg B kg−1 for the first and second harvests, respectively. The inclusion of NH4OAc‐extractable Ca into the regression equation of soil B vs. yield significantly increased the correlation (r2 = 0.77). Multiple linear regression analysis utilizing Mallow's Cp statistic increased the adjusted coefficient of determination (R2) to 0.87 for all of the soil B extractants upon inclusion of soil variables (pH, % clay, OM content) into the equation. Although NH4OAc‐extractable Ca did not appear in any of the best subsets, this was probably the result of it's high correlation with percent clay (r2 = 0.98) and OM content (r2 = 0.98).
Soil Genesis in a Developmental Sequence of Soils Formed in Sillimanite Mica Schist Residuum
Authors: Schumacher Brian A. , Perkins H. F.
Published: July 2010

Dystochrepts formed in mica schist residuum occur on steeply sloping sideslopes, whereas associated Hapludults are found on gently sloping ridgetops in the Piedmont province of Georgia. In this study, morphological, physical, chemical, and mineralogical properties of Dystrochrepts and associated Hapludults were examined to determine the influence of weathering intensity differences within the pedon and across the Dystrochrept → Hapludult developmental sequence. More intense weathering at the soil surface has resulted in higher exchangeable Al contents, lower pH values, and a relative accumulation of total Si, quartz, sillimanite, opaque minerals, and clay‐sized mica and vermiculite. In contrast, biotite was more abundant at depth. Total Al was closely related to clay distribution within the pedon. Less intense weathering in the Dystrochrepts, apparently related to shorter development time, has led to coarser textured sola with higher base saturations, higher total Mg, K, and Na contents, and a greater abundance of fine sand‐sized biotite and K‐feldspar. Quartz in the fine sand fraction was concentrated in the Hapludult. Kaolinite was the dominant clay mineral in the Hapludult. Regularly interstratified mica‐vermiculite was identified in subsurface horizons of the Dystrochrept and is believed to be a transitory intermediate in the transformation of mica to vermiculite.
Soil Properties Influencing Corrosion of Steel in Texas Soils
Authors: Moore T. J. , Hallmark C. T.
Published: July 2010

Corrosion of steel specimens was monitored in 15 Texas soils in order to test the current system for assessing soil corrosivity. Corrosion, measured in situ at two depths using electrical resistance probes, was a function of many soil properties and could not be adequately described using any single property. The current system, developed by the USDA‐SCS, which places soils into corrosion potential classes based on soil characterization data and descriptions, was found to overestimate corrosivity of many soils. A revised system was developed that more accurately predicted corrosion rates of buried steel under field conditions. Soil properties used in the revised system include electrical conductivity, texture, exchangeable acidity, and wetness class. When the two systems were tested using an independent set of data collected by the National Bureau of Standards, soil corrosion potential classes of the revised system correlated with actual corrosion better than the current SCS system.
Effects of Furrow Dikes on Water Conservation and Dryland Crop Yields
Authors: Jones Ordie R. , Clark R. Nolan
Published: July 2010

Eliminating or reducing storm runoff in the Southern Great Plains can increase soil‐water storage, decrease erosion, and increase crop yields. The primary objectives of this study were (i) to examine the potential of furrow dikes as a conservation practice to retain runoff and increase crop yields, and (ii) to examine the effects of furrow diking on sorghum [Sorghum bicolor (L.) Moench] and sunflower (Helianthus annuus L.) production. Analyses of 28 yr of runoff records show furrow diking has the potential to retain 25 to 30 mm of runoff annually. The maximum annual runoff retention by diking observed during the 14 crop years of research (three separate experiments conducted between 1980 and 1985) was 111 mm. The maximum increase in sorghum yield measured as a result of diking was 2.46 Mg/ha. Conditions responsible for maximum yield responses of sorghum to diking were: (i) annual cropping, (ii) large rainfall/runoff events occurring prior to or early in the growing season, and (iii) limited growing season precipitation. Diking increased annual cropped sorghum yields on graded and contour furrow treatments by 49 and 14%, respectively, whereas water use efficiencies were increased by 25 and 16%. Yields and water use efficiencies from diked treatments on graded and contour furrows were as great as yields and water use efficiencies from a leveled minibench treatment, indicating that from a crop production standpoint, furrow diking was as effective as land leveling in retaining runoff and increasing crop yields. Sunflower yields were increased significantly by diking during 1 yr out of 3 when sunflower was grown after 76 weeks of fallow, whereas sorghum yields were not affected by diking after fallow. Decreasing row spacing from 1.0 to 0.75 m resulted in a significant increase in the 3‐yr avg yield of sorghum and sunflower of 1.0 and 0.14 Mg/ha, respectively, when grown after fallow, indicating that considerable opportunity for improving summer crop production may exist simply by changing to a narrow row spacing. A regression equation relating runoff from graded furrows to runoff from contour flat‐tilled graded terraces showed increased runoff from graded furrows, particularly from small storms.
Infiltration and Soil Loss of Three Gypsum‐Amended Ultisols under Simulated Rainfall
Authors: Miller W. P.
Published: July 2010

By‐product phosphogypsum (PG) was applied to the surface of topsoil samples from three sandy Georgia Ultisols at a rate of 5 Mg ha−1 in 0.3‐m2 runoff trays to test the efficacy of this amendment in enhancing infiltration of these soils. Simulated rainfall was applied at 50 mm h−1 for 2.5 h in an initial 1‐h (dry) event and three subsequent 0.5‐h (wet) events applied 24 h later. In the absence of gypsum, infiltration rate stabilized at 10 mm h−1 for the Cecil soil (Typic Hapludults), 5 mm h−1 for the Wedowee (Typic Hapludults), and 1 mm h−1 for the Worsham (Typic Ochraquults), with surface crusting and sand sorting apparent on all the soils. Surface‐applied PG roughly doubled the final infiltration rate of the Cecil and Wedowee soils, and increased infiltration of the Worsham to a lesser degree. Cumulative and average infiltration was significantly higher on all of the PG‐amended soils. Soil loss on the Worsham and Wedowee soils was decreased by 50% with the use of PG, and was reduced by 30% on the Cecil. Sediment concentrations were somewhat lower during the wet events with PG treatment for the Worsham and Wedowee soils, showing that less detached soil was available for transport. Although sediment particle sizes for control soils were 15 to 30% clay and 60 to 75% silt, PG‐amended soils showed no clay‐sized sediment in the runoff, but higher silt contents. Electrical conductivity measurements of the runoff suggest the very low electrolyte concentrations in the untreated soils promote dispersion, resulting in pore blockage and high sediment transportability, whereas PG maintained a high enough electrolyte level (0.5–1.3 dS m−1) to keep soil clays flocculated, thereby reducing crusting and sediment availability.
Herbicide Treatment Effects on Properties of Mountain Big Sagebrush Soils after Fourteen Years
Authors: Burke I. C. , Reiners W. A. , Sturges D. L. , Matson P. A.
Published: July 2010

Soil properties under stands of vegetation dominated by mountain big sagebrush (Artemisia tridentata ssp. vaseyana) and grass were examined 14 yr after spraying with 2,4‐dichlorophenoxy acetic acid (2,4‐D) to control sagebrush. Changes in only a few soil chemical properties were found after conversion to grassland. Phosphorus and K were apparently redistributed from depth to the surface 5 cm of soil by grass‐dominated vegetation. Conversely, surface concentrations of N were lower under grass vegetation than under undisturbed vegetation. No changes attributable to vegetation conversion were found for total C, Na, Mg, cation exchange capacity, base saturation, pH, bulk density, or potential net N mineralization rates at any depth. In situ net N mineralization rates at a 5‐ to 15‐cm depth were measured under and between shrubs for both vegetation conditions 15 yr after spraying. Nitrogen mineralization was similar from positions between and under former shrubs in converted (grass) vegetation, whereas in the sagebrush vegetation, mineralization rates were higher under live sagebrush plants than in interspaces between plants. Undershrub net N mineralization rates were higher under shrubs in the sagebrush vegetation than under former shrubs in the grass vegetation. Essentially, control of big sagebrush, in the absence of grazing, had no effect on site fertility. The spatial distributions of the elements and of their cycling, however, have been altered.
Improved Method for Separating Light‐ and Heavy‐Fraction Organic Material from Soil
Authors: Strickland T. C. , Sollins P.
Published: July 2010

An improved method is presented for separating whole soil into a mineral‐free organic fraction (light fraction) and an organomineral fraction (heavy fraction) by flotation in a dense inorganic salt solution. In the existing method, the heavy fraction is settled by centrifugation and the light fraction decanted. In the improved method, the light fraction is aspirated from the solution surface by suction after the soil suspension is allowed to settle. The improved method costs less, is more reproducible, and is practical in coarse‐textured soils where heavy fractions do not form stable pellets during centrifugation.
Soils, Soil Scientists, and Civilization
Authors: McCracken Ralph J.
Published: July 2010

Several past civilizations have suffered and gone into eclipse or extinction due in greater part to lack of stewardship and/or knowledge of their soil resources. Since the middle of the 19th century, U.S. soil scientists have provided major findings, technological advances, and intellectual leadership for the development of a highly productive agriculture sector that has contributed to a vigorous, dynamic civilization. Our present civilization is being threatened by locally excessive soil erosion and other degradation of our natural resources, currently aggravated by rural economic problems. However, recent and current famines appear to be more closely related to economic and political factors than to deficiencies in soil resources. The quantity and quality of our global soil resources seem capable of supporting our civilization at least well into the 21st century, but local areas of hunger will continue due to local and regional economic conditions and various forms of political disruptions and repressions. Humans now have the capability of degrading and polluting soil, water, and air resources on a global scale—much too quickly. But technologies for monitoring and controlling these degradations and for increasing our productivity are now becoming available, or soon will be. The Soil Science Society of America collectively and its individual members have good opportunities for and real challenges in developing and applying soil science expertise toward solutions of the problems facing our civilization now and in the future. But more trained soil scientists will be needed to accomplish these contributions. The Society and its members need to assess what they can do by working together within their areas of interests and with scientists in other fields. May the next 50 years of the Soil Science Society of America be even more vigorous and productive than the first 50 years.
Kinetic Study of Citrate Effects on Orthophosphate Solubility in an Acidic, Montmorillonitic Soil
Authors: Traina Samuel J. , Sposito Garrison , Bradford Gordon R. , Kafkafi U.
Published: July 2010

Previous studies by the authors on the effects of pH, organic acids, ionic strength, and Ca on residual orthophosphate solubility in an acidic montmorillonitic soil (Typic Chromoxererts) were extended to include the variation of reaction time. The objective of the experiments was to determine the time dependence of the reactions and to elucidate further the mechanism of orthophosphate solubility in a montmorillonitic soil separate containing exchangeable Al and added citric acid, and suspended in 20 mol NaCl m−3. In the absence of added organic acids, soluble orthophosphate and Al3+ activities were found to be consistent with the presence of an amorphous hydroxy‐Al‐phosphate solid at elapsed t ≥ 24 h. Initial citrate concentrations of 10, 100, and 400 mmol m−3 resulted in citrate sorption by the soil separate and an increase in soluble orthophosphate and Al for t ≤ 1 h. Citrate sorption continued throughout the time course of the experiments. For 1 < t < 8 h, orthophosphate solubility was not affected by the initial citrate concentration. For 8 < t < 27 h, orthophosphate solubility decreased to constant levels. Soluble Al decreased for 1 < t < 30 h and then remained constant in the 10 and 100 mmol citrate m−3 treatments. The samples reacted with 400 mmol citrate m−3 exhibited a steady increase in soluble Al for the same time period. The time‐dependent changes in aqueous orthophosphate and Al were consistent with a previously proposed reaction describing organic ligand‐induced formation of an insoluble hydroxy‐Al‐phosphate. The time trends in the solution concentrations of Ca and Si were not affected by the addition of organic ligands nor were they related to the changes in soluble Al or orthophosphate.
Influence of Calcium and Magnesium Salts on Acid Soil Chemistry and Calcium Nutrition of Apple
Authors: Pavan Marcos A. , Bingham F. T. , Peryea F. J.
Published: July 2010

Field experiments were conducted in two Brazilian orchards to examine the effects of soil applications of calcitic lime (Ca‐lime), phosphogypsum, CaCl2, and magnesite (Mg‐lime) on soil chemistry and Ca nutrition of apple (Malus domestica Borkh. cv. Gala/MM 106). One orchard was on a low Ca, high Al Inceptisol; the second orchard was on a low Ca, low Al Oxisol. The resulting soil chemical changes were strongly influenced by the initial soil chemistry and the composition of the soil amendments. The effects of Ca‐lime, added at a rate calculated to neutralize the topsoil exchange acidity, were restricted primarily to the upper 20 cm of the soil, where it increased pH, increased total dissolved and exchangeable Ca, eliminated dissolved Al, and reduced exchangeable Al. Phosphogypsum, added at Ca rates equivalent to the Ca‐lime treatment, slightly reduced soil pH in the Inceptisol and slightly increased soil pH in the Oxisol. Phosphogypsum did not appreciably affect dissolved Al in the topsoil; however, it did reduce exchangeable Al but to a lesser degree than did Ca‐lime or Mg‐lime. Phosphogypsum increased exchangeable Ca and decreased exchangeable Al in the subsoil to a depth of 40 to 60 cm. Calcium chloride, added at Ca rates equivalent to the Ca‐lime treatment, produced dissolved and exchangeable Ca increases similar to the phosphogypsum treatment; however, soluble and exchangeable Al were increased and pH slightly decreased throughout the soil profiles. Mg‐lime, added at an acidity‐neutralizing rate equivalent to the Ca‐lime treatment, produced results similar to Ca‐lime except that soluble and exchangeable Mg rather than Ca were increased in the topsoil. Apple tree root densities were enhanced in the soil layers that were made simultaneously high in exchangeable Ca and low in exchangeable Al by the soil amendments. The trees with the more extensive root systems had higher leaf Ca concentrations and produced more and larger fruit. The Ca concentrations in these larger fruit were not reduced by fruit expansion, suggesting enhanced Ca supply from the soil
Interrill Soil Erosion Processes: II. Relationship of Splash Detachment to Soil Properties
Authors: Bradford J. M. , Ferris J. E. , Remley P. A.
Published: July 2010

Soil erodibility is often estimated using predictive equations based on easily measurable soil parameters. However, most predictive equations are valid for a limited group of soils and do not account for temporal changes in surface conditions. The objective of this study was to identify those soil properties that affect interrill splash and to develop an interrill detachment model based on both static and dynamic soil properties. Twenty soils ranging in texture from sand to clay were exposed to laboratory simulated rainfall with an intensity of about 63 mm/h. The development of a surface seal decreased infiltration rate, splash, wash erosion, and increased soil strength, as measured with a fall‐cone device. The best predictor of soil splash for the surface sealed condition was a combined kinetic energy/fall‐ cone strength (KE/τ) and total silt content term, and of total soil loss, a KE/τ and coarse silt content term. Comparing results from this study with previously reported studies, we conclude that for improvement of laboratory based indices, greater attention must be given to dynamic soil properties such as the soil's resisting force to raindrop impact and surface flow.
Microbial Reduction of Structural Iron(III) in Smectites
Authors: Stucki Joseph W. , Komadel Peter , Wilkinson Henry T.
Published: July 2010

Octahedral Fe(III) in the crystal structures of three different smectites was reduced to Fe(II) by actively growing microorganisms indigenous to the clay. The smectites were SWa‐1 ferruginous smectite from Grant County, Washington; API 33a, Garfield Nontronite; and API 25, Upton montmorillonite. Bacterial growth was supported by incubating clay suspensions at room temperature in a nutrient broth solution consisting of peptone and beef extract. Some samples were first sterilized (by autoclaving), then seeded with bacteria that had been isolated previously from the SWa‐1 sample. The effect of O2 on microbial reduction of Fe(III) was also tested. Results revealed that, in all three clays, about 0.30 mmol Fe(III)/g clay was reduced to Fe(II) by bacteria in a 28‐day period. The specific organism responsible for Fe reduction has yet to be classified, but it was more efficient in samples that had not been purged of O2, and it appears to be indigenous to the SWa‐1 clay.
Sand‐sized Kaolinized Feldspar Pseudomorphs in a California Humult
Authors: Southard R. J. , Southard S. B.
Published: July 2010

Deeply weathered soils forming on andesitic mudflows are common in the foothills of the Sierra Nevada of California. Many of these soils (Humults) have oxidic mineralogy based on extractable Fe and gibbsite detected by x‐ray diffraction and differential thermal analysis. Thermal analysis and differential thermal analysis of whole soil samples reveal kaolin and gibbsite percentages greater than clay percentages obtained by particle‐size analysis. X‐ray diffractometry of the fine (0.1–0.25 mm) and coarse (0.5–1.0 mm) sands shows fractions dominated by kaolin throughout the profile. Halloysite predominates in the saprolite; kaolinite increases in abundance toward the soil surface. Gibbsite is present in the surface and upper argillic horizons. Observation of the fine sand fraction with a polarizing light microscope reveals highly weathered feldspar grains with very low birefringence. Scanning electron micrographs of coarse and fine sands show pseudomorphic replacement of feldspar by halloysite resulting in discrete sand‐sized grains wherein simple albite twins are preserved. Energy dispersive analysis by x‐ray of unweathered feldspars produces Si/Al count ratios of 6:1 and indicates the presence of K and Ca in the feldspar structure. Analysis of the surfaces and interiors of kaolinized feldspar grains shows Si/Al count ratios of 2:1 and an absence of K and Ca, demonstrating that the feldspars are completely altered to kaolin by desilication and loss of hydrolyzable cations. The alteration appears to be crystallographically controlled because the original feldspar crystal morphology is preserved.
Air Encapsulation During Infiltration
Authors: Constantz Jim , Herkelrath W. N. , Murphy Fred
Published: July 2010

A series of field and laboratory experiments were performed to measure the effects of air encapsulation within the soil's transmission zone upon several infiltration properties. In the field, infiltration rates were measured using a double‐cap infiltrometer (DCI), and soil‐water contents were measured using time‐domain reflectometry (TDR). Before half of the infiltration experiments, CO2 was injected through the DCI into the soil to reduce the amount of air encapsulation in the soil's transmission zone. For a gravelly loam as steady infiltration rates were approached, the average volumetric water content was 0.38 cm3 cm−3 for control experiments and 0.43 cm3 cm−3 for CO2 experiments. The average steady infiltration rate was 0.42 cm min−1 for the control experiments compared to 4.40 cm min−1 for the CO2 experiments. For a sandy loam as steady infiltration rates were approached, the average volumetric water content was 0.43 cm3 cm−3 for control experiments compared with 0.45 cm3 cm−3 for CO2 experiments. The average final infiltration rate was 0.09 cm min−1 for the control experiments compared with 0.42 cm min−1 for the CO2 experiments. In the laboratory, infiltration experiments were performed using repacked soil columns (15‐cm i.d. by 140 cm long), again using TDR and CO2 flooding. For a medium sand as steady infiltration rates were approached, the average volumetric water content was 0.29 cm3 cm−3 for the control experiments and 0.36 cm3 cm−3 for the CO2 experiments. The average steady infiltration rate was 0.25 cm min−1 for the control experiments and 1.23 cm min−1 for the CO2 experiments. For a loam as steady infiltration rates were approached, the average volumetric water content was 0.45 cm3 cm−3 for the control experiments and 0.50 cm3 cm−3 for the CO2 experiments. The average steady infiltration rate was 0.02 cm min−1 for the control experiments and 0.10 cm min−1 for the CO2 experiments. These results suggest that a significant portion of the total encapsulated air resided in interconnected pores within the soil's transmission zone. For the time scale considered, this residual air caused the effective hydraulic conductivity of the transmission zone to remain at a level no greater than 20% of the saturated hydraulic conductivity of the soil.
Specific Cadmium Sorption in Relation to the Crystal Chemistry of Clay Minerals
Authors: Ziper Craig , Komarneni Sridhar , Baker Dale E.
Published: July 2010

Three possible locations on clay minerals exist where Cd can be sorbed by ion exchange. These are the external planar, interlayer, and edge surfaces. In this study, montmorillonite, kaolinite, vermiculite, and biotite minerals were used to separate these sorption sites. The vermiculite and biotite were fractionated into five size fractions ranging from <2 to 1000 µm. The relative effect of one surface type on the others was enhanced by further structural manipulations by K+ or Li+ treatments on the vermiculite and montmorillonite. Equilibrium adsorption and desorption of Cd was measured using 109Cd at 0.02 µCi/mL for isotopic dilution to a concentration range of 10−9 to 10−5 M in a 0.005 M CaCl2 background. The mineral concentrations were defined for a constant cation exchange capacity (CEC) or constant external surface area. The results using these different phyllosilicates suggest that the edge and high charge density planar sites (as in biotite) contribute the greatest influence. Generally an increase in the edge to planar surface area ratio with decreasing particle size, or the increase in edge to interlayer surface area ratio by either K+ or Li+ treatments, resulted in an enhanced sorption of Cd. These results suggest that CEC alone is not an accurate measurement to predict Cd sorption behavior for layer silicates. The concentration range used in this study allowed a full inspection of specific and nonspecific Cd‐clay interaction. Equilibrium desorption was used to infer the specific or nonspecific Cd‐clay interaction type. The structural manipulations such as K and Li fixation in vermiculite and montmorillonite, respectively, showed that edge sites retained Cd specifically. The high charge density edge and planar sites of biotite also desorbed Cd the least, suggesting the role of high charge density in specific Cd retention.
Seasonal Pore Water Dynamics in Marshes of Barataria Basin, Louisiana
Authors: Feijtel T. C. , DeLaune R. D. , Patrick W. H.
Published: July 2010

Sediment redox potential (Eh), interstitial pore water pH, sulfate, carbonate, and trace metals were measured monthly from August 1984 to August 1985, in a salt, brackish, and freshwater marsh in Barataria Basin, LA. The salt marsh was characterized by low Eh during the summer and fall, resulting in pyrite formation. Early spring oxidation of the sediments created extreme acid conditions, indicating that pyrite was oxidized completely to sulfate. Brackish and freshwater marshes exhibited a much greater seasonal variability, with strong vertical redox fluctuations. In the freshwater marsh, both Fe2+ and Mn2+ were controlled by temporal pH changes and were relatively independent of oxidation‐reduction phenomena, suggesting a possible organic control mechanism. However, in the brackish marsh, Fe2+ concentrations were governed by pH (r = −0.74** significant at the 0.01 probability level) and Eh (r = 0.65**) changes, indicating that Fe2+ concentrations were likely controlled by pyrite formation and oxidation. Ion activity product calculations indicated that iron and manganese phosphates and carbonates were unlikely to form in Barataria Basin marshes. However, iron and manganese sulfide supersaturation occurred in all three marshes. Brackish marshes were found to contain significantly higher pyrite concentrations (1.4% w/w), than salt (0.69% w/w) and freshwater (0.66% w/w) marshes. The dynamic pyrite cycling in Louisiana salt marshes, resulted in a low pyritic pool, characterized by single, fine grained euhedral crystals. Pyritic Fe represented 23% of the total Fe accumulation flux in the salt marsh, and 34% in the brackish marsh.
Microbial Colonization and Decomposition of Corn, Wheat, and Soybean Residue
Authors: Broder M. W. , Wagner G. H.
Published: July 2010

Decomposition studies were conducted on corn (Zea mays L.), wheat (Triticum aestivum L.), and soybean (Glycine max L.) residue with emphasis on quantitative determination of the microbial populations colonizing the residues and identification of the predominant fungi isolated from the residues. The study was conducted over a 2‐yr period in a Mexico silt loam (Udollic Ochraqualf) at Sanborn Field in Columbia, MO. Plant residues were placed in a porous net and buried in the field. At intervals these sacks were exhumed, washed, and the washings were plated on rose bengal and soil extract agars. The residue was dried and weighed to determine decomposition rates. The predominant fungi were isolated and identified. Microbial determinations were conducted on soil samples taken from the same plots. Of the three residues, soybean had the most rapid rate of decomposition, losing 68% of its total organic matter over the course of 32 d compared with 42 and 47% for corn and wheat residue, respectively. Despite a more rapid rate of decomposition in wheat in comparison with corn residue at 32 d, after 756 d in the soil corn retained 15% of its original organic matter in comparison with 18% for wheat. Bacterial and actinomycete populations were consistently higher on soybean residue in comparison with corn and wheat residue; however, fungal populations were consistently highest on corn residue and lowest on wheat residue. Size of microbial populations from soil were similar for the three plots over the course of the study. Aspergillus, Penicillium, and Trichoderma were the three predominant genera isolated from the residues. Aspergillus niger was consistently isolated at high levels from corn residue, and A. clavatus was isolated frequently, but at low levels from wheat residue. Penicillium spp. were isolated from residues mainly during drought conditions and during the latter stages of decomposition. Trichoderma spp. were isolated at their highest levels during the second summer of the decomposition study, but were found at substantially lower levels during the third summer. Myrothecium spp. was isolated consistently from soybean residue but only during the latter stages of the decay process.
Soil Organic Matter Turnover in Long‐term Field Experiments as Revealed by Carbon‐13 Natural Abundance
Authors: Balesdent J. , Wagner G. H. , Mariotti A.
Published: July 2010

Cultivation of C‐3 (Calvin cycle) plants after turning under a native prairie of grasses possessing C‐4 metabolism (Hatch‐Slack cycle) allows partitioning of soil organic matter as to origin. Contrasting natural 13C abundance for the two different contributing kinds of plant residues provides an in situ labeling of the soil organic matter. A study to exploit this approach used soil from a long‐term experimental field. Samples were collected under different continuous crops and at different dates and were analyzed for total C and for natural isotope composition of C. The results demonstrated an initial rapid loss of prairie C, suggesting the presence of an easily mineralizable component that was exhausted in 30 to 40 yr. The extent of this was dependent upon the type of cultivation. A pool of stable organic matter of prairie origin persisted under all systems during the approximate 100 yr of cultivation, which was no less than 50% of the current level. The half‐life, under cultivation, of the easily mineralizable compartment was shown to be 10 to 15 yr. Mechanical fractionation of soil mineral particles and associated organic matter showed a heterogeneity with regard to stability. The clay fraction included both the most stable C, and some labile C, whereas clay associated with fine silt demonstrated a turnover that suggested slow replacement of the whole of the fraction. The overall results demonstrate the potential value of long‐term field experiments for studying soil organic matter turnover by the natural 13C abundance technique.
Surface Soil Nutrient Distribution as Affected by Wheat‐Fallow Tillage Systems
Authors: Follett R. F. , Peterson G. A.
Published: July 2010

Research was conducted to determine long‐term effects of tillage on soil fertility. Our objective was to determine whether crop residue placement caused by differences in tillage would result in changes in levels of plant available nutrients and other metals in the soil. Two native grassland sites in Western Nebraska were managed under three tillage systems; no‐till, stubble‐mulch, and moldboard plow (bare fallow). The first site was in native sod until 1970 when it was plowed and an alternate wheat‐fallow rotation experiment with no fertilization begun. The second site was farmed from 1930 to 1957, then reseeded to crested wheatgrass (Agropyron desertorum) until 1969 when it was moldboard plowed and an alternate wheat‐fallow experiment with two rates of N‐fertilization (0 and 45 kg N ha−1 every other year) began. After 16 yr of cultivation, soil test values (NH4HCO3‐DTPA extract) were obtained for samples from the 0‐ to 5‐, 5‐ to 10‐, 10‐ to 20‐cm depths. Except at the lower depths, plow tillage, as compared to no‐till or stubble mulch, decreased levels of soil organic matter and extractable K, Zn, Cu, and Pb at both sites, while extractable Ni was decreased at only one site and extractable P, Fe, Mn and Cd were decreased at the other site. Extractable nutrients and metals were generally not affected by tillage in the 10 to 20 cm depths. Fertilization with N decreased soil pH and extractable inorganic P and Zn levels but increased extractable organic‐P, Fe, Mn, Pb, Cd, and Ni in the 0‐ to 5‐ cm depth. Soil organic matter and extractable P, K, Mn, Cu, Pb, and Cd levels decreased with depth. This study shows that the adoption of no‐till, compared to stubble‐mulch or plow‐tillage, maintains fertility status of topsoil nearer to that of native prairie soil. Accumulation of crop residues and maintenance of soil organic matter levels appear to be key factors in sustaining soil fertility status of Great Plains soils.