bluuebunny/crossref_metadata_2025 huggingface dataset:
Drainage of a Tropaqualf Before and After Water Extraction by a Crop
Authors: Klodpeng Thanom , Morris R. A.
Published: July 2010

To improve production of crops planted after lowland rice (Oryza sativa L.) in monosoonal Asia, there is a need to understand more clearly the drainage pattern during the transition from the wet to the dry season. For crops of 75 to 80 d maturity, the top 750 mm of soil contains the bulk of the root system. This study determined the flux of water across the 750‐mm plane and the water table recession patterns during the transition from wet to dry season and again after a crop had removed water from the soil. The study was conducted in three phases on a 9‐m by 9‐m plot of an Aeric Tropaqualfs. In the first phase, the soil was field saturated, covered with plastic sheeting, and drained for 30 d. In the second phase, a cowpea (Vigna unguiculata L. Walp) — sorghum (Sorghum bicolor L. Moench) intercrop was grown for 42 d. In the third phase, 22 mm of water was applied and soil was again covered and drained for 15 d. Volumetric water changes were determined by neutron scattering at 150‐, 300‐, 600‐, 900‐ and 1200‐mm depths. Tensiometers were placed at the same depths. The plot was surrounded by flow barriers to a 750‐mm depth. Drainage through the 750‐mm plane during the first phase amounted to only 11 mm. A perched water table formed in and above the B horizon at 600 mm. The ground water table receded at 30 mm d−1 after it appeared below the perched water table on day 10. During the second phase roots penetrated at about 25 mm d−1 suggesting that the initial high water content was not a major impediment to root development. After a 22‐mm irrigation, the drainage rate during the third phase was 1.2 mm d−1, with drainage apparently coming both from applied water and water remaining in the profile prior to irrigation. The results suggest both opportunities and problems for using soil water remaining after rice harvest during the transition from wet to dry season.
Some Equilibrium Considerations in the Formation of Chlorite in Soils and Sediments
Authors: Kittrick J. A.
Published: July 2010

Sufficient chlorite stability data are now available so as to permit initial consideration of chlorite equilibria in soils and sediments. Assuming a pH4SiO4 of 3.1 and other conditions approximating the soil solution, stability diagrams indicate that high‐Mg varieties of chlorite and smectite should be stable under an oxidizing condition (pe + pH = 17.7) and should control Mg or Al, or both. Under a mildly reducing condition (pe + pH = 11.5), high Fe2+ chlorites and probably smectites are predicted to dominate equilibria. The lack of rate information may be particularly restrictive considering the extremely low levels of Al anticipated.
Determination of 15N‐Labeled Dinitrogen and Nitrous Oxide with Triple‐Collector Mass Spectrometers
Authors: Mulvaney R. L.
Published: July 2010

Equations are derived that permit use of a triple‐collector mass spectrometer for determination of 15N‐labeled dinitrogen (N2) and nitrous oxide (N2O) by procedures recently developed for double‐collector instruments. These equations are based upon the ratios 29N2/28N2 and 30N2/28N2, instead of 29N2/28N2 and 30N2/(28N2 + 29N2).
Evaluation of Simplified Methods for Determining Unsaturated Hydraulic Conductivity of Layered Soils
Authors: Schuh W. M. , Bauder J. W. , Gupta S. C.
Published: July 2010

The simplified field method of L.R. Ahuja et al. (1980) for determining hydraulic conductivity as a function of soil water suction, K(S), and the simplified field method of P.L. Libardi et al. (1980) for determining hydraulic conductivity as a function of soil water content, K(θ), were compared with the instantaneous profile method, to evaluate their suitability for estimating hydraulic conductivity of layered soil. The Ahuja method worked well on coarse and fine‐textured soils and complex soil profiles with stratification. The Libardi method worked well on coarse and fine‐textured, homogeneous materials and homogeneous parent materials underlying stratified soil materials. A calculated matching value (Ko) was used with the Libardi method. Within layered soil materials slopes of the K(θ) curves, calculated with the Libardi method, were adequate; however, calculated Ko values were often inadequate. Fit of calculated values with measured values of hydraulic conductivity could have been improved by using field‐determined Ko values.
Kinetics of Arsenite Sorption in Soils
Authors: Elkhatib E. A. , Bennett O. L. , Wright R. J.
Published: July 2010

The sorption of As(III) by 10 surface and subsurface horizons was investigated. An Elovich type equation and a modified Freundlich equation were used to describe the kinetics of the As(III) sorption process. Both equations successfully describe As(III) sorption rates. However, the modified Freundlich equation proved to be superior when both coefficients of determination (R2) and standard errors of estimate (SE) were considered. The SE values from the modified Freundlich equation were consistently lower than those from the Elovich equation. Modified Freundlich equation parameters were regressed against soil chemical and physical properties to indicate possible sorption mechanisms and to identify soil properties that could serve as predictors of arsenite sorption. The regression equations indicated that iron oxides and Eh were the main soil properties controlling arsenite sorption rate.
Pathways of Phosphorus Transformations in Soils of Differing Pedogenesis
Authors: Tiessen H. , Stewart J. W. B. , Cole C. V.
Published: July 2010

Nine different organic and inorganic soil phosphorus fractions were obtained by a sequential extraction of samples from 168 USDA‐SCS benchmark soils, representing eight soil orders of the Soil Taxonomy. The distribution of P across the different fractions (resin, bicarbonate, hydroxide, sonification‐2nd hydroxide, acid, and acid‐peroxide digest fractions with separate organic and inorganic P determinations) and their relationships to other soil chemical properties were used to evaluate the effects of different soil development on phosphorus composition. Correlation and regression analyses of P distribution and chemical analyses confirmed the partial dependence of organic matter accumulation on available forms of P. Weathering indicators such as base saturation were related to the formation of secondary P forms. The relative proportions of available and stable as well as organic and inorganic P forms were dependent upon soil chemical properties and related to soil taxonomy. Path analysis of relationships between labile and stable P forms showed that in Mollisols much of the labile resin extractable P was derived from inorganic bicarbonate and hydroxide extractable P forms. In more weathered Ultisols, 80% of the variability in labile P was accounted for by organic P forms, suggesting that mineralization of organic P may be a major determinant of P fertility in these soils.
Loess‐Derived Soils, Mississippi Valley Region: I. Soil‐Sedimentation System
Authors: Ruhe Robert V.
Published: July 2010

Among 25 profiles of Typic Hapludalfs at approximately half degrees of latitude from southern Mississippi to southeastern Minnesota, the textural and clay‐mineralogic properties of the soils depend mainly on the sedimentation system at each site. Other physical, chemical, and hydrologic properties that relate to texture and mineralogy are also in part sedimentation‐dependent. Although temperature and precipitation decrease to the north, there is little climatic impact on these properties in these soils.
Weight Loss and Nutrient Dynamics in Decomposing Woody Loblolly Pine Logging Slash
Authors: Barber B. L. , Van Lear D. H.
Published: July 2010

Six clearcuts ranging from 0 to 11 yr since cutting in the Piedmont of South Carolina were sampled to estimate the rate of weight loss of logging debris and to study nutrient dynamics in decomposing loblolly pine (Pinus taeda L.) slash. Density changes in wood were characterized using a negative exponential model. Decay coefficient (k) for small‐sized pieces (< 2.5‐cm diam) was 0.051 while decay coefficients for medium‐ (2.5–7.5 cm diam) and large‐ (> 7.5‐cm diam) sized pieces were 0.079 and 0.072, respectively. Overall, woody logging slash exhibited a k value of 0.072. Logging slash in contact with the ground decayed at a 50% higher rate than aerial slash. Concentrations of N and P in woody slash remained relatively constant the first few years after cutting followed by an increase. Concentrations of K, Mg, and Ca decreased in the initial stages of decomposition and then increased in the later stages. A prediction model estimated that N and P quantities in woody slash initially decrease and then increase. After 7 yr, woody slash would contain 107% of the N and 94% of the P contained in the slash initially. Potassium, magnesium, and calcium quantities show a gradual decrease with time. Woody logging slash would lose 77, 56, and 50% of the initial amounts of K, Mg, and Ca, respectively, after 7 yr. Woody logging slash acts as a nutrient sink and may be important in nutrient conservation on cutover areas.
Catalytic Effects of Manganese (IV), Iron(III), Aluminum, and Silicon Oxides on the Formation of Phenolic Polymers
Authors: Shindo H. , Huang P. M.
Published: July 2010

The catalytic effects of three Mn(IV) oxides (birnessite, cryptomelane, and pyrolusite) and short‐range ordered Fe(III), Al, and Si oxides on the darkening of phenolic compound solutions (hydroquinone, resorcinol, and catechol) and the subsequent formation of humic acid (the precipitate formed by acidifying the darkening solution) were investigated. Manganese oxides are very powerful in causing the darkening of phenolic compounds. The rate and degree of the darkening vary with the kinds of Mn oxides, the chemistry of the phenolic compounds, and the pH values of the systems. In the Mn oxide systems, phenolic compounds are converted to humic acid with a relatively high degree of humification (Δlog K: 0.52–0.70; RF: 54–105) through oxidative polymerization. For example, at the initial pH of 6.0, the percent conversion of hydroquinone to humic acid ranged from 36 to 55%. The yields of humic acids formed in the Mn oxide systems are highly correlated with the degree of the darkening measured at 400 nm (r2 = 0.818) and 600 nm (r2 = 0.983). The catalytic effect of Fe oxide on the darkening and the formation of humic acid was relatively limited under the conditions studied. The catalytic effects were not observed in the Al and Si oxide systems. The results obtained in this study indicate that various Mn(IV) oxides common in the environment merit close attention in the abiotic formation of humic substances.
Expansion of Smectites as a Function of Vapor Pressure of Ethylene Glycol
Authors: Hsieh Y. P. , Tsai Ping‐Ping , Hsu Pa Ho
Published: July 2010

Magnesium‐saturated, 0.2‐ to 1‐µm fraction of six references smectites and two smectite‐rich soil clays were solvated with ethylene glycol vapor at 65°C under graded relative vapor pressures from 3 to 100%. Each smectite expanded over a range of relative vapor pressure. This observation implied that heterogeneity in layer charge distribution of the smectites was common in the specimens. Relatively, Wards 25 and Wards 27 were least heterogeneous, and Wards 31 and Wards 23 were most heterogeneous among the specimens. The relative expandability of smectites under solvation of ethylene glycol vapor followed the sequence of: SHe‐1>Wards 25 = Wards 27≥SWy‐1> Wards 23>Bowdoin C>LC> Wards 31. The sequence corresponded approximately with that of total layer charge of the specimens. Six of the eight smectites exhibited heterogeneity in a random interstratification manner, two exhibited heterogeneity in a zoned interstratification manner. The moisture‐ethylene glycol interaction enhanced the expansion of smectites when they were partially solvated with ethylene glycol.
Scaling Soil Water Properties and Infiltration Modeling
Authors: Ahuja L. R. , Naney J. W. , Nielsen D. R.
Published: July 2010

We examined variability and interrelation of the scaling factors for Green‐Ampt infiltration parameters of saturated hydraulic conductivity (Ks) and wetting‐front pressure head (hf) in a 9.6‐ha grassland watershed, containing three hydrologically similar silt loam Mollisols. Scaling factors for different depths at a given site appeared to be related. The scaled mean Ks decreased with depth, while the scale mean hf showed no trend. The Ks scaling factors had greater variability between sites than the hf factors, and the relationship between the two sets of factors deviated appreciably from a 1:1 line. However, there was a linear relationship between them, which was utilized in modeling infiltration. The composite infiltration for the watershed calculated by using different, but related, scaling factors for Ks and hf was very close to that obtained by using the same scaling factors, derived from either Ks or hf, for both. However, the distribution and range of the predicted infiltrations were greatly different.
Sodium‐Calcium‐Magnesium Exchange Reactions on a Montmorillonitic Soil: II. Ternary Exchange Reactions
Authors: Fletcher Philip , Holtzclaw Kenneth M. , Jouany Claire , Sposito Garrison , LeVesque C. S.
Published: July 2010

The exchange of magnesium for calcium at 298 K on a montmorillonitic soil separate (principally clay and silt) was investigated in a 50 mol m−3 perchlorate background at pH 5,6, and 7. The charge fraction of sodium in the aqueous solution phase was controlled at 0.70 or 0.85 during the exchange experiments, resulting in average exchangeable sodium percentages ranging from 5 to 25% on the soil. Exchange isotherms for magnesium indicated some preference on the soil for calcium over magnesium. This preference was attributed primarily to the presence of organic matter associated with the soil separate. However, the exchange isotherms showed no effect of pH in the range between 5 and 7, and no effect of exchangeable sodium percentage in the range between 0 and 25%.
Specific Adsorption of Copper on an Hydroxy‐Aluminum‐Montmorillonite Complex
Authors: Harsh J. B. , Doner H. E.
Published: July 2010

The adsorption of Na on a prepared hydroxy‐aluminum‐montmorillonite complex (OH‐Al‐SWy‐l) was investigated as a function of pH, time, and Cu concentration ([Cu]). It was found that Na adsorption from 0.01M NaClO4 increased with pH from 0.015 mol kg−1 at pH 4.5 to 0.33 mol (Na+) kg−1 clay at pH 6.6 Adsorption of 0.16 mol (1/2 Cu2+) kg−1 clay did not affect the amount of Na adsorption, showing that specific sites existed for Cu. Adsorption of Cu was found to increase with pH and both adsorption and resistance to extraction with 0.25M Ba(NO3)2 increased with time. At pH 4.6, Cu adsorption approached a maximum near 0.3 mol (1/2 Cu2+) kg−1 clay of which 0.13 mol (1/2 Cu2+) were extracted with Ba(NO3)2. Electron spin resonance (ESR) of the Cu on OH‐Al‐SWy‐l showed that both physi‐ and chemisorbed Cu were present and that solubilization as Cu(NH3)2+4 through exposure to NH3 vapor overnight was possible only if the sample had been previously treated with BaCl2. It was concluded that the OH‐Al‐SWy‐l system provided a much more reactive surface toward Cu adsorption than either montmorillonite or hydrous aluminum oxides. In comparison to smectites Cu was less labile to Ba extraction due, in part, to chemisorption by Al‐OH groups. Relative to values reported for Al(OH)3 polymorphs, Alx(OH)y3x‐y precipitated in the presence of montmorillonite adsorbed more Cu on a mass basis presumably due to a higher surface to mass ratio.
Spatial Variability of Rhizobium japonicum in Two North Carolina Soils
Authors: Wollum A. G. , Cassel D. K.
Published: July 2010

The spatial variability of Rhizobium japonicum populations was evaluated for two soils on the Coastal Plain of North Carolina. The Nahunta soil (fine‐silty, siliceous, thermic Arenic Paleudults) was somewhat poorly drained and had an organic matter content of 20 g kg−1 whereas the Pocalla soil (loamy, siliceous, thermic, Arenic Paleudults) was well drained and had 10 g kg−1 organic matter. One hundred and five soil samples from the Ap horizon were collected from an apparently uniform 18‐m by 18‐m area at each site and were subjected to analysis by the plant infectivity—most‐probable‐number (MPN) technique to determine the number of rhizobia. The log10 MPN (log MPN) of R. japonicum varied from 2.63 to 7.03 g−1 soil; mean log MPN values were 4.10 and 6.07 g−1 soil for Pocalla and Nahunta, respectively. Semivariograms for sample separation distances (h) < 2 m at each site were developed from soil samples collected on transects (fences). Semivariograms for h ≥ 3 m were developed using data collected on a 3‐m grid. Analysis of the semivariograms constructed from the log MPN data indicated a different variance structure at each site. Moreover, the variance structure for log MPN was found to be directional, i.e., it was different in the direction “parallel to the row” compared to the direction “perpendicular to the row.” For the Pocalla soil the semivariance in the “down‐the‐row” direction was greater for values of h < 1.05 m than it was for h ≥ 3 m. This apparent discrepancy is thought to be due to selection of the transect from which the 0.2‐m spaced samples were collected in a region of the field which is not typical of the field as a whole. This result demonstrates the importance of using a sampling regime which is not biased toward one particular area of a field. Root densities, inherent soil properties, seasonality, and management practices are possible contributors to the subtle changes in rhizobia populations that were observed.
Soil Phosphorus Supplying Capacity Evaluated by Plant Removal and Available Phosphorus Extraction
Authors: Aquino B. F. , Hanson R. G.
Published: July 2010

Many Missouri soils test high in extractable P after long periods of rock phosphate and processed P fertilization. This study was undertaken to determine the P‐supplying capacities of five Missouri soils possessing high levels of extractable P. Initial P levels were evaluated with selected extractants (Bray I, Bray II, Mehlich II, double acid, dilute SrCl2) and through evaluation of the P buffering index. Each soil was cropped under greenhouse conditions for 7 consecutive harvests of grain sorghum (Sorghum bicolor L. cv. Warner 744R). After each harvest, plant P uptake was calculated and extractable P measured as before. For each soil test, regression analyses of plant P uptake were performed. With only one exception, the decline in extractable P in all soils, as measured by all five extractants, was significantly correlated with cumulative P uptake. The highest correlations were obtained with Bray I for Sharkey clay (r = 0.95), Bray I and Bray II for Kennebec silty clay loam (r = 0.97), Bray II for Mexico silt loam and Broseley loamy fine sand (r = 0.95 and r = 0.90, respectively), and Mehlich II for Tiptonville silt loam (r = 0.96). Slopes of the decline in extractable P following intensive cropping show similarities between Bray I and Mehlich II, Bray II and double acid. The quantity of plant available P extracted by Bray II and dilute SrCl2 was found to be inversely related to the P buffer index (PBI). When extrapolating to critical P levels for Bray I (11 mg kg−1) and Bray II (24 mg kg−1) only the Bray II extracted predicted number of harvests in order of soil PBI.
Movement of Calcium and Magnesium in Ultisols from Dolomitic Limestone
Authors: Messick D. L. , Alley M. M. , Zelazny L. W.
Published: July 2010

Root growth and crop yield are limited on many soils by acid subsoil and toxic concentrations of Al and Mn, and deficiencies of Ca and Mg. Calcium and magnesium movement and neutralization of acidity below the zone of limestone incorporation were investigated on seven acid Virginia soils. Dolomitic limestone treatments of 0, 4.5, 9.0, and 13.4 Mg ha−1 on the Coastal Plains and 0, 4.5, 9.0, 13.4, and 18.0 Mg ha−1 on Piedmont and Valley soils were surface‐applied and incorporated (0–20 cm). Four years after limestone application, soil samples were collected at depth increments of 0 to 10, 10 to 20, 20 to 25, 25 to 30, 30 to 40, 40 to 50, and 50 to 60 cm. Samples were analyzed for exchangeable Ca, Mg, and Al, and pH. Calcium and magnesium movement and depth of neutralization decreased with increasing soil clay content. Liming increased cation retention in horizons that received direct lime application apparently due to increased pH‐dependent CEC. Depth of neutralization was lime rate dependent with greater neutralization of acidity at higher limestone rates. Magnesium movement was detected at greater depths than Ca in all soils, but neutralization of acidity did not accompany movement of either Ca or Mg. This demonstrated that the cation moved as a neutral salt or that pH change was not measurable.
Dispersion of Soils by an Ultrasonic Method that Eliminates Probe Contact
Authors: Busacca A. J. , Aniku J. R. , Singer M. J.
Published: July 2010

A cup‐type ultrasonic vibrator was evaluated for use in dispersing soils and was calibrated to the standard chemical dispersion plus shaking method. The “cup horn” device isolates the soil suspension from contact with, and potential contamination from, the Ti alloy of the ultrasonic probe‐tip or “horn.” Five soils (2 A horizons and 3 B horizons) representing four soil orders were tested. The soils varied in texture (16–48% clay), clay mineralogy (mixed to kaolinitic), pH (4.9–7.0), and free‐iron (1.9–5.0%). Twenty‐minute cup horn treatment at 200 watts yielded clay contents that were 0 to 9.5% lower than those from the standard method; 25‐minute treatment yielded values 1.5% lower to 21.5% higher than the standard method. Medium and coarse sand fractions in the soils were lower, and very fine sand and silt fractions tended to be higher after cup horn treatment than after the standard treatment. In a second test, approximately 11% (absolute) of sand samples (50–250, 250–2000 µm), and 6% (absolute) of coarse‐silt samples (20–50 µm) shifted to finer fractions after cup horn treatments. Part of this shift was the result of grain abrasion and part was the result of removal of coatings on grains left intact by the standard dispersion treatment. Four of the five soils formed stable dispersions when sonicated in pH 9.5 Na2CO3 solution. The fifth, a very strongly acid soil, flocculated unless titrated to pH 8.5 to 9.5 using 0.1M NaOH after ultrasonic treatment. Coefficients of variation of replicated sand, silt, and clay determinations after cup horn treatment ranged from < 1 to 4%; coefficients of variation of replicated determinations after the standard treatment ranged from 2 to 5%.
Soil Aggregates and Clod Strength Dependence on Size, Cultivation, and Stress Load Rates
Authors: Hadas A. , Wolf D.
Published: July 2010

A study was carried out (i) to determine soil clod fragmentation patterns' dependence on specific surface energy, aggregate or clod size, and stress loading rates; and (ii) to examine the hypothesis that the large clods produced during tillage operations performed on air‐dry soils are a result of soil compaction due to overtilling and machinery traffic on a moist soil during the cropping season. It was found that surface energy and specific energy required to reduce aggregate size are dependent on stress loading rates. Under a specific stress loading rate, suspected to be less than or equal to the stress wave velocity in the soil, both common methods—the unconfined compression test and the drop‐shatter test—are assumed to be equally efficient in determining the energy required for soil fragmentation. It was concluded, based on soil strength values obtained, that the fracture strength of the soils tested is attributed to CaCO3 bonding bridges and is practically uniform for all clod and aggregate size ranges tested. The observed huge clods created while tilling the air‐dry soils were size dependent on row spacing and tillage direction. These results are typical of fracturing patterns of material characterized by uniform strength. The fracture patterns for these materials follow the planes of maximal shear stresses unless obstructed by plants of lower strength (e.g., plant rows, major cracks); thus the size of fractured units depend on tillage direction, tillage implement, and row spacing.
Cone Index of Loamy Sands as Influenced by Pore Size Distribution and Effective Stress
Authors: Vepraskas M. J.
Published: July 2010

Tillage pans form in coarse textured soil horizons of the Atlantic Coastal Plain and develop high cone index values (soil strengths) which slow root growth and may decrease crop yields. Identification of soil properties that influence cone index may improve field identification of tillage pans and lead to the development of techniques to reduce their detrimental effects. This study examined the influence of pore size distribution, and effective stress on the cone index of loamy sand and loamy fine sand soil materials. Effective stress values were calculated from soil water characteristic curves and compared to cone index values for both natural cores and remolded materials. The remodeled samples of a loamy sand and a loamy fine sand developed different cone index values for relative saturations between 1.00 and 0.10, and these cone index differences were partially related to pore size distribution differences between materials. Pore size distribution influenced cone index by controlling effective stress. In both remolded samples and undisturbed cores of loamy sand, effective stress values ranged from 0 to 33 kPa for soil water potentials between 0.0 and −1500 kPa, respectively. For relative saturation values between 1.00 and 0.10, changes in effective stress closely conformed to changes in cone index for nondispersed soil materials. At a given effective stress, cone index was influenced by bulk density and soil particle characteristics that influence interparticle friction.
The Effects of Soil Properties on Nitrification and Nitrification Inhibition
Authors: Gilmour J. T.
Published: July 2010

An understanding of the impact of the soil environment on nitrification in the presence and absence of a nitrification inhibitor is important to proper use of this group of compounds. The objective of this study was to describe the kinetics of the nitrification process and define how a nitrification inhibitor, etradiazole (5‐ethoxy‐3‐trichloromethyl‐1,2,4‐thiadiazole), altered the reaction. Nitrification was found to obey zero‐order kinetics with the rate constant being a function of temperature, moisture, and pH. The absolute zero‐order rate was also a function of initial ammonium concentration. As temperature increased over the range of 16 to 28°C, the rate constant increased according to the Arrhenius equation. The relative influence of the inhibitor on the rate constant decreased with temperature increases. Below the optimum soil moisture for nitrification a linear decline in rate was observed as soil moisture decreased over the range of 0.20 to 0.12 g g−1 (−40 to − 140 kPa). This decline was greater in the control than in the soil amended with etradiazole. Nitrification linearly increased with soil pH over the range of 4.9 to 7.2. Using the above relationships, the rate of nitrification was predictable for an independent group of 19 soils. This same group of soils was evaluated for inhibition at two etradiazole rates at optimum moisture and 14°C. Inhibition decreased as organic carbon content increased above 13 g kg−1 with the extent of the decrease being modified by the amount of clay in the soil. As inhibitor rate increased, inhibition was enhanced by a constant amount, suggesting that the relationships described above remained in effect.
Effect of Water‐Filled Pore Space on Carbon Dioxide and Nitrous Oxide Production in Tilled and Nontilled Soils
Authors: Linn D. M. , Doran J. W.
Published: July 2010

The percentage of soil pore space filled with water (percent water‐filled pores, % WFP), as determined by water content and total porosity, appears to be closely related to soil microbial activity under different tillage regimes. Soil incubated in the laboratory at 60% WFP supported maximum aerobic microbial activity as determined by CO2 production and O2 uptake. In the field, % WFP of surface no‐tillage soils (0–75 mm) at four U.S. locations averaged 62% at time of sampling, whereas that for plowed soils was 44%. This difference in % WFP was reflected in 3.4 and 9.4 times greater CO2 and N2O production, respectively, from surface no‐tillage soils over a 24‐h period as compared to plowed soils. At a depth of 75 to 150 mm, % WFP values increased in both no‐tillage and plowed soils, averaging approximately 70% for no tillage compared with 50 to 60% for plowed soils. Production of CO2 in the plowed soils was enhanced by the increased % WFP, resulting in little or no difference in CO2 production between tillage treatments. Nitrous oxide production, however, remained greater under no‐tillage conditions. Substantially greater amounts of N2O were produced from the N‐fertilized soils, regardless of tillage practice. Production of CO2 and N2O was primarily related to the % WFP of tillage treatments although, in several instances, soil‐water‐soluble C and NO‐3 levels were important as well. Calculations of relative aerobic microbial activity between no‐tillage and plowed soils, based on differences in % WFP relative to maximum activity at 60%, indicated linear relationships for CO2 and N2O production between WFP values of 30 to 70%. Below 60% WFP, water limits microbial activity, but above 60%, aerobic microbial activity decreases—apparently the result of reduced aeration.
The Correlation Between Extracellular Polysaccharide Production and Acid Tolerance in Rhizobium
Authors: Cunningham Scott D. , Munns Donald N.
Published: July 2010

Rhizobial isolates from six host genera (Cicer, Phaseolus, Leucaena, Lens, Melilotus and Trifolium) were screened for ability to colonize successively more acidic agar plates. Sufficient isolates from Cicer and Phaseolus were screened to show that relative tolerance to acidic conditions was normally distributed. Extracellular polysaccharide (EPS) was isolated by ethanol precipitation from 10‐d‐old solution cultures of the most and least acid tolerant of these strains. Acid‐tolerant isolates from Cicer, Phaseolus, Leucaena and Melilotus produced significantly more (P < 0.001) EPS than did those which were acid sensitive. The differences between isolates from Trifolium were significant at the P < 0.05 level. No significant difference in EPS production was found among the 8 isolates from Lens. The correlation between EPS production and acid tolerance was tested further with EPS isolated from 20 strains of Rhizobium phaseoli. The quantity of EPS produced varied from 18 to 75 mg 100 mL culture, was normally distributed, and was positively correlated with acid tolerance (P < 0.01), albeit with an r2 value of only 0.331. It is postulated that EPS could modify the microenvironment of the rhizobia and so decrease the stresses induced by an acid soil.
Comparison of Chelating Agents as Extractants for Metals in Diverse Soil Materials
Authors: Norvell W. A.
Published: July 2010

Five chelating agents—DTPA, EDTA, EGTA, HEDTA, and NTA—were compared at pH 5.3 as extractants for Al, Fe, Mn, Zn, Cu, Cd, and Ni in 25 diverse soils. Extracting solutions contained 0.005M chelating agent, 0.01M CaCl2, and 0.1M acetic acid‐ammonium acetate buffer at pH 5.3. These extractants were compared to: a similar solution without added chelating agent, 0.1M HCl, and the DTPA soil testing solution (0.005M DTPA, 0.01M CaCl2, buffered at pH 7.3 by 0.1M triethanolamine). All extractants yielded clear filtrates that aspirated and burned cleanly during analysis by flame atomic absorption spectrometry. At the 5:1 extractant/soil ratio used, all buffered extractants maintained their pH satisfactorily. DTPA and HEDTA were among the most effective ligands for extracting all seven metals. EDTA extracted somewhat lower concentrations but was also a good extractant for all metals. NTA was among the best extractants for Al and Ni but among the least effective extractants for Fe, Mn, and Cu. EGTA was the least effective chelator of Fe, Zn, Ni, and especially Al. Despite its alkaline pH of 7.3, the DTPA soil‐testing solution was a moderately effective extractant for metals except Mn and ferrous Fe. Acid soils, reduced soils and sediments, and metal‐contaminated soils may release enough strongly complexed metal to reduce the effectiveness and the capacity of chelating extractants. Recently dredged lake sediment released particularly large concentrations of metals, primarily Mn2+ and Fe2+. Extracting metals effectively from metal‐rich soils may require increased concentration of chelating agents, higher extractant/soil ratios, or more than one extraction per sample.
Soil Survey Interpretations from Water Retention Data: I. Development and Validation of a Water Retention Model
Authors: McBride R. A. , Mackintosh E. E.
Published: July 2010

The prediction of spatial and temporal variations in the soil water regime provides the basis for a proposed soil survey interpretive system. A water retention model estimates the boundary desorption curve from saturation to pF 4.2 for mineral soils in situ using limited soil physical data (standard error of estimate <2.2% g g−1). The total porosity (structural parameter) and clay content (adsorptive parameter) define the position of the moisture characteristic in logarithmic coordinates and the silt content its configuration. Organic matter affects the structural parameter by reducing both the dry bulk and particle densities but only significantly influences the adsorptive parameter at organic matter contents of 5% or greater. Model validation shows that the state and quantity of water retained by field soils near equilibrium is dependent on the position of the phreatic surface. Under field conditions, the ψ(θ) relationship establishes an effective equilibrium midway between the predicted wetting and drying curves of the hysteresis loop.
Enriched Levels of Arsenic in Post‐Active Acid Sulfate Soils in Alberta
Authors: Dudas M. J.
Published: July 2010

Three post‐active acid sulfate soils derived from weathered pyritic shale were analyzed for total As. Levels found in B and C horizons were nearly 10 times higher than normal background abundances. Secondary iron oxides formed from the weathering of pyrite acted as scavengers of As. Samples of segregated iron oxyhydroxide collected from B horizons contained up to several hundred mg As kg−1. Natrojarosite and clay separates from the same horizons contained from 30 to 50 mg As kg−1. Pyrite is believed to be the source of the elevated levels of As.
Sensitivity Analysis Applied to Unsaturated Flow Modeling of a Retorted Oil Shale Pile
Authors: Freshley Mark D. , Reisenauer A. E. , Gee G. W.
Published: July 2010

Commercial recovery of oil from oil shale will require disposal of large quantities of retorted or spent shale. Because no commercial disposal piles have been constructed and monitored, uncertainties exist in predicting water movement through large spent‐shale disposal piles. To better understand these uncertainties, we investigated water movement through spent shale by numerical modeling. A first‐order sensitivity analysis was used as a part of the numerical investigation of water movement through a hypothetical pile of spent oil shale. The sensitivity analysis was useful in identifying the most important components of the flow model. Results indicate that the flow model is sensitive to parameters that directly supply water to or control extraction of water from the profile, namely the initial condition of spent shale, precipitation, and estimates of potential evapotranspiration. The flow model is less sensitive to parameters that control water movement, specifically hydraulic conductivity of the spent shale and soil cover. The sensitivity analysis demonstrates that the flow model is also sensitive to parameters describing the sink term, namely rooting depth and rooting density. To improve predictions of the flow model, the input parameters contributing the most to model sensitivity should be measured carefully; parameters that produce less model sensitivity can be estimated without as much effort.
Tensile Strength of Unsaturated Soils
Authors: Snyder V. A. , Miller R. D.
Published: July 2010

A better understanding of the nature of tensile failure in unsaturated soils is important if adequate theories explaining the behavior of soils under tillage or during processes such as frost heaving are to be developed. In this paper, the problem of tensile failure of uncemented soils is formulated by combining Aitchison's extension of the classic Haines‐Fisher model of capillary cohesion with Griffith's theory of the fracture of cracked elastic solids. Results suggest that once air intrusion has initiated desaturation, the maximum tensile strength which can be expected is about half the gauge pressure of the pore water. Effects of grain size on tensile strengths of moist soils are actually manifested through their effects on drying characteristic curves as demonstrated by similitude analysis. A parameter, χ, used to estimate tensil strength as a function of pore water pressure, is a function of the degree of pore saturation hardly influenced by the actual shapes of the drying characteristic curves. Results are presumably applicable to various analogues, including the initiation of ice‐filled cracks (ice‐lenses) in air‐free soils during the process of frost heaving.
Uptake of Nitrogen‐15 by Cotton under Salt Stress
Authors: Pessarakli M. , Tucker T.C.
Published: July 2010

Evidence was gathered to evaluate the effect of salt stress on 15N absorption rate by plants, to indicate how plant parts (roots and shoots) react to NaCl stress conditions. Nitrogen (15NH4) absorption studies were on cotton (Gossypium hirsutum L.) grown in complete Hoagland nutrient solution in pots with various NaCl concentrations (0, −0.4, −0.8 and −1.2 MPa osmotic potentials). Low and medium levels of salinity (−0.4 and −0.8 MPa) failed to exhibit a significant effect on the 15N absorption rate, while high levels of salinity (−1.2 MPa) resulted in substantial reduction of 15N absorption rate. Concentration of 15N in plants was significantly higher under moderate salinity stress than in the controls. Absorption rate of water significantly decreased with increasing salinity levels, and was directly proportional to plant growth and total dry matter production. Water uptake rate and plant growth were affected to a greater extent than 15N absorption rate. The effect of salinity was more pronounced at vegetative than at reproductive stages of growth. Nitrogen concentration was greater in roots than shoots.
Illuvial Versus Inherited Clays in a Cryoboralf of the Boulder Batholith, Montana
Authors: McDaniel P. A. , Nielsen G. A.
Published: July 2010

Some forested Mollic Cryoboralfs of the granitic Boulder batholith have smectite‐rich B horizons. A representative soil was studied to determine processes responsible for morphologically well‐developed argillic horizons in relatively young soils formed in coarsegrained quartz monzonite parent material. X‐ray diffraction and particle‐size analysis indicated that B horizons of this soil differ greatly from surface eluvial horizons in both type and amount of clay minerals present and in the degree of weathering of plagioclase feldspars. Illite is the dominant clay mineral in the andy loam eluvial horizons and plagioclase grains appear only slightly weathered when examined in thin‐section. In Bt horizons, smectite is the dominant clay mineral and few identifiable plagioclase grains are seen in thinsection. Soil fabric analysis indicated illite rather than smectite as the dominant clay mineral being translocated within the soil profile. Results suggest that smectite content of B horizons is most likely a result of in situ alteration of plagioclase by hydrothermal processes prior to soil formation. Thus, smectite inherited from parent material is primarily responsible for the mineralogical and morphological properties of the argillic horizon. Although some illuviation of clay has occurred, this process has played a relatively small role in influencing these properties.
Soil‐Saprolite Profiles Derived from Mafic Rocks in the North Carolina Piedmont: I. Chemical, Morphological, and Mineralogical Characteristics and Transformations
Authors: Rice T. J. , Buol S. W. , Weed S. B.
Published: July 2010

The chemical, morphological and mineralogical properties of two Enon sandy loam (fine, mixed, thermic Ultic Hapludalfs) soil‐saprolite profiles, one formed on gabbro and the other on metagabbro, are compared. Clay skins are scarce and stress cutans common in the argillic horizons of these soils. Iron‐manganese concretions are concentrated in soil horizons immediately above the argillic horizons. The high shrink‐swell capacities and slow permeabilities of the argillic horizons result in relatively shallow depths to paralithic contact with saprolite. The parent rock from the Enon profile near Albemarle, Stanly County, North Carolina is a medium‐grained metagabbro with chlorite, hornblende, quartz, and calcic plagioclase feldspar as the dominant primary minerals. Chlorite weathers to regularly interstratified chlorite‐vermiculite, which alters to randomly interstratified chlorite‐vermiculite and smectite. Particle size decreases with each mineral alteration. Hornblende weathers to smectite and goethite. Calcic plagioclase feldspar transforms to kaolinite in the saprolite and soil horizons. Quartz is relatively resistant to chemical weathering. The parent rock of the Enon profile near Concord, Cabarrus County, North Carolina is a coarse‐grained gabbro with hornblende and calcic plagioclase feldspar as the dominant primary minerals. Hornblende transforms to smectite and goethite. Calcic plagioclase feldspar alters to kaolinite in the saprolite and soil horizons.
Alteration of Basalt in Soils of Western Oregon
Authors: Glasmann J. R. , Simonson G. H.
Published: July 2010

Basalt alteration from different pedo‐microenvironments in western Oregon was studied using petrographic, electron microscope, X‐ray diffraction, and differential thermal techniques. Initial alteration was similar in each environment and consisted primarily of mineral dissolution associated with the formation of etch pits and hairline cracks and the development of isotropic domains within feldspar phenocrysts. The stage of alteration characterized by secondary mineral formation was distinctly microenvironment dependent. Smectite formed as the initial crystalline weathering product of basalts in the Oregon Coast Range, but was metastable with respect to hydrated halloysite along fracture zones in the weathering crust where more leaching micro‐environments occureed. Smectite altered to chloritic intergrade and halloysite in cyclic wet and dry pedoenvironments. The occurrence of gibbsite was related to the alteration of glassy basalt lithologies under acid leaching conditions. Goethite formed form the alteration of an initial non‐crystalline iron oxide phase.
Monte‐Carlo Simulation of Noninteracting Solute Transport in a Spatially Heterogeneous Soil
Authors: Persaud N. , Giraldez J. V. , Chang A. C.
Published: July 2010

Monte‐Carlo data generation techniques were used to obtain 200 pairs multivariate lognormal values of the physical parameters D (dispersion coefficient) and v (pore‐fluid velocity) which appear in the differential equation describing downward leaching of a noninteracting solute in the soil profile under steady‐state percolation. The time (tmax), at which the maximum concentration is attained at given soil depth L after a pulse input of solute has been applied at the soil surface for a time to, was obtained for each pair of generated D and v values. Values of the ratio ΔL/Δtmax representing the average rate of movement of the maximum concentration between two depths were also calculated. The effect of changes in the variance of v and the levels of correlation between D and v on the frequency distributions of tmax–t0 was investigated. The lognormal and gamma distributions were fitted to the calculated distributions of tmax–t0. Good fits were obtained with both theoretical distributions to the values of tmax–t0. The lognormal distribution was better in describing the values of ΔL/Δtmax. The parameters and properties of these calculated distributions were sensitive to changes in the variance of v but were less sensitive to changes in the correlation between D and v. The ensemble average of 200 concentration versus time curves was computed by substituting the generated parameters D and v in the solution to the differential equation. This curve was compared to that obtained using the sample mean values of D and v. The dissimilarity between these curves was sensitive to changes in the variance of v.
Indigenous Soil Properties Influencing the Availability of Iron in Calcareous Soils
Authors: Loeppert R. H. , Hallmark C. T.
Published: July 2010

Iron chlorosis in plants is commonly associated with calcareous soils; however, soil factors other than total carbonate may also influence the plant's ability to obtain adequate Fe for growth. Twenty‐four calcareous soils, which represent the expected ranges of clay, CaCO3, Fe oxide, and organic matter contents of agronomically important soils in Texas, were sampled and examined extensively with respect to these phases along with extractable ion and soil solution composition. [Sorghum bicolor (L.) Moench] was grown under greenhouse conditions to evaluate chlorosis and Fe uptake. Although total CaCO3 content was important in influencing availability of Fe, the quantity, mineralogy, and crystallinity of the Fe oxide phase assumed a dominant role. Clay and organic matter contents were positively correlated with plant available Fe. The influence of these phases may be attributed to stabilization of a poorly crystalline Fe oxide phase. The contents of solution phase and exchangeable Mg2+ were also positively correlated with the incidence of Fe chlorosis due to the influence of this ion on soil alkalinity.
Diffusional Constraints on Denitrification in Soil
Authors: Myrold David D. , Tiedje James M.
Published: July 2010

A model for NO−3 reduction and diffusion in aggregated soils is presented and used in conjunction with a derived constant, the Thiele modulus, to examine the conditions which could contribute to a NO−3 diffusion limitation of denitrification. The Thiele modulus is a function of the anaerobic radius of an aggregate, the maximum rate of NO−3 reduction for a given soil, the Km value for NO−3 reduction, and the intra‐aggregate NO−3 diffusion coefficient. Results from this theoretical exercise suggested that the anaerobic radius is the most important factor in determining whether denitrification is limited by NO−3 diffusion. The model predicts that under anaerobic conditions, only soils with a mean aggregate radius greater than 2 mm will experience a NO−3 diffusion limitation. This limitation may not be effective in practice if the bulk NO−3 concentration is much greater (100 times) than the Km for NO−3 reduction; this appears to often be the case in fertilized soils but may not be the case in soils of natural ecosystems. Under aerobic conditions, a diffusion limitation will exist in most aggregated soils, since only large aggregates have anaerobic microsites (i.e., large anaerobic radii) where denitrification can occur. A carbon limitation, through its lowering of the maximum denitrification rate, lessens the magnitude of any existing NO−3 diffusion limitation. Diffusive limitations were experimentally examined in two ways. First, the ratio of denitrification rates of anaerobic cores relative to anaerobic slurries were used to indicate the degree of any substrate supply limitation; the slurry rates were always greater suggesting either NO−3 or carbon was limiting. Second, soil cores were preincubated with either NO−3 or a diffusible carbon source (succinate) at 4°C to allow diffusion but to suppress biological responses. These results revealed that carbon, rather than NO−3, was limiting denitrification rates in this clay loam soil. These experimental results were in agreement with model predictions.