bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Infiltration through a Two‐Layer Soil Profile
Authors: Smith R. E.
Published: July 2010

Most soils in nature exhibit some degree of layering, while infiltration theory is largely confined to homogeneous profiles. This study was conducted to describe general infiltration features of a two‐layer system, including the often‐studied crust case as a limit. The general analytic theory for infiltration models leads to several related robust relations for homogeneous soils. The resulting analytic expressions relate infiltrability, f, to infiltrated water, I. This type of expression is uniquely general in describing the decay of f with I for either saturation or flux boundary conditions, and in describing the onset of ponding for flux boundary conditions. This study explores the applicability of this theory when the soil profile is composed of two layers. A numerical solution of Richards' equation is used as an experimental tool, applied to a general set of possible soil changes that may occur at the layer interface. The special case of layers with “absorption matched” infiltrability parameters exhibits complex behavior when the interface is encountered at large I. The behavior of the layered system exhibits the same unifying f(I) response to flux boundary conditions as does a homogeneous profile, which lends unexpected generality to the I‐based analytical infiltration model.
Zinc Adsorption by a Lateritic Soil in the Presence of Organic Ligands
Authors: Chairidchai P. , Ritchie G. S. P.
Published: July 2010

Soluble Zn in soils and its availability to plants may be influenced by the presence of organic ligands, particularly in the rhizosphere, where soluble organic matter may be present in high concentrations. Zinc adsorption by a lateritic podzolic soil was measured in the presence of 0 to 3 mmol L−1 of acetate, oxalate, citrate, tricarballylate, salicylate, or catechol, or 0 to 3 mmolc L−1 of humate. Zinc remaining in solution was measured by atomic absorption spectrometry after shaking the soil for 17 h at a soil/liquid ratio of 1:5 in a 0.003 mol L−1 KCl solution containing 0 to 500 µmol L−1 Zn and the ligands. In the absence of organic ligands, more than 95% of the zinc was adsorbed. The amount of adsorption was linearly correlated with pH and the concentration of ZnOH+ in solution after shaking (r2 = 0.98; multiple regression). Zinc adsorption and pH decreased in the presence of each of the ligands except catechol. Seventy four percent of the variation in adsorption was accounted for by the combined effects of the concentration of zinc‐ligand complex (Zn‐L) and the concentration of ZnOH+ that were present in solution after adsorption. However, other factors such as changes in the number of sites available for adsorption, the point of zero salt effect (pzse) of the soil, and the charge of zinc species also contributed to the magnitude of zinc adsorption.
Fluorescence Quenching and Polarization Studies of Naphthalene and 1‐Naphthol Interaction with Humic Acid
Authors: Morra M. J. , Corapcioglu M. O. , von Wandruszka R. M. A. , Marshall D. B. , Topper K.
Published: July 2010

Although it is known that the environmental behavior and fate of synthetic organic compounds are altered on association with humic materials, the nature of this interaction has been a source of controversy. Fluorescence quenching and polarization techniques were used to study the interaction between water‐soluble humic acid and naphthalene and 1‐naphthol. Stern‐Volmer plots constructed using intensity values for these fluorophores dissolved in humic acid solutions (0–25 mg L−1) were linear. The ultraviolet/visible (UV/VIS) absorption spectra of each fluorophore in the presence and absence of the humic acid quencher were identical. This, in addition to the observed increase in quenching with temperature, indicates a dynamic (collisional) mode of quenching. Fluorescent lifetimes of the probes decreased in the presence of humic acid, providing further evidence of dynamic quenching. However, the slopes of Stern‐Volmer plots constructed with lifetime values were considerably smaller than plots obtained with intensity values. Calculated bimolecular quenching constants of 5.2 × 1010 M−1 s−1 for naphthalene and 4.8 × 1011 M−1 s−1 for 1‐naphthol are above the maximum considered possible for a diffusion‐controlled interaction. Fluorescence‐polarization measurements indicate no rigid association between unquenched 1‐naphthol and humic acid. The interaction of naphthalene and 1‐naphthol with humic acid in aqueous solution occurs through a loose association in which humic acid surrounds the fluorophore in a cage‐like manner. This pseudomicelle confines the probe without rigidly binding it, promoting frequent quenching collisions and a combination of dynamic and static quenching.
Citrus Root Growth as Affected by Soil Aluminum Level under Field Conditions
Authors: Lin Zhongyan , Myhre Donald L.
Published: July 2010

Most research on the effects of Al on citrus rootstocks has been limited to nutrient‐solution studies. This study employed an implanted soil‐mass technique to determine the effects of Al level in soils on growth and mineral content of fibrous citrus roots under field conditions. The implanted soil, E horizon material from an Immokalee fine sand (sandy, siliceous, hyperthermic Arenic Haplaquod), had a pH of 4.2 and a very low exchangeable‐Al content. It was either limed, unamended, or amended with three levels of Al using AlCl3. Each of the five treatments was replicated 15 times. Mesh bags containing the treated soil were placed in holes at the drip line of mature trees (Citrus aurantium L. sour orange rootstock) in a producing citrus grove. The bags were removed after 46 d. Results showed that, at a concentration of 9.14 mg Al L−1 of soil saturation extract, root density was twice that of the unamended treatment (0.13 mg Al L−1) and equaled that of the lime treatment (0.03 mg Al L−1). More roots grew into the bag, and they produced more lateral roots. Aluminum concentrations in roots were lower than those in the unamended treatment, however. Root‐length density decreased to about 60% of the value for the unamended treatment when Al concentration increased to 34.60 mg L−1. The optimum Al concentration for root growth appears to be 10 mg L−1 calculated by a curvilinear regression equation. In general, the concentrations of Zn, Fe, and Mn in roots decreased with increased Al application to the soil, while concentrations of Ca, Mg, K, P, and B were unchanged.
Plant Availability of Phosphorus in the Water‐Insoluble Fraction of Commercial Triple Superphosphate Fertilizers
Authors: Mullins G. L. , Bartos J. M. , Bryant H. H. , Sikora F. J.
Published: July 2010

Water‐insoluble complexed P fractions can form during the production of phosphate fertilizers, and there is some concern regarding the potential impact of these chemical impurities on fertilizer performance. A greenhouse study was conducted to evaluate the plant availability of P in water‐insoluble residues from five commercial triple superphosphate (TSP) fertilizers. Fertilizers manufactured from rock‐phosphate sources in Florida, North Carolina, Idaho, and Morocco were evaluated. Each fertilizer was washed with deionized water to remove its water‐soluble P. The resulting water‐insoluble fertilizer residues, reagent‐grade monocalcium phosphate [MCP: Ca(H2PO4)2] and reagent‐grade dicalcium phosphate (DCP: Ca‐HPO4) were applied to a Mountview silt loam soil (fine‐silty, siliceous, thermic Typic Paleudult) to supply 0, 10, 20, 40, 60, and 80 mg P kg−1 soil. Sorghum‐sudangrass [Sorghum bicolor (L.) Moench] was harvested for forage yields at 21 and 42 d after planting. Each P source gave different (P ≤ 0.01) yield and P‐uptake responses to the rate of the sum of the water‐soluble and the citrate‐soluble P applied. Water‐insoluble fertilizer residues were a better source of P than reagent‐grade DCP, but they were not as effective as reagent‐grade MCP. Results from this study demonstrate that the plant availability of P in the water‐insoluble fraction of TSP fertilizers is source dependent, and that P in this fraction is not as available as P in pure MCP. The sum of the water‐soluble and the citrate‐soluble P overestimated available P in the fertilizer residues.
Laumontite in Soils of the San Gabriel Mountains, California
Authors: Taylor Kelly , Graham Robert C. , Ervin Jarel O.
Published: July 2010

Laumontite, a Ca‐rich zeolite, is widespread and locally abundant in the San Gabriel Mountains of southern California. It occurs in hydrothermally altered rocks of various origins and is inherited by the overlying soils. The objectives of this study were to determine the distribution and properties of laumontite in these soils. Laumontite was found in soils derived from anorthosite, arkosic sandstone, and granodiorite. All of the soils were Entisols, composed largely of colluvium, on steep, chaparral‐covered slopes. Soil depths ranged from 16 to 32 cm over 25 to 40 cm of saprolite (Cr horizon). Soil pH ranged from 5.0 in the A horizon of the soil on sandstone to 7.2 in the Cr horizon of the anorthosite‐derived soil. Laumontite was found in sand, silt, and clay fractions of the soils. Its particle‐size distribution in the soil depended on its grain size in the parent rock and its weathering within the soil. Comparisons of laumontite grain morphology using scanning electron microscopy showed grains in the A horizons to be rounded, dissolution pitted, and crusted with weathering products, whereas those in the Cr horizons tended to have more angular, fresher crystal faces. Halloysite tubes have formed on some laumontite grain surfaces. Although the low Si/Al ratio of laumontite indicates a high cation‐exchange capacity, only 17 cmolc kg−1 of native cations were extracted by shaking in 1 M NaCl solution for 17 d. Fewer cations were displaced by Ba, Sr, Cs, and NH4. Apparently, diffusion of cations from the one‐dimensional channels of laumontite is very slow. Laumontite does not contribute significantly to the cation‐exchange capacity of these soils, which also contain smectite and vermiculite.
Perturbation of Imogolite Formation by Humic Substances
Authors: Inoue K. , Huang P. M.
Published: July 2010

Imogolite formation is influenced by ionic factors. This study was conducted to investigate the perturbation of imogolite formation by humic substances. Interactions of hydroxy‐Al ions with orthosilicic acid as influenced by humic substances were studied at the Si concentration of 1.6 mM, a Si/Al atomic ratio of 0.5, an OH/Al molar ratio of 2.0, and concentrations from 1 to 1000 mg humic acid (HA) L−1 and 1 to 300 mg fulvic acid (FA) L−1. Chemical analyses of filtrates (<0.01 µm) and x‐ray diffraction patterns, infrared (IR) spectra, and electron micrographs of the precipitation products (>0.01 µm) clearly showed that the degree of perturbation of the formation of imogolite increased with the rising concentration of humic substances, leading to the formation of ill‐defined aluminosilicate complexes. These complexes are similar in IR spectra to allophane‐like constituents or freeze‐dried protoimogolite and are associated with humic substances. In addition, pseudoboehmite and hydroxy‐Al‐humus complexes were present in the reaction products. The formation of imogolite was completely inhibited at concentrations >30 to 50 mg FA L−1 and 300 HA L−1. These results reveal that the pedogenic significance of humic substances in impeding the formation of imogolite and in promoting the formation of ill‐defined aluminosilicate or hydroxy‐Al‐humus complexes in the Andisol A and Spodosol Bh horizons merits attention.
Shrinkage Geometry of a Heavy Clay Soil at Various Stresses
Authors: Bronswijk J. J. B.
Published: July 2010

The shrinkage geometry of a clay soil drying from saturation to oven dryness was investigated. Undisturbed samples in rings measuring 232 cm3 were taken in the field at depths of 0.0, 0.20, 0.40 and 0.60 m. Overburden pressures at these four depths were determined by wet bulk‐density determination. Samples were oven dried with various loads applied on top. Surface subsidence and total volume decrease after drying were measured. It appeared that, for each soil layer, shrinkage at overburden pressures equal to or larger than field pressures was isotropic. When the load was removed during drying, subsoil samples showed relatively large cracking in comparison with surface subsidence.
Analytical Expression for Soil Water Diffusivity Derived from Horizontal Infiltration Experiments
Authors: Meyer J. J. , Warrick A. W.
Published: July 2010

A technique is developed that utilizes a rational function θ = (A1 + A3λ)/(1 + A2λ) to fit water content (or other liquid) profiles resulting from horizontal infiltration as used in the Bruce‐Klute method for determining soil water diffusivity. In the above function, θ is water content (L3 L−3), λ is the Boltzmann variable, and A1, A2, and A3 are constants. The Boltzmann variable, λ, is equal to xt‐0.5, where x is the distance from the inlet of a horizontal soil column and t is time from the commencement of liquid imbibition. The function is easily fit to experimental data by either linear or nonlinear regression techniques and leads to analytical expressions for sorptivity and soil water diffusivity without further numerical approximation or fitting. If boundary conditions are specified, only one of the three coefficients is left to be determined. The rational function provided excellent approximations to liquid distribution for water and alcohol horizontal infiltration experiments in this study and is adequate for representation of experimental data of several other researchers. An example is included to illustrate that the approach is also applicable to determination of diffusivity for the hot‐air method.
Spatial Variation in Denitrification: Dependency of Activity Centers on the Soil Environment
Authors: Christensen Søren , Simkins Stephen , Tiedje James M.
Published: July 2010

The spatial variation in field denitrification rates was studied in an acid soil where the sole denitrification end product was N2O. The rate of N2O accumulation was measured under a soil cover at 30 fixed sampling locations arranged in a grid. Water and NO3 were added prior to all measurements to provide soil water contents at or above field capacity and excess NO3 for denitrification. No significant differences in N2O production rates were observed in samples incubated with or without C2H2, indicting that nitrification is not a significant source of N2O in this soil. Denitrification was found to occur in “hot spots” in moist soil and throughout the soil volume if the soil was flooded. Denitrification rates followed a skewed frequency distribution when soil water content was at field capacity: most locations had low activity, and a few locations exhibited high activity. The frequency distribution of denitrification rates was less skewed in samples after flooding, following large additions of glucose, or when the vegetation underwent decay in the fall. The intensity of denitrification was much higher after flooding than following glucose addition. A few sample locations occasionally showed outstandingly high denitrification rates when at field capacity, as well as when flooded. The activity in these hot spots approximated the potential denitrification activity of that soil.
Chemical Restrictions of Roots in Ultisol Subsoils Lessened by Long‐Term Management
Authors: Hardy David H. , Raper C. David , Miner Gordon S.
Published: July 2010

Exchangeable Al in subsoils of Ultisols in the southeastern USA can restrict rooting depth. Downward movement of basic cations (Ca, Mg, and K), applied as lime and fertilizer, may diminish that restriction over time. Materials from the argillic horizon were collected from three paired sites, having managed (long‐term cropping) and nonmanaged topsoils (Typic Paleudults and Hapludults). One managed site was cropped continuously for 15 yr while the others were cultivated for more than 30 yr. Concentrations of extractable cations and other nutrients from the paired sites were compared to determine the magnitude of change due to management. The ability of the subsoils to support plant growth was evaluated in a missing‐nutrient greenhouse experiment with sorghum [Sorghum bicolor (L.) Moench]. Subsoils of managed sites had greater effective cation‐exchange capacity (CEC) and base saturation than those of nonmanaged sites. While availabilities of Ca, Mg, and K in subsoils of nonmanaged sites were inadequate to support maximal plant growth, they were adequate in subsoils of managed sites. Compared with nonmanaged sites, KCl‐exchangeable Al in subsoils of managed sites was 23% lower at the 15‐yr location and 65 and 100% lower at the two other locations. In the absence of lime, sorghum growth was almost totally inhibited on nonmanaged subsoils amended with optimum nutrients. On the managed subsoils, where 100, 65, and 23% of the nonmanaged exchangeable Al had been neutralized by topsoil fertilization and liming, growth reductions under the same conditions were 0, 50, and 100%, respectively. Thus, relatively long‐term management had improved these Ultisol subsoils for root growth and development.
Prediction Technology for Soil Erosion by Water: Status and Research Needs
Authors: Nearing M. A. , Lane L. J. , Alberts E. E. , Laflen J. M.
Published: July 2010

This is a review of research related to soil‐erosion prediction technology. The trend in erosion prediction technology in the USA, Australia, and Europe is toward the development of process‐based simulation models. The emphasis in erosion research on strictly empirically based models, such as the Universal Soil Loss Equation, is declining. With the process‐based technologies come a new array of research needs. In the USA, The USDA Water Erosion Prediction Project (wepp) has produced a new generation of soil‐erosion prediction technology based on fundamentals of hydrologic and erosion science. The development of the new computer‐based wepp erosion model for estimation of rill and interrill erosion required an extensive review and analysis of current knowledge of the science of soil erosion by water. Research needs were identified. The relative importances of identified research needs were evaluated using a sensitivity analysis of the wepp model, which identified the more important of the input variables required to execute the model. The review of research reported here, along with a discussion of associated current needs for research, addresses four general areas: (i) fundamental erosion relationships, (ii) soil and plant parameters related to erosion, (iii) data bases, user interfaces, and conservation system design, and (iv) erosion model development and analysis.
Tillage and Canopy Cover Effects on Interrill Erosion from First‐Year Alfalfa
Authors: Sturgul S. J. , Daniel T. C. , Mueller D. H.
Published: July 2010

Alfalfa (Medicago sativa L.) establishment techniques commonly produce a soil surface susceptible to high runoff and soil losses prior to crop canopy development. Limited data are available on the erodibility and productivity of alfalfa seedbeds established with conservation tillage systems. Four alfalfa establishment techniques were investigated for runoff, erosion, and forage yield over two growing seasons on a Plano silt loam soil (fine‐silty, mixed, mesic Typic Argiudoll) with a 5% slope in south‐central Wisconsin. Alfalfa seedbeds were established on cropland previously in no‐till (NT) corn (Zea mays L.). Five simulated rainfalls were applied to moldboard (MB), moldboard‐nurse crop (MB/nc), chisel (CH), and NT alfalfa seedbeds. An additional seedbed investigated was no‐till with surface residue removed (NT/wo) immediately prior to rainfall simulation. Relative to MB, CH treatments reduced runoff volumes by 23 to 72% and NT treatments reduced volumes 59 to 100%. Soil‐loss reductions of 24 to 64% from CH and 71 to 100% from NT relative to MB were observed. Runoff volumes from NT/wo were the largest of all treatments for four of the five rainfall simulations. Soil losses from NT/wo were statistically similar (P = 0.05) to MB for all rainfall simulations. Comparisons of MB to MB/nc runoff volumes did not indicate an influence of canopy cover on runoff. A MB/nc soil loss of 87% less than MB at a rainfall simulation with MB/nc canopy cover of 93% relative to MB canopy cover of 47% did indicate a canopy effect on soil loss. No significant influence of canopy development on runoff volumes from similar treatments over time was evident. Canopy development contributed to reduced soil losses within all treatments, with a maximum reduction of 96% observed for MB/nc canopy cover of 93% relative to MB/nc soil loss at 0% canopy. Establishment year alfalfa yield and quality did not vary among MB, CH, and NT treatments at a significance level of P = 0.05.
Infiltration in Adjacent Cecil and Pacolet Soils
Authors: Radcliffe D. E. , West L. T. , Ware G. O. , Bruce R. R.
Published: July 2010

Cecil (clayey kaolinitic, thermic Typic Kanhapludult) and associated soils cover two‐thirds of the land area of the Southern Piedmont. Soybean [Glycine max (L.) Merr.] yields from severely eroded sites in these soils are about half of those from slightly eroded sites. Most of the severely eroded sites are on the Pacolet soil series (clayey kaolinitic, thermic, Typic Kanhapludult), which is shallower to the bottom of the Bt horizon. Differences in infiltration rates may cause these differences in yield. Our objectives were to quantify infiltration rate differences between Cecil and Pacolet soils and to determine the reason for the differences. Infiltration rate was measured using a cylinder infiltrometer at five sites with adjacent Cecil and Pacolet soils, and using a sprinkler infiltrometer at one site. Steady‐state infiltration in the Pacolet was significantly lower than in the Cecil, 4.2 and 30.1 mm h−1, respectively. Cecil infiltration rates increased as depth to the Bt horizon increased. On Cecil, final sprinkler infiltration rate was 61.1 mm h−1 with a sod surface, but surface sealing reduced infiltration with a bare surface to 3.6 mm h−1 within 1 h. The final sprinkler‐infiltration rates of the Pacolet soil were 4.5 mm h−1 for sod and 4.2 mm h−1 for bare surfaces. Pacolet infiltration rates were controlled by the Bt1 layer, which had a lower, saturated hydraulic conductivity (2.3 mm h−1) and fewer mesopores than adjacent horizons but was similar to the upper Bt of the Cecil soil. The Cecil soil's limiting Bt1 horizon occurred much deeper in the profile and had less effect on infiltration. Areas of Pacolet within the Cecil landscape, too small to map separately, can cause increased runoff and variability of yield potential of areas mapped as Cecil.
Tillage and Crop Rotation Effect on Characteristics of a Sandy Surface Soil
Authors: Bruce R. R. , Langdale G. W. , Dillard A. L.
Published: July 2010

In a thermic udic region, a summer crop species may be planted with or without tillage subsequent to a winter grain crop that was planted into a prepared seedbed. This study was conducted to identify the effect of tillage intensity associated with soybean [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] crop sequences following winter wheat (Triticum aestivum L.), and the effect of summer crop species on selected physical characteristics of a Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult). Through eight seasons, soybean and grain sorghum were grown in 10 crop sequences that were imposed on three tillage treatments: conventional tillage (CT), in‐row chisel (MT), and no‐tillage (NT). Following summer crop harvest in the eighth season, aggregate stability, organic C, bulk density, air‐filled pore space, particle‐size distribution, and infiltration of water were measured. Aggregate stability at 0 to 10 mm was significantly higher for MT and NT than for CT. The CT treatment exhibited significantly lower bulk density and higher air‐filled pore space than MT and NT. Infiltration was significantly greater on the MT than the CT and NT treatments. Greater aggregate stability, higher air‐filled pore space, and lower bulk density were measured after two or more years of grain sorghum than after soybean. The maintenance of wheat straw on the soil surface under the MT and NT treatment exhibited an effect to a depth of 75 mm and the in‐row chisel treatment affected infiltration. Crop‐rotational effects can be erased or modified by tillage and may only be observed under NT. Grain yield response of soybean and grain sorghum to changes in soil physical characteristics, as a consequence of crop sequence and tillage, may need to be interpreted in relation to crop species and cropping sequence.
Aluminum and Organic Matter Mobilization from Forest Soil Infiltrated with Acidified Calcium Sulfate Solutions
Authors: Berry Duane F. , Zelazny Lucian W. , Walker Hubert L.
Published: July 2010

Investigations of acid rain effects on forest soils have generally overlooked Ca, a major component of precipitation. This study was conducted to determine the effects of Ca on the mobilization of Al and organic matter in a Cecil soil (clayey, kaolinitic, thermic Typic Kanhapludult). Acidic solutions (pH 4.2) containing ambient or near‐ambient precipitation concentrations of Ca, K, and SO4 were used to infiltrate columns containing Oa, EB, or Oa/EB bihorizon soil material. Leachate was analyzed for dissolved organic carbon (DOC), Al, Ca, K, and H ions. A net release of protons was observed when the Oa surface horizon was infiltrated with 0.05 mol m−3 CaSO4 or 0.25 mol m−3 CaSO4 or K2SO4 leaching solutions, but not 0.05 mol m−3 K2SO4 solution. Infiltration of Oa horizon soil with Ca solutions resulted in release of more protons than with K solutions of comparable ionic strength. Calcium leaching solutions were also more effective than K solutions (7.7% and 28% for 0.05 and 0.25 mol m−3 solutions, respectively) in mobilizing Al from Oa/EB bihorizon soils. These differences were not found in EB horizon soils treated with the same leaching solutions. Our results suggest that CaSO4 leaching solutions, at concentration levels consistent with those in precipitation, displaced protons from the Oa horizon, which subsequently infiltrated the underlying EB horizon causing increased solubilization of Al. While some Al was undoubtedly associated with organic matter, overall, movements of Al and organic matter in Oa/EB bihorizon soil columns were found to be independent of one another.
Phosphorus and Aluminum Release from a Spodic Horizon Mediated by Organic Acids
Authors: Fox T. R. , Comerford N. B. , McFee W. W.
Published: July 2010

The ability of organic acids to affect surface and solution reactions of P and Al in soils containing Al‐oxide surfaces is related to their ability to form stable complexes with Al. This study was conducted to determine if the amount of P and Al released following the addition of an organic acid to a Bh horizon soil could be estimated based on the Al stability constant (logKAl) of the organic acid. The release of Al and inorganic P from spodic horizon material increased in the presence of organic acids that form stable complexes with Al. Overall, the logKAl value was a good indicator of the effect of the organic acid on inorganic P and Al release. Among the 16 organic acids studied, release of Al and inorganic P increased exponentially with increasing stability constants. A threshold value of approximately 4.1, however, was required before substantial amounts of inorganic P were released. This value may reflect the stability of P bond to Al‐oxide surfaces in this soil. Salicylic acid was a notable exception to the observed trend in release of both Al and P; despite a large stability constant, little inorganic P or Al was released. Although significant amounts of soluble organic P were released in all the organic‐acid solutions, the amount of soluble organic P released was not related to the stability constant of the organic acids.
Sampling the Atmospheres of Small Vessels
Authors: Breitenbeck G. A.
Published: July 2010

Gas‐tight syringes and other gas sampling devices are not entirely satisfactory for use in many studies of soil processes requiring precise repeated sampling of the atmospheres of glass bottles and other incubation vessels. This report describes the construction and use of a gas‐sampling apparatus that permits accurate, precise analyses of headspace gases contained in sealed vessels. The sampling apparatus consists of a 10‐port gas‐sampling valve fitted with a syringe used to fill a sampling loop with a representative sample of the atmosphere contained in the headspace of an incubation vessel. A supply of inert gas purges the apparatus between samples. Use of this technique is appropriate in experiments where repeated analyses of sample vessels are performed, because sampling removes a minimum of gas in excess of that used for analysis and does not appreciably alter the pressure within the vessel. Because the effects of previous sampling on headspace concentrations are calculated, small vessels can be repeatedly sampled with precision. The apparatus is easily assembled from readily available components.
Spatial Scale Dependence of In Situ Solute Transport
Authors: Van Wesenbeeck I. J. , Kachanoski R. G.
Published: July 2010

In field solute‐transport experiments, two spatial scales of the continuum of the dispersion process have been measured: local scale and field scale. The objective of this experiment was to develop a method for measuring in situ the transition from the local scale to the field scale during unsaturated flow conditions. The spatial variability of in situ solute dispersion was examined in two field sites. Soil‐solution samplers were installed in a transect at a 0.4‐m depth and 0.2‐m spacing in both a cultivated and never‐cultivated (forested) site. A pulse of KCl was applied to both sites under conditions of constant surface flux density of water, which was applied using a trickle irrigation system. The variance of solute travel time, V2(t), at different spatial scales was calculated from moment analysis of breakthrough curves (BTC) obtained by averaging local BTC across different spatial scales. The scale dependence of V2(t) indicated scales of at least 2.8 and 3.8 m were needed to reach an effective far field variance for the forested and cultivated sites, respectively. The larger scale in the cultivated site was due to an increase in horizontal correlation length scales of soil properties caused by tillage mixing. The scale dependence of V2(t) can be used to determine the minimum plot size necessary to include all major horizontal variations in solute travel time, which can then be compared with spatial distributions of soil properties affecting transport.
Construction of Isolinear Maps of Soil Attributes with Empirical Confidence Limits
Authors: Bregt A. K. , Wopereis M. C. S. , McBratney A. B.
Published: July 2010

Moisture‐deficit data were obtained at 398 point locations in the Mander area in the Netherlands by simulation using soil‐profile attributes. From this data set, a test subset of 75 points was selected at random. The test set was used to select the best of four prediction procedures: ordinary and universal kriging with the original data set, and ordinary and universal kriging with a log‐transformed data set. The mean square error of prediction (MSEP) was used to evaluate prediction quality. The lowest MSEP of prediction was obtained using ordinary kriging of the untransformed data. Ordinary kriging was then used to predict moisture deficits and estimate their associated kriging variances at points on a 50 by 50 m grid. The average ratio of actual square errors of prediction to the estimated kriging variances at the 75 test locations was used to adjust the kriging variance estimates on the regular grid to get more realistic estimates. These empirically derived, more realistic estimated kriging variances were then used to construct an isolinear map of moisture deficit with confidence limits. The resulting map showed that, in most of the region under study, the 90% confidence interval for moisture deficit contains 15 mm. This type of map allows the user to obtain confidence limits as well as the predicted value for any point on the map.
Pretreatment Effect on Dispersion of Carbonates in Calcareous Soils
Authors: Hartwig R. C. , Loeppert R. H.
Published: July 2010

A pH‐stat procedure was previously developed to determine the effective particle‐size distribution of soil carbonates. The results obtained by the pH‐stat procedure are influenced by the accessibility of carbonate surface sites to the titrant and, therefore, provide a methodology for the comparison of carbonate dispersion treatments. In this study, the influence of dispersion treatment on the determination of effective particle‐size distribution of soil carbonates was examined. The treatments consisted of agitation, sonication, or Na saturation of clay cation‐exchange sites of calcareous soils representing three series (Austin: fine‐silty, carbonatic, thermic Entic Haplustoll; Rio Grande: coarse‐silty, mixed (calcareous), hyperthermic Typic Ustifluvent; Victoria: fine, montmorillonitic, hyperthermic Udic Pellustert). Shaking and sonication pretreatments resulted in increases in the experimentally determined proportion of effective fine‐clay size soil carbonates and corresponding decreases in the effective silt‐ and sand‐size carbonates, when compared with the untreated soils. As the intensity of either of these pretreatments was increased, the proportion of effective clay‐size carbonates increased. Scanning electron microscopy indicated that the longer and more intense sonication treatments resulted in a higher degree of disruption or grinding of carbonate aggregates. Sodium saturation of the clay cation‐exchange sites resulted in the most effective disaggregation of the phyllosilicate‐carbonate complex, as indicated by the greatest proportion of effective clay‐size and lowest proportions of effective silt‐ and sand‐size carbonates. Sodium saturation may also result in a lower degree of disruption of carbonate particles or carbonate‐cemented aggregates than may occur with intense sonication. An initial Na saturation is, therefore, recommended as a pretreatment for the determination of effective particle‐size distribution of soil carbonates.
Humic and Fulvic Acid Adsorption by Silicon and Aluminum Oxide Surfaces on Clay Minerals
Authors: Schulthess C. P. , Huang C. P.
Published: July 2010

Natural (untreated) clays are most probably amorphous on their outermost surface layers due to the continuous and natural process of partial dissolution and reprecipitation of the clay components at the solid‐aqueous interface. The pH‐dependent adsorption on Al and Si oxides, mordenite, kaolinite, and montmorillonite of a humic acid (HA) and a fulvic acid (FA) was described as occurring on Al and Si sites. The surfaces of the clay minerals were modeled as mixtures of amorphous Al and Si oxides. The results showed a strong adsorption of the organics by the Al sites on the Al oxide and kaolinite, and a weak adsorption of organics by the Si sites on the Si oxide, mordenite, and montmorillonite. At low pH values, the Si sites on the Si oxide, mordenite, and montmorillonite adsorbed FA; these latter observations strongly suggest that the adsorption of FA by the interplanar spaces of expanding clays is driven by forces that can be studied using amorphous Si oxide as the adsorbent. Multivalent cations will form organo‐metallic complexes that significantly increase adsorption, particularly on Si sites; exceptions were found with some FA‐metal complexes, which were attributed to the degree of complexation. The implication of these observations is that, in natural systems, the adsorption of aqueous compounds is highly dependent on the type of (amorphous) surface present at the outermost layer of the solid phase in contact with the liquid phase.
Competitive Adsorption of Phosphate and Oxalate by Aluminum Oxides
Authors: Violante A. , Colombo C. , Buondonno A.
Published: July 2010

The aim of this work was to study: (i) the competitive adsorption of phosphate (P) and oxalate (OX) anions on an Al oxide as influenced by pH and order of anion addition; and (ii) the adsorption of P on and the desorption of OX from an Al precipitation product [Al(OH)x‐OX] formed in the presence of OX ions. The amount of P adsorbed on Al oxide in the absence of OX decreased with increasing pH. In the absence of P, OX adsorption exhibited a broad maximum between pH 5.0 and 7.0, but rapidly decreased at a pH <5.0 or >7.0. The order of anion addition strongly influenced the adsorption of both P and OX. Maximum reduction in P adsorption occurred when OX was introduced before P, whereas reduction was negligible when P was added before OX. The efficiency of OX in reducing P adsorption was relatively high at acidic pH values, but it was poor at a pH >7.0. The presence of P strongly depressed OX adsorption when P was added before OX or when the anions were added together. The efficiency of P in reducing OX adsorption increased with increasing pH. Finally, the ability of P in replacing OX ions from Al(OH)x‐OX was poor at pH values <7.0, but increased in alkaline environments with increasing pH. The data thus reveal that OX ions compete strongly with P for adsorption sites of Al oxides when they are added before the inorganic ions or are coprecipitated with Al in Al precipitation products, and mainly at acidic or neutral pH values.
Effect of Sulfur Source on Sulfur Oxidation
Authors: Lindemann W. C. , Aburto J. J. , Haffner W. M. , Bono A. A.
Published: July 2010

The rate of elemental sulfur (So) oxidation in soils may be affected by the source of So. This study was conducted to determine the effect of So source on So oxidation. Liquid culture studies with Thiobacillus thiooxidans and T. thioparus, laboratory incubations with a Holloman soil (loamy, gypsic, thermic, shallow Typic Torriorthent) and a Belen soil (clayey over loamy, montmorillonitic [calcareous], thermic Typic Torrifluvent), and a field study on the Belen soil were conducted. Periodic measurements included pH as a measure of So oxidation to H2SO4, electrical conductivity (EC) as a measure of dissolution of CaCO3 from H2SO4 production, and available Fe, Zn, P, and SO4 at the end of soil experiments as a measure of So‐oxidation effects on nutrient availability. The So sources included pure So (Sp), Wettable S (Sw), flowable So (Sf), and Disper‐Sul So (Sd). In liquid culture, Sw, Sf, and Sd inhibited or slowed So oxidation, compared with Sp, suggesting an ingredient of the commercial So sources was responsible for oxidation inhibition. Oxidation of Sw, Sf, and Sd were similar to Sp oxidation in laboratory soil incubations and in the field. Results indicate that the So source is not the cause of slow So oxidation in some New Mexico soils. Chemoautotrophic So oxidizers were present in unamended soils and their numbers increased in So‐amended soils. Although So amendment (25 g So kg−1) in the field decreased pH approximately 0.5 unit and increased SO4 tenfold, So amendment did not increase available Fe, Zn, or P. The slow rate of So oxidation in some New Mexico soils and failure of So amendment to increase nutrient levels are attributed to the buffering capacity of the calcareous soils.
Chemical Structural Studies of Forest Soil Humic Acids: Aromatic Carbon Fraction
Authors: Kögel‐Knabner Ingrid , Zech Wolfgang , Hatcher Patrick G.
Published: July 2010

Forest soil organic matter contains about 20 to 30% aromatic carbon moieties. In order to follow the changes in the structural composition of the aromatic C during humification a combination of cross‐polarization magic‐angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR) spectroscopy and CuO‐oxidation was used. Humic acids were extracted from the forest floor, A, and B horizons of a forested Typic Dystrochrept, an Entic Haplorthod, and a Lithic Udorthent. The materials collected differ in the degree of humification, from fresh litter material to humified mineral soil horizons, as determined by macromorphological observation. The humic acid fraction isolated from fresh litter of European beech (Fagus silvatica L.) and Norway spruce (Picea abies Karst) shows mainly peaks attributable to aromatic C derived from lignin and tannin structures, which are both partly extractable by alkaline solvents. The most prominent feature of the NMR spectra is the decrease of phenolic and methoxyl C with increasing degree of humification, accompanied by decreasing yields of lignin‐derived CuO‐oxidation products. Simultaneously, the signal intensity at 130 ppm in the 13C‐NMR spectra increased. Detailed structural assignments for this signal can be obtained by measuring the percentage of signal intensity from protonated and nonprotonated C by dipolar dephasing 13C‐NMR spectroscopy. The percentage of nonprotonated aromatic C, and more specifically the C‐substituted aromatic C fraction, increase when humification proceeds. Assuming that lignin is the primary precursor of the aromatic C components of humic acids in forest soils, then the lignin structure is altered considerably during humification, resulting in lignin‐derived aromatic structures with a high degree of C substitution and carboxyl functionality.
Drilling Method for Collection of Undisturbed Soil Monoliths
Authors: Persson L. , Bergström L.
Published: July 2010

In studies of water and solute movement in soils, use of undisturbed monoliths is usually preferred. A drilling technique to collect such monoliths (0.295 m i.d.; 1.0, 0.5, or 0.3 m in length) with minimal soil disturbance was developed. The drill consists of a steel cylinder with four mounted cutting teeth at the bottom, into which a plastic casing is inserted. The drill‐cylinder rotates around the casing and carves out a soil core that is gently pushed into the casing using only a minimum of hydraulic pressure. The technique has been used in a wide variety of research applications within soil science, including the measurement of hydraulic properties, soil evaporation, and soil aeration studies. Here, one application is described in which the monoliths were used as field lysimeters planted with either barley (Hordeum vulgare L.) or meadow fescue (Festuca pratensis Hudson). During a 6‐mo period, the grass lysimeters had a much lower total drainage (106 compared with 213 mm for barley) and also lower mean NO3 concentrations in the drainage water (<0.1 compared with 9.3 mg N L−1). The uniformity of response among the replicates and large differences between the two treatments was taken as indirect evidence that sidewall flows were of little significance when using this technique.
Precipitation of Dicalcium Phosphate Dihydrate in the Presence of Organic Acids
Authors: Grossl Paul R. , Inskeep William P.
Published: July 2010

Inhibition of dicalcium phosphate dihydrate (DCPD) precipitation rate by organic acids may play an important role in controlling phosphate activity and availability in P‐fertilized soils. The precipitation rate of DCPD was measured at pH 5.7 and 25 °C in the absence and presence of organic acids common to soil solutions using a seeded crystal growth method. Forward rate constants (kf) were determined from an integrated form of the second‐order rate law expression: rate = kfS[Ca2+][HPO2‐4]γ22, where brackets represent concentrations, S is the surface area (m2 L−1), and γ2 is the divalent ion activity coefficient calculated from the Davies equation. The average kf (L2 mol−1 m−2 s−1) for DCPD precipitation without organic acids was 9.7 ± 0.5. Additions of 0.26 to 2.06 mM C as humic acid and 1.1 to 3.3 mM C as fulvic acid resulted in induction periods lasting 2.0 to 632 and 1.5 to 10 min, respectively, prior to subsequent precipitation of DCPD. This indicates that DCPD precipitation was able to overgrow adsorbed humic and fulvic acids. Rates of DCPD precipitation were determined in the presence of humic, fulvic, citric, and tannic acids at concentrations ranging from 0.26 to 9.0 mM total soluble C (CTS). The highest levels of humic, fulvic, citric, and tannic acids added were 2.05, 7.8, 8.0, and 9.0 mM CTS, which resulted in decreased kf values of 1.1, 0.1, 0.6, and 2.1 L2 mol−1 m−2 s−1, respectively. Precipitation was inhibited by adsorption of these organic acids onto DCPD surfaces blocking sites acting as nuclei for new crystal growth. Adsorption characteristics of these organic acids were related to their functional‐group content and size. The ability of DCPD to precipitate on seed crystals with adsorbed C may explain the kinetically favored formation of DCPD vs. more thermodynamically stable octacalcium phosphate (OCP) and hydroxyapatite (HAP), where precipitation rates are more strongly inhibited by soluble C.
Rhizobacteria Suppressive to the Weed Downy Brome
Authors: Kennedy A. C. , Young F. L. , Elliott L. F. , Douglas C. L.
Published: July 2010

Rhizobacteria have the potential to suppress plant growth. We evaluated the effect of native pseudomonads on downy brome (Bromus tectorum L.), a troublesome weed in small‐grain‐producing lands. Pseudomonas spp. were isolated from winter wheat (Triticum aestivum L.) and downy brome roots and tested to determine their potential as biological control agents for this weed. Pseudomonads were screened in agar and soil for inhibition of downy brome root growth and lack of inhibition of winter wheat root growth. Of more than 1000 isolates tested, 81 inhibited downy brome and not winter wheat in the agar seedling bioassay. Six isolates consistently inhibited downy brome growth and not winter wheat in soil contained in pots in the growth chamber. In nursery field trials in which downy brome was planted in rows and adequately fertilized, some of the bacterial isolates reduced downy brome populations up to 30% and shoot dry weight up to 42%. Field studies were also conducted at three sites in eastern Washington in which brome‐inhibitory bacteria were applied to wheat fields infested with natural populations of downy brome. Of the three isolates studied in the field, two reduced plant populations and aboveground growth of downy brome up to 31 and 53%, respectively, compared with noninoculated controls. At two of the three locations, winter wheat yields were increased 18 to 35% because of the suppression of downy brome growth. Brome‐suppressive bacteria isolated from the rhizoplane of winter wheat and downy brome can be used as biological control agents for downy brome.
Theoretical Analysis of Carbon and Nutrient Interactions in Soils under Energy‐Limited Conditions
Authors: Bosatta Ernesto , Ågren Göran I.
Published: July 2010

The cycles of S and P in soil have received only limited attention from a theoretical or modeling point of view, relative to those of C and N. In this study, the interactions between the cycles of C, N, P, and S in decomposing litters and soils have been analyzed using a theory based on changes in substrate quality during decomposition. The C cycle requires information about microbial efficiency and growth rate as functions of substrate quality, with initial litter quality as a parameter distinguishing different materials. Nitrogen, P, and S are given similar descriptions and the parameter differentiating them are the concentrations of the elements in microbial populations and fresh litter. The theoretical predictions are compared with empirical data on C, N, P, and S behavior in a number of different conditions covering both steady states of soils and dynamics in incubation experiments in laboratories. The agreement between theoretical and empirical results indicate that the cycles of N, P, and S basically follow similar rules.