bluuebunny/crossref_metadata_2025 huggingface dataset:
An Apparatus for Application of Nitrogen‐15 Fertilizers Through Buried Drip Tubing
Authors: McGee E. A. , Thompson T. L. , McCreary T. W.
Published: July 2010

This study evaluated a new apparatus for applying 15N by fertigation to subplots under buried drip irrigation. Leaf lettuce (Lactuca sativa L. cv. Waldmann's Green) was planted in one unfertilized buried‐drip‐irrigated plot (4.06 by 53.34 m) with four north‐south beds. Six subplots (1.02 by 2.00 m) were established by placing a 15N injection apparatus into the drip tubing. Nitrogen‐rate treatments (71 and 176 kg ha−1) were replicated three times. Low‐ and high‐N plots received 1.60 and 1.15 atom % 15N urea applied at five times during the season. Plants were harvested at specific positions within and near the subplots. Uniform recovery of 15N by plants within subplots occurred. Uptake of 15N by plants was observed up to 45 cm outside subplots in the north‐south directions and in plants on beds immediately adjacent to the subplots. Uptake outside the subplots in the north‐south directions (apparent lateral movement) was no more than 21% of total 15N uptake.
Influence of Autocorrelation and Measurement Errors on Interpretation of Solubility Diagrams
Authors: Xu Shihe , Harsh James B.
Published: July 2010

The solubility method for determining solid‐phase controls on solute activities in aqueous systems is subject to potential sources of misinterpretation. Measurement errors cause deviation of solid‐phase solubilities from theoretical values, whereas autocorrelation between dependent and independent variables of a solubility diagram may lead to false interpretation of data points falling on a given solubility line. In this study, a Monte Carlo simulation was performed to determine the influence of measurement errors and autocorrelation on the interpretation of solubility data. For solid‐phase control of Al activity at pH <6 for natural gibbsite, basaluminite, and jurbanite, deviation of apparent solubility from theoretical solubility lines of the solids due to measurement errors in pH, total inorganic monomeric Al, ionic strength, and SO4 activity are usually small compared with the deviation expected when random numbers are used to generate a data set. As a result, solid‐phase control was distinguishable from autocorrelation of random data except at pH 6 to 7. For a given metal oxide, autocorrelation interference is significant in a solubility study only when the OH/metal ratio of the predominant dissolved metal species is close to the OH/metal or O/Metal ratio of the solid phase. We concluded that the solubility method is a reliable and useful tool to study Al chemistry in acid soils if used with caution.
Micromorphology of Pedogenically Derived Fracture Fills in Bandelier Tuff, New Mexico
Authors: Davenport David W. , Wilcox Bradford P. , Allen B. L.
Published: July 2010

Fractures in the Bandelier Tuff are potential paths for water movement and transport of contaminants from waste disposal sites and other contaminated areas at Los Alamos National Laboratory, Los Alamos, NM. Contaminants transported in this way could ultimately be found in Los Alamos drinking water or in the Rio Grande, which flows through heavily populated areas in both the USA and Mexico. We conducted this study to determine (i) the morphology and origin of soil‐like material in the fractures, and (ii) the likelihood of significant water movement through the fractures. We examined thin sections of fracture fills, soils, and tuffs to obtain fabric and mineralogical data, and collected field data on soil horizons, color, texture, structure, clay films, and root abundance. Fracture fills consist of clay, CaCO3, or combinations of the two with minor inclusions of tuff and sand grains. Clay consists of thick, highly oriented argillans aligned parallel to fracture walls, and of discrete books in fracture interiors. Carbonate consists of massive microcrystalline calcite, which completely fills some fractures, and laminae or infillings between clay laminae or books in clay‐dominated fractures. The carbonate was precipitated after clay deposition, suggesting a change to a more arid climate. Weaker development of argillans and carbonate features in the soils suggests that the fractures may be derived from older soils that have been stripped by erosion. The presence of live roots throughout the fracture fills indicates the presence of water, but the smectitic clay and massive carbonate make it unlikely that significant water movement is now taking place through the fractures. The potential creation of new macropores by a variety of processes, however, including seismic activity and biologic disturbance, could allow rapid water movement and contaminant transport.
Organic Anions' Effect on Phosphorus Release from Spodic Horizons
Authors: Lan Mu , Comerford N. B. , Fox T. R.
Published: July 2010

The purpose of this research was to investigate the release of P from the spodic horizons of common forested soils in the Lower Coastal Plain of Florida and Georgia. This was considered important because (i) these soils have a history of variable responses to P fertilization, (ii) roots are known to grow in this material, and (iii) previous research has suggested that the P in this material might be available to plants. Desorption experiments using 0.001 M concentrations of a variety of organic ligands (pH 4.3 for initial solutions) with a range of Al complexation constants were conducted by reacting the ligand solutions with spodic horizon soil. Inorganic P, organic P, and Al were measured in the resulting extracts. Results showed that the amount of extractable inorganic P in these soils was variable. Some soils had detectable levels of extractable inorganic P, while others are essentially devoid of it. In those soils that had extractable P, the inorganic P release was correlated to the release of Al as the release of both moieties was initiated by organic anions with logKAl values, the Al stability constant with that anion, of about 3.2 to 4.2 or greater. This suggests that root exudates with logKAlS less than these values would not be effective in making inorganic P in spodic horizons more available to plants. Organic P is a major component of the soil solution and is released by a mechanism unrelated to the logKAl of the organic ligand.
Improved Method for Measuring Water Imbibition Rates on Low‐Permeability Porous Media
Authors: Humphrey M. D. , Istok J. D. , Flint L. E. , Flint A. L.
Published: July 2010

Existing methods for measuring water imbibition rates are inadequate when imbibition rates are small (e.g., clay soils and many igneous rocks). We developed an improved laboratory method for performing imbibition measurements on soil or rock cores with a wide range of hydraulic properties. Core specimens are suspended from an electronic strain gauge (load cell) in a closed chamber while maintaining the lower end of the core in contact with a free water surface in a constant water level reservoir. The upper end of the core is open to the atmosphere. During imbibition, mass increase of the core is recorded continuously by a datalogger that converts the load cell voltage signal into mass units using a calibration curve. Computer automation allows imbibition rate measurement on as many as eight cores simultaneously and independently. Performance of each component of the imbibition apparatus was evaluated using a set of rock cores (2.5 cm in diameter and 2–5 cm in length) from a signle lithostratigraphic unit composed of non‐to‐moderately welded ash‐flow tuff (a glass‐rich pyroclastic rock partially fused by heat and pressure) with porosities ranging from 0.094 to 0.533 m3 m‐3. Reproducibility of sample handling and testing procedures was demonstrated using replicate measurements. Precision and accuracy of load cell measurements were assessed using mass balance calculations and indicated agreement within a few tenths of a percent of total mass. Computed values of sorptivity, S, ranged from 8.83 × 10‐6 to 4.55 × 10‐4 m s‐0.5. The developed method should prove useful for measuring imbibition rates on a wide range of porous materials.
Nonexchangeable Ammonium and Potassium Determination in Soils with a Modified Sodium Tetraphenylboron Method
Authors: Cox A. E. , Joern B. C. , Roth C. B.
Published: July 2010

The mechanism of NH+4 and K+ fixation by clay minerals is similar, yet different analytical methods are used to estimate nonexchangeable (fixed) amounts of these nutrients in soils. Sodium tetraphenylboron (NaBPh4) facilitates the release of nonexchangeable NH+4 and K+ by precipitation of these ions as NH4BPh4 and KBPh4. A NaBPh4 method was modified and evaluated as a common procedure for determination of nonexchangeable NH+4 and K+ in 10 midwestern soils that were either untreated or NH+4 − or K+‐saturated (treated with 2 M solutions of NH4Cl or KCl to saturate fixation sites with NH+4 or K+). Experiments were conducted to evaluate Cu2+ (CuCl2) as a substitute for Hg2+ (HgCl2) in the recovery of NH+4 and K+ released by NaBPh4 in soils. A 7‐d incubation with the modified NaBPh4 method (CuCl2 instead of HgCl2) released most of the NaBPh4‐ extractable NH+4 and K+. In untreated soils, the NaBPh4 method extracted 71% of NH+4 released by the conventional HF/HCl method. Nonexchangeable NH+4 release by both methods was related in untreated (r2 = 0.98) and NH+4‐saturated (r2 = 0.95) soils. Recently fixed NH+4 in the NH+4‐saturated soil was equally accessible to both methods. The NaBPh4 method extracted up to 10 times more nonexchangeable K+ than the conventional 1 M HNO3 method in both the untreated and K+‐saturated soils. Recently fixed K+ in the K+‐saturated soil was equally accessible to both methods, except in high‐fixing soils where K+ was held too strongly to be released by HNO3. The results show that the modified NaBPh4 method can be used as a common procedure to estimate nonexchangeable forms of both NH+4 and K+.
Incorporating Nonextractable Atrazine Residues into Soil Size Fractions as a Function of Time
Authors: Barriuso E. , Koskinen W. C.
Published: July 2010

Soil organic matter is directly implicated in pesticide nonextractable (bound) residues formation, but the role of different soil organic constituents is unknown. Physical soil fractionation allows separation, with minimal chemical modification, of organic constituents whose nature and properties are dependent on particle size. Physical fractionation was used to determine the role of soil organic constituents in atrazine (6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine) bound residues formation. 14C‐ring‐labeled atrazine was applied to the top of soil lysimeters (0.3 by 1.2 m) in the field. The lysimeters were periodically removed during 16 mo, and the soil was physically fractionated into seven size fractions by sieving, sedimentation, and centrifugation: >200, 50 to 200, 20 to 50, 5 to 20, 2 to 5, 0.2 to 2, and <0.2 µm. The largest proportion of total bound residues in the whole soil was in the clay size (0.2–2 µm) fraction, which also contained 50% of the total soil organic C (OC). The ratio of bound residues to OC content decreased with the particle size, and it was highest in fractions >50 µm, those rich in nonhumified organic matter. The low capacity of humified organic matter in the finest size fractions to form bound residues is presumably due to the chemical nature of the humified organic matter; however, accessibility of organic compounds stabilized on the fine mineral surfaces or included in aggregates structures is also a possibility. The most stable bound residues are associated with humified organic matter, especially in clay size fraction (0.2–2 µm). Physical soil fractionation as a function of incubation time allows definition of the different capacity of soil organic constituents to form bound residues in relation to their localization in the size fractions.
Porosity Factors that Control the Hydraulic Conductivity of Soil‐Saprolite Transitional Zones
Authors: Vepraskas M. J. , Kleiss H. J. , Amoozegar A. , Guertal W. R.
Published: July 2010

Slowly permeable transitional horizons separate soil and saprolite, but these horizons cannot be identified easily in the field. The objectives of this study were to determine why the soil‐saprolite transitional zone (BC and CB horizons) is slowly permeable, and to evaluate ways for identifying it in the field. Two saprolite deposits were studied in the North Carolina Piedmont. At each site, saturated and unsaturated hydraulic conductivities (Ksat and Kunsat) were measured for major horizons. Volume fractions of water‐conducting pores were also compared with the changes in hydraulic conductivity with depth. Horizon mean Ksat values at both sites ranged from virtually 0 to approximately 3 cm h‐1. The lowest Ksat values (<0.3 cm h‐1) occurred in or near the transitional horizons that were directly below the Bt horizons. Changes in the volume of pores within or between mineral grains (termed inter/intraparticle pores) with depth corresponded to changes in both Ksat and Kunsat. In the transitional horizons, the inter/intraparticle pores were plugged with clay and this caused the horizons to have low K values. In situ measurements of Ksat with depth were the most accurate technique to use for identifying transitional zones in the field. Examination of both the soil and rock structures in pits was also an acceptable technique. Texture and consistence were not considered reliable for pin‐pointing transitional horizons.
Water Distribution in Soil under Ridge‐Till and No‐Till Corn
Authors: Waddell J. T. , Weil R. R.
Published: July 2010

No‐till (NT) reduces runoff, but increases infiltration and macropore flow, compared with conventional tillage (CT). Because it controls traffic and creates a unique surface microtopography, we hypothesized that ridge tillage (RT) would alter water entry and distribution in the soil profile. Therefore, a field study using 5‐yr‐old NT and RT plots was conducted on a Monmouth fine sandy loam (fine‐loamy, mixed, mesic Typic Hapludult) in Maryland. Corn (Zea mays L.) plots in a corn‐soybean [Glycine max (L.) Merr.] rotation were studied for 2 yr. Soil sorptivity, determined by runoff from simulated rain, was 2.83 cm h‐1/2 on NT and 1.33 cm h‐1/2 on RT. Runoff began 26.3 min after rain began on NT vs. 7.2 min on RT. Also, NT retained more soil water than RT plots in 1991, when June to October rainfall was 290 mm. With 440 mm of June to October rainfall in 1992, depletion of water by corn was greater in NT than RT. The corn canopy funneled rain toward the corn row, largely offsetting interridge runoff in RT while the corn was present. Therefore the horizontal distribution of water was relatively uniform in RT soil, but water was concentrated in the corn rows in NT. After corn harvest in 1991, a dry period produced an upward water potential gradient in RT from − 18 kPa in the furrow to − 35 kPa on the ridgetops, but a downward gradient in NT from − 10 kPa near the surface to ‐25 kPa at 80 cm deep. The results suggest that RT may decrease water infiltration in the crop row, especially after harvest, compared with NT.
Soil Temperature, Water Content, and Barley Development of Level vs. Ridged Subarctic Seedbeds
Authors: Sharratt B. S.
Published: July 2010

Ridge tillage may promote early‐season warming of soils in subarctic regions and thereby optimize the plant growing environment. This study was conducted to assess soil temperature and water content, along with barley (Hordeum vulgare L.) development, on a level vs. ridged Pergelic Cryaquept at Fairbanks, AK. Ridges were oriented north‐south, east‐west, northeast‐southwest, and northwest‐southeast. Seed zone soil temperature and water content were measured, the former by thermocouples, at the ridge peak and furrow as well as on ridge slopes where barley was grown during the 1989 through 1991 growing seasons. Barley grown on the level surface and on southerly ridge aspects produced at least 25 g m‐1 more grain and 20 g m‐1 more straw than barley grown on northerly aspects. The vegetative developmental rate was 0.03 leaves d‐1 faster on southern ridge aspects or the level surface than on northern aspects, owing to 2°C higher temperatures of soil with a southerly or level exposure. Soil water content on northern ridge aspects was occasionally 0.05 m3 m‐3 higher than on southern aspects in the early growing season (<60 d after planting), but 0.04 m3 m‐3 lower than on the level soil surface in the late growing season (>60 d after planting). In the subarctic, the plant growing environment is as favorable on a level soil surface as on a south‐facing ridge aspect, owing to nearly equal early‐season soil temperatures and higher soil water content in the late season.
Specific‐Gravity Effects on Fertilizer Leaching from Surface Sources to Shallow Water Tables
Authors: Bonczek J. L. , McNeal B. L.
Published: July 2010

Subirrigated sands with surface‐applied fertilizer bands are susceptible to considerable gravity‐induced convection of fertilizer salts whenever the water table approaches within 30 to 45 cm of the soil surface and induces rapid fertilizer dissolution. Laboratory studies have been conducted on two sands from Manatee County in the vegetable and citrus production region along central Florida's Gulf Coast. Peak saturated‐zone electrical conductivity (EC) values of 14 and 9 dS m−1 were attained within 3 to 5 d at the 60‐cm depth for columns of local sand having a water table maintained 2.5 and 22.5 cm below the soil surface, respectively. Such movement is far too rapid to be ascribed to reasonable diffusional or traditional convective‐flow effects, and is instead attributed to gravity‐induced convective flow, or fertilizer “dropout”. Sectioned‐column studies demonstrated near‐surface EC values of 25 to 35 and 70 to 90 dS m−1 for water tables maintained at the 15‐ and 45‐cm depths, respectively. These same columns evidenced solute‐pulse movement to the 8‐ to 10‐cm depth and the 15‐ to 20‐cm depth after 6 and 24 h, respectively, for water tables maintained at the 45‐cm depth. Lower hydraulic conductivity, quite possibly as a result of increased soil organic matter content for these otherwise virtually identical fine sands, moderated such effects somewhat. Implications are discussed with respect to early‐season fertilizer management in vegetable production regions of the southeastern Coastal Plain.
Solution For Heat Flow in Soil with a Heat Source at a Fixed Depth
Authors: Álvarez J. , Sobrón F. , Bolado S.
Published: July 2010

We developed a computationally efficient model for estimating the transient soil temperature distributions resulting from a heat source at a fixed depth beneath a greenhouse. The model was developed for use as a submodel of the air‐soil systems in greenhouses where the soil is used as a heat storage medium, with a network of buried pipes acting as a heat exchanger. The model assumes soil thermal properties are spatially and temporally constant and that energy transfer between the greenhouse and soil is primarily a result of net radiation and sensible heat transfer. First‐order energy transfer terms are also used to account for lateral energy exchanges with the surrounding soil and the heat source is included as a plane at a fixed depth. This was achieved by obtaining a Green's function solution in the Laplace domain and performing a numerical inversion with a fast Fourier‐transform algorithm, which requires very little computational time. Model parameters are optimized using a Simplex algorithm during a 3‐d simulation to show the ability of the method to describe the greenhouse soil temperature. This method provides a reasonable description of the heat flux under these conditions.
Soil Texture and Residue Addition Effects on Soil Phosphorus Transformations
Authors: Huffman S. A. , Cole C. V. , Scott N. A.
Published: July 2010

The effect of soil texture on P transformation and the extent and timing of crop residue decomposition affects both P availability and the fate of the P added in the residue. Our objectives were to examine P transformation in sand, sandy loam, and loam soils during surface or incorporated wheat (Triticum aestivum L.) straw decomposition with and without N and P addition. Packed soil cores (4.8 cm diameter by 2.5 cm deep) were incubated in the dark for 10, 30, 60, and 90 d at 25°C and −0.033 MPa initial soil water pressure. We determined CO2 respiration, labile inorganic P (Pi), labile organic P (Po), microbial P, NaOH‐extractable Pi and Po, and HCl‐extractable Pi. Soil texture had a greater effect on P transformation than did residue placement. Microbial P was greatest at 10 d and was 13.0, 9.8, and 6.5 mg kg−1 for the loam, sandy loam, and sand, respectively. Labile Pi was lowest at 10 d and was 22.9, 18.0, and 11.5 mg kg−1 for the loam, sandy loam, and sand, respectively. More of the nutrient P added remained as labile Pi when the residue was surface applied. Residue placement did not affect microbial P, indicating that the effect of placement was indirect. Phosphorus transformations were closely linked to microbial activity and C dynamics.
Stability Constants of the Fungal Siderophore Rhizoferrin with Various Microelements and Calcium
Authors: Shenker M. , Chen Y. , Hadar Y.
Published: July 2010

Stability constants of metal‐ligand complexes determine their speciation in solution at equilibrium. Therefore, stability constants of siderophore‐metal complexes are of crucial importance in studies of their efficiency as Fe mediators. In this study, potentiometric titrations were used to determine protonation and stability constants of Fe3+, Fe2+, Cu2+, Ca2+, and Zn2+ with rhizoferrin, a siderophore produced by Rhizopus arrhizus, which has been shown in previous studies to be an effective carrier of Fe to plants. Rhizoferrin was found to be a specific Fe3+ chelator but with a stability constant lower than most microbial siderophores. The ferric complex of rhizoferrin is anionic throughout the pH range prevailing in soils, and therefore, it is expected to be mobile in the rhizosphere. The following log Kapp values at 25°C, pH 7.0, and 0.1 M ionic strength were determined: 19.1, 7.5, 6.2, 6.0, and 4.4 for Fe3+, Fe2+, Cu2+, Ca2+, and Zn2+, respectively. The apparent stability constant (Kapp) value for the ferric complex of rhizoferrin suggests that ligand exchange with mugineic acid is the mechanism facilitating the efficiency of rhizoferrin as an Fe carrier to graminaceous plants.
Phosphorus Availability from Phosphate Rock as Enhanced by Water‐Soluble Phosphorus
Authors: Chien S. H. , Menon R. G. , Billingham K. S.
Published: July 2010

Quantitative estimation of the enhancement effect of water‐soluble P on P availability from phosphate rock (PR) has not been reported. The objective of this study was to use radioactive 32P as a tracer to distinguish P availability from soil, PR, and TSP so that P uptake by crops from PR in the presence of TSP could be estimated. Three sets of 4‐kg soil samples of an acid Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult, pH 4.8) were mixed with the following treatments: (i) 32P solution and central Florida PR (CFPR), (ii) 32P‐tagged TSP, and (iii) 32P‐tagged TSP and CFPR at a P ratio of 50:50. The rates of P applied were 0, 12.5, 25, 50, 100, and 200 mg P kg−1. For treatment (iii), an additional rate of 400 mg P kg−1 was also prepared. Maize (Zea mays L.) and cowpea (Vigna unguiculata [L.] Walp. ssp. unguiculata) were planted and harvested at 42 d after planting for maize and 45 d for cowpea. The effectiveness of P sources in terms of increasing dry‐matter yield and P uptake followed the order of TSP >‐ (CFPR + TSP) > CFPR for maize and TSP = (CFPR + TSP) > CFPR for cowpea. Phosphorus uptake from CFPR in the presence of TSP was higher than P uptake from CFPR applied alone, indicating an enhancement effect of TSP on the effectiveness of CFPR. The increase in P uptake from CFPR due to TSP influence, across all the PR rates applied, was 3.48 mg P pot−1 for maize and 1.38 mg P pot−1 for cowpea. With respect to P uptake from CFPR applied alone, the corresponding relative increase in P uptake from CFPR due to TSP influence was 165% for maize and 72% for cowpea.
Anion Transport Involving Competitive Adsorption during Transient Water Flow in an Andisol
Authors: Katou Hidetaka , Clothier Brent E. , Green Steven R.
Published: July 2010

Andisols containing allophane and other poorly crystalline materials, carry variable surface charge, and adsorb otherwise inert anions such as Cl− and NO−3. The objective of this study was to predict composition‐dependent, retarded transport of anions during unsteady water flow in an Andisol. One‐dimensional absorption experiments in Kannondai subsoil (Hydric Hapludand) columns were conducted with CaCl2, Ca(NO3)2, and mixed CaCl2‐Ca(NO3)2 solutions at different concentrations (0.00462‐0.115 mol L−1). Because of nonlinear, competitive adsorption of Cl− and NO−3 by the soil, the observed retardation of anion penetration depended on the total concentration and composition of the invading solution. Nitrate ion had a smaller affinity to the adsorption sites than Cl− (the selectivity coefficient Kv = 0.51) and showed a greater penetration in the presence of Cl−. The adsorption of Cl− and NO−3 much exceeded the concurrent SO2−4 desorption from the soil. This suggests that SO2−4 was so strongly adsorbed that exchange reaction with the invading anions proceeded only to a limited extent. Thus, the adsorption of the monovalent anions was largely due to the increase in the anion exchange capacity of the soil in response to an increase in the ionic strength of the bulk solution. An approximate theory was developed for anion transport involving competitive adsorption in which total monovalent anion adsorption, obeying a Langmuir‐type equation, is allocated via Kv to the adsorption of Cl− and NO−3. Employing the adsorption parameters determined from separate steady state leaching experiments, the theory successfully described the measured anion content profiles.
Quantifying the Diffusive Mass Transfer of Nonreactive Solutes in Columns of Fractured Saprolite using Flow Interruption
Authors: Reedy O. C. , Jardine P. M. , Wilson G. V. , Selim H. M.
Published: July 2010

Subsurface transport processes of low‐level radioactive contaminants at hazardous waste sites are complex due to a nonuniform distribution of pore regions in heterogeneous media. During transport, contaminant mass is continuously transferred between the various pore regions via hydraulic and concentration gradients. Our objective was to quantify the diffusive mass transfer of a nonreactive solute between the matrix porosity and preferential flow paths in fractured subsurface media. A large, undisturbed soil column (41 cm long by 17 cm diameter) of weathered, fractured shale was acquired from a proposed waste site on the Oak Ridge Reservation in eastern Tennessee. We injected a nonreactive tracer, Br−, under saturated conditions, interrupting tracer flow for a designated time, and then reinitiating flow. Experiments considered tracer injection and displacement, variations in duration of flow interruption, and variations in flux. Transport of Br− through the undisturbed medium was characterized by asymmetric breakthrough curves (BTC), indicative of preferential flow coupled with movement into the matrix. Interrupting flow resulted in decreased and increased Br− concentrations during tracer infusion and displacement, respectively, when flow was reinitiated. More pronounced concentration perturbations were observed at high fluxes and long interrupt durations. These perturbations were driven by solute concentration gradients established between pore regions as a result of preferential flow. This confirmed the importance of a diffusion contribution to the overall physical nonequilibrium mechanism that affects solute transport. Observed effluent concentrations were adequately simulated with a two‐region flow interrupt model by using independently determined parameters and adjusting the mass transfer coefficient. Estimated mass transfer coefficients increased linearly with increased flux, probably due to enhanced nonequilibrium that was established between pore regions as flux increased.
Landscape‐Scale Variations in Leached Nitrate: Relationship to Denitrification and Natural Nitrogen‐15 Abundance
Authors: Farrell Richard E. , Sandercock Peter J. , Pennock Daniel J. , Van Kessel Chris
Published: July 2010

Evidence suggests that the natural 15N abundance (δ15N) of leached NO3 can be related to denitrification activity. In addition, spatial patterns for denitrification and leached NO3 are controlled by land‐scape‐scale interactions between topography and hillslope hydrology. Thus, this study was conducted to assess whether a landscape‐scale relationship exists between denitrification activity and the δ15N of deep‐leached (>120 cm) NO3 in an undulating landscape developed on silty glacio‐lacustrine sediments overlying a clay loam till of late Wisconsinan age, under semiarid conditions. The highest concentrations of NO3 occurred in shoulder and upper‐level landscape positions and the lowest concentrations in footslope and lower‐level positions. In areas of the landscape where water accumulation was at a maximum, denitrification rates were highest and there was no accumulation of NO3 in the upper 3 m of the solum. Conversely, in areas where water accumulation and denitrification activity were low, there was a buildup of NO3 below the root zone and within 3 m of the soil surface. The relationship between seasonal denitrification activity and the concentration of leached NO3 was characterized by a negative correlation (rs = −0.464**). Moreover, values of δ15N‐NO3 were highest in areas of the landscape where rates of denitrification were highest and there was a negative correlation (rs = −0.638***) between the concentration of deep‐leached NO3 and its δ15N. These data support the hypothesis that topographic and hydrologic controls on denitrification and leaching are reflected in the localized removal of NO3 from the soil profile, which is reflected in the δ15N value of leached NO3‐N.
Automated Chromatographic Analysis of Atmospheric Gases in Environmental Samples
Authors: McCarty G. W. , Blicher‐Mathiesen G.
Published: July 2010

The need for a single‐injection gas chromatographic procedure for detection of the principal atmospheric gases found in environmental samples has led to development of an automated system that permits measurement of CO2, N2O, O2‐Ar, and N2 in a single detector without interference from water vapor in samples. The injection of gas samples on the system was automated by interfacing a commercial headspace sampler with a gas chromatograph (GC) that was fitted with an ultrasonic detector and two automated multiport switching valves. The first switching valve was configured with short precolumns of Porapak Q (PQ) to retain and vent the water vapor in samples. The other valve was configured with two analytical columns connected in series that permit separation of the gas components. After water is removed by the precolumn, the gas sample flows onto a PQ column where CO2 and N2O are retained and separated while the composite peak of N2 and O2‐Ar elutes onto a molecular sieve (MS) column. The valve is then switched, causing reversal of the order of columns with respect to the gas flow without reversing the direction of flow through the columns. This allows the CO2 and N2O peaks to elute from the PQ column to the detector while the O2‐Ar and N2 components are separated on the MS column and later flow to the detector. The system has proven to be robust in that it permits routine, unattended analyses of moist gas samples with high sensitivity and without interference from water peaks. This, in conjunction with the highly controlled equilibrium conditions permitted by use of the headspace sampler, makes the system suitable for gas analysis of environmental samples including dissolved gas analysis of natural water samples.
Water and Solute Movement under Conventional Corn in Central Spain. II. Salt Leaching
Authors: Bustos A. , Roman R. , Caballero R. , Díez J. A. , Caballero A. , Cartagena M. C. , Vallejo A.
Published: July 2010

Leaching of salts under field conditions may be addressed through a combination of the soil water balance and the drainage and concentration of salts in the soil profile. A field experiment was conducted in the 1991 growing season on a Typic Xerofluvent soil planted to corn (Zea mays L.) to assess the leaching pattern of Ca2+, Mg2+, Na+, K+, Cl+, SO2−4, CO3H−, and NO−3 under conventional cropping. River and well irrigation water were used with salinities of 680 and 1580 mg L−1, respectively. Sampling of the soil water solution throughout the growing season was done for soil profile layers using a permanent ceramic‐candle extraction system. Neutron probes and tensiometers allowed seasonal measurements of soil water content and water movement in the profile. Leaching of salts was calculated as the product of deep drainage amounts times the salt concentrations at the 1.4‐m soil depth. Total salt drainage for river and well was 0.34 and 0.38 kg m−2, respectively. Accumulation of salts to a depth of 1.4 m in the soil profile showed values of 0.02 and 0.21 kg m−2 in plots irrigated with river and well water, respectively. Soil water balance and concentration of salts in the soil solution indicated discharge of salts to the groundwater table with conventional cropping practices. Groundwater pollution was addressed by matching irrigation to the evapotranspiration and by minimizing the concentration of salts in irrigation water.
Partitioned Flow Domains of Three Wisconsin Soils
Authors: Hart G. L. , Lowery B.
Published: July 2010

Preferential flow mechanisms have been the subject of increasing research interest because these phenomena contribute to solute transport. Commonly, preferential flow paths are associated with macropores or highly structured soils. Sandy soils are typically weakly structured or structureless. However, they exhibit rapid drainage, which may mimic the hydrology and solute transport effects of macropores. We tested whether a flow domain partitioning scheme could be applied on two sandy soils, by collecting drainage data with time domain reflectometry across small time increments and implementing analytical models using a nonlinear iterative fitting procedure. The analysis was applied to both observed and Leaching Estimation and Chemistry Water Model (LEACHW) drainage of Sparta (mesic, uncoated, Typic Quartzipsamments) and Plainfield sand (mixed, mesic, Typic Udipsamment), as well as strongly structured Dubuque silt loam (fine‐silty, mixed, mesic, Typic Hapludalf), where water content was measured with a neutron meter. We found significant differences (P < 0.05) between soils and profile depths relating macropore and matrix flow domains of observed data. Maximum hydrologically effective macropore volumes ranged from 0.018 (1.8%) in Dubuque silt loam to 0.294 (29.4%) in Sparta sand. Mixed results were obtained with flow domain partitioning of drainage simulated with LEACHW. In 5 of 15 cases, macropore and micropore parameter estimates failed to converge. Best agreement of micropore and macropore parameter estimates between observed and modeled drainage was observed in Dubuque soil and poorest concordance in Sparta sand. This analytical scheme may be applied to a wide range of soils if appropriate data describing the hydrological character were available.
Analytical Solution for Two‐Region Diffusion with Two Well‐Mixed End Chambers
Authors: El‐Farhan Y. H. , Rolston D. E. , Petersen L. W. , Glauz R. D.
Published: July 2010

Many methods have been developed for determining the effective gaseous diffusion coefficient (Dp) in soils. Some commonly used methods are the one‐ and two‐chamber apparatuses. In addition, laboratory apparatuses for the study of vapor diffusion, sorption, and biodegradation may consist of soil and vapor chambers. Existing analytical solutions for such apparatuses cannot accommodate diffusion through regions containing two distinct layers of differing porosity and diffusion coefficient. Such dual porosities can represent stagnant air layers, or crusting‐compaction at core ends. We developed an analytical solution for gaseous diffusion in a four‐region chamber system. The system consists of two diffusion regions (with two different porosities), and a well‐mixed end chamber attached at either end. The solution was used to simulate one‐dimensional gas diffusion in an apparatus consisting of two diffusion regions with constant‐concentration boundary conditions. The solution was also used to quantify errors made in estimating Dp using the one‐chamber apparatus when the air chamber is not mixed, or when a stagnant air layer exists above the soil surface. Errors due to non‐mixing decreased with time and increased with water content and air‐chamber size when analysis was done using concentrations at a point close to the soil surface. Analysis of the effects of a stagnant air layer showed that errors increased with time and air‐chamber size and decreased with increasing water content. Analysis done to test the effects of soil crusting on diffusion showed that, despite the thinness of the soil crust, large estimation errors in Dp are possible.
Secondary Carbonates in Three Fine and Fine‐loamy Alfisols in Michigan
Authors: Schaetzl Randall J. , Frederick William E. , Tornes Lawrence
Published: July 2010

Secondary pedogenic carbonates are usually associated with ustic or drier soil moisture regimes; when found elsewhere, their interpretation can be troublesome. We studied three Alfisol pedons in Michigan that contained secondary carbonates on ped faces. The purpose of the research was to (i) characterize these accumulations, (ii) examine possible genetic explanations for the accumulations, (iii) determine if these soils have calcic horizons, given the recent redefinition of this diagnostic horizon, and (iv) evaluate how current “k horizon” nomenclature might apply to these soils. Three different drainage classes and two soil temperature regimes were represented in the sampled pedons: a fine, mixed Glossic Eutroboralf; a fine, illitic, mesic Aquic Hapludalf; and a fine‐loamy, mixed, mesic Aeric Endoaqualf. All three pedons had thin (<50 cm) leached zones near the surface, and carbonate coatings (calcans) on ped faces within the lower B and/or upper C horizons. Two of the three pedons had horizons that met calcic horizon criteria. Horizons of preferential carbonate accumulation sometimes occurred near subtle textural breaks in the lower solum. Some B horizons in one pedon contained carbonate accumulations in amounts that exceeded that of the presumed parent material. The calcans have probably resulted both from vertical translocation of carbonates, followed by precipitation at depth, as well as internal redistribution of carbonates from ped interiors to ped faces. Use of the k subscript is warranted for some horizons in these soils. We recommend that its usage should be similar to t or s, i.e., horizons with evidence of secondary carbonates merit the k subscript.
Soil Morphology of Canopy and Intercanopy Sites in a Piñon‐Juniper Woodland
Authors: Davenport David W. , Wilcox Bradford P. , Breshears David D.
Published: July 2010

Piñon‐juniper woodlands in the semiarid western USA have expanded as much as fivefold during the last 150 yr, often accompanied by losses of understory vegetation and increasing soil erosion. We conducted this study to determine the differences in soil morphology between canopy and intercanopy locations within a piñon (Pinus edulis Engelm.)‐juniper [Juniperus monosperma (Engelm.) Sarg.] woodland with uniform parent material, topography, and climate. The woodland studied, located near Los Alamos, NM, has a mean tree age of 135 yr. We examined soil morphology by augering 135 profiles in a square grid pattern and comparing soils under piñon and juniper canopies with intercanopy soils. Only two of the 17 morphological properties compared showed significant differences. The B horizons make up a slightly greater proportion of total profile thickness in intercanopy soils, and there are higher percentages of coarse fragments in the lower portions of canopy soil profiles. Canopy soils have lower mean pH and higher mean organic C than intercanopy soils. Regression analysis showed that most soil properties did not closely correspond with tree size, but total soil thickness and B horizon thickness are significantly greater under the largest piñon trees, and soil reaction is lower under the largest juniper trees. Our findings suggest that during the period in which piñon‐juniper woodlands have been expanding, the trees have had only minor effects on soil morphology.
Characterization of Phosphorus in a Spruce‐Fir Spodosol by Phosphorus‐31 Nuclear Magnetic Resonance Spectroscopy
Authors: Dai K'o H. , David Mark B. , Vance George F. , Krzyszowska Anna J.
Published: July 2010

Factors affecting the distribution and biogeochemical cycling of soil P are only partially understood. Many previous studies have focused on P distribution within surface mineral soils and cycling of inorganic P. Few data are available on organic forms of P in forest floor and mineral horizons of forest soils. Therefore, we used 31P nuclear magnetic resonance (31P‐NMR) to characterize the P compounds in NaOH‐ethylenediaminetetraacetic acid (EDTA) extracts of three Spodosol profiles. The NaOH‐EDTA extracted most of the P in the three organic horizons (87, 83, and 69% of total P in Oi, Oe, and Oa horizons, respectively) and 39 to 67% in the Bhs horizon. Major P species detected in all horizons were inorganic orthophosphate and orthophosphate monoesters and diesters that ranged from 11 to 53%, 12 to 52%, and 13 to 45% of total P extracted, respectively. As is typical in Spodosol chemistry, considerable variation was found for organic P distribution in the organic horizons of the three profiles. However, on average, distribution patterns of P forms with depth were observed, including a decrease in the proportion of inorganic orthophosphate with greater decomposition in the forest floor (Oi > Oe > Oa), followed by an increase in the Bhs horizons. Pyrophosphate (5–19% of total P) and polyphosphates (5–13% of total P) were found mainly in the forest floor horizons, except for one profile where pyrophosphate had evidently accumulated in the Bhs horizon. Traces (≈2%) of phosphonates occurred only in the Oa horizon. Results suggest that biological activity, extractable Fe concentration, structural characteristics of P compounds, and pH are probably responsible for the distribution of P species in these Spodosols.
Organic Matter Decomposition following Harvesting and Site Preparation of a Forested Wetland
Authors: Trettin C. C. , Davidian M. , Jurgensen M. F. , Lea R.
Published: July 2010

Organic matter accumulation is an important process that affects ecosystem function in many northern wetlands. The cotton strip assay (CSA) was used to measure the effect of harvesting and two different site preparation treatments, bedding and trenching, on organic matter decomposition in a forested wetland. A Latin square experimental design was used to determine the effect of harvesting, site preparation, and relative position within the wetland on organic matter decomposition at soil depths of 5, 10, and 20 cm. Repeated measures analysis of variance was used to test for treatment effects on organic matter decomposition, soil temperature, and soil oxidation depth. Cellulose decomposition increased at each soil depth as site disturbance increased, with bedding > trenching > whole‐tree harvest > reference. The cellulose decomposition response was correlated with changes in soil temperature; the temperature coefficient Q10 equaled 6.0, which is greater than previously reported values. Position within the wetland relative to an adjoining river affected the decomposition and soil oxidation depth. Because the rate of decomposition is strongly controlled by temperature, higher rates of organic matter decay are expected to continue on harvested and regenerated sites until canopy closure reduces soil temperature.
The Thermodynamic Theory of Ion Exchange: A Single‐Phase Mixture Formulation
Authors: Snyder V. A. , Cavallaro N.
Published: July 2010

A longstanding problem in the thermodynamic theory of ion exchange has been lack of a general method for measuring activities of solid‐ion complexes or exchanger species. Existing theory, based on integrating the Gibbs‐Duhem relation for a solid exchanger phase immersed in an electrolyte solution, is often subject to uncertainties due to indeterminate amounts of solvent and electrolytes adsorbed onto the exchanger surface. We remove these difficulties by treating ion exchange systems as simple mixtures of solvent, electrolytes, and exchanger species, with no formal partitioning into phases. Through judicious choice of components, an integrable Gibbs‐Duhem relation is obtained that can be solved for the activity of any arbitrary exchanger species, requiring only reversibility of the system and measurable solvent and electrolyte activities. The theory is very general in principle and is applicable to variable‐ and permanent‐charge solid exchangers with positive and negative surface charge sites, in electrolyte environments containing any number of competing cation and anion species. In preliminary tests, the theory was used to calculate exchanger species activities and equilibrium constants from published data on binary and ternary NH4+‐Ba2+‐La3+ exchange in aqueous montmorillonite suspensions, for constant water potential conditions where the conventional two‐phase theory is also considered applicable. Results obtained with the mixture theory exhibited good internal consistency and were generally comparable to results obtained with the two‐phase theory.
Sulfate Retention by Kaolinitic Alfisols from Nigerian Savanna
Authors: Agbenin John O.
Published: July 2010

The low amount of available SO4 in savanna Alfisols necessitates investigation of mechanism of SO4 retention and availability in these soils. The study examines the mechanism and SO4 retention capacity of kaolinitic Alfisols from Nigerian savanna. Soil samples from 0‐ to 20‐cm depth from three cultivated plots and a native site were equilibrated with varying amounts of SO4 (0–0.003 M) in three supporting electrolytes, 0.01 M CaCl2, KCl, and NaCl, and three ionic strengths, 0.0 1, 0.1, and 0.2 M KCl at pH 5.6 ± 0.2, above the point of zero salt effect (PZSE) and point of zero net charge (PZNC) of the soils determined by potentiometric titration and ion adsorption method, respectively. The results of the study indicated that the soils had high SO4 retention capacity ranging from 15 to 17 mmol kg−1 soil, and the sorption isotherms were described by a modified Freundlich equation. Sulfate sorption was, however, not significantly affected by ionic composition and strength. If the forces of SO4 adsorption were simply electrostatic, increasing ionic strength would have significantly decreased SO4 adsorption above the PZSE or PZNC of the soils. The study suggested that SO4 retention by kaolinitic Alfisols might involve inner‐sphere complexation despite the difficulty of making mechanistic, molecular level interpretation from gross solution data of whole soils.