bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scale‐Dependent Correlations among Soil Properties in Two Tropical Lowland Rice Fields
Authors: Dobermann A. , Neue H. U. , Goovaerts P. 
Published: July 2010

AbstractLong‐term irrigated rice (Oryza sativa L.) cultivation is an important yet unstudied source of soil variation in tropical lowland rice fields. A field study was conducted to quantify spatial soil variability and to analyze correlations among soil properties at different spatial scales. Soil samples from the 0‐ to 20‐cm depth were collected from adjacent rice fields consisting of Typic Tropaquepts and Typic Tropaqualfs. Structural variogram analysis and factorial kriging (FKA) were used to describe the coregionalization of 14 soil properties. Coregionalization was described by a model comprising (i) a nugget effect, (ii) a spherical model with a range of 12 m, and (iii) a Gaussian model with a range of 36 m. Correlations among soil properties varied depending on spatial scale. Short‐range soil variation was caused by irrigation and land leveling, but results were not consistent for both fields. Similar autovariograms and high correlations between depth to the Cg horizon and extractable K in the Gaussian structure (ρ2uv = −0.95 to −0.99) revealed a strong influence of weathering of volcanic tuff on long‐range trends in K. Electrical conductivity (EC), Na, and B were spatially trended and correlated with depth to the Cg horizon (ρ2uv = 0.59–0.97) in the Gaussian structure. Subsurface water flow through cracks above an impermeable layer and surface water flow along the gentle field slope were sources of long‐range variation in EC, Na, and B caused by irrigation. The FKA provides quantitative measures of complex spatial process results and offers new ways for generating hypotheses about the phenomenon itself.
Light Nonaqueous‐Phase Liquid Movement in a Variably Saturated Sand
Authors: Oostrom M. , Hofstee C. , Dane J. H. 
Published: July 2010

AbstractNumerical simulations with the multifluid flow simulator STOMP are compared with quantitative results of a detailed lighter‐than‐water nonaqueous‐phase liquid (LNAPL) infiltration and redistribution experiment in a 1.67‐m‐long, 1‐m‐high, and 0.05‐m‐wide flow cell. The experiment was performed to test the ability of commonly used non‐hysteretic and hysteretic constitutive relations between relative permeability (k), fluid saturation (S), and capillary pressure head (h) to describe multifluid flow in two dimensions. The fluid and sand parameters necessary to apply the constitutive relations were obtained independently. The flow cell was filled with a homogeneous sand mixture under saturated conditions. After partial drainage of the sand, the LNAPL was slowly injected for 12 h from a small source area located at the surface. A dual‐energy gamma radiation system was used to determine LNAPL and water saturations at 255 locations during infiltration and redistribution. The results show a reasonable match between the experimental and numerical data, indicating that the constitutive relations used are adequate to describe relatively slow LNAPL infiltration and redistribution. The differences between the nonhysteretic and hysteretic simulations are small. This implies that hysteresis, a result of nonwetting fluid entrapment and pore geometry, was not important in this experiment.
Gypsum Solubility at Subzero Temperatures
Authors: Marion G. M. , Farren R. E. 
Published: July 2010

AbstractGypsum is an important mineral in many terrestrial and marine environments. Despite numerous studies that estimated the gypsum solubility product at temperatures ≥0°C, there are no estimates at temperatures <0°C. The objectives of this study were to estimate, for the temperature range from ‐25 to 25°C: (i) the gypsum solubility product and (ii) the Pitzer‐equation parameters needed to define Ca‐SO4 interactions to high solute concentrations (ionic strengths >10 M). The gypsum solubility product was extrapolated to subzero temperatures by integrating the vant's Hoff equation using a published equation for the standard enthalpy of reaction for gypsum. A least‐squares regression technique was developed to estimate eight temperature‐dependent Pitzer‐equation parameters that describe ion interactions among Ca, SO4, Na, and Cl. The calculated Pitzer‐equation parameters were in reasonable agreement with published values. Calculated gypsum activity products were independent of ionic strength to concentrations >17 M. The resulting Pitzer‐equation parameters coupled with gypsum solubility data fit the theoretical gypsum solubility product equation reasonably well. The calculated eutectic concentration and temperature for a pure gypsum solution are 0.01293 M and −0.06°C. Gypsum is a common mineral in many cold region soils. According to the current paradigm for seawater freezing, sulfate should exclusively precipitate as mirabilite; however, there is evidence that gypsum can also precipitate during seawater freezing. The parameters developed in this study will allow, for the first time, the theoretical exploration of mechanisms such as freezing on gypsum geochemistry.
Changes in Soil Microbial and Chemical Properties under Long‐term Crop Rotation and Fertilization
Authors: Omay A. B. , Rice C. W. , Maddux L. D. , Gordon W. B. 
Published: July 2010

AbstractWith renewed interest in maintaining our soil resources, it is important to establish criteria that can describe and quantify the effect of different crop management practices on soil organic matter (SOM). We conducted this study to assess changes in SOM and other soil properties after long‐term (>10 yr) continuous corn (Zea mays L.; CC) and corn‐soybean rotation [Glycine max (L.) Merr.; C/SB] with and without fertilizer. Soil samples were collected from two furrow‐irrigated CC and C/SB rotations on a Crete silt loam (fine, montmorillonitic, mesic Pachic Argiustoll) and a Eudora loam (coarse‐silty, mixed, mesic Fluventic Hapludoll). Long‐term (350‐d) laboratory incubation at optimum moisture and temperature conditions measured potentially mineralizable C (PMC) and N (PMN) as a measure of the active fraction of soil organic C and N. Microbial biomass C (MBC) and N (MBN), organic C and N, pH, and texture also were determined. Crop rotations that included high‐residue‐producing crops such as corn and addition of fertilizer increased soil organic C and N. Crop rotation did not affect PMC in the Crete soil, but addition of fertilizer significantly increased PMC by 32%. The PMN in both soils was not affected by crop rotation or fertilizer addition. Inclusion of soybean in the rotation decreased the stable and active fractions of organic C and N. Changes in soil organic C and N in response to crop rotation and fertilizer addition were related to the estimated amount of crop residues returned to the soil and to soil texture.
Mineralization of Selenium‐Containing Amino Acids in Two California Soils
Authors: Martens Dean A. , Suarez Donald L. 
Published: July 2010

AbstractOrganic forms of Se as the selenoamino acids, selenomethionine (SeMet) and selenocystine (SeCys), are detected in plants grown on seleniferous soil, yet little is known about the speciation and distribution of Se upon decomposition of SeMet and SeCys in soil. To determine the mineralization rate of selenoamino acids in soil, three concentrations of SeMet, SeCys, methionine (Met), or cystine (Cys) were added to samples of a Panoche (fine‐loamy, mixed [calcareous], thermic Typic Torriorthent) or a Panhill (fine‐silty, mixed, thermic Typic Haplargid) soil and aerobically incubated at 22°C for up to 168 h. The amino acid concentrations were analyzed by high performance anion chromatography. Methionine additions closely followed first‐order reaction kinetics and SeMet additions followed pseudo‐first‐order kinetics, with order dependent on SeMet concentration. The time required for 50% mineralization of SeMet additions in the Panhill and Panoche soils was 23.5 and 3.2 h (5 mg Se kg‐1), 41.6 and 15.5 h (25 mg Se kg‐1), and 47.1 and 36.0 h (50 mg Se kg‐1), respectively. The majority of the SeMet and Met additions were recovered as volatile species (50–80%). In contrast to SeMet, SeCys was rapidly nonextractable (<6 h) from both soils, with little to no volatile Se detected and was initially recovered as phosphate‐soluble selenite and selenide after 6 h of incubation. These results suggest that Se present in seleniferous plant tissue as SeMet will not accumulate in soil due to extensive volatilization. In contrast, additions of seleniferous plant residues rich in SeCys will result in organic Se mineralization to inorganic Se forms in soil.
Isotopic Study of Environmental Change from Disseminated Carbonate in Polygenetic Soils
Authors: Connin Sean L. , Chamberlain C. Page , Virginia Ross A. 
Published: July 2010

AbstractWe evaluated the extent to which δ13C and δ18O values of disseminated carbonate preserve a signal of Holocene and modern vegetation changes in polygenetic soils of the Jornada Basin, New Mexico. Factors and processes influencing carbonate chemistry were constrained in a relict grassland community and recent mesquite [Prosopis glandulosa var. torreyana (L. Benson) M. Johnston] dunes, using 14C dates and δ13C data of soil organic matter (SOM) as independent measures of site history. Total‐profile carbonate contents ranged from 39 to 451 kg m‐2 due to local patterns of soil water infiltration and erosion. In grassland soils, 14C ages and δ13C values of disseminated carbonate in A and B horizons were influenced by the presence of older detrital carbonate, reworked from surrounding surfaces. As a result, carbonate isotopes did not record mid‐Holocene climate and vegetation changes, which were inferred from δ13C values of coexisting SOM. Shrub expansion during the past century was recorded by changes in the δ13C values of disseminated carbonate and SOM from mesquite dunes. Carbon‐14 data and mass balance estimates indicated that at least 80% of the dune carbonate (in C horizons) has been isotopically altered by dissolution and recrystallization processes in <100 yr. The modern carbonate is apparently forming from soil waters composed of nearly equal amounts of summer and winter rainfall, as evidenced by carbonate δ18O values. Our analyses indicate that disseminated carbonate can provide a meaningful environmental signal in polygenetic soils, when pedogenic contributions to isotopic variability are constrained.
Surface Roughness Changes as Affected by Rainfall Erosivity, Tillage, and Canopy Cover
Authors: Eltz Flávio Luiz Foletto , Norton L. Darrell 
Published: July 2010

AbstractSurface roughness and canopy cover are important factors in preventing soil erosion. There is limited information on how soil surface roughness changes as a function of natural rainfall erosivity and canopy cover by plants. We hypothesized that canopy cover, tillage systems, and cumulative rainfall erosivity (CRE) would have unique effects on roughness. We tested this hypothesis on a Miami silt loam soil (fine‐silty, mixed, mesic Typic Hapludalf) using a portable laser microtopographer. Tillage treatments of conventional (moldboard plowing + disking), chisel plowing, and chisel plowing + dragging a chain produced three initial roughness levels. Surface cover was none (fallow) or soybean [Glycine max (L.) Merr.]. Random roughness (RR), standard deviation (SD), tortuosity (T), and fractal roughness functions, expressed by the fractal index (D) and the crossover length (l), were calculated from microtopography data. Chisel tillage had the greatest initial values of surface roughness, followed by chisel + chain and conventional tillage, as measured by the l index. All indices but D generally decreased with CRE. The RR and SD indices decreased quadratically with CRE, with decreases of 38 and 36%, respectively, from initial values after 200 units of CRE, while the T and l indices decreased exponentially, with decreases of 40 and 60%, respectively, from initial values after 200 units of CRE. Soybean cover lowered soil surface roughness 7% less than fallow, as measured by the l index. The l index was 50, 71, and 205% more sensitive to changes in CRE than RR, SD, and T indices, respectively. The fractal roughness functions, with D and l indices calculated, were the best approaches to characterize surface roughness at small scales, such as existing plant rows, mainly due to l index sensitivity to changes in CRE.
Electromelioration of a Sodic Horizon from an Illinois Natraqualf
Authors: Ahmad Efkar , Jones R. Lewis , Hinesly Thomas D. 
Published: July 2010

AbstractSodium‐enriched subsoils of Natraqualfs seriously limit crop production by impeding drainage on 150 000 ha in south‐central Illinois. We hypothesized that electromelioration of typical Natraqualf subsoils soils is feasible. Columns of natric material (subsoil of Huey silt loam, a fine‐silty, mixed, mesic Typic Natraqualf) were fitted with electrodes at either end of the column. Leachate generated by maintaining water at the column's top was collected at the bottom or cathodic end. Treatments were untreated soil or gypsum mixed with the natric material at rates of 38.5 and 77 Mg ha‐1. An additional column to which no potential was applied was prepared for each treatment. Fifty‐five volts direct current was maintained across the column, and current densities ranged from 0.04 to 0.35 mA cm‐2. Sodium leached rapidly from all treatments to which a potential was applied, but leachate was produced only in the treatment without potential and with the equivalent of 77 Mg ha‐1 of gypsum. Extractable Na reductions amounted to 96% in the column without added gypsum and 98% in each of the gypsum‐treated columns. Water required to leach Na was reduced by gypsum treatment from 138 cm for unamended columns to 84 and 55 cm for the 38.5 and 77 Mg ha‐1 treatments, respectively. Substantial changes in soil structure were observed at the end of the experiment. The power calculated to remove 96% of the extractable Na in 58 cm of natric material during 31 d of leaching amounted to 736 560 kW‐h ha‐1.
Rapid Determination of Hydraulic Conductivity in Clay Liners by Early‐Time Analysis
Authors: Odell B. P. , Groenevelt P. H. , Elrick D. E. 
Published: July 2010

AbstractTo predict the effects of water or leachate infiltration into unsaturated field soils requires measurements of both the field‐saturated hydraulic conductivity (Kfs) and the matric flux potential (ϕm). Measurement of these soil parameters commonly requires steady‐state infiltration rates, which, in the slowly permeable clay liners that are found underlying municipal landfills, can require several weeks or months to be attained. The transient, capillary‐dominated, early‐time method of determining Kfs and ϕm has been found to provide a much faster, yet still reliable estimate of these flow parameters. Here, an analytical solution was utilized for early‐time, one‐dimensional infiltration under the conditions of an initial constant head followed by a falling‐head phase. Six laboratory trials were conducted using precisely compacted clay cores to determine Kfs and ϕm during both early‐time and steady‐state flow domains. The results of these trials showed a favorable comparison between these two techniques, with the early‐time constant‐head and falling‐head methods producing Kfs estimates that were 60 and 75% of their respective steady‐state values. This suggests that the early‐time determination of Kfs and ϕm on slowly permeable media has a definite practical advantage over lengthy steady‐state analyses. A new, expeditious procedure for determining steady‐state Kfs values of highly compacted soil cores, involving use of a Mariotte‐equipped pressure plate chamber, was also developed and validated.
Modeling Mass Transfer Processes in Soil Columns with Pore‐Scale Heterogeneity
Authors: Haggerty Roy , Gorelick Steven M. 
Published: July 2010

AbstractRemoval of dissolved organic compounds from natural porous media is rate limited by multiple, simultaneous mass transfer processes, including slow diffusion from immobile zones of varying sizes and shapes, and rate‐limited sorption. We examined the variability in mass transfer rates and quantified the effects of multiple, simultaneous mass transfer processes on unsaturated column experiments using a diffusion model with a statistical distribution of diffusion rate coefficients. We examined the validity of conventional first‐order mass transfer and diffusion models to represent mass transfer in subsurface systems and compared this with a diffusion model with a lognormal distribution of diffusion rate coefficients. The main conclusions of our work are: (i) even in relatively homogeneous porous media, extreme variability (exceeding four orders of magnitude) in diffusion rate coefficients (Da/a2) must be invoked to represent mass transfer in the experiments we examined; (ii) models using a lognormal distribution of diffusion rate coefficients, while employing only one more mass transfer parameter than conventional models, generally represent mass transfer much better; (iii) single‐rate‐coefficient models (either first‐order or diffusion) very poorly represent mass transfer in all experiments examined, although some of this failure is attributed to our use of a linear isotherm; (iv) models with two diffusion rate coefficients, although containing twice as many estimated parameters, also offer poor representations of mass transfer.
Time Domain Reflectometry Measurements of Nitrate Transport in Manure‐Amended Soil
Authors: Nissen H. H. , Moldrup P. , Henriksen K. 
Published: July 2010

AbstractTo obtain more detailed information about N processes in agricultural soils, nondestructive measurement techniques with high spatial and temporal resolution are needed. The ability of time domain reflectometry (TDR) in combination with small polysulfone hollow fiber (PHF) solution samplers to follow NO−3 production and transport in soil fertilized with cattle slurry and exposed to different rainfall events was investigated. The experiments were conducted in minilysimeters using a coarse sandy soil and two different slurry application methods: (i) surface application followed by harrowing (homogenous incorporation) or (ii) direct injection (incorporation as a manure string). Comparison between soil‐water electrical conductivity (ECw) obtained with TDR and the sum of NO−3 and Cl− concentrations in the soil water measured with solution samplers showed a good agreement both with respect to concentration levels and temporal and spatial development. Except for an initial leaching of the natural ion content in the soil water when water application was started, NO−3 released from the manure was the dominating anion in the soil water and changes in NO−3 corresponded well to changes in ECw. Both slurry and water application strategy had a large effect on the temporal development in nitrification and NO−3 leaching. In the case of homogeneously incorporated slurry and constant water application for 3 wk, NO−3 formation and leaching started after 4 to 5 d, while it started after 9 to 10 d in the case of directly injected slurry. If water was applied only in the last (third) week to the directly injected slurry system, a large amount of the NH+4 in the slurry was oxidized to NO−3 before water application and subsequently leached. The TDR measurements of ECw with high spatial and temporal resolution combined with a few measurements of ion concentrations by PHF solution samplers is a new, valuable method for analyzing turnover and transport of nonconservative ions in soil.
Soil Dissolved Organic Matter Sorption as Influenced by Organic and Sesquioxide Coatings and Sorbed Sulfate
Authors: Kaiser Klaus , Zech Wolfgang 
Published: July 2010

AbstractThe sorption of dissolved organic carbon (DOC) and its fractions as influenced by organic C (OC), sesquioxides [amorphous Al(OH)3, ferrihydrite, goethite], and extractable SO2−4 was investigated by modifying the properties of the Bs horizon of an Entic Haplorthod. Coating the Bs material with OC extracted from the Oa horizon of a mor forest floor layer decreased the sorption of total DOC. The effects on the sorption of the hydrophobic DOC fraction were little, whereas the sorption of the hydrophilic fraction was strongly reduced. At the highest OC coating levels, a net release of hydrophilic DOC occurred, indicating a displacement of indigenous hydrophilic substances from the soil by the sorbing hydrophobic dissolved organic matter (DOM). Coating of the soil material with sesquioxides clearly increased the sorption of DOC and its fractions. The strongest effects occurred when amorphous Al(OH)3 was added, followed by ferrihydrite and goethite. Increased contents of extractable SO2−4 did not affect the sorption of DOC on soil material. With increasing addition of DOC, however, the concentrations of SO2−4 in the equilibrium solution increased. Adsorbing DOM seems to displace SO2−4 bound to soil materials. Thus, DOM shows a higher affinity to sorb on soil material than SO2−4.
Sorption of Atrazine and Simazine by Model Associations of Soil Colloids
Authors: Celis R. , Cornejo J. , Hermosín M. C. , Koskinen W. C. 
Published: July 2010

AbstractThe effect of association processes between single model soil components (i.e., Ca‐saturated montmorillonite [CaSWy], ferrihydrite [Ferrih], and soil and commercial humic acid [HA]) upon their association in binary and ternary CaSWy‐Ferrih‐HA systems on physicochemical properties (specific surface area, pH, and basal spacing) and on triazine herbicide sorptive behavior was determined. Ferrihydrite coatings on CaSWy increased the specific surface area of the clay and slightly decreased pH, whereas HA coatings on CaSWy and Ferrih decreased both specific surface area and pH. Further association of HA with the CaSWy‐Ferrih binary system decreased the specific surface area, but did not change the pH. Atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) and simazine (2‐chloro‐4,6‐bis(ethylamino)‐s‐triazine) sorption‐desorption data showed that the sorptive behavior of the associations is not the simple sum of the sorption on single components. The HA association with CaSWy increased sorption of both herbicides by the clay, as suggested by an increase in sorption capacity (Koc) for the CaSWy‐HA binary system. Although Ferrih did not sorb either triazine, Ferrih coatings on CaSWy increased sorption of both herbicides on the clay. The association of HA with Ferrih sorbed both triazines, but Koc decreased compared with HA alone. Further association of the CaSWy‐Ferrih binary system with soil HA decreased the sorption, whereas association with commercial HA increased it. Desorption isotherms of atrazine and simazine showed that sorption by the model associations was reversible.