bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thirty‐Year Crop Rotations and Management Practices Effects on Soil and Amino Nitrogen
Authors: Campbell C. A. , Zentner R. P. , Knipfel J. E. , Schnitzer M. , Lafond G. P. 
Published: July 2010

AbstractMethods of assessing how agronomic practices influence soil productivity and sustainability are required. The effects of various agronomic practices on soil organic N and hydrolyzable amino N in a Udic Haploboroll were determined in a long‐term (30‐yr) crop rotation study at Indian Head, Saskatchewan. Practices assessed included fertilization, fallowing frequency, green manuring, and inclusion of a grass‐legume forage crop in predominantly spring wheat (Triticum aestivum L.) systems. Fertilization, green manuring, or inclusion of a grass‐legume hay crop significantly (P < 0.10) increased soil and amino N (amino acid N plus amino sugar N), particularly as fallowing frequency was reduced. When the relative molar distribution of the amino acids was used to assess changes in soil organic‐N quality, significant and consistent increases in aspartic acid and decreases in arginine and leucine were observed; however, the differences were mainly associated with the 6‐yr mixed and fertilized continuous wheat (Cont W) rotations. Comparison of our N‐concentration results with an estimate of the initial (1958) N concentration suggests that all fallow‐containing monoculture wheat rotations and unfertilized Cont W have failed to maintain soil N, the unfertilized 3‐yr legume green manure‐wheat‐wheat system has maintained soil N, while the 6‐yr fallow‐cereal‐hay (grass‐legume) and fertilized Cont W systems have increased soil N. Hydrolyzable amino N was only marginally more effective than Kjeldahl N for describing changes in soil organic‐matter quality.
Sulfate, Aluminum, Iron, and pH Relationships in Four Pacific‐Northwest Forest Subsoil Horizons
Authors: Xue Dongsen , Harrison Robert B. 
Published: July 2010

AbstractSulfate‐adsorbing soils typically have a characteristic pH level at which maximum SO4 adsorption occurs, with the critical pH value depending on the properties of the individual soil. This study was conducted partially to determine the pH of maximum SO4 adsorption of SO4‐adsorbing forest subsoil horizons from the Pacific Northwest. In addition, the relationships between pH, SO4 adsorption and SO4, Fe, and Al release were also studied. Subsoil horizons from three Washington State Spodosols, Chinkmin (loamy‐skeletal, mixed, ortstein Typic Cryohumod), Barneston (sandy‐skeletal, mixed, mesic Typic Haplorthod), and Alderwood (loamy‐skeletal, mixed, mesic, ortstein Aquic Haplorthod) soil series, and one Alaska Inceptisol (unknown soil series) were studied. Soil properties that have previously been shown to be correlated with SO4 adsorption were also determined, including pH, cation‐exchange capacity (CEC), exchangeable cations, particle‐size distribution, soil C, and oxalate‐ and pyrophosphate‐extractable Al and Fe. In the three Washington subsoils, SO4 adsorption increased with decreasing pH until about pH 4.0, then decreased with further reductions in pH. A peak adsorption level of about 3.0 mmol kg−1 was observed in these three subsoils. Increasing release of Al and Fe was seen with decreasing pH levels below 4.0. The subsoils continued to adsorb SO4, even after amounts of Al higher than total oxalate extractable levels were solubilized, indicating that this fraction does not contain all of the SO4‐adsorbing sites. The Alaska subsoil showed the same general trend, but had a SO4‐adsorption peak of 1.7 mmol kg−1 at about pH 2.0, and had a much higher relative release of Fe compared with Al than observed in the Washington state subsoils. It was concluded that protonation of Al oxyhydroxide surfaces was probably responsible for increases in SO4 adsorption with decreasing pH, while the solubilization and destruction of these surfaces was responsible for decreasing SO4 adsorption below pH 4.0 in the Washington subsoils.
Equation for Extending Water‐Retention Curves to Dryness
Authors: Ross P. J. , Williams J. , Bristow K. L. 
Published: July 2010

AbstractSimple water‐retention functions in current use do not predict zero water content at oven dryness. Using the Campbell equation θ = a ψ‐c = θs (ψ‐c − ψ‐c0) relating volumetric water content, θ, to matric suction, ψ, as an example, we examined a modification to ensure that the curve terminates in a suction ψ0 = 1000 MPa, approximating oven dryness. The new equation is θ = a(ψ‐c − ψ‐c0) = θs (ψ‐c − ψ‐c0)/(ψ‐cc − ψ‐c0. It was compared with the unmodified equation by fitting to water‐retention data from Australia, the UK, and the USA. Results showed not only that the new equation fit the data slightly better than the original equation, with a mean standard deviation of 0.014 m3 m−3 about the regression, but also that its parameters could be calculated from those of the unmodified equation if original water‐content data were unavailable for fitting. Although lack of data hampered assessment of its predictions of water content in dry soils, its use appears preferable to extrapolating the unmodified equation.
Electron Spin Resonance Study of Copper Ion Complexation by Glyphosate and Related Ligands
Authors: McBride Murray B. 
Published: July 2010

AbstractGlyphosate (N‐phosphonomethylglycine) forms chelates with multivalent cations in aqueous solution, yet no detailed electron spin resonance (ESR) study of Cu‐glyphosate complexation has been conducted to date. In this study, the ESR spectra of Cu2+ complexes with glyphosate, iminodiacetic acid, and aminomethylphosphonic acid were obtained for aqueous solutions at room temperature and liquid N2 temperature in order to detail the coordination chemistry of these complexes. The Cu2+/ligand mole ratios as well as pH were varied to determine the effect on the ESR spectrum. These spectroscopic results were compared with speciation calculations based on stability constants from published potentiometric data in order to make reasonable assignments of the ESR spectra to particular Culigand complexes. The degree of complexation of aqueous Cu2+ estimated by ESR was in approximate agreement with that calculated from the published stability constants. The most reasonable interpretation of the ESR spectra pointed to the existence of both 1:1 and 2:1 ligand‐Cu complexes in which the amine N occupied one and two equatorial coordination positions, respectively. The carboxylate group complexed in preference to phosphonate in equatorial positions, and coordination at the axial positions in the 2:1 complexes was suggested. The spectra also suggested that the protonated 1:1 Cu‐ligand complexes were bonded via the amine N, indicating that proton addition was at carboxylate or phosphonate groups. The results indicated that Cu2+ bonded strongly to the amine groups, and by weaker forces to the carboxylate and phosphonate groups. Glyphosate was able to mobilize exchangeable Cu2+ on clays, forming uncharged or anionic complexes that diffused into solution.
Tillage and Cover Crop Management Effects on Soil Water and Corn Yield
Authors: Ewing R. P. , Wagger M. G. , Denton H. P. 
Published: July 2010

AbstractSubsoiling to alleviate compacted soil zones and planting cover crops to conserve soil water are accepted practices, but information regarding potential interactions between the two is limited. This study was designed to assess the effects of subsoiling and cover‐crop management on soil water availability and corn (Zea mays L.) grain yield on Coastal Plain soils known to be responsive to in‐row subsoiling. The experiment was conducted on a Norfolk loamy sand in 1985 and a Norfolk sand in 1986, both in the family of fine‐loamy, siliceous, thermic Typic Kandiudults. Factors evaluated were subsoiling, cover crop (fallow or crimson clover [Trifolium incarnatum L.]), primary tillage (chisel plow or no‐tillage) within fallow, and top‐growth removal of crimson clover. Compared with fallow treatments, crimson clover depleted soil water in the surface 15 cm before corn planting by 28% in 1985 and 55% in 1986. Corn grain yield was reduced in the presence of crimson clover by 0.5 Mg ha−1 in 1985 and 0.9 Mg ha−1 in 1986. In 1985 only, grain yield reduction in the presence of crimson clover was entirely overcome by subsoiling. Averaged across cover crop and primary tillage factors, subsoiling increased grain yields by 25% (1.3 Mg ha−1) in 1985 and 86% (1.9 Mg ha−1) in 1986. Increased yields due to subsoiling were attributed to greater use of subsoil water by the corn crop. These results suggest that cover‐crop desiccation should occur 7 to 10 d prior to corn planting to minimize the effects of soil water depletion under dry, early‐spring conditions. Additionally, in‐row subsoiling should be used on similar Coastal Plain soils responsive to deep tillage, irrespective of cover‐crop use.
Soil Properties after Twenty Years of Fertilization with Different Nitrogen Sources
Authors: Stone Darusman, L. R. , Whitney D. A. , Janssen K. A. , Long J. H. 
Published: July 2010

AbstractIncreased use of N fertilizers during the past 30 yr has been accompanied by a growing concern about their possible negative influence on soil properties. In 1969, research plots were established with fertilizer‐N source the treatment variable (NH3, NH4NO3, urea, urea‐NH4NO3 solution, and a no‐N check). In October 1988, we sampled the field plots and then examined the status of selected soil physical and chemical properties. Our objective was to determine if differences existed in soil properties between the N‐fertilized plots and the no‐N check or among the four N‐source treatments after 20 annual applications of N. For the soil properties evaluated, we found no significant difference among the four N‐source treatments. The 20 yr of N fertilization reduced soil pH significantly, compared with the no‐N check, in the surface (0.06‐0.14‐m) soil layer (pH 5.2 vs. 6.2). Nitrogen fertilization caused an increase in micronutrients (Fe, Cu, and Mn) and a decrease in available P and exchangeable bases (Ca, Mg, and Na). Compactibility analyses revealed no significant difference in either maximum bulk density or optimum water content for compaction among treatments. Our results show the primary effects of 20 yr of N application have been increased soil acidification and associated changes in nutrient availabilities and increased concentrations of NO−3‐N and NH+4‐N.
Phosphate Transport in Calcium‐Saturated Systems: I. Theory
Authors: Cho C. M. 
Published: July 2010

AbstractA theory of diffusive transport of orthophosphate in a Ca2+‐saturated cation‐exchange resin medium with free CaCO3 was formulated based on a model in which the cation of the applied phosphate salt replaced the exchangeable Ca2+ on the exchange complex, and this Ca2+ reacted with phosphate to precipitate CaHPO4. The precipitation reaction produced H+ ions, lowering the pH and affecting the relative distribution of H2PO−4, HPO2−4, HCO−3 and CO2−3 in solution. The local pH caused either the precipitation or dissolution of CaCO3, thus affecting the concentration of Ca2+. Four transport equations, one each for the displacing cation, displaced Ca2+, phosphate, and H+, were necessary to describe the phosphate transport. The analyses indicated that the phosphate transport was retarded due to the precipitation of phosphate as CaHPO4 in Ca‐saturated cation‐exchange media. The magnitude of CaHPO4 precipitation was dependent on phosphate concentration, CEC, pH, and solid CaCO3. In the presence of solid CaCO3, the H+ produced reacted with CaCO3 to supply Ca2+ to the solution, which in turn reacted with phosphate and produced H+. The buffering effect of the media, due to OH−, HCO−3, CO2−3, the cation‐exchange reaction, and solid CaCO3, was found to be important in controlling the media pH, which was primarily responsible for the ionic composition of the system. The proposed theory assumed that the phosphate ion and the displaced or dissolved Ca2+, both of which were mobile, interacted with each other. Consequently, the interaction of phosphate was not restricted to the solid surface. In addition, the amount of locally immobilized phosphate was not restricted to an arbitrary value such as maximum adsorption capacity.
Kinetics of Soil Chemical Reactions: Relationships between Empirical Equations and Diffusion Models
Authors: Aharoni Chaim , Sparks Donald L. , Levinson Sarah , Ravina Israela 
Published: July 2010

AbstractA variety of kinetic equations such as zero‐order, first‐order, second‐order, Elovich, fractional‐power, and parabolic‐diffusion equations have been used to describe the kinetics of soil chemical processes. Often, several of these expressions seem to equally well describe the kinetics of a particular reaction. In this research, it is shown that the kinetics of phosphate sorption/release can be described by an expression that is approximated at beginning times by a fractional‐power equation, at intermediate times by the Elovich equation, and at long times by an apparent first‐order equation. Such kinetics, which can be characterized by a sigmoidal z(t) plot of the reciprocal of the rate against the time [(dq/dt)−1 vs. t], are consistent with theoretical homogeneous and heterogeneous models based on diffusion of the sorbate in the solid phase or at the solid/liquid interface. These models were applied to data from the published literature on sorption and release of phosphates by soils. For some soils, the experimental results were accounted for by assuming a constant diffusion coefficient. For other soils, it was assumed that diffusion processes with various diffusion coefficients take place simultaneously. Using these models, diffusion parameters can be estimated.
Selenium Mobility and Distribution in Irrigated and Nonirrigated Alluvial Soils
Authors: Fio John L. , Fujii Roger , Deverel S. J. 
Published: July 2010

AbstractDissolution and leaching of soil salts by irrigation water is a primary source of Se to shallow groundwater in the western San Joaquin Valley, California. In this study, the mobility and distribution of selenite and selenate in soils with different irrigation and drainage histories was evaluated using sorption experiments and an advection‐dispersion model. The sorption studies showed that selenate (15–12400 µg Se L−1) is not adsorbed to soil, whereas selenite (10–5000 µg Se L−1) is rapidly adsorbed. The time lag between adsorption and desorption of selenite is considerable, indicating a dependence of reaction rate on reaction direction (hysteresis). Selenite adsorption and desorption isotherms were different, and both were described with the Freundlich equation. Model results and chemical analyses of extracts from the soil samples showed that selenite is resistant to leaching and therefore can represent a potential long‐term source of Se to groundwater. In contrast, selenate behaves as a conservative constituent under alkaline and oxidized conditions and is easily leached from soil.
Field Evaluation of Four Methods for Measuring Denitrification
Authors: Aulakh M. S. , Doran J. W. , Mosier A. R. 
Published: July 2010

AbstractReliable and direct monitoring of in situ denitrification N loss will aid understanding of the N cycle and development of efficient agricultural management systems. The objective of this research was to evaluate four approaches for measuring denitrification in the field. A method using coated CaC2 as a source of acetylene (C2H2) to block N2O reduction was compared with two existing C2H2 methods and a 15N method. Use of CaC2 granules in soil around gas‐measuring chambers produced soil atmospheric C2H2 concentrations comparable to those observed with continuous C2H2 flow through diffusion tubes, which were sufficient to inhibit N2O reduction for a 48‐h period. Acetylene concentrations in the soil atmosphere exceeded 1.0 mL L−1 and completely inhibited the reduction of N2O to N2, giving N2O‐N recoveries of 105 ± 7% of total denitrification. Daily denitrification rates (two gas samplings each day) and total N emissions over 4 d were comparable for 15N chamber, C2H2‐inhibition chamber, and CaC2‐C2H2‐inhibition chamber methods but were five‐ to sevenfold higher for the C2H2 inhibition method using intact soil cores. Where N‐gas flux was measured four times daily in chambers and intact soil cores, denitrification rates were associated with daily changes in soil temperature and decreases in soil water‐filled pore space (WFPS) in chamber soils due to evaporation/percolation. Either of three chamber methods may be used for measuring field denitrification, provided daily variation in gas‐N flux is considered in choosing sampling times. To avoid overestimation of denitrification using the acetylene‐inhibition soil‐core method, fresh intact soil cores should be taken daily to simulate field soil physical conditions, especially soil WFPS.
Spatial Variability of Nitrogen‐15 Natural Abundance
Authors: Sutherland R. A. , van Kessel C. , Pennock D. J. 
Published: July 2010

AbstractThe primary objective of this study was to investigate the spatial variability of 15N natural abundance (δ15N) in a non‐N2‐fixing plant (Triticum aestivum L.) on two fields. Two center intersecting 50‐point perpendicular transects were sampled on two separate fields, on Klassen (Udic Boroll) and Kruger (Typic Boroll) soils in Saskatchewan, Canada. Autocorrelation and semivariograms were used to assess the spatial structure of δ15N. Data from the Klassen field indicated that variation in grain δ15N was random, with no spatial structure at the scale of investigation (2–50 m). The pooled mean grain δ15N value and 95% confidence band was 5.43 ± 0.10‰, with a coefficient of variation of 8.9%. Observed variability in δ15N was primarily accounted for by analytical error in the Klassen field. The range in δ15N values for Klassen was 2.80‰, and the maximum difference between samples separated by 2 m was 2.00‰. These data indicate that, even in a low‐variability field, site‐to‐site variation may be significant. Thus, N2‐fixing plants should be grown in close proximity to the reference crop for quantifying N2 fixation. Spatial variability in δ15N for the Kruger field was significantly greater than in the Klassen field. Anisotropy was noted in δ15N in the Kruger field, with a pure nugget effect observed for one transect; for the other, a spherical model described the semivariance pattern with a range for spatial dependence of 16 m. The coefficient of variation and the minimum sample size required for estimating δ15N were corrected for the influence of serial correlation. Mean grain δ15N values for the two Kruger transects were 4.45 ± 0.13‰, and 4.29 ± 0.11‰. It is hypothesized that the greater variability in grain δ15N in the Kruger field resulted from a shorter lag time between fertilizer‐N application and sampling, that is 1.3 yr at Kruger, and 4 yr at Klassen.
Method to Determine Guaiacol Oxidase Activity in Soil
Authors: Nannipieri Paolo , Gelsomino Antonio , Felici Marcello 
Published: July 2010

AbstractA precise and sensitive method to assay guaiacol oxidase activity in soil is needed. The objective of this study was to set up this method by determining residual guaiacol spectrophotometrically after its extraction from soil with 0.5 M NaOH and 1 M CaCl2 and its separation from reaction products and humic molecules of the soil extract by high‐performance liquid chromatography (HPLC). A soil sample sterilized by autoclaving was used as a control. The rate of guaiacol oxidation reached the highest value at pH 4.5 to 6.0. The reaction rate of the enzyme approached zero‐order kinetics when the substrate concentration was 50 mM. Disappearance of guaiacol was linear with time for at least 1 h. The optimal temperature for guaiacol oxidation activity occurred at 60°C. Guaiacol oxidase activity was significantly correlated with soil total N.
Corn Root Distribution as Affected by Tillage, Wheel Traffic, and Fertilizer Placement
Authors: Kaspar T. C. , Brown H. J. , Kassmeyer E. M. 
Published: July 2010

AbstractInformation concerning early‐season corn (Zea mays L.) root distribution is needed so that fertilizer can be positioned to maximize root interception. The objective of this study was to examine corn root distribution as affected by tillage system, wheel traffic, and fertilizer placement. The study site was near Marshalltown, IA, on two silty clay loams, a Muscatine (fine‐silty, mixed, mesic Aquic Hapludoll) and a Tama (fine‐silty, mixed, mesic Typic Arguidoll). Three tillage systems (no‐till, ridge‐till, and chisel plow) with controlled traffic and two fertilizer‐placement treatments (in‐row and midpoint of the 76‐cm interrow) were investigated. Root length, root weight, and root weight/length ratio were determined between 36 and 40 d after planting from 10‐cm‐diam. soil core samples taken in rows and in interrow centers to a depth of 30 cm. Wheel‐traffic compaction and fertilizer placement altered corn root distribution, regardless of tillage system. The upper 15 cm of interrows with wheel‐traffic compaction had less than one‐half the root length (1.27 km m−3) and root weight (19 g m−3) of untracked interrows (3.88 km m−3 and 49 g m−3, respectively). Root length and weight increased and root weight/length ratio decreased in either interrow or row positions when fertilizer was placed there. Placing fertilizer in an untracked interrow increased root length from 2.57 to 5.20 km m−3. Tillage system affected only root growth in untracked interrows. Because root growth in wheel tracks is restricted, fertilizer‐use efficiency might be improved by not placing fertilizer in wheel tracks.
Timber Harvest Trafficking and Soil Compaction in Western Montana
Authors: Cullen Stephen J. , Montagne Cliff , Ferguson Hayden 
Published: July 2010

AbstractLittle evidence is documented regarding the effects of timber‐harvest traffic on volcanic‐ash‐mantled glacial till soils and clay‐rich Tertiary volcanic‐derived soils of northwestern Montana. We identified and characterized differences in the soil physical properties between trafficked and nontrafficked areas. Soil‐clod bulk density, infiltration, and soil‐clod water retention were measured on 54 pedons from nontrafficked and moderately and severely trafficked sites. Soil mechanical properties were characterized using 18 nontrafficked pedons. Compared with nontrafficked areas, bulk densities in severely trafficked areas at the 15‐cm depth were 76, 21, and 21% greater in ash over limestone till, ash over quartzite till, and Tertiary volcanic soils, respectively. Water retention at 0.002, 0.010, and 0.033 MPa was significantly lower at the 15‐cm depth in trafficked than in nontrafficked areas of ash over limestone till. Similar differences were observed in ash over quartzite till. Compared with nontrafficked areas, cumulative 1‐h infiltration in severely trafficked areas was 81% less in ash over limestone till, 79% less in ash over quartzite till, and 87% less in Tertiary volcanic soils. Similar but smaller differences were detected in moderately trafficked areas. Three independent measurements demonstrated significant differences in surface horizon physical properties between trafficked and nontrafficked areas. We detected significant physical manifestations of traffic‐induced soil compaction below 30 cm.