bluuebunny/crossref_metadata_2025 huggingface dataset:
Broadcast and Subsurface‐Banded Urea Nitrogen in Urea Ammonium Nitrate Applied to Corn
Authors: Maddux L. D. , Barnes P. L. , Raczkowski C. W. , Kissel D. E.
Published: July 2010

Lower yields of corn (Zea mays L.) have been reported in northeastern Kansas when urea ammonium nitrate (UAN) solution is broadcast incorporated rather than subsurface banded. Broadcast incorporated and subsurface‐banded 15N‐tagged urea in UAN were evaluated in 1982 and 1983 for N uptake by irrigated corn and N immobilization by a Eudora silt loam (coarse‐silty, mixed, mesic Fluventic Hapludoll). Uptake of N in corn plant components and residual inorganic and immobilized tagged urea N were measured, and an N balance calculated. Recovery of tagged urea N by all plant components was 61 and 68% for banded UAN in 1982 and 1983, respectively, but only 39 and 44% for broadcast incorporated UAN. The amount of tagged urea N immobilized in the top 90 cm of the soil profile was 58 and 14% greater with the broadcast incorporated than with the banded treatment for 1982 and 1983, respectively. Tagged urea N that was unaccounted for was 62 and 200% greater, respectively, for the 2 yr with the broadcast than with the banded applications. The difference in unaccounted‐for tagged N between treatments was attributed to variations in loss by leaching. The differences in uptake of tagged urea N were attributed to a combined effect of greater soil immobilization and loss by leaching with the broadcast incorporated application.
Hydraulic Resistance of Soil Surface Seals in Irrigated Furrows
Authors: Segeren Antonius G. , Trout Thomas J.
Published: July 2010

Soil surface seals resulting from overland flow in irrigation furrows reduce infiltration rates. A method was developed to quantify the hydraulic resistance of furrow seals. Infiltration was measured with a recirculating infiltrometer on two southern Idaho soils, Portneuf silt loam (coarse‐silty, mixed, mesic Durixerollic Calciorthid) and Bahem loam (coarse‐silty, mixed, mesic Xerollic Calciorthids). Surface sealing was prevented on half the furrow test sections with cheesecloth laid on the furrow perimeter. Subseal soil‐water potential was measured with a recording tensiometer. A two‐dimensional finite‐difference infiltration model with measured flux as the wetted perimeter boundary condition calculated matric potential directly beneath the seal. Seal resistance was then calculated by Darcy's law from the measured flux and calculated potential. Surface sealing on the bare furrows decreased infiltration by an average of 46% compared with the cloth‐covered furrows. The seal conductivity values, based on a constant seal thickness, decreased rapidly during the initial 100 min and reached 0.1 to 8% of the conductivity of the soil underlying the seal after 300 min. Potential gradients across the seal were inversely related to infiltration rate and the conductivity of the seal. The procedure successfully calculated seal conductivity changes with time and can be used to evaluate the effects of management practices on seal formation.
Noncrystalline Phosphates in Florida Phosphatic Soils
Authors: Wang H. D. , Harris W. G. , Yuan T. L.
Published: July 2010

Six Florida soils formed over phosphoritic deposits were analyzed by horizon to verify the presence of noncrystalline P and to determine the P forms associated with Ca, Fe, and Al. Each soil contained only one phosphate mineral, as detectable by x‐ray diffraction (XRD): carbonate‐fluorapatite, wavellite, or crandallite. Some horizons contained no detectable crystalline P, despite the presence of appreciable total P. Quantities of fluorapatite and wavellite, determined by XRD and thermal analysis, respectively, were insufficient to account for total P. Higher proportions of noncrystalline P near the surface were substantiated by a decrease in ratios of oxalate‐extractable P to total P with depth. Oxalate‐extractable P was higher for most samples than for standard minerals. Oxalate was more effective than dithionite‐citrate‐bicarbonate (DCB) in extracting P associated with Al, but DCB extracted more P associated with Fe. Endothermic differential scanning calorimetry peaks (90–100°C) were reduced in size or eliminated by oxalate or DCB extractions, suggesting that the peaks originated from the dehydration of noncrystalline Al and Fe with which some P could be associated. The fraction of total P extracted by soil‐testing reagents (Mehlich I and Olsen) was generally higher for horizons containing appreciable noncrystalline P associated with Al and Fe. Crandallite was resistant to dissolution by all extractants.
Kinetics of Sulfate Retention on Soil as Affected by Solution pH and Concentration
Authors: Schnabel R. R. , Potter R. M.
Published: July 2010

Knowledge of the time dependence of chemical retention by soil is crucial to a full understanding of how retention is affected by solution variables and to accurately simulate the fate of soil‐applied chemicals. The kinetics of SO2‐4 retention by and release from soil were examined in a continuously stirred reactor tank. The concentration‐time histories were processed with a number of commonly used kinetic equations. Of those tested, an equation that was first order in available retention sites consistently gave the best fit to the data. Sulfate‐retention kinetics were strongly influenced by SO2‐4 concentration and the presence of PO3‐4 in solution, but unaffected by a change in pH from 3 to 4. For example, when SO2‐4 concentration was doubled from 0.313 to 0.625 mM in the retention phase of the experiment, the average first‐order forward rate constant increased from 0.07 to 0.24 min−1. The addition of PO3‐4 to the solution increased the forward rate constant to 0.13 min−1 and decreased equilibrium retention from 8.1 mmol/kg when PO3‐4 was not present to 5.2 mmol/kg. In the release phase of the experiment, the presence of PO3‐4 increased the estimated reverse rate constants by an order of magnitude, and an even greater increase in the reverse rate constant was estimated when the initial sulfate concentration was increased from 0.313 to 0.625 mM. Although the data was closely approximated by first‐order kinetics, changes in the rate coefficients for the different influent solutions indicate that commonly determined kinetic parameters have limited applicability beyond the particular conditions of the experiment.
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

Methods 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

Sulfate‐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

Simple 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

Glyphosate (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

Subsoiling 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

Increased 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

A 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

A 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

Dissolution 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

Reliable 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

The 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

A 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

Information 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

Little 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.
Morphologic Development and Clay Redistribution in Lysimeter Soils under Chaparral and Pine
Authors: Graham R. C. , Wood H. B.
Published: July 2010

Lysimeter soils under 41‐yr‐old stands of chaparral species and a pine (Pinus coulteri B. Don) were studied to determine the biotic influence on soil morphologic development. The large (5.3 by 5.3 by 2.1 m) unconfined lysimeters at the San Dimas Experimental Forest in southern California were filled in 1937 with homogenized fine sandy loam soil material derived from diorite. After a 9‐yr stabilization period, the lysimeters were planted with monocultures of species common to California chaparral ecosystems. The species represented, each on a separate lysimeter and its surrounding buffer zone, are scrub oak (Quercus dumosa Nutt.), ceanothus (Ceanothus crassifolia Torr.), chamise (Adenostoma fasciculatum Hook. & Arn.), and Coulter pine. The soils were described and sampled in triplicate in 1987. Differences in earthworm (including Aporrectodea trapezoides Dugés and Allolobophora chlorotica Savigny) activity were related to plant species and played a major role in differentiating the soils. Earthworm activity under scrub oak and ceanothus produced A horizons (7 and 2 cm thick, respectively), composed largely of worm casts, that were darker and enriched in clay compared with underlying C horizons and archived fill material. Earthworm activity was minimal under chamise, and relatively little morphologic development was apparent. The soil under pine, where earthworms were absent, had a clay‐depleted A horizon (1 cm thick) and Bt horizons with sufficient clay increase, illuviation argillans, and thickness to qualify as an argillic horizon. Mixing and sorting of soil by earthworms has acted against argillic horizon development under the other plant species.
Polyacrylamide to Improve Water Flow and Salt Removal in a High Shrink‐Swell Soil
Authors: Malik M. , Amrhein C. , Letey J.
Published: July 2010

Reclamation of salt‐affected high shrink‐swell soils using chemical amendments combined with deep loosening and tile drainage is very expensive. As an alternative, the utilization of cracks as pathways for water and salts is possible if these cracks could be stabilized by the application of a polyacrylamide (PAM) polymer and their complete closure prevented upon rewetting. A laboratory column study was conducted on two soil samples with exchangeable sodium percentages (ESP) of 8 and 25 from a heavy‐textured, swelling soil. The soil samples were packed into columns, ponded with irrigation water for 24 h, then drained and dried to create cracks. After drying, the soil samples were ponded for 24 h with irrigation water containing 0, 25, 75, and 200 mg L−1 of an anionic polyacrylamide polymer, allowed to drain, and dried. The treated soils were then ponded without drainage for 1, 6, 12, and 24 h to allow crack closure and the hydraulic conductivity (HC) and effluent salinity were measured. The experiment was repeated except that the polymer solution was added to the soil without initially creating the cracks. An additional study was carried out to test the durability of the polymer when subjected to wetting and drying cycles. Increasing the amount of polymer significantly increased the HC and salt removal in the cracked soils. When the polymer solution was applied directly onto soils without initially creating cracks, there was no increase in HC on the ESP 8 soil and a small increase on the ESP 25 soil. The polymer had a stabilizing effect on soil cracks, but the increase in HC did not persist through several wetting and drying cycles.
Macropore Characterization for Two Tillage Systems Using Resin‐Impregnation Technique
Authors: Singh Piyush , Kanwar Rameshwar S. , Thompson Michael L.
Published: July 2010

This study used resin impregnation and image analysis to characterize macroporosity of a Nicollet loam soil (fine‐loamy, mixed, mesic Aquic Hapludoll) under no‐tillage and conventional tillage. Soil samples (7.5 by 5 by 5 cm) were taken at each 5‐cm depth interval to determine macroporosity after conducting solute‐leaching experiments on undisturbed soil columns. These soil samples were impregnated with either polyester or epoxy resin. Impregnated soil blocks were sectioned in the middle and ground to a smooth finish. Photographic slides were made of the horizontal faces and an automatic image analyzer was used to calculate the percentage of area occupied by macropores, and total perimeter, number, and size‐frequency distribution of macropores. Percentage of area, perimeter, and number of macropores were not statistically different for the two treatments. Macroporosity data obtained from the samples did not support the observations made in the solute‐leaching studies on saturated soil columns (i.e., a greater degree of preferential flow in no‐tillage columns) because the air‐dried samples and the saturated columns had different porosity characteristics and because small, two‐dimensional images were unable to sample any less frequently occurring larger pores. Another source of discrepancy between the results of the two studies may be macropore continuity. Two‐dimensional analysis of porosity images does not provide a measure of pore continuity, which can be a decisive factor in solute transport through soil columns under different tillage systems. Results from the resin‐impregnation study were not consistent with the results of a related field study. Inconsistency between the macroporosity data of these two studies were attributed to: the difference in minimum cut‐off diameter of macropores in the two studies, the difference in sample size, and the difference in moisture status of the field and lab samples.
Factors Controlling Denitrification in a Chihuahuan Desert Ecosystem
Authors: Peterjohn William T. , Schlesinger William H.
Published: July 2010

Denitrification may be an important pathway for N loss from desert ecosystems. Few studies, however, have investigated the factors limiting this process in a desert environment. A factorial experiment was conducted to determine the factors controlling denitrification in the northern Chihuahuan Desert. Specifically, we measured the response of denitrification to additions of water, C, N, and C + N. Soil cores were collected from four vegetation zones along an alluvial piedmont. Dry cores were subjected to five treatments: (i) water; (ii) water + NO3; (iii) water + C; (iv) water + NO3 + C; and (v) a control (no additions). When denitrification rates were averaged across vegetation zones and patch types (between or under vegetation), the following treatment effects were significantly different: water + NO3 + C > > > water + NO3 = water » water + C > control. These results indicate that denitrification at this site is limited by the availability of water. In wet soil cores, C additions immobilized available NO3 and suppressed denitrification. When water + NO3 + C was added (C/N = 22), however, denitrification was significantly greater than when water + NO3 were added. This result indicates that C and N interact to control denitrification in wet desert soils. No evidence for an overall NO3 limitation in moist cores was found. Surprisingly, denitrification rates in wet cores of nutrient‐poor desert soils (≈32.9 ng N cm−2 h−1) were similar to those measured in the nutrient‐rich soils of temperate and tropical forests. When extrapolated to an annual rate, denitrification for this site is 7.22 kg N ha−1 yr−1. Extreme drying‐wetting cycles common in desert ecosystems may account for the high rates observed.
Variation in Forest Soil Properties along a Great Lakes Air Pollution Gradient
Authors: MacDonald Neil W. , Burton Andrew J. , Jurgensen Martin F. , McLaughlin James W. , Mroz Glenn D.
Published: July 2010

A pronounced air‐pollution gradient exists across the Great Lakes region, with deposition of SO4, NO3, and H increasing from northern Minnesota to southern lower Michigan. Soils at six northern hardwood sites along this gradient were examined to characterize soil physical and chemical properties relevant to retention of pollutants, and to investigate the impact of differences in pollutant loading on soil chemical properties. Three randomly located pedons at each site were described and sampled. Soils at all sites were classified in closely related subgroups within the Spodosol order (Entic Haplorthods, Typic Haplorthods, Alfic Haplorthods, and Alfic Fragiorthods). Cation‐exchange capacity and SO4‐adsorption potential tended to decrease from north to south along the gradient, largely related to trends in inherent soil properties. In upper B horizons, additional significant positive deposition effects on water‐soluble and adsorbed SO4, and negative deposition effects on SO4‐adsorbing potentials were consistent with hypothesized pollutant impacts on soil SO4 pools and soil capacities to retain additional atmospheric SO4. Exchangeable nutrient‐cation contents (Ca, Mg, K) in upper B horizons tended to decrease as pollutant deposition increased. Regression analyses suggested that observed trends in nutrient‐cation contents were primarily related to inherent soil properties such as clay, organic matter, and cation‐exchange capacity. Differential effects of pollutant deposition and natural acidification processes on nutrient‐cation reserves could not be separated at this time.
Soil Water and Ammonia Volatilization Relationships with Surface‐Applied Nitrogen Fertilizer Solutions
Authors: Al‐Kanani T. , MacKenzie A. F. , Barthakur N. N.
Published: July 2010

Soil water content is an important factor influencing NH3 volatilization from N fertilizers. Information on the relationship between water evaporation and NH3 volatilization from urea (U) or urea‐ammonium nitrate (UAN) solutions, and on the kinetics of both processes is lacking. We examined NH3 volatilization from surface‐applied solutions of U and UAN in samples of St. Bernard (loamy, mixed, nonacid, frigid Typic Hapludoll) and Ste. Sophie (sandy, mixed, nonacid, frigid Typic Haplorthod) soils exposed to water potentials ranging from < −1.5 to −0.01 MPa. An air‐train system was used. Ammonia volatilization increased as soil water content increased. Volatilization differences between moist (> −0.038 MPa) and air‐dry (< −1.5 MPa) samples were reduced as the clay content of the soil increased. However, the effect of clay content on NH3 volatilization became more pronounced as soil approached air dryness. Water evaporation was consistent with first‐order kinetics, whereas NH3 volatilzation followed two first‐order kinetics. The initial rate constants (k1) for NH3 volatilization (0.338–0.348 d−1) from U solution were consistently higher than those for water evaporation (0.099–0.104 d−1) at −0.01 MPa water potential and 70% relative humidity. Differences could be attributed to different energy requirements. Ammonia volatilization vs. water evaporation followed a logarithmic relationship.
Simulation of Surface Energy Balance and Soil Temperature under Strip Tillage: I. Model Description
Authors: Hares Mohammad A. , Novak Michael D.
Published: July 2010

Conservation‐tillage practices that reduce soil erosion and conserve moisture are becoming more widespread. In northern latitudes, germination and early crop development may be hindered due to slower soil warming under mulched surfaces. Strip tillage, in which mulch or stubble strips alternate with bare planting strips, represents a compromise between conservation of soil and water by mulch or stubble and more rapid spring warming of bare soil. The object of our research was to identify the processes that determine surface energy‐balance components and soil temperatures under strip tillage and simulate them using a physically based numerical model, which consists of soil‐temperature and surface‐energy‐balance submodels. Dynamic inputs to the model are solar irradiances, air temperatures, water‐vapor densities, and wind speeds measured above the surface. The energy‐balance model determines radiation, heat, and water‐vapor transfers within the mulch and between the mulch surface and atmosphere, as well as the surface energy balance in the bare strip, including shading, shortwave and longwave reflection, and emission effects of the mulch sides. An explicit finite‐difference numerical technique is used to predict soil temperatures and heat fluxes. The soil‐temperature model was in excellent agreement with analytical solutions to periodic heat‐transfer problems in one‐dimensional nonbomogeneous and two‐dimensional homogeneous semi‐infinite soils with surface boundary conditions of the third kind (linear combination of soil heat flux and temperature specified at the surface).
Potential Sampling Error: Trace Metal Adsorption on Vacuum Porous Cup Samplers
Authors: McGuire P. E. , Lowery B. , Helmke P. A.
Published: July 2010

The adsorption of trace metals on ceramic, polytetrafluoroethylene (PTFE or Teflon), fritted glass, and stainless steel vacuum pore‐water samplers and silica packing material used to seat samplers was evaluated with respect to potential sampling errors. A solution containing radio‐labeled Cd+2, Co+2, Cr+3, and Zn+2 and a mix of ions typically found in soil solutions was used to assess specific absorption of inorganics to porous cups of samplers and to silica. Four sets of samplers were cleaned with acid or water and then treated with a solution containing trace metals at concentrations near primary or secondary drinking‐water standards or one order of magnitude lower for 2 or 7 d. After treatment, the samplers were rinsed with 10 or 30 pore volumes (PV) of simulated soil solution and radioassayed. Duplicate silica samples were treated with the high‐trace‐metal solution adjusted to a pH of 4, 6, or 8 for a 5‐d period, rinsed with simulated soil solution, and radioassayed. Adsorption was greatest on samplers treated with high trace‐meal concentrations and samplers cleaned with water. Desorption of both Co and Zn occurred with the 30‐PV soil solution rinse for all sampler types except stainless steel. The general pattern of metal adsorption on samplers was ceramic > stainless steel >> fritted glass = PTFE. The general order that trace metal adsorbed to samplers and silica was Zn >> Co > Cr > Cd. At pH values of 6 to 8, trace‐metal adsorption on silica (mass of adsorbent/mass of adsorbate) was similar to or greater than that observed for ceramic samplers. This study shows that adsorption‐desorption processes can cause sampling error when analysis of trace metals at microgram‐per‐liter concentration levels is necessary.
Characterization of Humic Acids, Composts, and Peat by Diffuse Reflectance Fourier‐Transform Infrared Spectroscopy
Authors: Niemeyer J. , Chen Y. , Bollag J.‐M.
Published: July 2010

Transmission infrared (IR) spectroscopy, either dispersive or Fourier transformed (FTIR), has been used extensively in studies on humic substances. A variety of bands characteristic of molecular structures and functional groups have been identified for these substances. The development of an attachment mounted onto FTIR spectrophotometers has allowed the determination of diffuse reflectance Fourier‐transformed infrared (DRIFT) spectra. The purpose of this work was to study the applicability of DRIFT to soil organic‐matter research and to compare the use of this instrumentation to dispersive and Fourier‐transformed transmission IR spectroscopy. The DRIFT spectra were determined for humic acids, peat samples, and composts. In addition, the possibility of using DRIFT spectra to quantitatively measure sample concentration and measuring the relative concentration of functional groups was assessed. Sample preparation for DRIFT is much simpler than for transmission IR spectroscopy, interferences due to water adsorption are reduced, and resolution is improved. The spectra obtained using DRIFT had a higher degree of resolution as compared with dispersive and Fourier‐transform transmission IR spectroscopy. Bands indicative of aliphatic C‐H, carboxyl and corboxylate functional groups, aromatic C=C, and C‐O stretch of polysaccharides were prominent and very well resolved. The DRIFT spectra obtained can also he used to fingerprint organic matter acquired from various sources. Spectra obtained at various concentrations of humic acid indicated that DRIFT cannot be used to estimate concentrations of organic matter in a given mixture. Relative concentrations of functional groups, however, were found to be fairly constant regardless of sample concentration. Therefore, changes in the relative concentration of functional groups can he measured during the humification process. It is expected that the application of DRIFT to organic‐matter research will prove especially useful for characterizing bulky heterogeneous samples such as peat and composts.
Changes in a Sandy Sahelian Soil Following Crop Residue and Fertilizer Additions
Authors: Geiger S. C. , Manu A. , Bationo A.
Published: July 2010

The use of crop residues as surface mulches has been shown to have a beneficial effect on the growth of pearl millet [Pennisetum glaucum (L.) R.Br.] in the Sahelian zone of West Africa. This study was conducted to discern the mechanism(s) responsible for yield increases resulting from crop‐residue additions in a field trial located on a sandy soil at the ICRISAT Sahelian Center near Niamey, Niger. Soil chemical and physical properties were examined to a depth of 120 cm after 5 yr of application of millet residue as a surface muich, P and N fertilizer, or a combination of fertilizer and residue. Annual residue application resulted in a higher exchangeable‐base content, lower Al saturation, and slightly higher available‐P values than the control. The use of fertilizer resulted in an increase in available P and exchangeable Ca. The combination of residue plus fertilizer resulted in greater enhancement of soil fertility parameters than the use of tbese inputs alone. Differences in soil chemistry were operative in only the top 20 cm of the soil profile, bowever, the surfaces of the plots receiving residues were 15 to 20 cm higher than the surfaces of the control and fertilizer‐only plots. The surfaces of the residue plots also had lower clay contents than the surface soils in the nonresidue plots. The increase in soil fertility following the application of millet residue as a surface mulch was due to two mechanisms: (i) the recycling of nutrient elements to the soil following termite and microbial decomposition of the residue, and (ii) the entrapment of eolian materials, which generally have better fertility characteristics than the subsoil, or protection of the more fertile surface soil from the erosive effects of the strong winds that are common in the Sahel.