bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphate Sorption‐Desorption Behavior of Some Acidic Soils of South and Southeast Asia
Authors: Sanyal S. K. , Chan P. Y. , De Datta S. K.
Published: July 2010

The equilibrium phosphate sorption and release behavior and the kinetics of adsorption were studied in some acidic soils of South and Southeast Asia. Phosphate sorption data at 25 °C were fitted to the Tempkin, Freundlich, and Langmuir adsorption isotherms. The soils varied widely in their capacity to sorh and retain P. During desorption, the amount of sorbed P at a given equilibrium P concentration was always higher than that during sorption, indicating low desorbability of the sorbed P. The kinetic P sorption data at 21 and 35 °C were fitted to a modified Freundlich type of kinetic equation to obtain a parameter related to the sorption rate coefficient. The effect of temperature on the kinetics of sorption was small, suggesting the process is diffusion controlled. Equilihrium and kinetic P sorption parameters were found to he closely correlated with clay and organic matter contents and surface area of soils. A negative correlation between specific P sorption by clay or organic matter and clay or organic matter content of the soils suggests an association between the two colloidal components of the soils, causing loss of effective P‐sorhing surface area. An attempt was further made to evaluate the differential change in free energy of P sorption at infinite dilution from the corresponding thermodynamic equilibrium constant for P sorption by the given soils. The results suggest that the stability of the P sorption reaction products in the given soils contribute to the P‐fixing characteristics of these soils.
Mycorrhizal Development and Phosphorus Absorption in Maize under Conventional and Reduced Tillage
Authors: McGonigle Terence P. , Miller Murray H.
Published: July 2010

Arbuscular mycorrhizae participate in P uptake by maize (Zea mays L.). Previous studies using pot‐grown plants have shown that P uptake by maize is greater when soil is not disturbed between cropping and planting. This study was conducted to determine if mycorrhizal colonization and shoot P absorption in the field are higher under reduced tillage, under conditions of soil fertility and tillage management representative of commercial farming. Maize was sampled in 1990 and 1991 from plots maintained under no‐till (NT), and ridge tillage (RT). These were contrasted with maize from plots given moldboard plow (MP) tillage each year, which disturbs the soil to a greater extent. Plots were fertilized at recommended rates. In the early part of both years, shoot P concentration in NT and RT were significantly greater than under MP. These differences in shoot P did not persist after the six‐leaf stage. Greater development of mycorrhizae in the early season was seen in the RT and NT systems relative to that in MP. There were no significant effects of tillage on final yield, possibly due to the relatively high soil P levels. Under NT and RT, arbuscular colonization had a maximum at 48 d after planting (DAP) of 55% and 60%, respectively, followed by a linear decrease to near 10% at 166 DAP. Under MP, a plateau of 45% arbuscular colonization was sustained between 48 and 97 DAP, followed by a linear decrease similar to that in NT and RT.
Tillage and Furrow Diking Effects on Water Balance and Yields of Sorghum and Cotton
Authors: Baumhardt R. L. , Wendt C. W. , Keeling J. W.
Published: July 2010

Information on the combined effects of deep or no‐tillage together with furrow dikes (small earthen dams constructed in the furrow) on water conservation in semiarid regions is limited. The purpose of this study was to compare the amount of rain conserved and the yields of forage sorghum [Sorghum bicolor (L.) Moench] and cotton (Gossypium hirsutum L.) as affected by furrow dikes and tillage for a 3‐yr period. An Olton clay loam (fine, mixed, thermic Aridic Paleustoll) was alternately cropped to cotton and sorghum. Forage sorghum was grown in (i) disk or (ii) chisel‐disk tilled 16 by 23.8 m field plots with and without furrow diking. Cotton was grown in rotation following sorghum after (i) conventional moldboard‐disk or (ii) no‐tillage, with furrow dikes in one‐half of the tillage treatment plots. Crop yield, rainfall amount, soil water content, and runoff of natural rainfall and of simulated rainfall, applied at 80 mm h−1 for 1 h, were measured. Compared with conventionally tilled undiked plots, cumulative nonponded infiltration of simulated rainfall was significantly greater with notillage treatments and greater (not significant) in furrow‐diked treatments. Runoff of natural rainfall from plots with furrow dikes averaged ≈22 mm less than from undiked plots, and it was as much as 57 mm less; however, runoff from diked fields was observed. Under the conditions of this 3‐yr study, diking did not significantly increase crop water use and yield, but no‐tillage significantly increased crop water use and yield 1 yr. We conclude that furrow dikes installed during the growing season did not increase water conservation and crop yields under the conditions of this 3‐yr study due to seasonal dike consolidation that reduced the detention capacity and to the limited runoff from level fields. We also conclude that no‐tillage is more effective than chisel tillage for increasing water conservation and crop yields for the conditions of this study.
Soil Carbon Dioxide Characteristics under Different Forest Types and after Harvest
Authors: Fernandez Ivan J. , Son Yowhan , Kraske Chuck R. , Rustad Lindsey E. , David Mark B.
Published: July 2010

To characterize soil CO2 under different forest types and several years after a clear‐cut harvest, soil CO2 evolution and soil air CO2 concentrations were measured at three sites in Maine: the Howland Integrated Forest Study (HIFS) site, the Bear Brook Watershed in Maine (BBWM) site, and the Letter E township (Letter E) site. Soil CO2 evolution means ranged from 0.19 to 0.32 g m−2 h−1 among sites, whereas soil air CO2 concentration means ranged from 1023 µL L−1 for the O horizon to 3296 µL L−1 for the C horizon for the 1990 growing season. Soil CO2 evolution and soil air CO2 concentrations were similar under deciduous and coniferous forests and 4 to 6 yr after harvest. Limited multiple‐year data suggest that significant annual variations in temporal patterns of these properties exist as a function of short‐term climatic factors. These data suggest that soil CO2 evolution and soil air CO2 concentrations may be somewhat similar across a diversity of soil types, forest types, and forest conditions at any point in time for northern New England.
Organic Matter Role in Illitic Soil Colloids Flocculation: I. Counter Ions and pH
Authors: Heil Dean , Sposito Garrison
Published: July 2010

Dispersed soil particles have a negative impact on soil structure and contribute to soil erosion and contaminant movement. The colloidal properties of soil clays have been found to be different from specimen clays. The purpose of this study was to investigate the effect of organic matter on the flocculation of soil colloids as a function of electrolyte concentration, pH, and exchangeable or soluble bivalent cation type. The flocculation of suspensions of two illitic soils was studied using light transmission. Soil suspensions were prepared in Na‐K‐Ca and Na‐K‐Mg perchlorate solutions at a total electrolyte charge concentration of 5, 10, and 15 molc m−3 at pH 6 and 8. Flocculation at a given soluble bivalent cation charge fraction was increased as the organic C content of the soil colloids decreased. Calcium was more effective than Mg as a flocculant at the same soluble or exchangeable bivalent cation charge fraction. Increasing pH caused an increase in the flocculation of one of the soils, but this trend was reversed after the removal of organic matter by H2O2 treatment. The amount of electrolyte required for flocculation, the effect of pH, and the relative effectiveness of Ca vs. Mg all depended on soil organic matter content.
Solubility and Cation Exchange in Phosphate Rock and Saturated Clinoptilolite Mixtures
Authors: Allen E. R. , Hossner L. R. , Ming D. W. , Henninger D. L.
Published: July 2010

Mixtures of zeolite and phosphate rock (PR) have the potential to provide slow‐release fertilization of plants in synthetic soils by dissolution and ion‐exchange reactions. This study was conducted to examine solubility and cation‐exchange relationships in mixtures of PR and NH4‐ and K‐saturated clinoptilolite (Cp). Batch‐equilibration experiments were designed to investigate the effect of PR source, the proportion of exchangeable K and NH4, and the Cp to PR ratio on solution N, P, K, and Ca concentrations. The dissolution and cation‐exchange reactions that occurred after mixing NH4‐ and K‐saturated Cp with PR increased the solubility of the PR and simultaneously released NH4 and K into solution. The more reactive North Carolina (NC) PR rendered higher solution concentrations of NH4 and K when mixed with Cp than did Tennessee (TN) PR. Solution P concentrations for the Cp‐NC PR mixture and the Cp‐TN PR mixture were similar. Solution concentrations of N, P, K, and Ca and the ratios of these nutrients in solution varied predictably with the type of PR, the Cp/PR ratio, and the proportions of exchangeable K and NH4 on the Cp. Our research indicated that slow‐release fertilization using Cp/PR media may provide adequate levels of N, P, and K to support plant growth. Solution Ca concentrations were lower than optimum for plant growth.
Soil Solution Composition Relative to Mineral Distribution in Blue Ridge Mountain Soils
Authors: Norfleet M. L. , Karathanasis A. D. , Smith B. R.
Published: July 2010

Soils with large quantities of gibbsite are normally associated with tropical climates and very intense weathering. The abundance of this mineral in the clay fractions of soils in the temperate climate of the Blue Ridge Mountains raised questions about the soil environment and possible mineral weathering trends. The composition of interstitial soil solutions of three highly weathered soils in the mountains of South Carolina was studied in order to explain contrasting distributions and prevalence of gibbsite and kaolinite. Extensive leaching caused by high amounts of rainfall was evidenced from the low solution ionic strengths and soluble Si content of these soils. The solubility data suggested gibbsite to be the most stable mineral in subsurface horizons serving as Al sinks (mineral precipitation), with kaolinite being more stable in surface horizons. These two minerals appeared to be in a dynamic equilibrium with hydroxy‐interlayered vermiculite, which is controlled by kinetic gradients imposed by site characteristics rather than solution chemistry alone. While the solution composition is consistent with the mineralogical suite of these soils, the residence time of Al and especially Si appears to be the determining factor for secondary mineral formation, weathering transformations, and distribution in the soil profile.
Basic Edta as an Extractant for Soil Organic Phosphorus
Authors: Bowman R. A. , Moir J. O.
Published: July 2010

Soil organic P is an important source of plant‐available P in the Great Plains. It is, therefore, important in conservation tillage agriculture, that we know the size and the potential availability for crop use of this large P pool, which could exceed one‐half of the total P. We propose a one‐step procedure with hot basic EDTA (ethylene diaminetetraacetic acid) for total soil organic P that requires minimum manipulation and analytical prowess. Soil samples (0.5 g) were incubated for 2 h at 85 °C with 25 mL of 0.25 M NaOH + 0.05 M Na2EDTA, after which time the organic P in the extracts was determined by persulfate oxidation. Results from the evaluation of nine soils from various parts of the USA and one Canadian soil showed significant correlations with an existing wet sequential extraction and a dry high‐temperature ignition method for total organic P determinations. With the high‐organic‐matter Canadian soil, the EDTA method extracted 32% more organic P than the wet extraction method, and essentially the same as the dry ignition method. The new method appears to be especially useful for soils where organic acids and chelation mechanisms with P may be more dominant than ester‐type formations.
Potential Errors in Measuring Nitrogen Content of Soils Low in Nitrogen
Authors: Wang Deane , Snyder Michael C. , Bormann F. Herbert
Published: July 2010

Samples of sandy soils of low N content were analyzed using a variety of procedures to assess N levels and sources of variation and bias. We assessed subsampling of collected soil, sample preparation by grinding, and two methods for measuring nitrogen. Micro‐Kjeldahl and CHN combustion procedures differed in accuracy and precision; the micro‐Kjeldahl method generally provided greater precision and accuracy across a variety of soil sample types. The greatest potential error was due to a particle‐size bias in removal of small subsamples (30–200 mg) required for each method. To eliminate this error, we recommend either pulverization of large samples to at least 0.5 mm before subsampling, or separation of soils into three or more homogenous particle‐size classes prior to chemical analysis.
Corn Yield and Salinity Response to Irrigation on Slowly Permeable Subsoils
Authors: Reichman G. A. , Trooien T. P.
Published: July 2010

Crop yields in the northern Great Plains often could be improved with irrigation but many soils of this region have been considered nonirrigable because of their low hydraulic conductivity. This project was initiated to determine the leaching characteristics when irrigating two of these soils and to determine if harmful salinity increases would result from irrigation. We measured corn (Zea mays L.) yield and soil saturation extract electrical conductivity (ECe) and sodium adsorption ratio (SARe) in response to irrigation plus precipitation of one, two, and three times the calculated evapotranspiration and to N fertility of 100 and 200 kg N/ha. The study was conducted for 5 yr at one site and 6 yr at another site, both in the northern Great Plains. Yield and increase of ECe at 100 kg N/ha were less than at 200 kg N/ha. At both sites, ECe increased but corn yield did not decrease during this experiment. The SARe increased for all treatments but the maximum observed was <10. Excess irrigation usually had no effect on yield and did not decrease yield. Such excess irrigation provided salinity control by leaching. Precipitation also leached these soils. Our data indicate that the soils tested, the top 2.3 m of the soil profiles at two sites, allow enough leaching to permit effective well‐managed irrigation.
Root Zone Effects on Tracer Migration in Arid Zones
Authors: Tyler S. W. , Walker G. R.
Published: July 2010

The study of groundwater recharge and soil water movement in arid regions has received increased attention in the search for safe disposal sites for hazardous wastes. In passing through the upper 1 to 2 m of most soil profiles, tracers indicative of recharge such as Cl, 2H, 18O, Br, 3H, and 36Cl are subjected to a wide range of processes not encountered deeper in the profile. This transition zone, where water enters as precipitation and leaves as recharge, is often ignored when environmental tracers are used to estimate deep soil water flux and recharge, yet its effect may be profound. In this work, we reexamine the processes of root extraction and its effect on the velocity and distribution of tracers. Examples are presented for idealized conditions, which show clearly the relation between the root zone processes and the deep drainage or recharge. The results indicate that, when recharge is small and root zone processes are not accounted for, tracer techniques can significantly overestimate recharge until the tracer has moved well below the root zone. By incorporating simple models of root zone processes, a clearer understanding of tracer distributions and a more accurate estimate of recharge can then be made.
Soil Water Diffusivity Estimates from One‐Dimensional Absorption Experiments
Authors: Warrick A. W.
Published: July 2010

A method to estimate soil water diffusivity from experimental absorption data was explored. The purpose was to directly match measured sorption curves (water content vs. distance or the Boltzmann transform variable) to scaled forms of the solutions and thus provide consistent hydraulic properties. Evaluation of such parameters is critical to prediction of water and solute transport within the vadose zone. The method is relevant to several, if not most, of the commonly used hydraulic functional relationships. Generally, the results gave two independent relationships of the parameters. Ane xample was considered and calculations performed for three alternative models. The best choice of each model was easily found and the evaluated parameters were shown to be consistent. The soil water diffusivities were compared for the estimated parametric relationships. Individual models provide alternative shapes for the diffusivity function, but tend to converge for the wetter range of water contents.
Agrichemical Detection in a Shallow Unconfined Aquifer as Influenced by Sampling Technique
Authors: Clay D. E. , Holman P. W. , Clay S. A. , Schumacher T. E. , Scholes K. A. , Bender A. R.
Published: July 2010

The sample collection system may influence the ability to describe the complex temporal and spatial variation of contaminants within an aquifer. The objective of this study was to evaluate the probability of detecting atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine) using a bailer or skimmer in an unconfined aquifer located below an atrazine‐treated surface soil. In the simulated aquifer, the surface skimmer collected more Br− than the fixed sampling port located 15 cm below the aquifer surface and bailer. In the unconfined aquifer, the probability of an atrazine detection was higher when samples were collected with a surface skimmer tban a bailer. These results suggest that the ability to determine vertical transport of contaminants from surface soil to shallow aquifers at the point of agrichemical application is dependent on surface sampling of the aquifer.
Carbon and Nitrogen Dynamics of Soil Organic Matter Fractions from Cultivated Grassland Soils
Authors: Cambardella C. A. , Elliott E. T.
Published: July 2010

The amount of organic matter present in soil and the rate of soil organic matter (SOM) turnover are influenced by agricultural management practices. Because SOM is composed of a series of fractions, management practices will also influence the distribution of organic C and N among SOM pools. Our study examined SOM fractions that are occluded within the aggregate structure. Aggregates were disrupted by sonication and the disrupted soil suspensions were passed through a series of sieves to isolate size fractions. Densiometric separations were carried out on the size fractions, creating size‐density fractions. Fine‐silt‐size particles having a density of 2.07 to 2.22 g/cm3 isolated from inside macroaggregates contained the highest percentage of total soil C and N for all cultivation treatments and, because of its properties, will be referred to as the enriched labile fraction (ELF). As cultivation intensity was reduced, the amount of N in the ELF increased from 110 mg N/kg in the bare fallow treatment to 405 mg N/kg in the no‐till treatment. About 5% of the N in the ELF was mineralized during a 28‐d laboratory incubation, averaged across treatments. The proportion of N mineralized from the ELF (4.7%) was significantly higher than from intact macroaggregates (2.1%), which suggests this fraction may be protected from decomposition within the aggregate structure. We postulate that the ELF is a byproduct of microbial activity and that it contributes to binding microaggregates into macroaggregates in cultivated grassland soils.
Quantification of the Effect of Soil Organic Matter Content on Soil Productivity
Authors: Bauer Armand , Black A. L.
Published: July 2010

The positive effects of soil organic matter (OM) on soil properties that influence crop performance are well documented. But definitive and quantitative information of differential effects of soil OM contents is lacking for the northern Great Plains. The objective of this study was to quantify the contribution of a unit quantity of soil OM to productivity. Experiments were conducted on Williams loam (fine‐loamy, mixed, Typic Argiboroll) for 4 yr in the same field. The variables were soil OM content of the upper 30.5 cm together with all combinations of three postplanting soil available N levels (55, 90, and 125 kg N ha−1 as NO3‐N to 1.2 m) and three water levels. Water levels were uniformly maintained with a trickle system that independently metered water to each plot for each soil available N level. Pretillering spring wheat (Triticum aestivum L.) plant population decreased as soil OM content decreased in 3 of 4 yr. On an annual basis, highest total aerial dry matter and grain yields were associated with highest OM contents. The contribution of 1 Mg OM ha−1 to soil productivity, across the range of 64 to 142 Mg OM ha−1, was calculated as equivalent to 35.2 kg ha−1 for spring wheat total aerial dry matter and 15.6 kg ha−1 for grain yield. Loss of productivity associated with a depletion of soil OM in the northern Great Plains is primarily a consequence of a concomitant loss of fertility.
Soil Drainage Class Probability Mapping Using a Soil‐Landscape Model
Authors: Bell James C. , Cunningham Robert L. , Havens Matthew W.
Published: July 2010

The direct application of quantitative soil‐landscape models for soil mapping has been limited by technological constraints. This study combines a statistically based soil‐landscape model and geographic information system (GIS) technology to create soil drainage class maps. An existing soil‐landscape model that predicts soil drainage class from parent material, terrain, and surface drainage feature proximity variables was used. A digital geographic database of parent material, terrain, and surface drainage feature proximity variables stored in a geographic information system were used as model inputs. Combinations of these landscape variables were defined by overlaying the digital maps and by applying the soil‐landscape model to create predictive maps of soil drainage class probability and most‐likely soil drainage class. The modeled soil drainage class map agreed with an Order II (1:20000 scale) soil survey for 67% of the study area. A majority of the disagreement was attributed to areas predicted as somewhat poorly to moderately well drained by the model and well drained by the soil survey. This technique consistently assigns soil drainage class based on landscape attributes, documents the data and decision criteria used for drainage class assignment, estimates the uncertainty associated with drainage class assignment, and generates a digital map for GIS applications.
Theory of Minirhizotron Root Directionality Observation and Application to Wheat and Corn
Authors: Merrill S. D. , Black A. L. , Bauer A. , Upchurch D. R.
Published: July 2010

Root growth orientation, termed root directionality (RD), is a property of root systems conveying information on response to soil environment and about branching character in root development. Observation of the orientation and configuration of the fine, branched roots in soil is very important for understanding response to soil environment, but is currently difficult or effectively impossible. Root directionality may be determined with root observation tubes (minirhizotron, MR) utilizing the statistical probability that, for a given soil depth increment, the ratio of root numbers impinging on the upper sides to numbers on the lower sides (the directionality ratio, DR) of MRs installed at an angle to the vertical is a function of the vector mean of RD. The theory of RD observation by MRs is presented with calculations indicating that DR increases with greater downward RD and with increased installation angle of MRs. Measurements of DRs were conducted in MRs installed in spring and winter wheat (Triticum aestivum L.) and corn (Zea mays L.) crops established on a Typic Argiboroll soil. The majority of the measurements yielded DR values >1 in the upper 0.5 m of the root zone, indicating downward RD, shifting to lower DR values (many <1.0) at soil depths >0.5 m, indicating sideward to upward RD, or less downward RD. The greater probability of observing axile (seed‐ or stem‐attached) roots in the upper root zone and lateral (branch) roots at greater soil depth is an explanation. The majority of RD values of wheat observations were considerably higher than for corn. The greater downward RD observed for wheat is believed to be linked to a greater degree of root branching in corn and possibly to more favorable water availability for corn.
Survival of a lacZY‐Containing Pseudomonas putida Strain under Stressful Abiotic Soil Conditions
Authors: Hartel P. G. , Fuhrmann J. J. , Johnson W. F. , Wolf D. C. , Lawrence E. G. , Staley T. E. , Lopez C. S. , Wollum A. G. , Mullen M. D. , Skipper H. D. , Zuberer D. A.
Published: July 2010

Little is known about the effect of soil factors on genetically altered bacteria. We altered Pseudomonas putida PH6 to contain the Escherichia coli genes for lactose utilization (lacZY). Except for lactose utilization, the genetically altered mutant, P. putida PH6(L1019), and the wild type strain were indistinguishable in the tests we employed. Both strains were tested for survival in eight different soils, and in one soil at temperatures of 15, 25, 35, and 40°C and soil water pressures of −0.03, −0.07, and −1.5 MPa. Few differences in survival of the two strains were observed in seven of the eight soils, but in the most acid soil (pH 5.0), numbers of PH6 were at least 100‐fold higher than PH6(L1019) after 28 d. The percentage of lactose‐positive (lac+) isolates averaged >95% in all eight soils unless PH6(L1019) numbers declined below 104 colony‐forming units (CFU) g−1 of soil. Neither PH6 nor PH6(L1019) survived at 40°C after 3 d, and few differences in survival were observed between the two strains at 15 and 25°C. At 35°C, PH6 declined from ≈108 to ≈103 CFU g−1 of soil after 35 d, whereas PH6(L1019) declined from ≈108 CFU g−1 of soil to below the limit of detection (<10 CFU g−1 of soil) after 14 d. Few differences in survival between PH6 and PH6(L1019) were observed at −0.03 and −0.07 MPa, but at −1.5 MPa, PH6 survival was greater than PH6(L1019) at all sampling times. These results are the first to suggest that a soil abiotic factor can exert differences in survival between a wild type and genetically altered bacterium.
Microbial Biomass Dynamics in Tallgrass Prairie
Authors: Garcia Fernando O. , Rice Charles W.
Published: July 2010

The temporal dynamics and effects of burning, mowing, and N fertilization on microbial biomass (MBM) in tallgrass prairie were studied in a field experiment established in 1986. Microbial C (MC) and microbial N (MN), determined by the fumigation‐incubation procedure during the growing seasons of 1989 through 1991, averaged 217 mg C kg−1 and 32.6 mg N kg−1, respectively, for the 0‐ to 30‐cm depth. Accumulation of litter and greater production of roots near the surface resulted in stratification of MBM. Seasonally, MBM was higher in early spring, decreased with the initiation of plant growth, and then recovered by late summer or early fall. Decreases of MN between March and July coincided with plant N uptake. The increase of MC and decrease of MN during the 3 yr of the study were related to increased plant production. Burning had a short‐term and variable effect on MC. Burning tended to reduce MC during dry years and increase it in normal to wet years. Mowing and raking decreased MC and MN, probably because of reduced root biomass and removal of standing vegetation. Nitrogen addition resulted in higher MN and tended to reduce MC, possibly by modifying the composition of the microbial population. Microbial biomass seems to play a critical role in conserving N in the tallgrass prairie ecosystem.
Concurrent Transformation of Lignosulfonate Carbon and Urea Nitrogen in Clay Soil
Authors: Xie R. J. , MacKenzie A. F. , O'Halloran L. P. , Fyles J. W.
Published: July 2010

Lignosulfonate (LS), a waste product from the pulp and paper industry, can be a potential source of soil organic matter. Its transformation in soil may affect the relative amounts of soil N and organic matter fractions. A clay soil was incubated with urea at rates of 0, 500, or 1000 mg N kg−1 soil and NH4LS at rates of 0, 25, 50, 100, or 150 g NH4LS kg−1 soil at 70% field moisture capacity for 60 d. The incubated soil was analyzed for NH4‐N, NO3‐N, and total N. Soil organic carbon was partitioned into humin (HM)C, humic acids (HA)C, and fulvic acids (FA)C. In general, both urea and NH4LS additions increased total N, NH4‐N, and organic N (difference between total N and NH4‐N) but reduced NO3‐N. The higher the NH4LS rate, the greater the regression slope of N fractions (except NO3‐N) on urea addition rates, and the higher the urea rate, the greater the regression slope of N fractions (except NO3‐N) on NH4LS rates, indicating the effect of interaction between urea and NH4LS on N distribution in the soil. Ammonium LS increased and urea decreased the C/N ratio of soil organic matter. Proportions of HM‐C and HA‐C decreased while that of FA‐C increased with increasing NH4LS rates. Urea reduced the HA‐C and increased the FA‐C fraction. The results showed that simultaneous application of urea and NH4LS can increase soil organic matter content (particularly the FA‐C fraction) and enhance N transformation into NH4‐N and organic N fractions and reduce NO3‐N.
Bulk Density and Fragipan Identification in Loess Soils of the Lower Mississippi River Valley
Authors: Lindbo D. L. , Rhoton F. E. , Bigham J. M. , Jones F. S. , Smeck N. E. , Hudnall W. H. , Tyler D. D.
Published: July 2010

High bulk density (ρb) compared with overlying soil horizons has long been considered one of the principal characteristics of fragipans, yet recent investigations have noted inconsistent relationships between fragipans and ρb. This study was conducted to evaluate the fragipan‐ρb relationship in several major loessial soils of the lower Mississippi River Valley. Average ρb (field‐moist, saran‐coated clods) obtained from five Memphis‐Loring‐Grenada catenas extending from northwest Tennessee to southeast Louisiana show that ρb in the fragipans of the Loring (fine‐silty, mixed, thermic Typic Fragiudalf) and Grenada (fine‐silty, mixed, thermic Glossic Fragiudalf) pedons range from 1.45 to 1.78 Mg m−3 (x̄ = 1.56). A wider range of 1.38 to 1.86 Mg m−3 (x̄ = 1.55) occurred at similar depths in the Memphis (fine‐silty, mixed, thermic Typic Hapludalf) pedons. Within most Loring and Grenada pedons, the ρb of the fragipan horizon is not statistically unique (based on Duncan's new multiple‐range test) and does not always represent the maximum for a given pedon. There is also a weak positive correlation (r2 = 0.44) between total sand content and ρb, suggesting that higher ρb in these soils are more closely related to lithologic factors than to pedogenic densification. Specifically, pedons with a significant influence of Coastal Plain sediment have higher ρb than those developed entirely in loess, suggesting that the high ρb are partially inherited. These results indicate that ρb should not be used as a principal test for differentiating between fragipan and nonfragipan horizons in these soils. It appears that root and water restriction typically associated with fragipans in the lower Mississippi River Valley are related to physical or chemical characteristics of the fragipans other than ρb.
Modeling Oxygen Diffusion in Aggregated Soils: I. Anaerobiosis inside the Aggregates
Authors: Renault Pierre , Stengel Pierre
Published: July 2010

Denitrification may appear in anaerobic regions of soil aggregates. In order to evaluate the dependence of anaerobiosis on aggregate shape, on contact with other aggregates, and on surface occlusion by water, a numerical method was used to simulate O2 diffusion and consumption in three‐dimensional models of water‐saturated aggregates. The aggregates were assumed to be homogeneous in regard to porosity, gas diffusion, and microbial respiration. After equilibration, the calculated anaerobic fractions of simulated aggregates were compared with those obtained for homogeneous spherical ones having the same unblocked external surface area/total aggregate volume ratio. Anaerobiosis of unoccluded aggregates may be predicted by the spherical model with an uncertainty less than ≈5%. When there are occlusions, anaerobiosis may still be predicted by the spherical model for aggregates with a radius greater than some critical radius, but the uncertainty may be as high as 100%. The critical radius corresponds to the radius of the smallest homogeneous spherical aggregate that has an anaerobic center when there is no occlusion of its external surface. For smaller aggregates, we proposed an empirical reduction of the anaerobic fraction predicted by the spherical model in order to predict their actual anaerobic fraction.
Degradation of Fenamiphos in Soil with a History of Continuous Fenamiphos Applications
Authors: Ou L.‐T. , Thomas J. E. , Dickson D. W.
Published: July 2010

The efficacy of the nematicide fenamiphos [ethyl‐3‐methyl‐4‐(methylthio)phenyl (1‐methylethyl) phosphoramidate] often is reduced when applied annually or biannually for extended periods to turfgrasses in Florida. This study was conducted near Gainesville, FL, on a Blichton sand (loamy, siliceous, hyperthermic Arenic Plinthic Paleaquults) to determine whether the degradation of fenamiphos was enhanced by long‐term applications to a turfgrass golf course fairway and putting green. 14C‐fenamiphos was used for determination of mineralization rates, metabolites, and mass balance. Initial mineralization of 14C‐fenamiphos in soil collected from the turfgrass site was more rapid than in soil collected from the rough (untreated). Fenamiphos sulfoxide (FSO) was the main metabolite detected, whereas fenamiphos sulfone (FSO2) was either not detected or only occasionally detected in trace amounts. Half‐life values for total toxic residues (TTR, fenamiphos + FSO + FSO2) in soil samples collected from the site were all small, ranging from 0.9 to 4.2 d, and half‐life values for TTR in soil collected after the fenamiphos application were smaller than in soil collected before the application. Total 14C recovery from 14C‐fenamiphos‐treated surface soil collected 0.7 mo after the annual application was well below 100%. Rapid initial mineralization of fenamiphos was also observed in this sample. Applications of fenamiphos to the same site for prolonged periods appear to increase the potential for enhanced degradation of TTR.
Measuring Nutrient Availability in Arctic Soils Using Ion Exchange Resins: A Field Test
Authors: Giblin A. E. , Laundre J. A. , Nadelhoffer K. J. , Shaver G. R.
Published: July 2010

We tested the suitability of ion exchange resin (IER) bags for in situ measurement of nutrient availability in arctic ecosystems where nutrient mineralization rates are exceptionally low. We deployed IER bags for 2 to 44 wk in a variety of ecosystem types on the North Slope of Alaska and compared N and P accumulation on the resins to several other measures of plant‐available N and P, including net N mineralization rates measured using in situ soil incubations. We also tested various factors that could affect nutrient accumulation on IER to optimize the performance of IER. Long deployment times gave lower estimates of nutrient availability than did a series of shorter deployments. Nitrate and phosphate were desorbed in the field when resins were preloaded with these nutrients, but NH+4 was not. Neither the amount of resin nor the small soil disturbance associated with its placement appeared to affect nutrient accumulation rates on IER. Nutrient accumulations on IER did not correlate well with other measures of NH+4, NO−3, and phosphate availability. However, land‐scape differences in N vs. P availability ascertained from resins corresponded well with N/P ratios in soils and soil solutions and with results from factorial fertilizer experiments. Seasonal patterns of nutrient availability determined by resins were also consistent with plant uptake data.
Spatial Distribution of Water and Chloride Macropore Flow in a Well‐Structured Soil
Authors: Quisenberry V. L. , Phillips R. E. , Zeleznik J. M.
Published: July 2010

Macropore flow is recognized as an important component of water and solute transport in many soils. Our understanding of its magnitude and significance is not well developed. The objective of this experiment was to measure the effect of application rate on the magnitude and spatial distribution of macropore flow in a Maury silt loam (fine, mixed, mesic Typic Paleudalf). An undisturbed block of soil (32.5 by 32.5 by 32.5 cm) was obtained and placed on a specially designed apparatus that allowed effluent to be collected under —2.0 kPa vacuum and separated into 100 cells. Water tagged with Cl− was applied by 100 needles, 0.25‐mm i.d., which were positioned directly above the 100 collection cells. Approximately 7.5 cm of solution was applied at four application rates: 3.14, 1.97, 1.23, and 0.5 cm h−1. A large fraction of the water and solute moved through a small percentage of the total soil for all application rates: 50% of the water and Cl− were collected in <20 and 10%, respectively, of the cells. Displacement of antecedent water by applied water was much higher for the 0.5 cm h−1 application rate than for the higher three rates. The position and spatial pattern of macropore flow remained fairly constant for the three highest flow rates. Areas of high soil water flow and high Cl− concentrations were clustered, not randomly distributed across the column. We believe these findings support our hypotheses that flow takes place in the same network of pores for similar rainfall events and that interpedal voids between tertiary structural units are important pathways of flow.
A Unified Approach to Stochastic‐Convective Transport Problems
Authors: Jury William A. , Scotter David R.
Published: July 2010

A stochastic‐convective transport process is one in which solute is advected in isolated stream tubes that do not exchange mass during the time of transport. As a field scale model, it has certain advantages compared with a convective‐dispersive model formulation, which requires complete mixing of regions with different velocity. Use of a stochastic‐convective model formulation has been limited, in part because the theory has not been developed sufficiently to unify the description of initial value and boundary value problems. This study develops the complete theory for a vertically homogeneous soil by creating a stochastic‐convective medium made up of stream tubes that do not exchange solute during transport. Each tube has uniform properties within it, but the properties vary from one tube to the next. By creating a field‐scale medium made up of an ensemble of such tubes, we were able to derive both solute travel time and travel distance probability density functions (pdfs) for the stochastic‐convective problem, thereby producing a consistent description of both the initial value and boundary value problems. With this description, it is possible to perform a single calibration of a travel time or travel distance pdf and use it as the foundation for all subsequent transport modeling. We show that there are two possible formulations of the pdfs, depending on the way in which mass is introduced to the solute transport volume during the time of calibration. After development of the theory, we use three examples to illustrate the application of the principles of stochastic‐convective modeling to practical problems of interest in solute transport research.
Intrinsic Mesoscopic Spatial Variability in Macroscopically Uniform Soils
Authors: Miller R. D.
Published: July 2010

A soil judged to be uniform when viewed at a macroscopic scale may be a highly diversified population of grains and pores when viewed at a microscopic scale. If so, at intermediate scales, it will exhibit an intrinsic mesoscopic spatial variability (IMSV) that cannot be eliminated by thorough mixing and fastidious packing. For a given soil, data from a stepwise mechanical analysis or a stepwise drying curve can be conventionally construed as counts of grains or pores assigned to specific size classes. For any set of parcels of equal volume, it is postulated that counts for the jth size class will be normally distributed about the mean. The smaller the parcels, the greater the expected amplitude of normalized deviations. A description of IMSV uses the raw data and a table of probabilities of suggest replies to questions about how small parcels of macroscopically uniform soil must be if there is to be some predetermined probability that the data for the jth size‐class in any one parcel will deviate to a predetermined degree from the mean for that class. In effect, IMSV suggests lower limits on parcel‐sizes that could be called representative elementary volumes once a tolerable probability has been chosen for specified deviations from the mean for all parcels.
Evaluation of a Diffusion Method for Preparing Low‐Nitrogen Samples for Nitrogen‐15 Analysis
Authors: Lory J. A. , Russelle M. P.
Published: July 2010

Ammonia diffusion techniques have been advocated to eliminate crosscontamination problems associated with distillation methods for concentrating low‐N‐content samples for 15N analysis. Two potential problems with diffusion are nonquantitative N recovery and isotopic fractionation. These are most likely to have significant effects for low‐N‐content samples. We evaluated the ability of a diffusion method to accurately prepare low‐N (<1000 µg N), high‐volume (55 mL) simulated acidic digest samples and quantified sinks for N in the diffusion system. This diffusion system trapped N on acid‐impregnated glass fiber disk suspended above the sample solution. The 15N/14N isotopic ratio of N recovered on the disk declined linearly as the quantity of N in the original sample solution decreased below 500 µg N. Nitrogen‐15 values adjusted for contamination detected in reagent blanks still differed significantly from nondiffused reagent blanks. Significant sinks of N other than the acidified disk existed despite efforts to minimize them. The method produced unexplained changes in isotopic composition of the sample. These results emphasize the importance of thoroughly evaluating any NH3 diffusion technique with representative sample types in each laboratory before adoption of the technique for routine use. In addition, we recommend standard curves as a more robust method for adjusting 15N values for errors associated with diffusion.
Soil Crusting and Water Infiltration Affected by Long‐Term Tillage and Residue Management
Authors: Pikul J. L. , Zuzel J. F.
Published: July 2010

Soils with low organic carbon (OC) are prone to crusting. The objective of this study was to investigate effects of tillage and N‐fertility on crusting and water infiltration. Experiments were conducted on two long‐term winter wheat (Triticum aestivum L.) ‐fallow studies. Primary tillage treatments on a tillage study started in 1940 were moldboard plow, disk, and sweep, with fertilizer rates of 45 and 180 kg N ha−1. Primary tillage on a residue management study started in 1931 was spring moldboard plowing. Residue management consisted of wheat straw burned in fall with no added N (FB), 22.4 tons ha−1 of strawy manure every other year (SM), and 90 kg N ha−1 every other year (N90). Water infiltration did not differ among tillage treatments but was 57% greater on 180 kg N ha−1 than on 45 kg N ha−1. Porosity of the surface crust on 180 kg N ha−1 was 12% greater than on 45 kg N ha−1 and 29% greater on SM than on FB. There was a 14% increase in porosity of the surface crust during winter on SM and N90 and a decrease in porosity on FB. Organic C was 62% greater on SM than on FB. Porosity was significantly correlated (r = 0.75) with OC on the tillage and residue studies. Management practices that conserve or increase OC are important to develop porous soils with high infiltrability.
Sulfate Adsorption in Forest Soils of the Great Lakes Region
Authors: MacDonald Neil W. , Burton Andrew J. , Witter John A. , Richter Daniel D.
Published: July 2010

Sulfate adsorption by forest soils modifies the impact of pollutant deposition on cation leaching processes. We examined relationships among SO2−4 adsorption, soil properties, and seasonal variation in soil solution chemistry at 13 sites representing deciduous forest ecosystems common in the Great Lakes region. Objectives of the study were to test the validity of previously proposed SO2−4 adsorption indices, to examine within‐ and among‐site variability in SO2−4 adsorption potential, and to investigate the effects of seasonal changes in soil solution chemistry on SO42‐ retention. Mineral soils were sampled by horizon at all sites, and soil solutions were sampled at lower E and lower B horizon boundaries at 10 sites. Proposed indices overpredicted sulfate adsorption in certain SO2−4 releasing subsurface horizons, seriously limiting the applicability of the published regression equations. We developed improved regression equations using the sum of initial extractable SO2−4 and additional SO2−4 adsorbed under laboratory conditions as the dependent variable. Sulfate retention indices predicted by the improved equations were independent of existing levels of extractable SO2−4 and past history of atmospheric SO2−4 deposition. Examination of within‐ and among‐site variability in SO2−4 adsorption potentials suggested that soils need to be grouped tightly on a taxonomic basis for modelling purposes. Seasonal variation in soil solution SO2−4 concentration and fluxes was consistent with an annual cycle of SO2−4 retention and release. Although seasonal patterns in SO2−4 concentrations and fluxes appeared to be controlled by hydrologic and S‐cycling processes, the magnitude of SO2−4 fluxes was primarily related to atmospheric SO2−4 deposition rates.
Soil‐Stratigraphic Correlation of a Doline in the Valley and Ridge Province
Authors: Crownover S. H. , Collins M. E. , Lietzke D. A.
Published: July 2010

Dolines of the Valley and Ridge Province of eastern Tennessee act as sediment traps and can provide detailed information on the recent geomorphic history of the surrounding landscape. The objective of this study was to determine the soil stratigraphy, age, morphology, and late Quaternary history in an upland doline on the Mascot Formation in eastern Tennessee. Soils were sampled on the doline rim (DR), upper sideslope (US), lower sideslope (LS), and near the doline center (DC). Pedogenesis of this large upland doline is related to parent material and geomorphic processes. Stratigraphy, age, and morphology varies among the soils. Pedon DC has two buried soil profiles. The upper buried A horizon (2Ab) was radiocarbon dated to 320 ± 70 years before present (YBP). This horizon separates a weakly developed, yellowish brown soil above, with 10 to 20% chert that formed in post‐European agricultural‐related sediments (late 18th and 19th centuries) with laminae, from silty pre‐European sediments (middle to late Holocene) that are low in chert but contain an argillic horizon. The second buried horizon (3Ab) was dated at 6100 ± 100 YBP and provides evidence of landscape stability during the middle Holocene, probably during the Hypsithermal Interval. Below this horizon, the soil has less clay and chert content varies. In contrast, Pedon DR has only a veneer of cherty silt loam late Holocene colluvium and cherty clay Mascot residuum. Geomorphic processes of mass wasting and slope wash on the doline sideslopes have provided a variety of sediments that have been trapped within this doline and subsequently subjected to pedogenesis.