bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractRoot 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

AbstractLittle 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

AbstractThe 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

AbstractLignosulfonate (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

AbstractHigh 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

AbstractDenitrification 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

AbstractThe 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

AbstractWe 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

AbstractMacropore 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

AbstractA 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

AbstractA 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

AbstractAmmonia 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

AbstractSoils 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

AbstractSulfate 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.