bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and Temporal Fine‐Root Distribution in Three Louisiana Forest Soils
Authors: Farrish K. W.
Published: July 2010

The distribution of fine plant roots (≤3‐mm diam.) in three northern Louisiana forest soils was investigated. Two upland mixed pine‐hardwood sites and one bottomland hardwood site were sampled periodically for a year. Fine‐root biomass and surface area were determined on root samples extracted using wet sieving of soil corings. Both fine‐root biomass and surface area decreased abruptly with increasing depth on all sites, with 60 to 64% of the biomass and 63 to 70% of the fine‐root surface area occurring in the top 20 cm of soil. Prolonged soil wetness or dryness during the growing season caused reductions in fine‐root‐biomass concentrations. A contradictory increase in fine‐root surface area occurred, however, during prolonged soil saturation in the bottomland site, suggesting a possible change in fine‐root morphology during inundation. Total fine‐root biomass was similar on the three sites, averaging 8.4 and 10.5 Mg ha−1 on the two upland sites, and 9.9 Mg ha−1 on the bottomland site. Total fine‐root surface area was much higher on the bottomland site, however, averaging 1.48 × 105 m2 ha−1 vs. 9.5 × 104 and 7.0 × 104 m2 ha−1 on the upland sites. These data indicate that fine‐root concentrations in these forest soils decrease rapidly in response to unfavorable soil environmental conditions such as prolonged saturation or drying. These data also indicate that maximum root concentrations generally occur in the spring and early summer, with minimums during late summer, fall, and winter.
Phosphate Mineralogy and Equilibria in Two Kentucky Alfisols Derived from Ordovician Limestones
Authors: Karathanasis A. D.
Published: July 2010

The phosphate mineral distribution as it relates to in situ soil solution composition of two Alfisols developed from phosphatic Ordovician limestones in the inner Bluegrass Region of Kentucky was investigated. At both sites, microcrystalline apatite appeared to be the primary source of P. Surface weathering under a moderate pH (5.7–6.7) and a carbonate‐free environment has apparently induced apatite transformations to wavellite, crandallite‐like, and barrandite‐like minerals as indicated by x‐ray diffraction (XRD), differential scanning calorimetry (DSC) or scanning electron microscopy (SEM) analyses. The possible stability of othe phosphate minerals such as millisite, montgomeryite, variscite, strengite and MnPO4·1.5H2O was supported by solution‐composition data, but it was not confirmed by XRD, DSC, or SEM analyses. Sequential‐fractionation extractions suggested the presence of significant amounts of discrete or occluded Al‐ and Fe‐phosphates in soil and nodular materials, mostly in amorphous or poorly crystalline forms. The solution ion‐activity products in most cases were consistent with amorphous Fe‐ or Al‐phosphates approaching the stoichiometry, but exceeding the solubility, or strengite or variscite‐like minerals. Solution data and SEM observations suggested that the formation of secondary Ca‐Al‐, Al‐, and/or Fe‐phosphates in these soils may occur through an apatite congruent‐dissolution stage, which is followed by gradual adsorption and precipitation of P on chemically etched clay‐mineral and amorphous‐hydroxide surfaces.
Using an Electro‐Optical Switch to Measure Soil Water Suction
Authors: Cary J. W. , Gee G. W. , Simmons C. S.
Published: July 2010

A simple and inexpensive electro‐optical switch (infrared light‐emitting diode; IR LED) was used to show that soil water suctions can be measured accurately by employing nylon filter disks with different pore sizes. Nylon filter disks that become translucent when water is absorbed were shown to open or close an electro‐optical switch at specific soil water suctions associated with the air‐entry suction of a disk, thereby demonstrating the principle of a digital tensiometer. Sensors constructed by inserting a nylon filter disk in a switch were shown to operate across a suction range of 0.004 to 2.4 MPa and were tested in a silt loam soil under drying and wetting conditions. The switch‐sensor's performance was compared with a second type of sensor (CdS photoresistor with LED) made with a layered fritted‐glass disk instead of nylon. This second sensor was able to continuously detect changes of water content from air dry to saturated. We concluded, however, that the first type of sensor was superior for precisely measuring soil water suction.
Saturated Hydraulic Conductivity Reduction Caused by Aerobic Bacteria in Sand Columns
Authors: Vandevivere Philippe , Baveye Philippe
Published: July 2010

Bacterial reductions of the saturated hydraulic conductivity, Ks, of natural porous media have been traditionally associated with the development of anaerobic conditions and the production of large amounts of extracellular polymers by the bacteria. Various researchers have also reported that these reductions occur predominantly at or very near the surfaces of injection of nutrients within the porous media. Attempts to describe mathematically the resulting clogging process have, in the past, been based on the assumption that bacterial cells form impermeable biofilms uniformly covering pore walls. A series of percolation experiments was carried out to determine the extent to which an obligately aerobic bacterial strain, Arthrobacter sp., is able to clog permeameters filled with fine sand. A second objective was to elucidate the mechanism(s) responsible for this process. The experimental results indicate that strictly aerobic bacteria are able to reduce Ks by up to four orders of magnitude. Rapid reductions in Ks are associated with the formation of a bacterial mat at the inlet boundary of the sand columns. When the colonization of the inlet is prevented, clogging proceeds within the bulk of the sand at a noticeably slower rate. Under O2‐ or glucose‐limited growth conditions, this decrease in Ks within the sand does not appear on scanning electron micrographs to be caused by exopolymers, which are entirely absent, but rather seems to be due to the presence of large aggregates of cells that form local plugs within the pores. Under conditions of severe N limitation, the same mechanism seems to be largely responsible for the observed clogging, in spite of the production by the cells of extracellular substances, visible under light microscopy and on scanning electron micrographs. In all cases, the coverage of the solid surfaces by the bacterial cells is sparse and heterogeneous, contrary to the basic tenets of the biofilm model.
Simulation of Surface Energy Balance and Soil Temperature under Strip Tillage: II. Field Test
Authors: Hares Mohammad A. , Novak Michael D.
Published: July 2010

Strip tillage may be a viable management technique for annual crops in northern latitudes, since the mulch strip should conserve soil and water while higher temperatures in the bare strip should yield good germination. 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. We tested the model with micrometeorological data collected at Vancouver, BC. Soil temperatures and evaporation rates in bare and uniformly covered straw‐mulch plots were predicted reasonably well, except for the bare plot when evaporation was soil limited. The disagreement was attributed to variability associated with patchy soil drying and inadequacy of the simple surface‐resistance model used to calculate evaporation. Good agreement for evaporation rates under 10 and 20 t ha‐1 mulches was achieved by enhancing transfer rates within the mulch layers by at least a factor of 4.5 above molecular diffusion rates. For the strip‐tillage plots, the model underestimated (energy‐limited) evaporation rates and soil temperatures in 0.1‐m‐wide bare strips separated by 0.3‐m‐wide mulch strips. This disagreement was attributed to micro‐scale advection of warmer and drier air from the mulch strips to the bare strips, a phenomenon neglected in the model (and in all such models in the literature). The measurements showed that springtime soil temperatures in bare strips oriented in various directions were nearly equal to those in an adjacent bare plot. Therefore, considerable erosion protection should be possible without deleterious soil thermal regimes for seed germination.
Rainfall Intensity Affects Transport of Water and Chemicals through Macropores in No‐Till Soil
Authors: Edwards W. M. , Shipitalo M. J. , Owens L. B. , Dick W. A.
Published: July 2010

Water that infiltrates through cropland soils can carry agricultural chemicals through and below the root zone, possibly reaching groundwater. We investigated the effect of rainfall intensity on movement of water and chemicals through no‐till soil containing earthworm (Lumbricus terrestris L.) burrows and other macropores. Nine 30 by 30 by 30 cm blocks of soil from the surface of a no‐till corn (Zea mays L.) field received a surface application of 7.7 kg ha‐1 atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) and 105 kg ha‐1 SrBr2·6H2O and were subjected to simulated rainfall treatments of 30 mm (2700 mL) of water applied in 15‐, 30‐, or 120‐min periods. Percolation through the blocks during and after the rainfall treatments was collected in 64 3.75 by 3.75 cm cells at the base of each block. Average time to start of percolation was 2.2, 4.4, and 51.5 min for the 15‐, 30‐, and 120‐min rainfall treatments, respectively. For the same treatments, percolation volumes averaged 468, 334, and 33 mL block‐1. Of the 64 possible percolation sampling cells, the average number of cells that collected percolate was 13.3 for the fast, 5.3 for the medium, and 3.3 for the slow treatments. The largest percolate sample for each block averaged 34, 60, and 51% of the total percolate for these intensity rates, emphasizing the lack of homogeneous flow through soils containing macropores. Average concentration of atrazine in the percolate ranged between 7 and 9 mg L‐1 and was not affected by rainfall intensity. A second 30‐min‐intensity storm was applied 1 wk later to all blocks, producing more percolate with lower chemical concentrations. Transport of each chemical was dominated by percolate volume rather than by rainfall intensity.
Contribution of Nitrogen Fixation to Sugar Cane: Nitrogen‐15 and Nitrogen‐Balance Estimates
Authors: Urquiaga Segundo , Cruz Kátia H.S. , Boddey Robert M.
Published: July 2010

Continuous sugarcane (Saccharum spp.) culture in Brazil, with low N inputs and almost total removal of plant biomass at each harvest, has not depleted soil N reserves. This, and high numbers of N2‐fixing bacteria associated with the plants, suggests that the crop may be obtaining considerable N from biological nitrogen fixation (BNF). This 3‐yr study assessed the importance of such contributions to three sugarcane species (S. officinarum L., S. barberi Jesw., and S. spontaneum L.), and seven commercial Brazilian hybrids. The plants were grown in a concrete tank containing 15N‐labeled soil in order to use 15N isotope dilution to estimate the BNF contributions. A grass, Brachiaria arrecta (cv. IRI 442), was included as a non‐N2‐fixing control. All aerial tissue was harvested annually, and the roots and stem bases were removed at the end of the experiment. For all 3 yr, the commercial hybrids and the S. spontaneum cultivar (Krakatau) accumulated more N at significantly lower 15N enrichments than the control. These data suggest that the plants obtained considerable BNF contributions, but interpretation of the 15N data was prejudiced by (i) the steadily declining 15N enrichment of the soil mineral N, (ii) carry‐over of N from one harvest to the next in the roots and stem bases, and (iii) shading of the control crop by the tall cane plants. Several of the sugarcane cultivars had significantly positive N balances, however, and there was good agreement between the estimates of BNF contributions derived from N balance and isotope dilution. Krakatau and the commercial hybrids CB 45‐3 and SP 70‐1143 obtained the largest contributions from BNF, but methodological problems did not allow exact determinations.
Soil Water and Crop Yield Spatial Variability Induced by Irrigation Nonuniformity
Authors: Or Dani , Hanks R. J.
Published: July 2010

Experimental evaluation of different irrigation management practices under similar conditions of soil variability often requires several plots having similar soil variability. These types of field plots are difficult to find or not available for experimental use. This study examined crop yield and soil water variability resulting from nonuniform irrigation applications as a surrogate for soil variability within an otherwise homogeneous field. The study conducted at Logan, UT, in 1989 on a Millville silt loam soil (coarse‐silty, carbonatic, mesic Typic Haploxeroll) used a drip irrigation system with spatially variable application rates. The mean dripper application rate was 5.6 L/h with a standard deviation of 3.18 L/h and a spatial‐correlation range of 5.3 m. Corn (Zea mays L.) was grown in 0.75‐m‐wide rows at a plant density of 8.9 plants/m2 in 30 by 15 m plots. Irrigation‐scheduling treatments were (i) a predetermined calendar schedule (NPT), and (ii) optimized for the nonuniformity of the irrigation system (OPT). There were three replicates. Soil water, crop height, and crop‐yield variability exhibited spatial structures similar to the applied‐irrigation variability, but crop‐yield variability (mean CV of 0.227) was less than the irrigation variability (CV of 0.57). Crop yield was highly correlated to the dripper flow rate and was 13% higher on the OPT than on the NPT schedule. Nonuniform irrigation can be used to induce a desired spatial pattern of available soil water. Irrigation scheduling methods should consider soil variability and irrigation uniformity.
Surface Sealing and Hydraulic Conductances under Varying‐Intensity Rains
Authors: Giménez D. , Dirksen C. , Miedema R. , Eppink L.A.A.J. , Schoonderbeek D.
Published: July 2010

In the past, investigations on surface seals developing under simulated rains usually were performed with uniform rainfall intensities. Recent studies, however, showed that varying‐intensity rains affect erosion and volumes of runoff. We conducted a study on surface sealing under varying‐intensity rains using physical and morphological methods. Four 1‐h‐duration rainfall patterns were used: S1, S2, S3 and S4, with mean rainfall intensities of 83, 69, 65, and 51 mm h‐1, respectively, and highest intensities of 148, 120, 111, and 100 mm h‐1, respectively. Two experiments were performed in triplicate: (i) in packed soil columns, pressure heads at 1‐cm depth were measured, and runoff (Rt) and wash sediment (St) collected at short time intervals during S1, S3, and S4 patterns; and (ii) packed shallow soil flumes were successively exposed to 10, 15, 30, 40, and 60 min of S2 and S4 patterns, and the surface was then characterized by micromorphological analysis of thin sections (S2) and top‐view photographs (S2 and S4). The largest differences between rainfall patterns occurred during the intensity peaks (10–30 min): at the end of these periods, measured surface seal hydraulic conductances (β) attained values of 0.80, 0.25, and 0.51 h‐1 for S1, S3, and S4, respectively. These relative β values are thought to be due to partially open surfaces as a result of microrill erosion (S1), complete sealing without erosion (S3), and incomplete sealing (S4). Presented Rt, St, and morphological data support these conclusions. After 5 min of the intensity peaks of S2, surface seals attained maximum observed thickness and minimum macroporosity (>30 µm). Planar voids (>500 µm) were eliminated at this point. Under continuing rain, erosion reduced the seal thickness and increased macroporosity, mainly as planar voids.
Field‐Scale Bromide Transport as Affected by Tillage
Authors: Agus F. , Cassel D. K.
Published: July 2010

Tillage alters soil physical properties and modifies the rates of many physical, chemical, and biological processes. The purpose of this study was to determine if subsoiling increased the depth of leaching of the nonreactive Br‐ anion in a Norfolk soil (fine‐loamy, siliceous, thermic Typic Kandiudult) having a tillage‐induced pan. Three tillage treatments, replicated three times, were selected: (i) current‐year subsolling (S88); (ii) one‐year subsoiling carry‐over (subsoiled in 1987: S87); and (iii) double disk tillage (DD). Mechanical impedance was measured at 35 d after tillage with a recording cone penetrometer to a depth of 60 cm on transects normal to the soybean (Glycine max [L.] Merr.) row. Cone index exceeded 3000 kPa for the DD treatment at the 20‐ to 45‐cm depth; current‐year subsoiling reduced cone index at that depth to 1300 to 2500 kPa. Six days after planting soybean, KBr was uniformly broadcast on the soil surface at the rate of 280 kg Br‐/ha. Soil samples were taken after the plots received 130, 260, 545, and 1217 mm of cumulative rain and/or irrigation (28, 64, 128 and 351 d, respectively, after applying KBr). Soil samples were collected using a hydraulic probe at seven positions on duplicate transects normal to the soybean row in each plot. Bromide concentration measured with a specific‐ion electrode was highly variable at all depths. For the four consecutive sampling dates, the center of Br‐ mass occurred at the 11‐, 17‐, 51‐, and 90‐cm depths, respectively, for Treatment DD; at the 19‐, 27‐, 71‐, and 1002‐cm depths for Treatment S88; and at the 13‐, 20‐, 57‐, and 108‐cm depths for Treatment S87. Both subsoil treatments loosened the soil and increased the depth of Br‐ transport. Although the depth of Br‐ transport was slightly deeper for the subsoiled treatments, it leached below the rooting depth for all treatments. No definitive relationship between cone index and Br‐ leaching depth was observed.
Soil Dispersibility, Rain Properties, and Slope Interaction in Rill Formation and Erosion
Authors: Shainberg I. , Warrington D. , Laflen J. M.
Published: July 2010

Soil erosion increases with slope steepness. We hypothesized that the rate at which short‐slope soil erosion increases with slope steepness depends on the prevailing erosion mechanism, which in turn depends on soil dispersibility and rain properties (impact energy of drops and water quality). Soil dispersion, as a function of exchangeable sodium percentage (ESP) and water quality, was determined by shaking soil samples in deionized water (DW) or tap water (TW). Clay dispersion increased with increases in soil ESP and was prevented by the electrolyte concentration in TW. We studied the effect of soil ESP, water quality, and the impact energy of rain on soil erosion while maintaining similar runoff. To do so, we first exposed the soil samples to DW rain on a 5% slope until a surface seal developed. Then we increased the slope to 35% and changed the water quality and impact energy of the rain. Runoff volumes were unaffected by rain properties at the 35% slope. Soil losses increased with increases in the ESP of the soil. Soil losses varied with rain properties in the following order: DW rain > TW rain = DW rain with low energy (mist) > TW mist. Rills were formed by both DW rains (high impact energy and mist). The extent of rilling increased with soil ESP. No rills were formed by TW rains. Under dispersive conditions (sodic soils and DW), runoff was sufficient to initiate rilling and soil losses increased sharply with slope.
Infiltration of Simulated Rainfall: Tillage System and Crop Residue Effects
Authors: Unger Paul W.
Published: July 2010

Low precipitation limits dryland crop yields in semiarid regions. Irrigation can increase yields, but declining water supplies, competition for water, and high pumping costs have caused an increased emphasis on water conservation in many regions. Water conservation, however, often is hindered by soil surface conditions that cause runoff, even from small rainstorms. The objective of this study was to determine the effect of tillage system and crop residue [winter wheat, Triticum aestivum L.; grain sorghum, Sorghum bicolor (L.) Moench] treatments on infiltration of simulated rainfall on Pullman (fine, mixed, thermic Torrertic Paleustoll) soil at Bushland, TX. Treatments were moldboard plowing plus disking, rotary tillage, sweep tillage with residues removed, sweep tillage with residues left in place, no‐tillage with residues removed, and no‐tillage with residues left in place. Different tillage systems caused significant differences in soil aggregate size, aggregate stability, organic‐matter concentration, initial water content, sediment loss during the rainstorms, bulk density, surface residue cover, and surface roughness. Compared with the no‐tillage treatments, moldboard plowing usually caused the greatest differences in the soil conditions. There was no close relationship, however, between any soil condition and infiltration. With limited residues, soil‐loosening tillage increased infiltration.
Influence of Oxalate Loading on Phosphorus and Aluminum Solubility in Spodosols
Authors: Fox T. R. , Comerford N. B.
Published: July 2010

Organic anions can increase the solubility of P and Al in soils and may influence nutrient availability and soil weathering. In Spodosols of the southeastern USA, oxalate has been identified as the dominant organic anion. Therefore, the objectives of this study were to examine the influence of oxalate on the release of inorganic P, organic P, and Al from A, and Bh horizons of two forested Spodosols from the Lower Coastal Plain. Oxalate loading rates ranging from 0 to 125 mmol kg‐1 soil were examined in a series of batch experiments using single, one‐time additions and repeated sequential additions of oxalate. Oxalate had a negligible effect on P and Al release from the A horizon soils. In contrast, oxalate had a large effect on both inorganic and organic P, as well as Al release from the Bh horizon soils. The effect of sequential additions of oxalate on P and Al release from these soils was found to be cumulative. The amount of Al or P released was primarily controlled by the cumulative oxalate loading rate. In addition, the manner of oxalate loading (single vs. sequential) had relatively little effect. At the same total, cumulative oxalate loading rate, the cumulative amount of Al or P released following sequential additions of oxalate at low concentrations were essentially the same as the amount released following a single addition of oxalate at a much higher concentration. This suggests that a continuous release of even small amounts of organic anions in forest soils could solublize large amounts of P and Al on an annual basis.
Analysis of Measured, Predicted, and Estimated Hydraulic Conductivity Using the RETC Computer Program
Authors: Yates S. R. , van Genuchten M. Th. , Warrick A. W. , Leij F. J.
Published: July 2010

A nonlinear least‐squares optimization program, RETC, which uses empirical relationships for describing the water‐retention curve and predictive models for characterizing the unsaturated hydraulic conductivity relationship was used to analyze 36 unsaturated hydraulic conductivity distributions obtained from the literature for 23 different soils. By comparing the measured, predicted, and estimated relative conductivity for the group of data, the efficiency and accuracy of this approach for characterizing the soil hydraulic properties was determined. The analysis consisted of comparing measured, predicted, and estimated conductivities using three predictive methods and two simultaneous methods (which include known values of the conductivity). The results indicate that for this group of data, the best method for determining the model parameters that will accurately describe both the water retention and unsaturated hydraulic conductivity relationships is to use a simultaneous approach with either five or six parameters. It was also found that the predictive approach introduces a bias into the estimates of the unsaturated hydraulic conductivity and a predictive approach with scaling did not significantly improve the estimates of the unsaturated hydraulic conductivity.
X‐ray Tomography of Soil Water Distribution in One‐Step Outflow Experiments
Authors: Hopmans J.W. , Vogel T. , Koblik P.D.
Published: July 2010

The application of an optimization procedure to indirectly infer soil hydraulic functions from measured outflow in pressurized soil samples (one‐step outflow method), although widely used, has not been fully accepted. Reported problems are associated with the nonuniqueness and instability of the solution, as well as with the flow conditions that exist in the soil as a result of the high pressure difference across the sample. Computed tomography (CT) imaging of two soils with different texture was used to measure soil water distribution during the outflow process. Tomographic results show that unfavorable conditions exist if the soil is initially saturated. Richards' equation, which is employed in the optimization technique, assumes air continuity everywhere in the sample at all times. However, the ceramic plate at the outflow end of a pressurized saturated soil sample prevents the existence of a continuous air phase during initial desorption. We suggest that better results are obtained with the one‐step outflow method if the sample is initially unsaturated when pressure is applied.
Diffusion Kinetics of Multinutrient Accumulation by Mixed‐Bed Ion‐Exchange Resin
Authors: Yang Jae E. , Skogley Earl O.
Published: July 2010

Conventional batch or miscible‐displacement methods for studying nutrient release in the soil‐solution‐root continuum have been confined to single‐ion‐release reactions that result in the disintegration of concentration gradients due to excessive water and chemicals used in the procedure. The Phytoavailability Soil Test (PST) accumulates all nutrients simultaneously, as a function of diffusion to a mixed‐bed resin sphere. Objectives of this research were to compare kinetic models to describe empirically multinutrient accumulation by the PST method, and to test its sensitivity to conditions that influence diffusion kinetics. Accumulation of nutrients by resin was measured by inserting resin spheres into saturated soil pastes for 96 h at 25, 35, or 45°C, and stripping resin‐accumulated nutrients with HCl. Existing kinetic models all described multinutrient accumulation, except for NO3‐N. The parabolic diffusion law model consistently provided the best fit. Values for reaction rates and net reaction energy (Ean) were of similar magnitude to those reported in the literature. Positive values of ΔGo‡ and ΔHo‡ and negative values of ΔSo‡ (pseudo thermodynamic parameters) for K and P accumulation were similar to those reported for release of these nutrients. Significant relationships were found between rate constants of K, P, S, and NH4‐N and respective ion activities in soil solution. Accumulation of all nutrients was directly related to temperature, except NO3‐N, which was temperature and soil specific. These results suggest that the PST method has advantages over conventional methods for measuring nutrient dynamics, as it more closely simulates field conditions, while providing for multinutrient studies.
Transport of Naturally Occurring Dissolved Organic Carbon in Laboratory Columns Containing Aquifer Material
Authors: Dunnivant F. M. , Jardine P. M. , Taylor D. L. , McCarthy J. F.
Published: July 2010

The subsurface transport of ionic and nonionic pollutants may be strongly impacted by the movement of naturally occurring dissolved organic carbon (DOC) in aquifers. Thus, the adsorption, desorption, and transport of DOC in laboratory columns containing well‐packed aquifer material was investigated. Data showed that the breakthrough of DOC from aquifer columns was the result of complex adsorption reactions between DOC and the aquifer material. Breakthrough curves (BTCs) of the DOC were characterized by an initial rapid concentration increase followed by extended tailing to long times. The extensive tailing of the BTCs was attributed primarily to the slow adsorption kinetics of DOC to the aquifer material and the nonlinear nature of the adsorption isotherm. Independent experiments suggested that the size exclusion of DOC from aquifer pores was negligible. The time required to saturate the aquifer material with organic C was dependent on the influent DOC concentration, with lower organic influent levels requiring longer pulse durations to fully saturate the aquifer sediment with organic C. Hydrophobic constituents of the DOC were preferentially adsorbed while hydrophilic components were rapidly transported through the aquifer columns. Spectral analysis (light absorbance at 260 nm) of the column effluents confirmed that the composition of the mobile organic C changed during the breakthrough of DOC. Data from this investigation demonstrate that DOC can be mobile in soil systems, and emphasizes the need to evaluate the cotransport of pollutants by DOC.
Comparison between Pyrocatechol Violet and 8‐Hydroxyquinoline Procedures for Determining Aluminum Fractions
Authors: McAvoy Drew C. , Santore Robert C. , Shosa Jennifer D. , Driscoll Charles T.
Published: July 2010

There is currently considerable interest in quantifying concentrations of Al species in solution because of: (i) concern about the potential toxicity of inorganic forms of Al to plants and aquatic organisms, (ii) the need to better understand the processes contributing to soil development, and (iii) ongoing assessments of the biogeochemistry of Al. This study was conducted to compare the pyrocatechol violet (PCV) and 8‐hydroxyquinoline (oxine) methods for the determination of monomeric Al fractions. A strongly acidic cation‐exchange resin was used in automated PCV and nonautomated oxine procedures to separate aqueous Al into inorganic (labile) and organic (nonlabile) monomeric forms. Both synthetic and natural solutions were used in this analysis. Results showed good agreement between the two methods, suggesting that the PCV method is an acceptable alternative to the oxine method for the estimation of monomeric Al. In addition, the cation‐exchange column fractionation procedure was verified using an F ion‐selective electrode. Interference to the PCV method by Fe, F, and dissolved organic C was not significant across the range of solution concentrations studied.
Modeling Soil Organic Matter in Organic‐Amended and Nitrogen‐Fertilized Long‐Term Plots
Authors: Paustian Keith , Parton William J. , Persson Jan
Published: July 2010

To study the effects of organic matter and fertilizer additions on soil organic‐matter (SOM) dynamics, we analyzed results from a 30‐yr‐old Swedish field experiment, using the CENTURY model. Field treatments on a sandy clay loam included biannual addition (up to 4000 kg C ha−1) of straw, sawdust, and no organic additions, with and without N fertilizer (80 kg N ha−1), and green manure, farmyard manure, and bare fallow. Soil C and N, crop production (small‐grain and root crops), N uptake, and mineralization and immobilization of N were modeled and compared with field measurements. Changes in soil C and N, as much as 30% after 30 yr, were generally well represented by the model. Most of the treatment differences in SOM could be explained by the rate of organic‐matter input, its lignin content, and C/N ratio, plus the effect of N fertilizer on belowground C inputs. However, there appeared to be additional positive effects of N supply on SOM accumulation that were not fully explained by the model. The quality of organic amendments strongly influenced N uptake and crop productivity, through controls on N mineralization and immobilization. Mean annual N uptake ranged from a low of 3.1 g m−2 in sawdust‐amended soil to a high of 9.2 g m−2 in fertilized, straw‐amended soil. Simulated N losses accounted for 7 to 20% of total N inputs. Nitrogen‐balance estimates by the model were consistent with the observed data for four of the treatments, but treatments with low N availability appeared to have additional, unexplained N inputs.
Pedogenesis of Two Forest Soils (Kandiustults) Derived from Metamorphosed Granite in Korea
Authors: Cho Hi Doo , Mermut A. R.
Published: July 2010

Soils derived from granite rocks occupy 66% of the land in Korea. Two soils from the southern part of Korea formed on metamorphosed granite under forest vegetation, containing high amounts of ferruginous chlorite, were studied to evaluate weathering and formation of clay minerals. The soils are deeply weathered, strongly acid, low in organic matter and cation‐exchange capacity (CEC), and the amounts of clay in the very thick Bt horizons are almost three times higher than in the BC horizons. Micromorphology of the thin O horizon showed common characteristics of moder humus and evidence of high biological activity. High contents of coarse grains and low plasma impart to the E horizon an enaulic‐related distribution pattern. The most striking micromorphological features are multilaminated, generally limpid ferriargillans in the Bt and BC horizons. While some chlorites are intact or partly weathered in the E and BC horizons, they are entirely weathered in the Bt horizons. High clay contents in the Bt horizons are not only due to clay translocation, but also to intensive in situ mineral weathering in this zone. The most significant pedogenic processes, as revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were formation of Fe oxyhydroxide and tubular halloysite from the weathering of chlorite and other primary minerals. Iron oxides imparted a typical red color to the soils. Total chemical analysis of clays revealed extensive loss of Ca, K, and Na and concentration of Fe and Al. Almost equal proportions of Al and Si oxides support a clay fraction dominated by halloysite and kaolinite. Mineralogical studies of clays in the Bt horizon showed that, while feldspars were partly weathered, chlorite, under a well‐drained, acid, humid temperate to semitropical environment, was completely weathered to kaolinite, halloysite, hematite, goethite, gibbsite, and a chlorite‐vermiculite intergrade, probably hydroxy‐interlayered vermiculite (HIV). Some dioctahedral mica appeared to be resistant in the soils.
Mapping Soil Salinity Using Calibrated Electromagnetic Measurements
Authors: Lesch S. M. , Rhoades J. D. , Lund L. J. , Corwin D. L
Published: July 2010

A statistical modeling approach is presented that predicts spatial soil salinity patterns from aboveground electromagnetic induction (EM) readings. In this approach, EM readings are obtained from a field sampled on a uniform (centric systematic) grid. A small number of these sample sites are chosen for soil sampling, based on the observed EM field pattern. The salinity levels for these soil samples are determined and then the remaining nonsampled salinity values are predicted from the corresponding EM readings through a multiple linear regression equation. Experimental results suggest that this approach will work well in fields having low to moderate levels of soil textural variability. For example, 95% of the spatial variability in soil salinity within typical 16.2‐ha (40‐acre) cotton (Gossypium hirsutum L.) fields could be accounted for with only 36 soil samples, as opposed to the 200 to 300 soil samples typically required if no EM readings were available. This approach makes EM readings a more practical and cost‐effective tool by substantially reducing the number of soil samples needed for accurate mapping of spatial salinity patterns at the field scale.
Dry‐Soil Aggregate Stability as Influenced by Selected Soil Properties
Authors: Skidmore E. L. , Layton J. B.
Published: July 2010

Dry aggregate stability is an important soil physical property for evaluating tillage and wind‐erosion research. Research in this study was aimed at developing a model for predicting soil aggregate stability as influenced by intrinsic soil properties, with particular application to wind erosion. Aggregates from 10 Kansas soils with a wide textural range were tested periodically for stability during a 3‐yr period. The logarithm of aggregate stability was regressed against the intrinsic soil properties (geometric mean diameter of primary particles, specific surface area, water content at −1500 J/kg matric potential, and clay content). Clay content and water content at −1500 J/kg were both good predictors of mean aggregate stability. A resulting empirical model estimates mean aggregate stability from either clay or water content with coefficients of determination of 0.97 and 0.96, respectively. Further testing is planned by running the model with several independent data sets to estimate the probability of aggregate stability within specified limits for particular soils.
Miniaturized Method to Measure Carbon Dioxide Production and Biomass of Soil Microorganisms
Authors: Heilmann B. , Beese F.
Published: July 2010

Microbial activities and biomasses in soils exhibit steep gradients across short distances, forming microhabitats with different qualities. A methodological study was carried out to determine CO2 production of soil microorganisms in miniature. Soil samples (2–4 g) from 28 different soil types of southern Germany were incubated directly in a small glass ampoule within a 20‐mL gas‐tight syringe. A high correlation (r = 0.96) between CO2 production and heat output suggests that this micromethod is useful for the determination of CO2 respiration and the estimation of microbial biomass of small soil samples.
Alkalinity Measurements in Water Extracts of Calcareous Soils
Authors: Marion G.M. , Schlesinger W.H. , Fonteyn P.J.
Published: July 2010

In soil carbonate solubility studies, it is usually assumed that total alkalinity is equal to inorganic‐C alkalinity. Recent studies have raised questions about the validity of this assumption. This study reexamined previously published soil data from grass‐oak (Quercus spp.) woodlands and deserts to test the hypothesis that total alkalinity is equal to inorganic‐C alkalinity. Total alkalinity was measured with strong‐acid titration, while inorganic‐C alkalinity was calculated from pH and the partial pressure of CO2 (pCO2) measurements. Within the limits of error, calculated inorganic C alkalinity (Y) was equal to measured total alkalinity (X) (Y = 0.01 + 0.998X, r2 = 0.97). A recommendation was made for overdetermining the state of experimental systems in solubility studies; this allows one to check the internal consistency of experimental measurements, equilibrium constants, and model assumptions.
Thermally Driven Water and Octane Redistribution in Unsaturated, Closed Soil Cells
Authors: Prunty Lyle
Published: July 2010

Temperature‐gradient influences on non‐aqueous‐phase liquid (NAPL) distribution in soil have received little detailed study, although there have been proposals to employ such gradients in remediation of NAPL contamination. The goal of this study was to characterize the time dependence and ultimate steady‐state distributions of water and octane after a constant temperature difference had been imposed across a volume of soil. Cells 5 cm long were packed with soil of initially uniform water and octane content. Temperatures at opposite ends of the cells were established and maintained at 40 and 6°C. Cells were destructively sampled at seven times from 1.5 to 100 h. Octane moved toward the cool end of the soil within 1.5 h. Water redistributed more slowly, but continued to do so for > 12.5 h. Water concentrating at the cool end of the cells resulted in reversal of the initial movement of octane at times > 1.5 h. The final steady‐state distribution of water in the cells had > 95% of the total water within the 3 cm nearest the cool end. In contrast, octane showed a peak at the location where water content dropped sharply. The interval 3 to 4 cm from the cool end contained 28% of the total octane in the cells. This study indicates that using thermal gradients effectively for concentrating NAPL will be a complex undertaking.
Macropore and Surface Seal Interactions Affecting Water Infiltration into Soil
Authors: Ela S. D. , Gupta S. C. , Rawls W. J.
Published: July 2010

Macropores can increase water infiltration into soils whereas surface sealing decreases infiltration. Using Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) and Port Byron silt loam (fine‐silty, mixed, mesic Typic Hapludoll) soils, this study examined the effect of simulated rainfall on water infiltration into soils with earthworm (Aporrectodea tuberculata) and artificial macropores. Treatments included bare and covered soil surfaces, soils with and without macropores formed by earthworms, and soils with artificially formed macropores of 2‐, 3‐, 4‐, and 5‐mm diameter. During simulated rainfall, infiltration was measured by continuously monitoring the increase in container weight. Comparison of infiltration rates between bare and covered treatments showed that a surface seal developed on bare soils. The surface seal was effective in sealing visible macropores varying in diameter from 2 to 5 mm. Subsequent measurements with a disk permeameter at the surface and three subsurface depths showed that open macropores at the surface were ineffective in conducting water to deeper depths because they lacked continuity below the surface. Likewise, measurements of the water flux through individual earthworm macropores demonstrated that much of the increase in water flux due to macropores was due to the contribution of only a few of the visible macropores. The description of macropore size and number by themselves may be insufficient for developing models of water entry into soils containing earthworm macropores.
Changes in Aluminum and Phosphorus Solubilities in Response to Long‐Term Fertilization
Authors: Hetrick J. A. , Schwab A. P.
Published: July 2010

Continuous fertilization with NH4 and phosphate fertilizers often has profound effects on the chemistry of soils. The resulting decreased pH and increased orthophosphate activities can impact the solid‐ and solution‐phase equilibria. The objective of this study was to determine the effect of long‐term fertilization of Al and P soil solution activities and to relate these activities to mineralogical components of the soil. Soil fertility treatments were established in Manhattan, KS, on a Smolan silt loam (fine, montmorillonitic, mesic Pachic Argiustoll) and annually received high rates of NH4NO3 and superphosphate for >40 yr. High rates of NH4 applied to these soils decreased the soil pH from 6.9 to 4.1, and it was anticipated that the activities of Al and P might have been affected by pH changes. Solubilities of Al and P were measured after equilibrating soils for 36 d in 0.01 M CaCl2, and ionic activities were calculated. Apparent equilibria with amorphous Al(OH)3 and hydroxyapatite were observed in unfertilized soils. Phosphorus fertilization did not affect Al solubilities but increased P activities to apparent equilibrium with tricalcium phosphate and Al phosphates. The mean ion activity product for AlPO4·nH2O was −2.29 ± 0.38 compared with −2.50 for AlPO4 (variscite) and −0.92 for AlPO·2H2O (amorphous). Aluminum solubilities in the N‐treated soils were undersaturated with respect to Al oxides, Al oxyhydroxides, Al hydroxides, and all phosphate minerals but may have been in equilibrium with montmorillonite.
Particulate Soil Organic‐Matter Changes across a Grassland Cultivation Sequence
Authors: Cambardella C. A. , Elliott E. T.
Published: July 2010

Many models have been constructed in an attempt to describe the dynamics of soil organic‐matter (SOM) turnover, most of which include 2 to 3 kinetically defined organic‐matter pools. Physical and chemical definition of these conceptualized SOM pools has been difficult. We describe a simple method for dispersion of soil to isolate a particulate organic‐matter (POM) fraction that may represent an important SOM pool in grassland soils. The POM fraction was isolated by dispersing the soil in 5 g L−1 hexametaphosphate and passing the dispersed soil samples through a 53‐µm sieve. We compared POM and mineral‐associated C among three tillage treatments (20 yr under cultivation) and an undisturbed grassland at Sidney, NE. The POM C in the native sod represented 39% of the total soil organic C. Twenty years of bare‐fallow, stubble‐mulch, and no‐till management reduced the C content in this fraction to 18, 19, and 25%, respectively, of the total organic C. The mineral‐associated organic‐matter fraction showed no reduction in C content in the bare‐fallow treatment compared with the grassland soil but increased in the no‐till and stubble‐mulch treatments. Nitrogen dynamics generally mirrored those observed for C. Analysis of the POM fraction for lignin and cellulose content indicated that this fraction was 47% lignin and had a lignocellulose index of 0.7. The stable C‐isotope composition of the POM fraction suggests that wheat‐derived POM turns over faster than grass‐derived POM. We suggest the POM fraction closely matches the characteristics of a SOM pool variously described as slow, decomposable, or stabilized organic matter.
Grain Sorghum‐Soybean Rotation and Fertilization Influence on Vesicular‐Arbuscular Mycorrhizal Fungi
Authors: Ellis J. R. , Mason S. C. , Roder W.
Published: July 2010

Vesicular‐arbuscular mycorrhizal fungi (VAMF) can reduce plant stress resulting from nutrient deficiencies, drought, and other factors. The objective of this work was to measure the effect of soybean [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] rotation and fertilization on plant response and VAMF root colonization and diversity, and relate effects to soil environment. Fertilizer treatments consisted of no fertilizer, N, and manure. Rooting densities correlated with previous crop, VAMF colonization, and soil NO3. Root colonization by VAMF was affected by previous crop, rooting density, N fertilization, soil P, and water‐filled pore space. Root colonization by VAMF ranged from 93% at 15 cm to 15% at the 120‐cm soil depth. Root density and VAMF colonization were least when soybean was grown the previous year and manure was applied. Root colonization by VAMF for control, N, and manure treatments were 54, 53, and 30%, respectively, for continuous soybean and 61, 55, and 44%, respectively, for soybean from rotation plots. Root colonization by VAMF for control, N, and manure treatments were 69, 59, and 54%, respectively, for continuous grain sorghum and 56, 48, and 31%, respectively, for grain sorghum from rotation plots. These agricultural soils contained a diverse mixture of 26 VAMF species, which is probably a major factor in the region's soil productivity. Plants stressed due to cropping system or fertilizer practice have greater VAMF colonization and VAMF activity. A diverse VAMF population could increase the ability of VAMF to respond to different stresses.
New Formulae for Mass Spectrometric Analysis of Nitrous Oxide and Dinitrogen Emissions
Authors: Arah J. R. M.
Published: July 2010

Formulae currently used in mass spectrometric studies of N2 and N2O emissions require the initial atmosphere to be in a state of isotopic equilibrium with a 15N atom fraction equal to that of the global background (γ). This is not always the case (e.g., in sequentially sampled incubations and those conducted under artificial atmospheres). Here I present new formulae that are valid whatever the initial conditions. These formulae are simpler than previous versions. They are expressed directly in terms of the 15N atom fractions and 30N2 molecular fractions of two gas samples (taken before and after emission). I have provided secondary expressions for converting the instrumental output of any (single‐ or dual‐inlet, double‐ or triple‐collector) mass spectrometer into the atomic and molecular fractions required. In common with previous treatments, my new calculations hypothesize a homogeneous soil N pool. I have proven that where this hypothesis is false the calculated value of the apparent pool enrichment is wrong (too high where the actual enrichment exceeds that of the atmosphere; too low in the exceptional case where the atmospheric enrichment exceeds that of the pool) and the flux is invariably underestimated. Computer simulations suggest that this underestimation may be relatively constant (about 25%) if the atmosphere is initially at isotopic equilibrium with 15N fraction γ, but that it may be larger (about 40%) and more variable where this is not the case.