bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phosphate Sorption in Relation to Extractable Iron and Aluminum in Spodosols
Authors: Yuan G. , Lavkulich L. M. 
Published: July 2010

AbstractPhosphorus is an important plant nutrient and of concern from the environmental point of view. Numerous studies on the relationship between P sorption characteristics and other soil properties have been done; however, most of these studies do not include originally sorbed (oxalate‐extractable) P (Po). Since Po accounts for 17 to 66% of the total sorption capacity (Po + Xm, where Xm is the P sorption maximum) in 43 Spodosol samples from British Columbia, Canada, it should not be ignored in P sorption models. The good correlations between oxalate‐extractable Fe and Al (Feo + Alo) and P sorption parameters (Po, Xm, or Po + Xm) indicate amorphous Fe and Al oxides are the major P sorbents in the soils studied. Phosphorus sorption capacity is predictable from Alo and Feo by two existing models. The relationship between organically complexed Al and P sorption parameters may be important in forest and soil management, since the organically complexed fraction is relatively easily altered if environmental factors or management practices change.
Micromorphological Characteristics of Long‐Term No‐Till and Conventionally Tilled Soils
Authors: Drees L. R. , Wilding L. P. , Karathanasis A. D. , Blevins R. L. 
Published: July 2010

AbstractConservation tillage practices have been shown to affect a number of soil physical properties, but less is known about their effect on the size, shape, and arrangement of soil constituents. To evaluate soil structural differences between tillage treatments, six paired conventionally tilled and no‐tilled plots of Maury silt loam soil (fine, mixed, mesic Typic Paleudalf) were analyzed. Oriented undisturbed samples (16 by 9.5 by 5.5 cm) were taken from each plot at depths of 0 to 5, 10 to 15, and 20 to 25 cm. The samples were impregnated with polyester resin and two vertical thin sections were prepared from each sample. The micromorphic features were described, and the size (equivalent spherical diameter), shape, and orientation of pores and aggregates were measured using an interactive image analysis system. The no‐tilled plots had platy structure near the surface and interconnection of fine pores (50–100 µm) throughout the profile. Eartbworm channels with excrement infillings were abundant in the no‐till plots at all depths, but absent in conventionally tilled plots. The conventionally‐tilled soil was composed of granular and fragmented structural units with no evidence of earthworm activity. The no‐till plots contained about 11% pore area >50 µm, compared with about 16% for conventional tillage management. However, the no‐till plots have an average pore size (0.18–0.26‐mm diam.) that is greater than the conventionally tilled plots (0.12–0.17‐mm diam.). The finer aggregate size of the conventionally tilled plots (0.25–0.39‐mm diam.) compared with the no‐till plots (0.41–1.08‐mm diam.) is probably due to plowing and disking.
Determining Almond Root Zone from Surface Carbon Dioxide Fluxes
Authors: Ben‐Asher J. , Cardon G. , Phene C. J. , Hutmacher R. B. , Peters D. , Rolston D. E. , Biggar J. W. 
Published: July 2010

AbstractSize and distribution of roots in the soil is affected by irrigation method and water quantity and quality. The number of replications required to characterize it at a significant level is so large that it cannot be included in routine sampling. Our objective was to evaluate the effects of irrigation regimes on almond (Prunus amygdalus Batsch. cv. Butte) root zones from measurements of surface CO2 flux. A dynamic chamber quantifying the spatial distribution of CO2 fluxes at the soil surface was used to predict root distribution as affected by experimental treatment in an almond orchard. The treatments were two rates of water application by trickle irrigation and two salinity levels. Roots were sampled in a trench 3‐m width by 2‐m depth that exposed soil profiles. Soil‐surface CO2 flux was described by a descending function of the distance from the trunk of the tree. This function was combined to another regression model estimating the depth of the root zone from CO2 flux measurements. The combined model was used to describe the shape and the size of the root zone. Results show that favorable treatments are characterized by a larger root volume. The depth of the roots may exceed 1.5 to 2.0 m and lateral expansion 2.5 to 4.0 m even when water is applied by drip irrigation.
Clay Dispersion in Relation to Sodicity, Electrolyte Concentration, and Mechanical Effects
Authors: Curtin D. , Steppuhn H. , Selles F. 
Published: July 2010

AbstractClay dispersion is one of the major processes causing structural problems in lands irrigated with sodic waters. The dispersion characteristics of a group of prairie soils (Haploborolls) from southern Saskatchewan (Canada) were determined after reaction with solutions that had a range of sodium adsorption ratios [SAR = Na/(Ca/2)1/2, where concentrations are expressed in mmolc L−1], and electrolyte concentrations. When the input of mechanical energy was high (i.e., 16‐h shaking), a well‐defined threshold electrolyte concentration existed at each SAR, below which extensive clay dispersion occurred. The threshold concentration for dispersion ranged from 1 to 3 mmolc L−1 at SAR 0 and increased linearly as SAR increased to reach 21 to 50 mmolc L−1 at SAR 40. In contrast, when dispersion was measured after minimal shaking by hand, distinct thresholds were absent. Instead, dispersion increased gradually at each SAR as electrolyte concentration decreased. Threshold concentrations determined with low‐energy inputs are likely to be most indicative of field dispersibility. Such threshold values can be substantially lower than those measured using vigorous agitation techniques, particularly when sodicity levels are low. Our results do not support recent reports that silt dispersion is a better indicator of structural stability in the presence of exchangeable Na than is clay dispersion. Such findings are probably the result of an experimental artifact caused by the inappropriate use of Stokes' law in estimating the particle size distribution of soil suspensions. Simple tests of clay dispersibility in water or of aggregate stability may be useful in screening soils for sensitivity to sodic irrigation waters.
Long‐Term Management and Clay Dispersibility in Two Haploborolls in Saskatchewan
Authors: Curtin D. , Campbell C. A. , Zentner R. P. , Lafond G. P. 
Published: July 2010

AbstractThe water dispersibility of clay influences soil physical properties such as water infiltration, surface crusting, and water erosion. The development of the Water Erosion Prediction Project (WEPP) model, which uses water‐dispersible clay in the algorithm for estimating interrill erosion, has created a need to understand the factors controlling clay dispersibility. This study evaluated the effects of long‐term (≥24 yr) crop rotations and management on water‐dispersible clay in two contrasting soil types in southern Saskatchewan. Cultivated soils were 0.4 to 21 times more dispersive than nearby grassland soils. Among the rotation treatments, a 6‐yr rotation, which included 1 yr of summer fallow, 2 yr of spring wheat (Triticum aestivum L.), and 3 yr of bromegrass (Bromus inermis Leyss.)‐alfalfa (Medicago sativa L.) hay, had the greatest impact, giving dispersible clay values (151–244 g kg−1) that were substantially lower than those for continuous wheat (361–441 g kg−1) and wheat‐fallow rotations (354–483 g kg−1). Fallow frequency and fertilizer treatment had little effect. Water‐dispersible clay was negatively correlated (r = −0.79*** and −0.86***) with wet aggregate stability. The results suggested that both of these characteristics are influenced by organic binding agents produced during crop growth. Although soil management had a major effect on clay dispersibility, total clay content may be the dominant factor when a wide range of cultivated soil types are considered. However, management history and aggregate stability data should be taken into account when attempting to predict dispersible clay from total clay content.
Modeling Oxygen Diffusion in Aggregated Soils: II. Anaerobiosis in Topsoil Layers
Authors: Renault Pierre , Sierra Jorge 
Published: July 2010

AbstractDenitrification may appear in soil anaerobic regions. In order to estimate the anaerobic fraction of a soil, a finite element method was used to simulate O2 diffusion and consumption in topsoil layers. The soil is considered as a set of aggregates of various shapes and dimensions. Their external transport areas are reduced by contacts between the aggregates and by areas covered with water in the intercrumb pore space. In some simulations, the role of water from the intercrumb pore space in partially occluding the aggregate surface area has not been taken into account. In this case, anaerobiosis only becomes significant near saturation and is due to the reduction of the intercrumb O2 diffusion. When water of the intercrumb pore space is considered, anaerobiosis appears at lower water contents and is due primarily to the reduction of the aggregate external transport area. In this case, O2 concentration in the intercrumb pore space is high at all depths, except near soil saturation. The results of this study were compared with some published relationships between the water saturation level and denitrification, obtained from experimental data. There is a good agreement between our calculations and these functions. In addition, our simulations show that the relationship between the soil anaerobic fraction and the water content is highly dependent on soil structure, soil temperature, and microbial activity. Thus, multiplicative functions are inadequate to describe the effects of water and temperature on soil anaerobiosis or denitrification.
Evaluation of a Mechanistic Model of Potassium Uptake by Cotton in Vermiculitic Soil
Authors: Brouder S. M. , Cassman K. G. 
Published: July 2010

AbstractThe Cushman‐Barber model was evaluated for K uptake by cotton (Gossypium hirsutum L.) from vermiculitic soils of high K‐fixation capacity and low solution‐phase K+ concentration. On these soils, cotton exhibits late‐season K deficiency while other crop species remain unaffected. Four soil treatments of NH4‐N, K, or both were combined factorially in a vertically split‐pot system to create eight plant treatments of different uniform and nonuniform soil nutrient environments. Depending on the treatment, initial model output produced both substantial under‐ and overpredictions of whole‐plant K accumulation. Model precision was greatly improved by changing the Michaelis‐Menten kinetic parameters for uptake at the root surface to reflect differences in shoot K/N balance, a more accurate measure of plant K demand in the presence of variable soil N supply. Regression revealed a linear relationship between the predicted and the observed K uptake (r2 = 0.87) but, across treatments, the model underpredicted accumulation by 43%. Model predictions were further improved by estimating soil buffer capacity from a Langmuir fit of a K adsorption isotherm rather than from the relationship between exchangeable solid‐phase and solution‐phase K pools. Sensitivity analyses were performed to identify key determinants of cotton K acquisition from vermiculitic soils of high K‐fixation capacity. The analyses demonstrated that both Michaelis‐Menten kinetic and soil supply parameters were strong determinants of K uptake on these soils and thus warrant more emphasis than previously suggested by model validations conducted on soils with greater K supply and less K‐fixation capacity.
Leaching Characteristics of Repacked Soil Columns as Influenced by Subsurface Flow Barriers
Authors: Kiuchi M. , Horton R. , Kaspar T. C. 
Published: July 2010

AbstractReducing the leaching of NO−3‐N is of great interest. The effects of different types of subsurface barriers on delaying and reducing anion leaching and the effect of barrier size on anion leaching were investigated. Three repacked soil columns filled with soil from a Sparta loamy fine sand (sandy, mixed, mesic Entic Hapludoll) mapping unit were used to run Cl− breakthrough experiments under saturated, steady‐flow conditions. Subsurface barriers used were no barrier (NB), a polyethylene disk placed above the Cl−, the same disk placed below the Cl−, a compacted soil layer created outside of the column and placed above the Cl− (CA), and a compacted layer formed in situ above the Cl−. Compared with NB, all barriers tested delayed initial breakthrough of Cl− and reduced peak Cl− concentration. Subsurface barriers delayed occurrence of the peak concentration, indicating that harriers prolonged residence time of Cl− in the soil column. Among subsurface barriers used, the CA was most effective in delaying and reducing Cl− leaching. Initial breakthrough of Cl− was delayed by 0.9 relative pore volumes, and peak concentration was reduced by >50% with the CA treatment compared with the NB treatment. The occurrence of the peak concentration was also delayed by 1.2 relative pore volumes. Compared with the NB treatment, a 3‐cm plastic disk, just large enough to cover the applied Cl−, reduced peak concentration of Cl−. A 5‐cm‐diam. barrier also delayed initial breakthrough of Cl−, reduced peak concentration by 40%, and delayed occurrence of the peak by 0.6 pore volumes.
Model Comparison of Unsaturated Steady‐State Solute Transport in a Field Plot
Authors: Costa Jose Luis , Knighton R. E. , Prunty Lyle 
Published: July 2010

AbstractModels of solute movement in soil are seldom compared using independently generated data. The objectives of this study were to leach Br− through a Hecla fine sandy loam (sandy, mixed Aquic Haploboroll) and to compare the results with four previously published solute transport models. Solute was applied over the surface of four 9‐m2 subplots within a 65.5‐m2 plot and leached at constant rates: 1.28, 2.53, 4.28, and 5.94 µm s−1. Soil solution samples were taken from 0.3‐, 0.6‐, 1.0‐, 1.5‐, 2.0‐, 2.3‐, and 2.5‐m depths. At the same depths, water content and soil suction were measured using a neutron probe and tensiometers. Data from this experiment were used to evaluate four solute transport models. Model performance was evaluated using the observed to expected sum‐of‐squares ratio, the normalized objective function, and the Kolmogorov‐Smirnov statistic. A numerical finite‐difference solution of the convective‐dispersive equation (LEACHM) was more successful in predicting solute movement under unsaturated steady‐state conditions than the analytical solution for the convective‐dispersive equation (CDE), the continuous‐time Markov process (CTMP), or the transfer function model (TFM). The CTMP model predicts observed solute concentration better than the TFM. The TFM needs to be calibrated by a solute transport experiment while CTMP requires water flow and soil moisture as input data.
Extractable Soil Boron and Alfalfa Uptake: Calcium Carbonate Effects on Acid Soil
Authors: Su Chunming , Evans L. J. , Bates T. E. , Spiers G. A. 
Published: July 2010

AbstractSince soil tests for B in fine‐textured soils give inconsistent predictions and the amendment of acidic soils with CaCO3 is a common practice, the suitability of extractants for plant‐available B in a CaCO3‐amended clayey soil was studied. This research investigated the pH effect on B adsorption, the changes in the amounts of hot‐water‐extractable B (HW‐B), mannitol‐extractable B (MANN‐B), and soil solution B (SOLN‐B) as a result of B and CaCO3 addition to a silty clay soil (a clayey, mixed, mesic Typic Humaquept) with an initial pH of 4.2. The relationship between the amounts of extractable B and B uptake by alfalfa (Medicago sativa L.) was also studied. Amounts of extractable B in soil were in the order HW‐B > MANN‐B > SOLN‐B, decreasing with increasing pH and after growth of alfalfa. Addition of 2.5 and 5.0 g CaCO3 kg−1 increased alfalfa dry matter yield; whereas addition of 0.5 and 1.5 mg B kg−1 had no effect. In the absence of added B, the B concentration in alfalfa shoots decreased with increasing pH. Linear correlations between B concentration in alfalfa shoots and extractable B in soil were significant for all three cuts and for all three extractants. Total uptake of B was significantly correlated with all forms of extractable B except HW‐B for the third cut only. Inclusion of pH improved the relationship for the other cuts. The dilution of B in plant shoots by CaCO3‐stimulated growth may result in B deficiency.
Tillage, Residue, and Rainfall Effects on Movement of an Organic Tracer in Earthworm‐Affected Soils
Authors: Trojan M. D. , Linden D. R. 
Published: July 2010

AbstractA field study was conducted to determine the effects of tillage, residue, and rainfall on the movement of rhodamine WT (C29H29N2O5Na2Cl), a strongly adsorbed organic dye, in earthworm‐affected soils. Rhodamine WT was uniformly applied to the surface of two separate, 0.063‐m2 areas within either no‐till or conventionally tilled treatments in the presence or absence of residues. One area was exposed to a high intensity rainfall of 12 mm, whereas the second area received 193 mm of rainfall in 13 events during a 28‐d period. Following rainfall, soils were excavated in layers to a depth of 40 cm and dye concentrations were determined. For the single rain event, dye concentration at the 28‐ to 40‐cm depth was 1.20 and 0.63 mg kg−1 in the no‐till and conventionally tilled treatments containing residues, respectively, compared with concentrations near the detection limit (0.10 mg kg−1) in treatments without residues. For multiple‐rain plots, dye concentrations of 1.80 and 0.93 mg kg−1 were detected at the 28‐ to 40‐cm depth in the no till with surface residue and no till without residue treatments, respectively, compared with concentrations near the detection limit for the conventionally tilled treatments. Staining patterns indicated that earthworm channels were responsible for dye movement below 20 cm. The differences in dye movement for single‐ and multiple‐rain events suggests that properties of the macropore system, such as continuity and surface position, control preferential flow under differing tillage, residue, and rainfall conditions.
Legume Green Manures and Conservation Tillage for Grain Sorghum Production on Prairie Soil
Authors: Sweeney Daniel W. , Moyer Joseph L. 
Published: July 2010

AbstractWith increased emphasis on conservation tillage, information is needed on the use of spring‐ or fall‐seeded legumes as green manures for eastern Great Plains grain sorghum [Sorghum bicolor (L.) Moench] production. This study was conducted to determine whether legumes can be beneficial to subsequent grain sorghum crops grown in conservation tillage systems on prairie soil. Comparisons included the effects of (i) red clover (Trifolium pratense L.) and hairy vetch (Vicia villosa Roth) before grain sorghum vs. continuous grain sorghum, (ii) reduced or no‐tillage, and (iii) fertilizer N rates on grain sorghum grown on two sites of a Parsons silt loam (fine, mixed, thermic Mollic Albaqualf). Surface soil at Site 1 was higher in pH (7.2 vs. 6.2), P (12 vs. 4 mg kg−1), and K (80 vs. 60 mg kg−1) than at Site 2. Yield of the first sorghum crop after legume kill‐down in 1987 ranged from 79 to 131% more than for continuous grain sorghum. At the higher fertility Site 1, red clover residual increased yields to 3.7 from 2.7 Mg ha−1 with continuous grain sorghum in the third year; at the lower fertility Site 2, the legume residual did not influence yield after the first year. First‐year grain sorghum yielded 1.1 to 1.6 Mg ha−1 more with reduced tillage than with no‐tillage, but the difference was less in subsequent years. In 1987, yield was not affected by fertilizer N even following grain sorghum, but the response was significant in subsequent years. Low N response on this high organic matter prairie soil contributed to uncertain fertilizer N equivalencies and suggested other non‐N benefits from the legumes.
Detachment of Soil by Flowing Water Under Turbulent and Laminar Conditions
Authors: Nearing M. A. , Parker S. C. 
Published: July 2010

AbstractFluid turbulence of water flowing over soil surfaces imparts instantaneous and localized levels of shear stress to the fluid‐solid interface that are much greater than the average shear stress of flow. It has been hypothesized that these high levels of instantaneous shear are the driving mechanism for detachment of cohesive soil by flowing water. The purpose of this study was to test the hypothesis that detachment of soil by flowing water at a given shear stress is dependent on turbulence. Detachment rates of three soils were measured in a hydraulic flume at seven combinations of flow depth and bed slope under both turbulent and laminar flow conditions. For all soils and all slope/depth treatments, detachment was dramatically greater for the turbulent case compared with the laminar case. Detachment that occurred under laminar flow conditions was thought to be due in part to localized turbulence associated with pitting of some of the samples.
Denitrification in Soil Aggregates Analyzed with Microsensors for Nitrous Oxide and Oxygen
Authors: Højberg Ole , Revsbech Niels Peter , Tiedje James M. 
Published: July 2010

AbstractDenitrification in soil microenvironments is difficult to study by conventional techniques. By use of O2 and N2O microsensors, it was possible to study the spatial distribution of oxygen respiration and denitrification in soil aggregates kept at field capacity. Aggregates with diameters of 20 to 25 mm often contained anaerobic centers but exhibited only low rates of denitrification due to a limiting availability of electron donors. Addition of organic matter such as clover leaves or tryptone to the surface of the aggregates greatly stimulated respiratory activity and caused anoxia and high rates of denitrifying activity within the organic hot‐spot and in the underlying soil. Due to imbalance between N2O production and N2O reductase activity, the creation of a hot‐spot led to an initial accumulation of N2O even when acetylene was absent. Denitrification within the center of a hot‐spot rapidly became limited by the diffusional supply of NO−3, even when the underlying soil contained 5 mM NO−3, and such hot‐spot centers depleted of NO−3 served as sinks for N2O while N2O concentrations of up to 400 µ M were building up immediately below. The bulk N2O production rate of the soil was thus the result of a net production in some microenvironments and simultaneous net consumption in other microenvironments.
Rapid Bioassay for Inhibitory Rhizobacteria Using Digital Image Analysis
Authors: Doty J. A. , Kennedy A. C. , Pan W. L. 
Published: July 2010

AbstractCurrent methods for assaying the potential effects of rhizobacteria on plant growth are tedious and time consuming. A rapid, automated bioassay has been developed using a flatbed scanner and digital image analysis. Comparisons were made between manual measurements of root length and computed values based on an edge discrimination image analysis procedure. The assay consisted of bacterial cultures of filtrates added to 18 mL of 0.9% agar in square petri plates. Seeds were planted along a marked axis and incubated for 4 d at 15°C, and then the roots were measured. Total root length measurements for the two methods, manual and image analysis, were well correlated (r2 = 0.94), and both were equally able to identify bacteria inhibitory to plant growth. Root measurements by the scan method were five times faster than the manual method. Each sample required 53 s to read with the scan method vs. 250 s with the manual method. The scan method provides a quick and accurate method for screening inhibitory activity of rhizobacteria based on seedling root length and has potential in the screening of toxic substances of other origin.