bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling Root Water Potential and Soil‐Root Water Transport: II. Field Comparisons
Authors: Bruckler L. , Lafolie F. , Tardieu F. 
Published: July 2010

AbstractIn a previous article, a theoretical approach to the calculation of root water potential (RWP) and water uptake by roots in the two‐dimensional case was proposed. The RWP was assumed to show a threshold value that controlled plant transpiration by means of chemical messages triggered by roots. This article compares model predictions with data from field experiments. Measured maximum evapotranspiration (MET), basic soil hydraulic properties, and a map of soil‐root contacts in a soil profile (vertical case) were taken as inputs to the model. Field experiments were performed in a clay loam soil (a Typic Hapludalf) planted with maize (Zea mays L., F1 hybrid LG1), where sections were compacted using wide tractor wheels. At silking, precise maps of soil‐root contacts were drawn for vertical planes. Volumetric water content and matric potential measurements were performed during a 17‐d experiment under dry climatic conditions. Computed and field‐measured soil volumetric water content values showed large gradients between compacted and noncompacted zones. Calculated and measured mean root water‐uptake rates were similar, and depended strongly on root densities. Mean individual root water‐uptake rates were considerably greater in zones where the root density was low. Finally, the proposed model could be useful for calculating the root water potential if chemical messages from roots are confirmed as being an important control mechanism of stomatal conductance and photosynthesis.
Aluminum‐Binding Ability of Soluble Organics in Douglas Fir Litter and Soil
Authors: Tam Shuk‐Ching , McColl John G. 
Published: July 2010

AbstractOrganic matter from litter and soil are important metal‐mobilizing agents. This study was conducted to characterize the Al‐binding abilities of soluble organics from both Douglas fir litter and soil (fine‐loamy, mixed, mesic Ultic Haploxeralf). A modified ion‐pairing chromatographic technique was used to differentiate organics according to their Al‐binding abilities. Further identification with high‐performance liquid chromatography (HPLC) found gallic, catechol, salicylic, and phthalic as the most strongly Al‐binding ligands among the aromatic acids identified. Moderate binding ability was exhibited by 3,4‐dihydroxybenzoic acid; benzoic, vanillic and 4‐hydroxybenzoic acids were the least strongly binding. The identified aliphatic acids (shikimic, oxalic, succinic, fumaric, malic, and citric) were not differentiated, due to their weaker binding to Al and to the fractionation column. For the unidentified organics, suggestions are made on their functional structure that will be useful for more exhaustive studies. Greater amounts of Al‐binding ligands were found in litter than in soil. The effect of different litter types on Al solubilization in underlying mineral soils can be obtained by comparing their Al‐fractionation characteristics.
Upper Bounds on Evaporation Losses from Buried Sources
Authors: Philip J. R. 
Published: July 2010

AbstractEvaporation losses at the soil surface are important in subirrigation. This study yields upper bounds on fractional evaporation loss from buried sources. Quasilinear solutions are given for evaporation at the soil surface from buried steady point and line sources at finite depth. These yield the very general result that e‐2z1 is the upper bound on the fractional evaporation loss from any arbitrary configuration of steady sources at dimensionless depth z1. This dimensionless depth is the ratio of the physical depth to the sorptive length 2α−1, where α is the sorptive number entering the quasilinear analysis. A simple general theorem gives the upper bound on fractional evaporation loss from arbitrary configurations of steady sources distributed throughout an arbitrary range of depths.
Identifying and Removing Spatial Correlation from Yield Experiments
Authors: Bhatti A. U. , Mulla D. J. , Koehler F. E. , Gurmani A. H. 
Published: July 2010

AbstractIn classical statistics, the effect of soil trends is compensated for by replication and randomization of treatments. Two field experiments were conducted at sites with significant soil trends to evaluate the use of semivariograms for identifying spatial correlation in plot yield, and evaluate the ability of nearest‐neighbor analysis (NNA) in removing trend. The first experiment involved a P‐fertilizer trial with winter wheat (Triticum aestivum L.) on an eroded hillslope in eastern Washington. The second experiment involved a N‐ and P‐fertilizer trial with cotton (Gossypium hirsutum L.) in Dera Ismail Khan, Pakistan. One of the difficulties in using semivariograms of plot‐yield data to evaluate spatial correlation in experimental errors is that yield is affected by the presence of trends as well as by the pattern in treatment randomization and replication. To remove the influence of treatment randomization, the measured mean for each treatment was subtracted from the measured yield for that treatment in each plot. Semivariograms of these deviations in yield relative to the treatment mean showed significant structure for both experiments, indicating spatial correlation between plots resulting from soil trends. We used NNA to adjust measured plot yields for the effects of spatial correlation. Semivariograms of yield deviations after this adjustment exhibited no spatial structure, indicating removal of spatial correlation between plots. Analysis of variance (ANOVA) on measured yields before adjustment by NNA in both experiments showed nonsignificant treatment effects, while block effects were highly significant. Thus, without adjustment, the experimental results showed no response to the applied fertilizer treatments. In contrast, ANOVA on adjusted yields after NNA showed highly significant treatment effects, while block effects were nonsignificant.
Improved Solute‐Sampling Protocol in a Sandy Vadose Zone Using Ground‐Penetrating Radar
Authors: Kung K‐J. S. , Donohue S. V. 
Published: July 2010

AbstractSoil solution samples taken from a vadose zone by current monitoring techniques are randomly obtained because it is assumed that the representativeness of the samples is dependent on the total number of samples instead of the location of the samples. In the presence of preferential flow (i.e., “macropore”, “fingering”, or “funnel” flow), however, the locations as well as the number of samples and not just the number of samples determine the representativeness. The purpose of this study was to: (i) demonstrate that current sampling protocols could underestimate solute breakthrough in a soil with preferential flow; and (ii) show that ground‐penetrating radar (GPR) has great potential to nondestructively map the location of interbedded soil layers with textural discontinuities so that suction‐cup samplers could be correctly installed along the preferential paths triggered by funnel flow. A 24 by 24 m plot at the Hancock Research Station, Wisconsin, was scanned with GPR in 1989. Based on the GPR images, four ceramic suction‐cup samplers were installed at a depth of 1.85 m in locations with layering structures and abrupt textural discontinuities. Four other ceramic suction cup samplers were installed randomly at a depth of 1.5 m. The plot received a uniform pulse of Br solution. Breakthrough curves collected by samplers installed with the aid of GPR have higher concentrations than those collected by randomly installed samplers. This result indicates that random solute sampling in a sandy vadose zone exhibiting preferential flow could underestimate solute movement.
Selenate Reduction in an Alluvial Soil
Authors: Sposito Garrison , Yang Andrew , Neal Rosemary H. , Mackzum Adrienne 
Published: July 2010

AbstractRecent studies of the mobility and solubility of Se in western San Joaquín Valley soils suggest that this potentially hazardous element can be managed by controlling its oxidation‐reduction reactions. The soluble species, SeO4, which is highly mobile and toxic, can, in principle, be reduced to SeO3, which is strongly adsorbed, or to organoselenium species, which may volatilize under suitable conditions. Chemical thermodynamics predicts that the reduction sequence in soils should be: NO3 → SeO4 → MnO2 at pH >5. The objective of this study was to establish the position of SeO4 in the kinetic reduction sequence for a representative western San Joaquín Valley soil incubated in suspension with its own saturation extract. In a series of replications of an incubation experiment, it was observed that native NO3 (plus NO2) concentrations became undetectable after 100 h in the soil suspension without O2 supply. Soluble Se, either added as Na2SeO4 or indigenous to the soil, disappeared after 50 to 200 h. Native soluble Mn began to rise after 50 h and showed a sharp increase after 100 h of incubation. Retardation of SeO4 reduction in the presence of added NO3 was noted. The results indicated that, at native levels of NO3, effective microbial catalysis of SeO4 reduction occurred in the soil under the conditions of the experiments, in agreement with the recent isolation of bacterial species that can respire SeO4 while oxidizing organic acids typical of suboxic soil environments.
High‐Elevation Forest Soils of the Southern Appalachians: I. Distribution of Parent Materials and Soil‐Landscape Relationships
Authors: Feldman S. B. , Zelazny L. W. , Baker J. C. 
Published: July 2010

AbstractBecause of geomorphic instability imparted both by present‐day slope processes and past periglacial activity, soils in the high‐elevation spruce‐fir (Picea rubens Sarg.‐Abies fraseri [Pursh.] Poir) zone of the southern Appalachians have similar morphological features that make it difficult to assess their variability on the landscape, despite widespread differences in parent material and local geology. We used multiple discriminant analysis to (i) determine whether soils from three extensive areas of southern Appalachian spruce‐fir forests could be separated by physical, morphological, chemical, and mineralogical properties, (ii) determine the relative effectiveness of these properties as differentiae, and (iii) assess the contribution of mineral weathering in offsetting potential base‐cation depletion induced by strong‐acid anion loading associated with atmospheric deposition. A total of 35 pedons at elevations >1450 m were characterized on the high mountain peaks of eastern Tennessee, western North Carolina, and southwestern Virginia. Physical and morphological properties used to separate and field classify these soils were not significantly different between study areas. Soil chemical and mineralogical properties inherited from different parent materials, however, were sufficiently different between study areas to result in the clear separation of soils into distinct groups with >95% classification accuracy. Soils formed from siliceous metavolcanic parent materials were dominated by K‐feldspar and quartz in both the sand and silt fractions. Soils with parent materials derived from more high‐grade metamorphic rocks were less quartzitic, had plagioclase as the dominant feldspar, and had high contents of expansible 2:1 phyllosilicates. Slope processes involved in the transport of solutes and sediments resulted in sorting of surficial materials, higher pH, and greater amounts of silt‐size mica and kaolinite in depositional areas.
Soil Temperature and Organic Matter in a Disturbed Forested Wetland
Authors: Aust W. Michael , Lea R. 
Published: July 2010

AbstractSoil temperature and organic‐matter content are useful indices of ecosystem recovery after disturbance. This study was designed to evaluate soil temperature and organic‐matter changes associated with different levels of disturbance within a forest wetland. Soil temperatures and organic‐matter contents were monitored in a palustrine water tupelo (Nyssa aquatica L.)‐baldcypress (Taxodium distichum [L.] Rich. var. disticum) wetland forest in southwestern Alabama for two growing seasons following timber‐harvest‐related disturbances. Three forms or levels of disturbance were applied: helicopter logging, rubber‐tired skidder logging, and helicopter logging followed by herbicide application. An adjacent undisturbed stand served as a reference area. Analyses of post harvest data revealed that during the 2‐yr postharvest period, soil temperatures in the reference area were coolest, helicopter and skidded areas were warmer, and herbicide plots had the warmest soil temperatures. Soil organic matter followed the same trend. Both parameters were related to vegetative cover and indicated recovery following timber harvest.
Adsorption of Atrazine on Smectites
Authors: Laird D. A. , Barriuso E. , Dowdy R. H. , Koskinen W. C. 
Published: July 2010

AbstractSmectites may strongly influence the fate of pesticides in soils due to their large surface area and abundance in agricultural soils. This research was undertaken to determine the effects of smectite properties on the affinity of smectitic clays for atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1, 3, 5 triazine). Samples of the <2‐µm fraction were separated by sedimentation from 13 reference smectites and treated with H2O2 for removal of organic matter. A soil smectite sample was separated (<0.02‐µm fraction) from a H2O2 and dithionite‐citrate‐bicarbonate‐treated Webster (fine‐loamy, mixed, mesic Typic Haplaquoll) soil by a dispersion‐centrifugation‐decantation technique. All 14 samples were Ca saturated, dialyzed free of excess electrolyte, and freeze dried. The mineralogy of each sample was evaluated by a combination of x‐ray diffraction and chemical analysis. Values for cation‐exchange capacity (CEC), surface charge density (SCD), surface area (SA), and percent tetrahedral charge (TC) were based on structural interpretations of the chemical analyses. Freundlich adsorption isotherms for atrazine adsorption on each sample were determined using the batch‐equilibration method. Smectite was the dominant mineral in 13 of the clay samples; the 14th sample was a mixture of interstratified smectite‐illite, quartz, and kaolinite. For the smectitic clays, atrazine adsorption ranged from 0 to 100%, and the logarithm of the Freundlich adsorption constant [log(Kf)] decreased linearly with the CEC (r2 = 0.82) of the clays. Stepwise multiple‐regression analysis indicated that log (Kf) values were correlated with SCD and SA values (r2 = 0.83). Inclusion of TC and suspension pH as independent variables in the regression analysis did not significantly improve the correlations. The results indicate that the affinity of smectites for atrazine decreases with increasing SCD, which suggests that atrazine is primarily adsorbed by smectites as a neutral species.
Measuring Field Variability of Disturbed Soils for Simulation Purposes
Authors: Finke P. A. , Bouma J. , Stein A. 
Published: July 2010

AbstractSpatial variation of soil profiles disturbed by leveling was inventoried on a field scale to obtain representative data for simulation purposes. Depth of occurrence, thickness, and morphology of functional layers, which are different pedogenetic horizons with comparable soil physical properties, were considered to be regionalized variables. The layers served as carriers of physical information, such as water‐retention and hydraulic‐conductivity characteristics and organic‐matter content. An impression of the variability within each layer was obtained by six fold sampling. Spatial variability, expressed by variations in thickness of functional layers, was inventoried in a two‐step soil survey. First, semivariograms were constructed using data obtained following a nested sampling scheme supplemented by a nugget estimation procedure. Variograms were used to evaluate cost/quality ratios at varying potential grid sampling densities, using the root of the prediction error variance (RPEV) to compare quality of interpolations. Based on these evaluations and a sequential sampling test, a grid mesh of 12 m was chosen. Second, a grid soil survey and an independent quality test were done, in which root mean square errors (RMSE) on test points were compared with RPEV. The RPEV to RMSE ratios varied between 0.7 and 1.1 for the sampled grid mesh, and had comparable values for other grid meshes. Estimations on test points by an hypothesized spatial mean, based on 26 measurements by a sequential sampling method, produced RMSE values not significantly different from RMSE values from kriging interpolations. However, sequential sampling required 26 observations whereas kriging required 153, a saving of 83%.
Micromorphology and Mineralogy of Cracking Soils from the Accra Plains of Ghana
Authors: Acquaye D. K. , Dowuona G. N. , Mermut A. R. , St. Arnaud R. J. 
Published: July 2010

AbstractFour soil profiles, uncultivated and cultivated examples of Akuse and Prampram series from the Accra Plains of Ghana, developed in situ from garnetiferous hornblende gneiss, were examined in this study to establish their physical and chemical properties, macromorphology, micromorphology, and mineralogy. Cracking is well expressed in both soils; however, slickenside formation is found only in the deeper and moderately weathered Akuse soils. Although the clay content of the soils is only slightly >30%, the soils are still capable of developing cracks. The cation‐exchange capacity (CEC) values are all >32 cmolc kg‐1 and smectite is the dominant clay mineral. Moderate to minor amounts of vermiculite, chlorite, mica, and kaolinite occur throughout the profile. The amount of kaolinite is largest in the coarse‐clay fraction, which also contains considerable amounts of quartz and feldspar, especially in the Prampram soils. Weathering of amphiboles, micas, and feldspars in the solum is responsible for the formation of swelling clay minerals and Fe‐Mn nodules. Total chemical composition of both the coarse and fine clays suggests that clay minerals contain considerable structural Fe. The large proportion of vughs and interconnected vughs makes these soils unique and separates them from other cracking soils with higher clay contents. The Akuse soils have greater frequency of voids than the Prampram soils. Carbonate nodules with dendritic Fe‐Mn precipitation, and Fe‐Mn nodules are particularly distinct pedogenic features. A greater concentration of Fe‐Mn nodules in the Akuse than the Prampram soils represents a greater mobility of Fe and Mn because of long‐term moisture retention. A majority of the nodules at depth are formed in situ, but those at the surface are probably displaced upwards by the swell‐shrink process. Considering the overall soil properties, the Akuse soils may be classified as Typic Haplusterts and the Prampram soils, because of the absence of slickensides, as Vertic Ustochrepts.
Conceptual and Statistical Modes to Characterize Soil Materials, Landforms, and Processes
Authors: Evans C. V. , Roth D. C. 
Published: July 2010

AbstractWithin landscape units of interest to soil surveyors and to soilgenesis researchers, economic and physical constraints generally prohibit collection of sufficient data to develop adequate predictive models of spatial variability. Conceptual models are more legitimate at these scales, and modal concepts based on central‐tendency values can be used effectively to develop these models. Our objectives were to obtain central‐tendency values for genetically important properties of two similar New Hampshire soils, to use these values to quantify modal concepts of each soil, and to relate these modal concepts to depositional processes. We examined central‐tendency values of particle‐size distribution, porosity, landform relief, and drumlin axis ratios in nine map‐unit delineations of Becket and Marlow series (coarse‐loamy, mixed, frigid, Typic Haplorthods) in southern New Hampshire. Modal concepts of Becket and Marlow were successfully defined by these parameters: Marlow soils were significantly finer and less porous, and occurred on steeper, more linear drumlins than Becket soils. These properties indicate that till lodgement is singularly influential in the genesis of Marlow soils. Becket soils also exhibit some degree of till lodgement, but subsequent melting of ice lenses accounts for removal of finer particles, higher porosity, and lower relief and linearity. The modal concepts defined in this study enabled soil scientists to discriminate more efficiently between Becket and Marlow soils in mapping, and to develop process‐oriented models of these soils.
Stemflow, Rain Throughfall, and Erosion under Canopies of Corn and Sorghum
Authors: Bui Elisabeth N. , Box James E. 
Published: July 2010

AbstractModern soil erosion prediction technology, such as the Water Erosion Prediction Project, requires detailed information about plant status in the interrill and rill erosion processes. The total amount of rain that reaches the soil and is available for erosion under vegetated surfaces is a function of rain throughfall and stemflow. The objective of our research was to determine the effects, including the production of stemflow of canopies, of corn (Zea mays L.) and sorghum (Sorghum bicolor [L.] Merr.) on interrill soil erosion. A series of rainfall simulations of similar intensity (6.35 cm h‐1) was performed in 1989 and 1990 on experimental plots of Cargill SX 383 corn and Garst 5503 sorghum grown on Cecil soil (clayey, kaolinitic, thermic Typic Kanhapludult). Runoff and sediment were collected at 5‐min intervals over a 1‐h period for two sets of treatments each under corn and sorghum: canopy and canopy minus stemflow. Stemflow, plant‐height, and leafarea data were collected from a total of 18 corn and 16 sorghum plants and used to estimate stemflow. Rain throughfall was estimated as the difference between total rainfall and calculated stemflow and was compared with observed runoff. Both corn and sorghum were observed to have high stemflow, the amount being highly correlated to total leaf area. Runoff under sorghum indicated that all the stemflow was potentially available for infiltration. Under corn, however, about one‐third of the stemflow may have contributed to runoff. The average sediment concentration was not sensitive to canopy type. Erosion due to stemflow appeared negligible compared with that caused by throughfall.
Time Domain Reflectometry Response to Lateral Soil Water Content Heterogeneities
Authors: Hokett S. L. , Chapman J. B. , Cloud S. D. 
Published: July 2010

AbstractWater‐content heterogeneities can occur between the parallel rods of the time domain reflectometry (TDR) probe if TDR is used in cracked soils or in laboratory studies with probes oriented in a variety of directions. The accuracy of water‐content measurements using TDR under such heterogeneous conditions was investigated in a series of laboratory experiments. Two cases were studied: (i) one TDR rod in dry soil and the other in wet soil; and (ii) an artificial soil crack filled with water or air between the two TDR rods. In Case 1, TDR readings were heavily biased toward the water content of the dry soil. This effect occurs because the electromagnetic wave (EMW) reaches the end of the waveguide quicker in dry than in wet material. Because the time delay of the earliest reflection signal is read from the TDR, the travel time of the dry material is measured. In Case 2, the air‐filled crack between the waveguide rods had only a small effect on measured water content when the soil was dry; however, water‐content measurements were reduced by as much as 46% in wetter soils. The effect of water‐filled cracks was small in both dry and wet soils. The effect of soil cracks is explained by a static capacitance model. Results from the experiments do not contradict previous work that demonstrated that TDR measures the average water content of heterogeneous layers oriented perpendicular to the TDR probe axis. In the two cases examined here, knowledge of the orientation of soil water heterogeneities relative to the TDR waveguide rods is necessary for correct data interpretation.