bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computer‐Controlled Variable Intensity Rain Simulator
Authors: Lascano R. J. , Vorheis J. T. , Baumhardt R. L. , Salisbury D. R. 
Published: July 2010

AbstractNatural rainstorms have dynamic intensities; thus, a large portion of total precipitation may be received during a short time. Natural rainstorms also have both variable drop sizes and kinetic energy. Accurate studies of sediment transport and infiltration require realistic duplication of natural rain kinetic energy and intensities. Rain simulator designs must be capable of producing dynamic multiple intensities and corresponding multiple drop sizes to simulate variable kinetic energies. Many simulators are capable of producing rain with multiple and, in some cases, dynamic intensities, but a simulator that can vary both the intensity and kinetic energy is needed. Our objective was to design and build a rain simulator for field use that realistically duplicated natural rain storms. A computer‐controlled solenoid‐valve multiple nozzle type rain simulator was developed. The computer not only controls solenoid valve activation of the rain simulator during operation but also measures runoff and records rain application and runoff data to a log file for processing. The simulator has control software that controls and monitors all processes. The rain simulator is capable of uniformly applying water (coefficient of uniformity = 84–94%) with a dynamically changing intensity of up to 200 mm h−1 and kinetic energies ranging from 15.0 to 23.5 J m−2 mm−1. Uniformity of application was achieved by oscillating the nozzles in two directions. Field operation of the simulator is enhanced by its portability. The measurement area is easily modified using in‐line handrail connectors to change support frame dimensions, thus accommodating infiltration and chemical or sediment transport studies.
Prediction of the Saturated Hydraulic Conductivity‐Porosity Dependence Using Fractals
Authors: Giménez D. , Allmaras R. R. , Huggins D. R. , Nater E. A. 
Published: July 2010

AbstractFractal theory has been used to quantify morphological properties of pore systems in soil, but predictive capabilities of the derived fractal dimensions have remained largely untested. The objective of this study was to use morphologically derived fractal dimensions to predict an exponent N in a power law relation between saturated hydraulic conductivity, Ksat, and porosity. A Kozeny‐Carman equation was used to derive N as a function of two fractal dimensions (pore volume, Dv, and pore surface roughness, Ds) and a connectivity parameter, α. The α parameter was used as a matching factor between fitted and calculated N values. Values of Dy and Ds characterizing pores in both undisturbed and packed soil were obtained from images with pixel sizes of 0.06 and 0.29 mm. Porosity was measured on the 0.29‐mm pixel images, while Ksat was measured in undisturbed cores and packed soil columns. Also, published data on porosity, Ksat, and Dv and Ds from dye‐stained patterns of four undisturbed soils were used. Lower coefficients of variation and lower absolute values of α were obtained with fractal dimensions from the 0.06‐mm pixel images. Values of α were related to parameters from probability distributions of hydraulic radii as calculated from the 0.06‐mm pixel images, and to the connectivity of pores as inferred from dye‐stained patterns. Fractal characterization of pore structure proved useful for predicting N, but predictions would probably be improved by considering only flow‐active pores in the calculation of a fractal dimension. Methods to obtain such fractal dimensions were suggested.
Phosphorus Sorption Characteristics of Bh and Bt Horizons from Sandy Coastal Plain Soils
Authors: Zhou M. , Rhue R. D. , Harris W. G. 
Published: July 2010

AbstractRetention of land‐applied P is an environmental concern in sandy Coastal Plain regions. Compositional differences between Spodosol Bh and Ultisol Bt horizons are likely to have major consequences for P retention. The purpose of this study was to compare P sorption‐desorption characteristics of Bh and Bt horizons using selective chelation to evaluate the effects of organically complexed Fe and Al in Bh samples. The Bh and Bt samples sorbed comparable amounts of P but Bh samples desorbed a higher proportion of their adsorbed P. After alkaline acetylacetone extraction of metal‐organic complexes, Bh samples lost most of their P adsorption capacity, but their desorption behavior was more like that of samples whose clay fractions were dominated by inorganic metal oxides. Aluminum‐organic matter complexes appear to be responsible for the high P adsorption capacity of Bh horizons as well as for the tendency of these horizons to release P more readily at low solution P concentrations.
Accumulation and Redistribution of Fertilizer Nitrogen‐15 in Soft Red Winter Wheat
Authors: Bashir R. , Norman R. J. , Bacon R. K. , Wells B. R. 
Published: July 2010

AbstractInformation is lacking on N accumulation in soft red winter wheat (Triticum aestivum L.) and the fate of residual fertilizer N in soil. The objectives of this study were to determine the uptake and redistribution of fertilizer and total N within the wheat plant as well as the amount and distribution of fertilizer N in the soil profile at wheat maturation. Urea‐15N was applied at the rate of 112 kg N ha−1 at tillering. Plant samples were taken at six growth stages and partitioned into top and bottom leaf blades, stem + leaf sheaths, and spikes, and analyzed for total and fertilizer N accumulation. Soil samples were taken at wheat harvest and analyzed for total N and fertilizer N recovery in inorganic, organic, and total N fractions. Nitrogen accumulation in the wheat plants increased until flag leaf emergence and then displayed no significant change during later growth stages or at maturity. Leaf blades and stem + leaf sheaths attained maximum N accumulation at flag leaf emergence and heading, respectively. Spikes continued to accumulate N from heading until maturity. Nitrogen loss from the leaf blades and stem + leaf sheaths exceeded N gain in the spikes. A maximum fertilizer N accumulation of 74.4% in the wheat plants was found by the flag leaf stage and then the fertilizer N accumulation steadily declined to only 46.7% by maturity. Fertilizer N accumulation for plant parts was similar to total N accumulation; however, significant fertilizer N losses occurred after flag leaf emergence. Fertilizer N recovered in the 0‐ to 100‐cm soil layer following harvest was only 11.6% of that applied and was mainly concentrated in the organic fraction of the top 10 cm of soil.
Isotopically Exchangeable Phosphate in Size Fractionated and Unfractionated Soils
Authors: Sinaj S. , Frossard E. , Fardeau J. C. 
Published: July 2010

AbstractThe acquisition of precise information on soil phosphate availability is a prerequisite to its sustainable management in agroecosystems. The objective of this study was to assess the exchangeability of phosphate in the particle‐size fractions (2000–50, 50–2, and <2 µm) of seven soil samples. Samples were completely dispersed with a Nasaturated cation‐exchange resin, and phosphate exchangeability was assessed by the isotopic exchange kinetic method on each particle‐size fraction and on the unfractionated samples. Isotopically exchangeable phosphate was then divided into five pools containing phosphate that is exchangeable within different time frames. In the 2000‐ to 50‐µm fraction, an average of 91.8% of the acid‐extractable (1.0 M H2SO4) inorganic phosphate could not be exchanged within 1 yr while 5.5% of it was exchangeable within 1 min. These results are consistent with the presence in this fraction of slowly exchangeable phosphate in the form of condensed Ca phosphates and rapidly exchangeable phosphate associated with plant debris. In the <2‐µm fraction, a mean of 44.8% of the acid‐extractable phosphate was exchangeable within 1 yr. This confirms that this fraction is the main source of phosphate available to plants, and the main sink for water‐soluble phosphate. A comparison between the sum of the single pools assessed in fractions with the phosphate pools of unfractionated soils showed that, on dispersion, up to 30% of the acid‐extractable phosphate was transferred from slowly to more rapidly exchangeable phosphate pools. This result strongly suggests that unfractionated soils contain phosphate that is physically protected from isotopic exchange, probably within water‐stable aggregates.
Pedologic Assessment of Radionuclide Distributions: Use of a Radio‐Pedogenic Index
Authors: Evans C. V. , Morton L. S. , Harbottle G. 
Published: July 2010

AbstractNaturally occurring radionuclides in soil profiles can provide a useful pedological tool, if their distribution can be calibrated to pedogenesis. As a first step toward such calibration, this study presents a radio‐pedogenic index that compares differences between sola and parent material with respect to distributions and equilibrium relationships of 214Pb and 228Ac activity. The ratios 228Ac/214Pb were used to indicate concurrent secular equilibrium within the parent 232Th and 238U decay series. Among the 12 Typic Haplorthod pedons examined, equilibrium prevailed in C horizons, but not in A, E, Bs, and BC horizons. The C horizon levels of both 214Pb and 228Ac were significantly (P < 0.05) higher than those of E horizons, and considerably higher than those of Bs and BC horizons (P = 0.052 and 0.058, respectively). Nuclide deficiencies were not significantly correlated to podzolization indicators such as the optical density of the oxalate extract (ODOE), melanization, or rubification. Relationships of nuclide deficiencies to KCl pH were strong (r2 > 0.8, P < 0.0001), however. The 228Ac deficiencies were larger than 214Pb deficiencies and more strongly differentiated, particularly in E horizons. Profile distribution of 214Pb was relatively homogenous, compared with that of 228Ac. Analytical methodology ensured equilibrium between 228Ac and 228Ra and between 214Pb and 226Ra. Therefore, deficiencies can be interpreted as a pedogenically directed loss of Ra. Distribution differences, however, are probably due to radiogenic factors, such as half‐life differences between the two Ra isotopes or chemistry of decay‐chain precursors.
Crop‐Pasture Rotation for Sustaining the Quality and Productivity of a Typic Argiudoll
Authors: Studdert Guillermo A. , Echeverría Hernán E. , Casanovas Elda M. 
Published: July 2010

AbstractInclusion of pastures in a rotation may reverse the effects of conventional cropping and tillage on soil degradation. We hypothesized that crop‐pasture rotations could be defined with a minimum pasture component and a maximum conventional cropping component to accomplish sustainable management. Soil organic carbon (SOC), light‐fraction carbon (LFC), microbial biomass nitrogen (MBN), and aggregate stability index (ASI) were measured in the surface 0 to 0.15 m of a fine, mixed, thermic Typic Argiudoll with 2% slope under a long‐term crop rotation experiment at Balcarce, Argentina. Treatments were continuous cropping and crop‐pasture (50:50 and 75:25) rotations. All seedbeds were prepared with conventional tillage. All soil quality indicators decreased with cropping and increased with pasture. Data for each variable were fitted to an exponential model to describe their variation in time. Soil organic C decreased 4.4 g kg−1 in 6 to 7 yr under cropping and rose to the original level (37.2 g kg−1) after 3 to 4 yr under pasture. Light‐fraction C, MBN, and ASI fell 0.9 g kg−1, 39.0 mg kg−1, and 43.9, respectively (97–100% of the estimated decline), after 7 yr under cropping, while they recovered to the values at the beginning of the cropping period (1.8 g kg−1, 99.5 mg kg−1, and 76.7, respectively) in a few years under pasture. Rotations including a maximum of 7 yr of conventional cropping alternated with a minimum of 3 yr of pasture would maintain soil properties within acceptable limits and meet the goals of sustainable agriculture under conditions similar to this experiment.
Landscape Effects on Desiccation Cracking in an Aqualf
Authors: Baer J. U. , Anderson S. H. 
Published: July 2010

AbstractThe rapid transport of water and solute through desiccation soil cracks can lead to crop water and nutrient stress as well as ground and surface water contamination. This study hypothesized that desiccation cracking varies with landscape positions. Cracking was quantified at three landscape positions in a Mexico silt loam (fine, montmorillonitic, mesic Mollic Endoaqualf). The elevation changes of seven disks placed at 15‐cm depth increments in the profile were measured to determine changes in soil layer thickness. Crack volume in the upper 90‐cm profile was determined from thickness changes of the six soil layers. Disk elevation and soil profile water content measurements were made weekly during the crop season (April–November) in 1992 and 1994 on summit, backslope, and footslope positions. During both years, the backslope position profile developed the largest amount of crack volume (4.3 cm3 cm−2 in 1992, 4.8 cm3 cm−2 in 1994) and had the least amount of water depletion (10.0 cm3 cm−2 in 1992, 9.7 cm3 cm−2 in 1994). At the backslope position, a thin, high‐clay‐content Ap horizon and a shallow, clay‐rich Bt horizon (both high in smectite clay) lead to these developments. Differences in shrinkage characteristics of aggregates from Ap, Bt, and C horizons across landscape positions were related to textural and mineralogical differences. Bt horizon clay contents as high as 64.4%, comprised of up to 75% smectite, produced the greatest volume reductions (41%) of aggregates from the Bt horizon compared with volume reductions of aggregates from the Ap and C horizons. Soil texture and mineralogy influenced the magnitude of desiccation soil cracking and water depletion.
Nitrogen‐15 Tracers Combined with Tensio‐Neutronic Method to Estimate the Nitrogen Balance of Irrigated Maize
Authors: Normand Béatrice , Vachaud Georges , Recous Sylvie , Kengni Lucas , Garino Bernard 
Published: July 2010

AbstractIn response to a very high increase of groundwater NO−3 pollution, largely connected with intensive agricultural practices, a long‐term experimentation has been set up close to Grenoble, France, with the following aims: first to characterize the response of maize (Zea mays L.), a predominant crop in the area, to fertilization, and second to quantify the N balance during and after the crop cycle. This study relates to results concerning the second issue; experiments were conducted on irrigated maize in 1991, 1992, and 1993 on the Experimental Farm at La Côte Saint‐André, France, in the heart of one of the most important agricultural zones between the French Alps and the Rhone Valley. The dynamics of soil and fertilizer N (NO−3 transport and N balance during cropping and intercropping periods) were continuously monitored using 15N isotopic tracing and the tensio‐neutronic method (i.e., continual measurement of soil water balance using a neutron moisture meter and tensiometers), together with porous suction cups installed at 0.3‐, 0.5‐, and 0.8‐m depths. Water drainage and leaching of NO−3‐N, with a partition between that derived from fertilizer and that produced by soil mineralization, were thus obtained during and after the crop cycle. The balance of the labeled fertilizer at harvest was also determined by conventional soil coring and plant sampling. The two methods were used successfully during the 3 yr in which there were different climatic conditions and different fertilizer application rates. The results show that the traditional fertilizer input in the area (260 kg N ha−1) could be reduced nearly 30% without any substantial loss in grain yield but with a considerable reduction of nonpoint source pollution due to NO−3 leaching. It is also shown that with the combined use of the two methods, it is possible to characterize separately fertilizer‐N uptake, fertilizer‐N leaching, and N immobilization and to estimate N‐gaseous losses.
Weathering of Mt. St. Helens Tephra under a Cryic‐Udic Climatic Regime
Authors: Dahlgren R. A. , Dragoo J. P. , Ugolini F. C. 
Published: July 2010

AbstractThe initial stages of chemical weathering in tephra were examined during a 10‐yr period under field conditions in a cryic‐udic climatic regime. Unleached tephra from the 1980 eruption of Mt. St. Helens was applied to the surface of soils in 5‐ and 15‐cm depths to simulate natural tephra deposition on subalpine forest ecosystems. Solid‐phase tephra samples were collected 10 yr after addition and compared chemically and mineralogically to the original, unweathered tephra. The solid‐phase pH of the tephra decreased by approximately one unit, with the 5‐cm treatment being ≈0.2 units lower than the 15‐cm treatment. The accumulation of Al and Fe as alteration products in the weathered tephra was detected by selective dissolution analyses. Aluminum accumulated as Al‐humus complexes, hydroxy‐Al polymers in the interlayer of 2:1 layer silicates, and possibly as hydroxy‐Al precipitates external to the interlayer space; Fe accumulated primarily as a noncrystalline oxyhydroxide (e.g., ferrihydrite) and Fe‐humus complexes. The increase in the active Fe and Al fraction (i.e., oxalate extractable Fe and Al) contributes to a sevenfold increase in phosphate retention. Hydroxy‐Al interlayering of detrital 2:1 layer silicates present in the tephra was suggested from x‐ray diffraction and selective dissolution analyses. There was no evidence of opaline silica, allophane, or imogolite forming in the tephra. Preferential incorporation of Al into Al‐humus complexes and hydroxy‐Al interlayers of 2:1 layer silicates appears to inhibit formation of allophane and imogolite during the initial stages of weathering.
Air Flow Measurements to Describe Field Variation in Porosity and Permeability of Soil Macropores
Authors: Granovsky A. V. , McCoy E. L. 
Published: July 2010

AbstractLimited data are available on spatial variation in hydrologic behavior of soil macropores. This study examined field variatiou of soil water release and permeability in the pressure head range that influences macropores. One hundred twenty‐seven undisturbed soil cores were collected from a no‐tillage field containing a Lobdell silt loam (fine‐loamy, mixed, mesic Fluvaquentic Eutrochrept) soil. An air flow device that eliminates the gravitational gradient was used to measure water release, θ(h), and air permeability, ka(h), in the pressure head, h, range of 0 to ‐240 mm. Mean air‐filled porosity, εa, of 0.044 m3 m‐3 and geometric mean ka equal to 1.3 µm2 at h = 0 indicated that macroporosity in a majority of these cores failed to exhibit negative air‐entry pressure heads. Generalized scaling of water release curves and air permeabilities using water contents expressed as degree of capillary saturation ([θ(h) + εa(0)]/θs) yielded considerable scatter reduction, implying a high degree of pore geometry and flow similarity for this soil. The spherical semivariogram model of water release scaling factors, α(h)r, had a range of 14.1 m, whereas the linear semivariogram of air permeability scaling factors, α(ka)r, had a range of 21.1 m. Further, sill values for α(ka)r were 7.6 times greater than for α(h)r. The poor correlation, dissimilar statistical distributions, and dissimilar spatial dependence of scaling factors suggested that characteristic lengths related to total macroporosity and fluid‐conducting macroporosity were substantially different.
Real‐time Soil Water Dynamics Using Multisensor Capacitance Probes: Laboratory Calibration
Authors: Paltineanu I. C. , Starr J. L. 
Published: July 2010

AbstractThere is a continued need for better methods to perform accurate, real‐time, nearly continuous soil water measurements at specific depth intervals, with minimal soil disturbance, and covering field‐scale areas. The objectives of this research were to assess the characteristics of a newly developed multisensor capacitance probe and to calibrate the sensors against a Mattapex silt loam (fine‐silty, mixed, mesic Aquic Hapludult) soil. The soil was uniformly packed in small increments, with the aid of a large hydraulic press, in a wooden box (35.5 by 35.5 cm, 40.5 cm deep). Probe installation in the boxed soil mimicked that required for correct field installation. A highly significant (r2 = 0.992 for n = 15, and RMSE = 0.009 cm3 cm‐3 water), nonlinear (θv = 0.490 SF2.1674) relationship was found between the soil volumetric water content (θv, cm3 cm‐3) and the scaled frequency [SF = (Fa − Fs)(Fa − Fw)‐1]. The SF represents the ratio of individual sensor's frequency (inside PVC pipe) response in soil (Fs) compared with sensor responses in air (Fa) and in nonsaline water (Fw) at room temperature (≈22°C). Axial and radial sensitivity studies showed that these capacitance sensors give integrated readings over a primary depth interval of 10 cm and a radial capacitance fringe within 10 cm of the wall of the access pipe. Temperature effects of air and water were measured, and the calculated effects on assessment of θv were less than the RMSE for a temperature range of 10 to 30°C. Our calibration studies indicate that these multisensor capacitance probes can be used to accurately measure volumetric soil water contents in a soil water monitoring system.
Infiltration Models for the Disk Infiltrometer
Authors: Zhang Renduo 
Published: July 2010

AbstractThe disk infiltrometer is becoming a widely used device for determining soil hydraulic properties in the field. To describe the infiltration process from the disk infiltrometer, a two‐term equation was developed. The first and second terms characterize water flow out of the disk due to capillary forces and gravity, respectively. The parameter of the first term in the equation was a product of a nondimensional coefficient and soil sorptivity. The parameter of the second term was a product of another nondimensional coefficient and soil hydraulic conductivity. Time‐dependent relationships were obtained from numerical models to determine the coefficients based on physical parameters of the infiltrometer, such as the radius and tension used, and soil retention parameters. The cumulative infiltration and steady‐state infiltration rate calculated using the two‐term equation were in excellent agreement with numerically simulated results for various soils, and radii and tensions of disk infiltrometers. Absolute relative errors of predicted infiltration were <5% for soils ranging from clay to sand. The infiltration solution is an accurate, yet simple approach to estimate fluxes from an axisymmetric source. It can also be applied to estimate soil sorptivity and hydraulic conductivity using inverse methods.