bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial Variation of Crop Residue Incorporated by Tillage
Authors: Staricka J. A. , Allmaras R. R. , Nelson W. W. 
Published: July 2010

AbstractSpatial distribution of crop residues incorporated by tillage is generally unknown even though the soil environment for roots, soil microbes, and water flux may be greatly affected. Variations in depth and concentration of oat (Avena sativa L.) residue and tracers (ceramic spheres and polyethylene chips) were measured after incorporation by disk, chisel, or moldboard plow as a primary tillage. Depth distribution of root tissue in an untilled area was also measured. In 1987 and 1988, 60 to 120 soil cores (1.8‐cm diam.) per treatment were taken to a 30‐cm depth immediately after tillage and sectioned into 2‐cm increments (a 5‐cm3 volume). Residue amount, tracer presence, and soil bulk density were measured in each 5‐cm3 sample. Moldboard‐plowing treatments incorporated crop residue to a depth of 28 cm; chiseling and disking incorporated residue to 10 cm. Despite differences in depth of incorporation between tillage treatments, residue and tracers were generally in a 10‐cm band of each 30‐cm‐deep core from all tillage systems. Frequency distributions of residue concentration in individual 5‐cm3 samples were not normal (Gaussian); rather, they were monotonic and positively skewed. Maximum concentrations of crop residue in a 5‐cm3 sample (135.0 mg cm−3 in 1987 and 48.1 mg cm−3 in 1988) were similar among tillage treatments and were greater than the average concentration by a factor of 10 for disk and chisel and 30 for moldboard plow. Samples containing incorporated residue had a distinctly higher soil porosity than samples in general. Primary tillage buries crop residue without effectively dispersing in a microscopic scale throughout the tilled zone. Ceramic spheres and polyethylene chips worked equally well as tracers for incorporated residue.
Soil Solution Phosphorus Dynamics in a Whole‐Tree‐Harvested Northern Hardwood Forest
Authors: Yanai Ruth D. 
Published: July 2010

AbstractForest harvest drastically alters nutrient cycling, yet stream water and mineral‐soil solutions typically show little change in P concentrations after forest disturbance. Changes in P availability and movement are more likely to be detected in forest‐floor solutions, since P can be strongly sorbed in soil. Tension‐free lysimeters were used to compare forest‐floor and mineral‐soil solution total‐P concentrations in whole‐tree‐harvested and undisturbed forest sites for 2 yr after harvest in the Hubbard Brook Experimental Forest in New Hampshire. Mean total‐P concentrations in solution in the forest floor (Oa horizon) were significantly higher in whole‐tree‐harvested sites (248 µg P L−1) than in undisturbed forest sites (67 µg P L−1), presumably due to reduced plant uptake of P. Mean P concentrations in mineral‐soil solution remained low after whole‐tree harvest (32 µg P L−1 in the Bh and 15 µg P L−1 in the Bs), consistent with the high P‐sorption capacity of the mineral soil. Phosphorus flux in soil solution from the Oa to the B horizon, calculated from monthly mean P concentrations and monthly water flux simulated by a hydrologic model, was greater in whole‐tree‐harvested sites (1.0 kg P ha−1 yr−1) than in undisturbed forest sites (0.3 kg P ha−1 yr−1) in the first 2 yr after the disturbance. This redistribution of P from the forest floor to the mineral soil far exceeds stream‐water export of dissolved P (0.02 kg P ha−1 yr−1) but is small compared with forest‐floor stores (85 kg P ha−1).
Calcination Effect on the Agronomic Effectiveness of Apatitic North Carolina Phosphate Rock
Authors: Chien S. H. , Hammond L. L. 
Published: July 2010

AbstractCalcination of apatitic phosphate rock (PR) is one of the means to increase the grade (total P content) of the mineral. The objective of this study was to investigate the effect of calcination on the solubility and agronomic effectiveness of apatitic North Carolina PR in a greenhouse experiment. A Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult) with pH 4.8 was used. Fertilizers were mixed with the soil at P rates of 0, 50, 150, and 300 mg P kg−1. Funks G5757 maize (Zea mays L.) was grown for 6 wk for each of two crops. The results showed that the degree of carbonate substitution for phosphate in the apatite structure was decreased from 1.20 to 0.32 mol after calcination. The corresponding decrease in neutral ammonium citrate solubility was from 2.7 to 0.8%. Dry‐matter yield and P uptake by maize in two successive crops also decreased due to calcination. Across the range of the P rates used in two maize crops, an average reduction in dry‐matter yield of 77% was calculated for the calcined PR relative to uncalcined PR. Thus, apatitic PR used for direct application should not be calcined, even though calcination can increase its total P content.
Estimation of Hydraulic Conductivity from Effective Porosity Data for Some Indiana Soils
Authors: Franzmeier D. P. 
Published: July 2010

AbstractHydraulic‐conductivity data are needed to predict how soils will respond to various uses. Saturated hydraulic conductivity (Ks), however, has been determined for only a few soils. Ahuja et al. proposed a model by which Ks can be estimated from effective porosity (φ3), the difference between total porosity and the volumetric soil water content at 33 kPa of suction. If this relationship were known, Ks could be predicted for many more soils using available water‐retention information. Previously, Ks had been determined in saturated soil horizons by the piezometer method for a set of soils in Indiana. These data were summarized by soil classes, called lithomorphic classes, based on origin of parent material, kind of soil horizon, and soil texture. More recently, bulk‐density and water‐retention measurements were summarized using similar classes. In this study, Ks is related to φe for some Alfisols and Mollisols of Indiana. The relationship is Ks = 5.01 × 10−3 × φ3.21e, where Ks is in m/s and φe is in m3/m3. This compares favorably with the relationships found by Ahuja et al.
Complexation of 1‐Naphthol by Humic and Fulvic Acids
Authors: Chen S. , Inskeep W. P. , Williams S. A. , Callis P. R. 
Published: July 2010

AbstractComplexation of organic solutes with dissolved humic substances may have a significant effect on the chemistry and fate of contaminants in natural systems. The complexation of 1‐naphthol with dissolved humic and fulvic acids (HA and FA) in 0.01 M KCl was studied using fluorescence quenching. No increase in quenching at elevated temperature and an increase in quenching ratio at higher viscosity both indicated that the quenching was due to the formation of naphthol‐HA water‐soluble complexes. Conditional equilibrium constants for the association of 1‐naphthol with humic and fulvic acids were estimated from the Stern‐Volmer equation, and ranged from 9.7 to 33.4 L/g C. In general, HA showed a stronger affinity for 1‐naphthol than FA. The ionic strength of the solution, adjusted using KCl and CaCl2, did not significantly affect the complexation of 1‐naphthol with HA. The quenching ratio increased as the pH of the solution increased, suggesting that changes in the dispersion of HA polymers or additional binding mechanisms result in increased HA complexation of naphthol at higher pH. The complexation of 1‐naphthol with HA was enhanced in the presence of Cu2+ and Zn2+ at a pH higher than the dissociation constant (pKa) of 1‐naphthol (9.34). This suggests that cation bridging between functional groups of anionic organic solutes and humic or fulvic acids is an additional binding mechanism for the association of organic solutes with soluble humic substances.
Ethylene Inhibition of Ammonium Oxidation in Soil
Authors: Porter Lynn K. 
Published: July 2010

AbstractSmall quantities of ethylene (C2H4) are produced by bacteria and fungi in soils. Ethylene is produced when nitrogenase activity is measured by acetylene (C2H2) reduction. Acetylene has been used as a nitrification inhibitor and has been shown to produce C2H4 in flooded rice soils. Whether C2H4 affects the oxidation of NH4 by the soil's nitrifying organisms and at what concentrations was the focus of this study. A Weld clay loam surface soil (fine, montmorillonitic, mesic Aridic Paleustoll) was treated with (NH4)2SO4, subjected to various partial pressures of C2H4 and incubated at 30 °C. At designated incubation times, the atmospheres of the incubation flasks were analyzed for O2, CO2, and C2H4 by gas chromatography (GC) and the soil was analyzed for NH4, and NO3 plus NO2 by steam‐distillation procedures. At a C2H4 partial pressure of 0.017 kPa, NH4 oxidation was similar to untreated samples. At a C2H4 partial pressure of 0.17 kPa, NH4 oxidation was partially inhibited and, at a C2H4 partial pressure of 4.55 kPa, inhibition was nearly complete.
Injection of Nitrogen‐15 into Trees to Study Nitrogen Cycling in Soil
Authors: Horwath William R. , Paul Eldor A. , Pregitzer Kurt S. 
Published: July 2010

AbstractMost 15N dilution techniques disturb either the soil or N‐pool size. The objective of this study was to develop a method of labeling the roots of Populus trees with 15N without physically disturbing the soil. Such a method would enable the direct measurement of the flux of 15N from dead roots into the soil organic matter. Leaf and root biomass were labeled by injection of 15N directly into the vessel elements of hybrid Populus trees during their second growing season. The 15N was uniformly distributed throughout the canopy and root system. The rate and amount of 15N turnover from plant tissue can be determined by pool transfer or through differences in plant 15N concentrations. The 15N was detected in the dead‐root pool 8 wk after injection, indicating root turnover. Results demonstrate the ability to measure the contribution of fine‐root litter to N‐cycling processes without disturbing the soil environment.
Bromide and Nitrate Movement in an Irrigated Cotton Production System
Authors: Silvertooth J. C. , Watson J. E. , Malcuit J. E. , Doerge T. A. 
Published: July 2010

AbstractA field experiment was conducted for the purpose of determining the worst‐case potential for solute leaching under furrow‐irrigated conditions, and to assess the spatial variability associated with solute movement. The experiment was carried out on a Mohall sandy loam soil (fine‐loamy, mixed, hyperthermic Typic Haplargid) within a field of upland cotton (Gossypium hirsutum L.), with uniformity of all management factors including fertilizer N and irrigation water. Six mainplot areas were identified throughout the study area to provide characterization of spatial variability. Within each main plot, five subplots (1 m2 each) were further identified. To each subplot area, 20 g KBr was applied in 500 mL of solution using the Br‐ as a biologically conserved tracer. Soil from each subplot was sampled to a depth of 180 cm and separated into 30‐cm depth increments. Soil samples were then subjected to a 1:1 (soil/water) extraction and analyzed for Br‐ and NO‐3‐N. Appreciable amounts of solute movement were measured, with a very high degree of spatial variability. The highest degree of leaching potentials was measured early in the season, when soil water depletions were the lowest and crop root development would not be extended past very shallow regions of the soil profile. The results reinforce the need to split fertilizer‐N applications throughout the course of a growing season, and to base fertilization rates and frequency on properly calibrated plant‐tissue tests.
Fiberglass Wicks for Sampling of Water and Solutes in the Vadose Zone
Authors: Boll J. , Steenhuis T. S. , Selker J. S. 
Published: July 2010

AbstractSampling solute concentrations in the vadose zone provides an early‐warning system for groundwater pollution. Various sampling devices are available. This study evaluates the functionality of fiberglass wicks in a soil solution sampler. Fiberglass wicks act as a hanging water column, drawing water from the undisturbed field soil without external application of suction. Flow characteristics of wicks were observed in the laboratory by miscible‐displacement tests using Br and an organic dye. The matric potential in the wick as a function of flow rate was measured. Fiberglass wicks behaved like a porous medium that effectively could apply a suction to the soil while only minimally retarding the organic dye. The relationship between matric potential, moisture content, and unsaturated conductivity was determined for several wicks. Based on these relationships, a set of curves was produced depicting travel time of nonadsorbed chemicals and the matric potential in the wick as a function of flow rate. These curves can be used for selecting optimum wick length and diameter for a given sampler configuration.
Nitrogen Uptake of Mesquite Seedlings at Conventional and Exponential Fertilization Schedules
Authors: Imo M. , Timmer V. R. 
Published: July 2010

AbstractExponential nutrient additions have been shown to induce steady‐state nutrition in plants and enhance seedling growth and nutrient status, which suggests improved nutrient efficiencies during the growing season. The objective of this study was to compare periodic growth, plant nutrient status, and N uptake of desert mesquite (Prosopis chilensis Mol.) seedlings that received 200 mg N seedling−1 as complete fertilizer delivered either conventionally (as single dose or constant top dressing) or exponentially (as pure or modified exponentially increasing additions) during a 12‐wk rotation. Steady‐state nutrition (characterized by a stable tissue nutrient concentration) was induced for the cultural period in the modified‐exponential fertility regime. The nutrients were supplied exponentially except for higher initial amounts that compensated for the incomplete accessibility of growing medium to the small root systems. These seedlings showed consistently higher N accumulation that matched dry‐matter production, reflecting higher fertilizer‐N uptake efficiency throughout the growing season. During the same growing season, pure exponential nutrient‐addition rates appeared to achieve steady‐state conditions 4 wk later because of incomplete interception of applied nutrients by small root systems during establishment. Conventional fertility regimes caused nutrient dilution in plants with time. Nutrient uptake did not match growth in these seedlings, resulting in nutrient stress at varying stages of seedling development.
Analysis of Soil Textural Porosity Relative to Skeleton Particle Size, Using Mercury Porosimetry
Authors: Fiès J. C. 
Published: July 2010

AbstractSoil textural porosity represents the pore space due to packing of soil particles. The characteristics of this pore space are affected by particle‐size distribution. Binary mixtures of clay and skeleton (<2‐µm and coarser particles, respectively) were studied to evaluate whether the textural‐space division into clay‐fabric pore space and its complementary space, lacunar pore space, could be modified by decreasing skeleton size. Skeleton particles with diameters of 400 µm (glass beads), 20, 13, 6, and 4 µm (silt) were mixed in the wet state with various clay contents (5–90%), then dried. Mercury porosimetry was used to characterize textural pore space by volumetric pore density distribution curves (VPD) and volumes intruded into small pores of diameter <0.05 µm (VSP). For clay‐bead (400‐µm) mixtures, bimodal VPD curves occurred for all clay‐content levels, corresponding to distinct intrusion of either lacunar or clay‐fabric pores. Values of VSP, however, were only related to intrusion into clay‐fabric pore space. In clay‐silt mixtures, unimodal VPD curves occurred, and VSP values were greater, when the clay content was >60 to 70%. Similarly, VSP values and the unimodal VPD curve were both explained by hidden lacunar pores, i.e., lacunar pores intruded only via clay‐fabric pores. Clay‐fabric pore space and lacunar pore space were always present in clay‐silt mixtures, but the proportion of hidden lacunar pore space increased with clay content and at a greater rate the smaller the particle size.
Interactions between Organic and Inorganic Components in Particle‐Size Fractions Separated from Four Soils
Authors: Schnitzer M. , Kodama H. 
Published: July 2010

AbstractLittle information is available in the literature on the mechanism(s) of interaction of organic matter (OM) and inorganic crystalline and noncrystalline components in particle‐size fractions. To obtain a better understanding of this subject, five particle‐size fractions, ranging from coarse silts to fine clays, were separated from two soils from eastern Canada (Armadale and Bainsville) and from two prairie soils (Melfort and Regina). Each size fraction was characterized by chemical and mineralogical methods. Humic acids (HAs), fulvic acids (FAs), and humins were found to accumulate in size fractions ranging from medium silts to coarse clays, while aliphatics were concentrated in fractions from medium silts to fine clays. Amino acids tended to be enriched in clay fractions of the two prairie soils, but accumulated in the silt fractions separated from the two soils from eastern Canada. Except for one soil, NH3‐N accumulated in the fine silt and finer fractions, which were rich in expandable phyllosilicates. In general, amounts of OM, aliphatics, and NH3‐N tended to accumulate in fractions rich in noncrystalline inorganics. Noncrystalline inorganics separated from the two prairie soils were rich in Si, which appeared to contribute to the preferential accumulation of humin, HA, and neutral amino acids. On the other hand, noncrystalline components from the two soils from eastern Canada were rich in Al, which may have been associated with the accumulation of NH3‐N and acidic amino acids in these soils. The pH‐dependent charges of noncrystalline inorganics may also have contributed to the accumulation of OM.
Plant‐Available Nitrogen from Lentil and Wheat Residues during a Subsequent Growing Season
Authors: Bremer E. , van Kessel C. 
Published: July 2010

AbstractLentil (Lens culinaris Medikus) is being grown increasingly on the Canadian prairies as a pulse or green manure crop, and may increase N availability to a succeeding crop. This study was designed to compare the effects of lentil green manure, lentil straw, and wheat (Triticum aestivum L.) straw on plant‐available N during the growing season after application. The fate of 15N from fall‐applied (1988) lentil green manure, lentil straw, and wheat straw and spring‐applied (1989) fertilizer (NH4)2 SO4 was determined four times during the 1989 growing season at a field site located at Outlook, Saskatchewan, Canada, on a Bradwell sandy loam (Typic Boroll). Denitrification and leaching losses of 15N from added lentil and wheat straw were negligible, but 24 and 30% of the 15N in lentil green manure and fertilizer, respectively, were lost in the 6‐wk period after planting (8 May 1989). By wheat harvest (8 Aug. 1989), 7% of the 15N in lentil and wheat straw and 37% of the 15N in lentil green manure were mineralized. Addition of green manure increased net mineralization of indigenous soil N at the time of planting by 0.4 g m−2, equivalent to 10% of added green manure N. Immobilization of soil and fertilizer N was similar for lentil and wheat straw. The smaller fraction of 15N assimilated from green manure (19%) than from fertilizer (34%) by wheat was due solely to less net mineralization of green‐manure N rather than net immobilization of fertilizer N. Of the 15N added in lentil and wheat straw, 5.5% was assimilated by wheat. Thus, lentil straw was not a significant source of N in this study, while ≈40% of the N in lentil green manure was potentially available for plant uptake.
Estimating the Water‐Dispersible Clay Content of Soils
Authors: Brubaker S. C. , Holzhey C. S. , Brasher B. R. 
Published: July 2010

AbstractSoil erodibility is influenced by several soil properties including the extent to which the clay fraction will disperse in water. Because early methods for estimating soil erosion were empirical methods and did not utilize water‐dispersible clay as a parameter, few data have been collected. The recent development of the Water Erosion Prediction Project (WEPP) model, a process‐based model for predicting water erosion that uses water‐dispersible clay in the algorithm for computing interrill erodibility, resulted in an increased demand for these data. In order to accommodate this and similar models, a method for estimating the water‐dispersible clay content of soils based on existing information is needed. Data collected by the National Soil Survey Laboratory in support of the WEPP were used to identify soil properties that were significantly correlated with water‐dispersible clay and to develop equations to estimate the water‐dispersible clay content of soils based on those properties. The property most strongly correlated with water‐dispersible clay is total clay. Other properties significantly correlated with water‐dispersible clay are the water content at 1.5 MPa, dithionite‐citrate‐extractable Fe and Al, the coefficient of linear extensibility, Wischmeier's M, the very‐fine‐sand content, the ratio of cation‐exchange capacity (CEC) to total clay, Bouyoucos' clay ratio, and the CEC. A simple linear regression of water‐dispersible clay vs. total clay revealed that, for the soils included in this study, approximately one‐third of the total clay was water dispersible. However, the model only had an R2 of 0.604. When the ratio of the CEC corrected for organic carbon (CCEC) to total clay was included in the model, the R2 improved to 0.723. However, sorting the data by the ratio of CCEC to total clay instead of including it in the model improved the overall fit of the model and increased the R2 to 0.879.
Miscible Displacement: An Interacting Flow Region Model
Authors: Skopp J. , Gardner W. R. 
Published: July 2010

AbstractNo existing microscopically based models of solute transport in porous media are completely satisfactory. In particular, it is difficult to a priori provide an estimate of the hydrodynamic dispersion coefficient. We developed a model of solute movement in saturated porous materials that starts with a continuous velocity distribution instead of an average velocity. The model allows transfer of solute between regions of differing velocity. This transfer is characterized by an interaction coefficient. An approximate solution for large interaction is obtained using the method of moments. This technique shows the equivalence of the model moments to those of the classical dispersion equation. The second moment yields the dependence of the dispersion coefficient on average velocity. The empirical dependence of dispersion on average velocity is recovered if the interaction is assumed to be a linear function of the average velocity. The model also predicts the increase in dispersion observed for heterogenous materials over that for a similar homogeneous material.
Improved Apparatus for Measuring Hydraulic Conductivity at Low Water Content
Authors: Nimmo John R. , Akstin Katherine C. , Mello Karen A. 
Published: July 2010

AbstractA modification of the steady‐state centrifuge method (SSCM) for unsaturated hydraulic conductivity (K) measurement improves the range and adjustability of this method. The modified apparatus allows mechanical adjustments to vary the measured K by a factor of 360. In addition, the use of different flow‐regulating ceramic materials can give a total K range covering about six orders of magnitude. The increment of K adjustment is a factor of about 1.6. This makes it potentially useful for measuring targeted values of K or, through a trial and error procedure, of water content (θ). The range extension afforded by this modification has led to the lowest steady‐state K measurement to date: 1.1 × 10−11 m/s at θ of 0.068 m3 water/m3 for a sandy soil of the Delhi series (mixed, thermic Typic Xeropsamment).