bluuebunny/crossref_metadata_2025_split huggingface dataset:
Strongly Contrasting Redoximorphic Patterns in Virginia Valley and Ridge Paleosols
Authors: Stolt M. H. , Ogg C. M. , Baker J. C. 
Published: July 2010

AbstractSoils with bisequel morphology and classified as Typic or Plinthic Paleudults are common in the Virginia Valley and Ridge Province. Horizons in the older materials have redoximorphic features that are strongly contrasting with respect to color and distinctness of boundary. Research documenting these horizons is nonexistent. We examined the physical and chemical properties of these horizons to describe the strongly contrasting redoximorphic patterns (SCRP) and investigate their genesis. Two types of SCRP occur. In both types, redox concentrations have Munsell colors of 2.5 YR 3/6, 4/6, or 3/2. In one case, depletion features (10YR 5/6 or 6/2) are randomly distributed throughout the horizon. These horizons are dense (bulk density of 1.75 g cm−3), which restricts water movement and promotes Fe segregation. In the other type of SCRP, most Fe concentrations, depletions, and planar voids are oriented parallel to the soil surface. These soils have a fluctuating water table. Dithionite‐extractable Fe ranges from 70 g kg−1 in redox concentrations to 4 g kg−1 in adjacent depletion features. Goethite occurs in both redox concentration and depletion clay fractions. Hematite only occurs in the redox concentration clay fractions. Depletion features have lower coarse/fine ratios (separated at 20 µm), more oriented clay, and 10 to 20% more clay than associated redox concentrations. Horizons with SCRP are dominated by nodules and masses in ped interiors, and Fe depletion features along voids. Thus, Fe is primarily reduced along voids and moves into the matrix. Horizons with a fluctuating water table also contain Fe‐rich pore linings. Iron is concentrated on these surfaces because these pores are the first to drain as the water table recedes.
Morphology, Chemistry, and Mineralogy of Isotropic Aluminosilicate Coatings in a Guadeloupe Andisol
Authors: Jongmans A. G. , van Oort F. , Buurman P. , Jaunet A. M. , van Doesburg J. D. J. 
Published: July 2010

AbstractFew micromorphological and in situ submicroscopical studies exist of neoformed amorphous and crystalline clay coatings, and little is known about the genesis and distribution patterns of these coatings and their dependence on site conditions. Our study describes the distribution and composition of isotropic coatings, infillings, and pseudomorphs after roots in a Hapludand on Holocene andesitic pyroclastics in humid tropical Guadeloupe. Field observations show the occurrence of fine‐textured, very pale brown to yellow (10YR 8/3‐8/6) coatings, infillings, and pseudomorphs after roots in large pores in the Bw2 and 2C horizons of the soil. Thin‐section analyses demonstrated that these features are isotropic, translucent, nonlaminated, and appear pale yellow in plane polarized light, indicating that they consist of amorphous material. In situ submicroscopical analyses revealed that the coatings in the Bw2 horizon consist of allophane and imogolite with an Al/Si ratio of 2, whereas those in the 2C horizon consist exclusively of allophane with an Al/Si ratio of 1.4. The fine groundmass adjacent to the coatings in the Bw2 horizon has an Al/Si ratio of 1.4. The coatings resulted from precipitation of weathering products of mainly volcanic glass and plagioclase. The observed differences in composition of the coatings in the Bw2 and 2C horizons are thought to be the result of different leaching conditions.
Long‐Term Effects of Crop Management in Wheat‐Fallow: II. CENTURY Model Simulations
Authors: Parton William J. , Rasmussen P. E. 
Published: July 2010

AbstractThere is increasing need to develop models to assess the long‐term effects of management practices on soil and environmental quality, and to test these models across a wide range of environments. The CENTURY model was used to simulated long‐term management practices for wheat (Triticum aestivum L.)‐fallow agriculture. The objectives were to compare the accuracy of predicted vs. observed data and use the model to help interpret observed data and to determine the long‐term impact of crop management on C and N stabilization in soil. The model simulated grain and straw yield and grain N uptake within ±10% of the observed data, and 0‐ to 30‐cm soil C and N within ±5%. Improvement in performance requires addition of a dynamic plant growth submodel to represent the effect of soil N on C and N allocation to roots, straw, and grain. Soil C changes were a linear function of aboveground C inputs; an input of 200 g C m−2 yr−1 (4650 kg straw ha−1) was required to stabilize soil C at its present level. Estimates of soil C stabilization efficiency ranged from 12 to 27% and was highest for the high N fertilizer treatment. Soil N stabilization efficiency was higher for organic N additions (37–46%) than for inorganic additions (18–26%). Inorganic N treatments had similar N removal in grain, higher other nonidentifiable N losses, but lower N stabilization in soil than organic N treatments. Soil N data suggest that mineralization of N from the 30‐ to 60‐cm layer needs to be considered in the N budget, as nearly 39 g m2 were mineralized between 1931 and 1986.
Spatial Distribution of Soil Nutrients in a Northern Everglades Marsh: Water Conservation Area 2A
Authors: DeBusk W. F. , Reddy K. R. , Koch M. S. , Wang Y. 
Published: July 2010

AbstractIncreased nutrient loading to the northern Everglades from the nearby Everglades Agricultural Area (EAA) has raised concerns of eutrophication of this oligotrophic wetland. A field study was conducted to determine the influence of nutrient loading on spatial distribution of P, N, C, and related physico‐chemical parameters in the peat soils (Histosols) of Water Conservation Area 2A (WCA‐2A) in the northern Everglades. Field sampling of the top 30 cm of soil was performed at 74 sites across WCA‐2A. Isarithmic plots of N and P forms based on geostatistical analyses revealed widespread enrichment of P, especially in areas proximal to surface inflows importing nutrient‐laden water from the EAA. Enrichment of less magnitude was shown for soil N, while spatial variability of C, bulk density, ash content, and pH were minimal. Concentration of soil porewater NH+4‐N was typically in the 1.5 to 2.5 mg L−1 range in the interior (less impacted) region of WCA‐2A, compared with 4 to 8 mg N L−1 near surface inflows at the northern end of WCA‐2A. In contrast, soluble reactive P in the porewater varied from ≈ 100 µg L−1 or less in the interior marsh to >1000 µg L−1 near inflow structures. Mean soil total P at a depth of 0 to 10 cm was 473 mg kg−1 in the interior marsh, compared with 1338 mg kg−1 in the areas adjacent to inflows. Results of this study show that WCA‐2A soil has served as a net storage for the increased load of P in nutrient‐laden surface inflows. Much of the additional soil P is available for plant uptake, based on the magnitude of P enrichment across a large area. Nutrient enrichment in the soil corresponded with the occurrence of cattails (Typha domingensis Pers. and T. Latifolia L.) in areas previously dominated by sawgrass (Cladium jamaicense Crantz).
Unsaturated Hydraulic Conductivity from Transient Multistep Outflow and Soil Water Pressure Data
Authors: Eching S. O. , Hopmans J. W. , Wendroth O. 
Published: July 2010

AbstractSoil water retention and unsaturated hydraulic conductivity functions [K(θ)] estimated by the inverse solution technique through minimization of differences between measured and simulated transient outflow may be nonunique and differ from independently measured soil hydraulic data. Numerical and experimental studies have shown the benefit of using simultaneously measured soil water pressure head in the estimation of the soil water retention curve by the inverse technique. In this experimental study, soil water pressure head and transient cumulative outflow measured simultaneously are used to estimate K(θ). An alternative method for the direct measurement of K(θ) from transient multistep outflow experiments was adopted. Desorption experiments were carried out for disturbed Yolo silt loam (fine‐silty, mixed, nonacid, thermic Typic Xerorthent), Panoche loam (fine‐loamy, mixed [calcareous], thermic Typic Torriorthent), Hanford sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Xerorthent), and Oso Flaco fine sand columns. The optimized K(θ) values agreed well with the directly measured data for all soils, except the sand. Additionally, soil hydraulic functions so obtained for the Panoche loam agreed well with those determined using the evaporation method. Measured infiltration in a column of the Panoche loam matched numerical results using optimized parameters as determined from a sorption multistep experiment. The addition of soil water pressure head values in the optimization procedure provides unique parameters for the unsaturated hydraulic conductivity functions under our experimental conditions.
Infiltration and Redistribution of Organic Liquids in Layered Porous Media
Authors: Cary J. W. , Simmons C. S. , McBride J. F. 
Published: July 2010

AbstractThe remediation of many toxic waste sites throughout the world requires a better understanding of the flow of organic liquids in the vadose zone. The infiltration and redistribution of three water‐immiscible oils into columns filled with porous material containing different textural layers are reported. In some experiments, oil followed water into the columns and in others, water followed oil. An explicit, one‐dimensional, multiphase flow code was used to model the results. The numerical model contains elements of code that: (i) mimic the Haines jump phenomenon in dry sand, (ii) account for oil entrapment when water infiltrates, (iii) include forces on the oil phase caused by surface‐spreading pressures at the oil front in water‐wetted pores, (iv) include forces on the oil phase caused by water intrusion into hydrophilic oil‐saturated pores, and (v) generate a factor that matches the water potentials of textural layers for the initial boundary conditions. In general, the model did a reasonable job of predicting the distribution of both water and oil 8 h after infiltration was started, though some unresolved problems persist. The liquid potential matching factor and the hydrophobicity of the mineral particles induced by a transmission oil have practical applications. The matching factor may be easily adapted to all codes that model flow through layers. The in situ creation of hydrophobic mineral particles may prove useful for containing immiscible organic liquids that leak into the vadose zone.
Pore‐Scale Network Modeling of Compaction and Filtration during Surface Sealing
Authors: Ewing Robert P. , Gupta S. C. 
Published: July 2010

AbstractSurface sealing increases the probability of runoff and soil erosion, and occurs on a variety of soils worldwide. Filtration (“washing‐in”) and compaction have been reported as mechanisms of surface sealing, but the relative importance of each has not been established. We developed a pore‐scale network model to simulate these mechanisms, with the objective of determining their relative importance. Filtration was more effective than compaction in reducing soil hydraulic conductivity during seal formation, even though compaction reduced seal porosity more than filtration. Most of the particles available for filtration were deposited on the network surface rather than being washed into the network. This suggests that surface deposition may be more important than compaction or filtration in determining the seal hydraulic conductivity. The network model can predict seal hydraulic conductivity from pore‐ and particle‐size distributions and the initial hydraulic conductivity, and is potentially a useful research tool in understanding pore‐scale mechanisms in soil structure research.
Interlayer Adsorption of Polymeric Hydroxy‐Aluminosilicate Ions by Montmorillonite
Authors: Lou G. Q. J. , Huang P. M. 
Published: July 2010

AbstractAdsorption of polymeric hydroxy‐aluminosilicate (HAS) ions by montmorillonite and the formation of siliceous Al interlayers were studied. The interaction of HAS ions with Ca‐montmorillonite exhibited a linear C‐type adsorption isotherm within the range of solution Al and Si levels commonly found in acidic soils (10−5 to 10−4 M), suggesting a high capacity of Ca‐montmorillonite to adsorb HAS ions from solution. A soluble Si concentration of >6.6 × 10−5 M was required for the formation of HAS species and their adsorption by montmorillonite. The interlayer spacing (12.2–16.8 Å at 25°C and air dried) and the intensity of the major infrared bands of the adsorbed HAS ions (940 and 3500 cm−1) in the HAS‐montmorillonite complexes were found to increase with the increasing amount of HAS ions adsorbed, which further substantiated the interlayer adsorption mechanism for HAS‐smectite interactions. The partial interlayering of HAS ions in Ca‐montmorillonite resulted in the formation of HAS‐clay complexes with basal spacings of ≈12Å (at 25°C, air dried). The data suggest that the partial hydroxy‐interlayers of natural clays in acidic environments in temperate and subtropical regions may be siliceous in nature, depending on the Si level in soil solutions and other natural waters.
Aggregate‐Protected and Unprotected Organic Matter Pools in Conventional‐ and No‐Tillage Soils
Authors: Beare M. H. , Hendrix P. F. , Cabrera M. L. , Coleman D. C. 
Published: July 2010

AbstractNo‐tillage (NT) practices can result in greater soil aggregation and higher soil organic matter (SOM) levels than conventional‐tillage (CT) practices, but the mechanisms for these effects are poorly known. Our objectives were to describe the size and quality of biologically active pools of aggregate‐associated SOM in long‐term CT and NT soils of the southeastern USA. Samples were collected from replicated CT and NT plots on a Hiwassee sandy clay loam (clayey, kaolinitic, thermic Rhodic Kanhapludult) and separated into four aggregate size classes (>2000, 250–2000, 106–250, 53–106 µm) by wet sieving. Potentially mineralizable C and N and N2O emissions were measured from 20‐d laboratory incuhations of intact and crushed macroaggregates (>250 µm) and intact microaggregates (<250 µm). Three primary pools of aggregate‐associated SOM were quantified: unprotected, protected, and resistant C and N. Aggregate‐unprotected pools of SOM were 21 to 65% higher in surface soils of NT than of CT, with greater differences in the macroaggregate size classes. Disruption of macroaggregates increased the mineralization of SOM in NT but had little effect in CT. Rates of mineralization from protected and unprotected pools of C were higher in surface soils of CT than of NT. Macroaggregate‐protected SOM accounted for 18.8 and 19.1% of the total mineralizable C and N (0–15 cm), respectively, in NT but only 10.2 and 5.4% of the total mineralizable C and N in CT. Our results indicate that macroaggregates in NT soils provide an important mechanism for the protection of SOM that may otherwise be mineralized under CT practices.
Pelletizing and Soil Water Effects on Gaseous Emissions from Surface‐Applied Poultry Litter
Authors: Cabrera M. L. , Chiang S. C. , Merka W. C. , Pancorbo O. C. , Thompson S. A. 
Published: July 2010

AbstractSeveral studies have shown that the application of animal manures to soil can increase N2O and CO2 emissions. Little information is available, however, on the effect that physical characteristics of the manure can have on these emissions. The objective of this work was to evaluate the effects of physical characteristics of poultry litter (fine particles or pellets) and soil water‐filled porosity (WFP, 58 or 90%) on rates and total amounts of N2O and CO2 emissions from surface applications of poultry litter to soil. Poultry litter at 30.7 g N m−2 was surface applied to samples of Cecil loamy sand (clayey, kaolinitic, thermic, Typic Kanhapludult) that were packed in acrylic plastic cylinders. Each cylinder was placed inside a jar that was closed with a screw‐cap lid fitted with a rubber septum, and all jars were placed in an incubator at 25°C for 28d. Periodic air samplings were conducted for N2O and CO2 analyses. Maximum rates of N2O and CO2 emission occurred within the first 4 d and were highest for fine‐particle litter at 90% WFP. Cumulative CO2 emission did not differ between treatments, but cumulative N2O emission was significantly lower for fine‐particle litter at 58% WFP than for the other treatments. Expressed as a percentage of the applied N, the N2O lost represented 0.2% for fine‐particle litter at 58% WFP, and an average of 2.8% for the other treatments. These results suggest that for surface applications under the conditions of this study, pelletized litter may produce similar CO2 emission as fine‐particle litter, and may cause equal or larger emissions of N2O than fine‐particle litter.
Soluble Carbon and Nitrogen Pools of Prairie and Cultivated Soils: Seasonal Variation
Authors: DeLuca T. H. , Keeney D. R. 
Published: July 2010

AbstractRecent evidence indicates that long‐term cultivation of prairie soils reduces the ambient concentrations of soluble amino N and soluble sugars. It is not known whether cultivation has affected how these constituents fluctuate with season. This study was performed to determine if cultivation has affected how soluble sugars, soluble C, and soluble amino N fluctuate with season and whether this fluctuation corresponds with seasonal changes in microbial biomass and extractable N. Soils were sampled bimonthly and analyzed for 0.5 M K2SO4 soluble sugars (anthrone‐reactive carbon [ARC]), soluble organic C, microbial biomass, and 2 M KCl extractable amino N, NH4, and NO3. Cultivation has clearly reduced the levels of microbial biomass C, soluble ARC, and soluble amino N in these soils. Microbial biomass C was greatest in late February after thaw. Soluble ARC generally was greater in prairie soils than in cultivated soils but did not increase in concert with microbial biomass. Soluble amino N declined when microbial biomass and N mineralization increased in February. The ratio of soluble ARC to NO3‐N indicates that there is generally insufficient C available, as soluble sugars, to allow for immobilization of ambient NO3 in cultivated soils throughout the course of a year. The high ratio of soluble C to biomass C in cultivated soils may also be evidence of a reduction in organic matter quality as higher levels of soluble C appear to support lower levels of microbial biomass. Cultivation has reduced concentrations of soluble sugars and amino N and has affected how these constituents change with season. However, the relation of soluble sugars and amino N to microbial biomass is not clear.
Maintenance of Yields and Soil Fertility in Nonmechanized Cropping Systems, Bolivia
Authors: Barber R. G. , Díaz O. 
Published: July 2010

AbstractSlash and burn farmers in the tropical rain forests of eastern Bolivia are abandoning land after one rice (Oryza sativa L.) crop because of declining yields. A trial was conducted on a Typic Paleudult for 41 mo to investigate whether alternative low‐input nonmechanized cropping systems could prolong soil fertility and yield maintenance, and whether soil fertility or weeds were responsible for declining yields. Twelve cropping systems were investigated in a factorial design, with three summer‐winter crop sequences: rice‐peanut (Arachis hypogaea L.), corn (Zea mays L.)‐bean (Phaseolus vulgaris L.) later substituted by cowpea [Vigna unguiculata (L.) Walp.], and rice‐fallow (control); two weed control treatments: minimal and optimal; and two fertilizer treatments: with and without 60 kg N ha−1 and 17.5 or 35 kg P ha−1. Crop sequences significantly increased exchangeable acidity; the rice sequences significantly reduced exchangeable Ca, and corn‐bean/cowpea and rice‐peanut significantly reduced exchangeable Mg. Fertilization significantly increased soil P but decreased Ca. Foliar analysis revealed N, Mg, and Zn deficiencies in all cropping systems. Rice yields, unlike corn, were significantly increased by optimal weeding. Corn yields were dominated by fertilization, whereas rice yields were mainly influenced by fertilization in the first and fourth years, and by weeds in the intervening years. Without fertilizers, rice‐fallow was not sustainable, and only corn‐bean/cowpea was sustainable for 3 yr. With fertilization, rice‐fallow plus optimal weed control and corn‐bean/cowpea with minimal or optimal weeding were sustainable for 3 yr. Additional fertilization and future liming would be necessary for more prolonged sustainability.
Chronosequence in Almar River Fluvial‐Terrace Soil
Authors: Dorronsoro C. , Alonso P. 
Published: July 2010

AbstractThe aim of this work was to analyze how soils formed fundamentally from the erosion of granites evolve under a subhumid Mediterranean climate as a function of age. Their evolution was evaluated by means of the changes in components and properties, as well as the use of developmental indices. The soils are Xerorthents (Holocene), Haploxeralfs (Upper Pleistocene), and Palexeralfs (Middle Pleistocene). The properties have been subject to several trends: (i) some properties increase with regularity throughout the chronosequence (available water and coefficient of linear extensibility [COLE] of the Bt horizons) (ii) other properties increase strongly only during the first phases, while some continue to increase with age but only moderately (Ap horizon water retention and cation‐exchange capacity, Bt horizon dithionite‐citrate‐extractable Fe, solum thickness, clay accumulation, quartz content, and quartz/feldspar ratio), whereas other Middle Pleistocene age soil properties cease to increase (the Ap horizon silt and available water, and Bt horizon water retention and cation‐exchange capacity; (iii) others decrease with age, with pronounced decreases during the first phases (Ap and Bt horizon feldspar content and sand content and Bt horizon bulk density); and (iv) some properties are not age related (the Ap horizon base saturation and N content and the Bt horizon silt content). The horizon development indices and the soil development indices indicate good relationships with age. In most cases the rate of increase declines strongly for the oldest soils. In the great majority of cases, the properties and development indices continue to evolve through the chronosequence without reaching a steady state.