bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Soil Nutrient Distribution as Affected by Wheat‐Fallow Tillage Systems
Authors: Follett R. F. , Peterson G. A. 
Published: July 2010

AbstractResearch was conducted to determine long‐term effects of tillage on soil fertility. Our objective was to determine whether crop residue placement caused by differences in tillage would result in changes in levels of plant available nutrients and other metals in the soil. Two native grassland sites in Western Nebraska were managed under three tillage systems; no‐till, stubble‐mulch, and moldboard plow (bare fallow). The first site was in native sod until 1970 when it was plowed and an alternate wheat‐fallow rotation experiment with no fertilization begun. The second site was farmed from 1930 to 1957, then reseeded to crested wheatgrass (Agropyron desertorum) until 1969 when it was moldboard plowed and an alternate wheat‐fallow experiment with two rates of N‐fertilization (0 and 45 kg N ha−1 every other year) began. After 16 yr of cultivation, soil test values (NH4HCO3‐DTPA extract) were obtained for samples from the 0‐ to 5‐, 5‐ to 10‐, 10‐ to 20‐cm depths. Except at the lower depths, plow tillage, as compared to no‐till or stubble mulch, decreased levels of soil organic matter and extractable K, Zn, Cu, and Pb at both sites, while extractable Ni was decreased at only one site and extractable P, Fe, Mn and Cd were decreased at the other site. Extractable nutrients and metals were generally not affected by tillage in the 10 to 20 cm depths. Fertilization with N decreased soil pH and extractable inorganic P and Zn levels but increased extractable organic‐P, Fe, Mn, Pb, Cd, and Ni in the 0‐ to 5‐ cm depth. Soil organic matter and extractable P, K, Mn, Cu, Pb, and Cd levels decreased with depth. This study shows that the adoption of no‐till, compared to stubble‐mulch or plow‐tillage, maintains fertility status of topsoil nearer to that of native prairie soil. Accumulation of crop residues and maintenance of soil organic matter levels appear to be key factors in sustaining soil fertility status of Great Plains soils.
Crust Formation and Clay Migration Effects on Infiltration Rate
Authors: Helalia Awad M. , Letey J. , Graham R.C. 
Published: July 2010

AbstractA rainfall simulator study was conducted in the laboratory to investigate the effects of a cationic polymer (CP‐14), soil column thickness, water quality, and initial soil‐water content on infiltration rate (IR) and clay migration through soil. The water quality variable was imposed by synthesizing waters typical of canal water (CW) and well (WW) water from the San Joaquin Valley in California. The main difference between the waters was the electrical conductivity, which was 0.05 and 0.70 dS m−1 for CW and WW, respectively. The IR increased with increasing polymer concentration, and the highest incremental effect was between 0 and 5 mg L−1 polymer. The effluent clay concentrations were very small with WW but high with CW. The effluent clay concentrations tended to decreased with increased polymer concentration. The IRs increased, whereas the effluent clay concentrations decreased, with increased woil column thickness. There was, however, appreciable migration of clay beyond the 30‐cm soil thickness. The IR was slightly higher and the effluent clay concentration slightly lower in initially prewet as compared to air dry soil. If clay retention in columns clogged pores, the IR would be expected to decrease as soil column thickness increases. The results were opposite, suggesting that other mechanisms were involved. The formation of a crust at the soil surface having low hydraulic conductivity would be consistent with the observed results. Increased polymer concentrations were associated with increasing hydraulic conductivity of the crust, but had no consistent effect on the hydraulic conductivity of the underlying layer. Thus, the main treatment effect was on crust formation. Scanning electron micrographs showed loose, bare particles on the soil surface underlain by a dense compacted layer with or without polymer treatments. Below the dense layer the structure was more open. Therefore, under our experimental conditions, crust formation appears to be a more significant factor affecting IR than clogging of pores by clay migration. The relatively small difference in IR between CW and WW could be larger in the field where long‐term soil clogging could be more effective.
Soluble Organics from Forest Litter and their Role in Metal Dissolution
Authors: Pohlman Andrew A. , McColl John G. 
Published: July 2010

AbstractThe effect of soluble organics from O1 and O2 litter of seven overstory and understory forest species on dissolution of Al, Fe, Mg, and Mn from two forest soils was investigated. Litter was leached in absence and presence of soil under controlled laboratory conditions, and the leachates were analyzed. In absence of soil, different litters varied widely in their ability to release dissolved organic carbon (DOC) and metals. No significant correlations (p > 0.1) between protons consumed and DOC, Al, Mg, and Mn released from litter were found. In the presence of soils there was a direct relationship between organics released from litters and Al and Fe dissolved from soils but not for the other two metals. The predominant class of organics found in all litter leachates were acids and neutrals, and their contents were directly proportional to total organics dissolved. Thus, hydrophobic plus hydrophilic acid, base, and neutral content of litter leachates corresponded to mean values of 49.6, 8.8, and 41.1%, respectively, for all litters. Total acid content was composed of 30.6% hydrophobics and 18.5% hydrophilics. A good correlation was obtained between soil dissolved Al and hydrophobic acids (r = 0.91, p < 0.001), Al and Fe, and hydrophilic acids (r = 0.93, r = 0.85, p < 0.001, respectively). Polyphenolics constituted from 10 to 23% of the DOC content of both O1 and O2 litter extracts. Polyphenolic content was highly correlated with dissolved Al (r = 0.94, p < 0.001) and with dissolved Fe (r = 0.80, p < 0.001). Five aliphatic acids and six aromatic acids were detected and quantified. Free‐organic acids with high chelating abilities such as oxalic, malic, gallic, and protocatechuic acids made up 60 to 80% of the identified free‐acid content of six litter leachates. Significant correlation was obtained between total free‐organic acid content and dissolved Al (r = 0.87, p < 0.001) and Fe (r = 0.82, p < 0.001) from soils.
Goethite and Hematite Formation in the Presence of Clay Minerals and Gibbsite at 25°C
Authors: Schwertmann U. 
Published: July 2010

AbstractAfter 8.4 yr at 25 °C under water, ferrihydrite was almost completely converted into a mixture of goethite and hematite. In contrast, aging in the presence of various clay minerals and gibbsite retarded (kaolinite, illite, smectite, gibbsite) or even blocked (soil smectite, allophane) transformation. The conversion rate was inversely related to the final Si concentration in solution. In addition, the presence of clay minerals resulted in higher hematite to goethite ratios, lower mean crystallite dimensions for both oxides, and the incorporation of Al into the goethite and hematite structures. Similar effects have been observed for coexisting goethite and hematite in soils.
The Effect of pH on Sodium‐Calcium and Potassium‐Calcium Exchange Selectivity for Cecil Soil
Authors: Rhue R. D. , Mansell R. S. 
Published: July 2010

AbstractCation exchange capacity (CEC) and cation‐exchange equilibria involving Na, K, and Ca were measured on the <50µm fraction of Cecil sandy loam soil (Typic Hapludult) at pH values between 4 and 8. This was achieved by equilibrating the soil separate in acetate buffers followed by equilibration in 0.1 M chloride solutions. Exchangeable cations were removed by five sequential extractions with 0.5 M Mg(NO3)2. The CEC increased two‐ to threefold between pH 4 and 8, indicating the presence of a large amount of pH‐dependent charge. CEC measured with Ca exceeded that measured with Na and was presumed to result from a greater amount of exchange between Ca ions in solution and hydrogen on the soil organic fraction. In Na‐Ca and K‐Ca exchange systems, Ca accounted for most of the increase in adsorbed metal cation charge as pH increased from 4.5 to 6.5. Estimates of exchangeable hydrogen were obtained from the relationship between CEC and pH and included in calculations of adsorbed mole fractions. Vanselow selectivity coefficients indicated that the Cecil soil preferred Ca over Na but that selectivity for Na increased sharply at low pH and low Na mole fractions. The selectivity for K relative to Ca also increased with decreasing K mole fraction with K preferred over Ca at low K mole fractions. Potassium added to Na‐Ca systems displaced more Na than Ca from the exchanger, resulting in an apparent increase in selectivity for Ca relative to Na.
The Point Representation of Soil
Authors: Holmgren George G. S. 
Published: July 2010

AbstractThe ambiguities of the current pedon concept are shown to derive from a dual reference to the incompatable logics of J.S. Mill and P.W. Bridgeman. It is argued that location is the proper referent for soil observations and that operational definitions should apply only to the process of sampling and not to the creation of spatial bodies. An alternate pedon definition is proposed that spatially and temporally relates individual observations to a common point of geographic reference. This allows for the systematic assignment of one‐, two‐, and three‐dimensional soil features to point locations as realizations of a sampling procedure.
Factors Influencing the Dispersibility of Clay in Worm Casts
Authors: Shipitalo M. J. , Protz R. 
Published: July 2010

AbstractEarthworm activity is believed to be beneficial for the maintenance of good soil structure; however, some research suggests that it promotes soil degradation. Factors affecting the contribution of casting activity to aggregate stability were assessed by measuring clay dispersibility in casts produced by Lumbricus terrestris L. and Lumbricus rubellus Hoff. in laboratory cultures when provided alfalfa (Medicago sativa L.), bromegrass (Bromus inermis Leyss.), red colver (Trifolium pratense L.), or corn (Zea mays L.) leaves or no food. Fresh, moist casts were 26 to 41% more dispersible than uningested, moist soil. Aging reduced dispersibility of moist casts produced under alfalfa, red clover, and corn leaf diets and after 32 d casts were 26% more to 16% less dispersible than uningested, moist soil. Casts aged moist and analyzed after air drying were unaffected by aging but were 9% more to 49% less dispersible than uningested, dried soil. The effects of aging and drying increased as cast organic carbon content increased, therefore L. rubellus casts, which contained more incorporated organic matter than those of L. terrestris, were less dispersible than L. terrestris casts for most treatments. The initial dispersibility increase was due to interparticle bond disruption caused by ingestion and peristalsis. Restoration and improvement in stability was probably due to thixotropic hardening and bonding of clay with incorporated organic debris. Because fresh worm casts are highly dispersible, surface casting activity in areas exposed to raindrop impact may contribute to soil erosion and crusting. Casting activity should enhance soil aggregate stability if casts are aged or dried before being subject to dispersion.
Soil and Plant Response to Three Subsoiling Implements
Authors: Busscher W. J. , Karlen D. L. , Sojka R. E. , Burnham K. P. 
Published: July 2010

AbstractMany Southeastern Coastal Plain soils require deep (>0.45 m) inrow tillage or subsoiling to disrupt dense tillage/traffic pans and/or eluvial (E) horizons. Three subsoiling implements [Super Seeder (SS), ParaTill (PT), and Kelly (KE)] were compared on Norfolk (Typic Paleudult) loamy sand to assess their effectiveness in developing and maintaining a proper rooting environment for corn (Zea mays L.). Soil strength (cone index) for the implements was evaluated with and without conventional surface tillage (disking). All three subsoiling implements effectively disrupted the E horizon regardless of surface tillage, but the 67% stand establishment in nondisked treatments was significantly lower than for disked treatments (92%). However, yields were not significantly different. Significant differences in soil strength were measured among subsoiling implements at the beginning of each growing season. In 1985 mean profile soil strength was lower (P ≤ 0.10) for SS and PT than for KE. In 1986, soil strength was lower (P ≤ 0.10) for SS than either PT or KE. The consistent difference between SS and KE occurred because SS disrupted a larger area than the thinner‐shanked KE. Nondisked treatments had mean soil strength that was 0.32 MPa lower within the row than disked treatments, but disked treatments had mean soil strength that was 0.37 MPa lower between the rows. Soil strength results suggest that Coastal Plain soils, which have been subsoiled, are less likely to restrict root development regardless of implement with, or without, prior surface tillage.
Neutron Moisture Meter Calibration in Large Diameter Boreholes
Authors: Tyler Scott W. 
Published: July 2010

AbstractIn studies of soil moisture flux in the arid, alluvial basins of Nevada, drilling technologies have been developed to easily and economically install 15‐cm diam. Steel casing to depths of up to 100 m. Laboratory and field calibration of a low source strength (3.7 × 108 Bq or 10 mCi) neutron moisture meter was carried out to determine the impact of such large casing on tool performance. Both laboratory and field tests showed that a quadratic calibration equation relating returned thermal neutron counts (N) to the volumetric water content (θ) of the form
urn:x-wiley:03615995:saj2sssaj198803615995005200030053x:equation:saj2sssaj198803615995005200030053x-math-0001 was acceptable to determine soil profile water content. The density of thermal neutrons returned to the detector was considerably reduced when compared to reported fluxes in traditional small diameter aluminum access pipe. This reduction is attributed to the increased air gap between the tool and the soil, and neutron capture by the steel casing.
Integral Estimates of the Sorptivity
Authors: Lockington D. , Parslow J. , Parlange J.‐Y. 
Published: July 2010

AbstractThe second‐order accuracy of several well‐known integral estimates of the sorptivity is shown to be limited to a particular class of rapidly varying diffusivities. This class includes the exponential and power‐law diffusivities commonly used in the description of soil‐water flow. The derivation of the sorptivity estimates and the argument for second‐order accuracy are clarified and a new formula for the sorptivity is derived that applies to a wider class of diffusivities.
Quasi‐Analytical Solutions of the Soil Water Flow Equation for Problems of Evaporation
Authors: Novak Michael D. 
Published: July 2010

AbstractQuasi‐analytical solutions of the one‐dimensional soil water flow equation applied to problems of evaporation are derived and compared with exact numerical solutions available in the literature. Constant‐concentration and constant‐flux surface boundary conditions and semi‐infinite and finite soil columns are considered. For the semi‐infinite soils the quasi‐analytical technique of Philip and Knight (1974) is very successful in predicting the water content profiles for the constant‐concentration condition, and only moderately so for the constant‐flux condition. Their iterative procedure for the flux‐concentration function converges rapidly in the constant‐concentration case but an analogous procedure diverges in the constant‐flux case.For finite soils the simple assumption that the rate of drying of the column is independent of depth in the flow equation leads to accurate predictions of the water content profiles for the constant‐concentration case, and for the constant‐flux case if the potential evaporation is low, the soil is shallow, and/or the initial hydraulic diffusivity is high. For conditions other than these roughly accounting for the higher rate of drying that occurs near the surface in this case greatly improves the agreement.
Inhibition of Hydroxyapatite Precipitation in the Presence of Fulvic, Humic, and Tannic Acids
Authors: Inskeep William P. , Silvertooth Jeffrey C. 
Published: July 2010

AbstractThe kinetics of precipitation of hydroxyapatite (Ca5(PO4)3OH, HAP) may be important in explaining the oversaturation of many natural waters with respect to pure HAP. Consequently, the objectives of this study were to determine the rate of HAP precipitation in the absence and presence of organic acids commonly found in soil solutions, which might act as potential inhibitors of solid phase precipitation. In well‐stirred solutions, the forward rate of HAP precipitation (R) between pH 7.4 to 8.4 was described with the experimentally derived rate equation: R = skfγ2γ3[Ca2+][PO3‐4], where s = HAP surface area (m2L−1), kf = forward rate constant (L2mol−1m−2s−1), γ2 and γ3 = di‐ and trivalent ion activity coefficients calculated from the Davies equation, and brackets represent concentrations of free hydrated species (mol L−1). The average kf in the absence of organic acids was 173 ± 11 L2mol−1m−2s−1. In the presence of 0.6 mM, 0.68 mM and 0.98 mM CTS (total soluble organic C) added as fulvic, humic, or tannic acid, the kf decreased to 2, 19, and 16 L2mol−1m−2s−1, respectively. The mechanism of precipitation inhibition in the presence of these acids appears to be adsorption of the organic ligand on the HAP seed crystals, thereby blocking sites for crystal growth. Smaller molecular weight organic acids such as citric, gallic, syringic, adipic, and azealic acid were not as effective at inhibiting HAP precipitation per unit CTS present, which may indicate the importance of larger molecular weight acids on actual physical coverage at the HAP surface. The inhibition of HAP precipitation in the presence of humic, fulvic, and tannic acids may explain why many soil solutions are supersaturated with respect to pure HAP, and why increases in P concentrations are observed in many agricultural studies in the presence of sludge or manure.
Potentially Mineralizable Nitrogen in Disturbed and Undisturbed Soil Samples
Authors: Cabrera M. L. , Kissel D. E. 
Published: July 2010

AbstractCalculation of the correct nitrogen (N) fertilizer rate for a crop requires an estimate of the amount of N that mineralizes from soil organic matter during the growing season. A method proposed by Stanford and Smith for estimating N mineralization sometimes results in overpredictions which may be due to the use of disturbed soil samples. To study the effect of soil disturbance, we measured N mineralized in disturbed and undisturbed soil samples, and determined models that properly described the data for each type of sample. A double exponential model was required for disturbed samples, whereas a single exponential model was adequate for undisturbed samples. Although in general, models fitted to disturbed samples could not be used to predict N mineralized in undisturbed samples, they could be used to estimate the parameters of the single exponential model for undisturbed samples. Parameters estimated using this approach, together with daily values of soil temperature and water content, allowed reasonable predictions of the amounts of N mineralized in fallow plots on Haynie (coarse‐silty, mixed, calcareous, mesic Mollic Udifluvent) and Wymore (fine, montmorillonitic, mesic Aquic Argiudoll) soils. Parameters of the single exponential model for undisturbed samples could also be estimated from total N and clay contents of the soil. The results suggest that it may be possible to obtain accurate estimates of N mineralized in the field by estimating, instead of determining, the parameters of the single exponential model for undisturbed samples.
Horizontal and Vertical Kriging of Soil Properties Along a Transect in Southern New Mexico
Authors: Nash M. H. , Daugherty L. A. , Wierenga P. J. , Nance S. A. , Gutjahr A. 
Published: July 2010

AbstractThe application of geostatistical analysis to evaluate a soil transect was explored by measuring soil properties in four equal depths (0–0.3, 0.3–0.6, 0.6–0.9, and 0.9–1.2 m), at 30‐m intervals along a transect of 1800‐m length in southern New Mexico. Semivariograms were computed for clay, sand, coarse fragments, and CaCO3 percent for each depth along the transect. The horizontal semivariograms were combined to form one semivariogram to account for the anisotropy in the measurement procedure. A similar procedure was used for vertical semivariograms to account for the anisotropy in the measurement units. The combination of the equations describing the horizontal and vertical semivariograms was used in a kriging program. The kriging program was used to estimate values of soil properties at 2245 grid points from the 240 original measurements. Two‐dimensional, kriged contour maps of clay, sand, coarse fragments, and CaCO3 percent were constructed. It appears the kriging technique has excellent potential in preparation of two‐dimensional vertical contour maps of soil properties.
Potentially Available Nitrogen and Phosphorus Along a Chaparral Fire Cycle Chronosequence
Authors: Marion G. M. , Black C. H. 
Published: July 2010

AbstractThe objectives were to examine the effect of time, aspect, and soil horizon on N and P availabilities across a 4‐ to 85‐yr‐old post‐fire chaparral chronosequence. Nitrogen and P availabilites were measured with plant bioassays, soil incubations, soil chemical extractions, and field leaf analyses. The A horizons contained significantly higher levels of available N and P than B horizons. In general, N availability was higher in north aspect stands than in south aspects stands, while P availability was higher in south aspect stands than in north aspect stands. Nitrogen availability increased with increasing stand age up to 50 to 60 yr (aggradation phase); beyond 60 yr, N availability declined (degradation phase). Phosphorus availability decreased logarithmically with increasing age. Declining N availability in the older stands was due to declining total soil N and a decline in the fraction available; the declining P availability in the older stands was due to a decline in the fraction available. The lowering of both soil and plant N and P concentrations in older stands may contribute to stand senescence.
Estimating Soil Nitrogen and Carbon Pools in a Northern Hardwood Forest Ecosystem
Authors: Huntington T.G. , Ryan D.F. , Hamburg S.P. 
Published: July 2010

AbstractAn intensive soil sampling design was evaluated to determine what resolution could be obtained in N and C pool size estimates in a northern hardwood forest soil. Pits of measured volume were excavated by horizon in the forest floor and in three depth strata in the mineral soil. Future comparisons should be able to detect differences in N and C pool sizes ranging from 8 to 25% of the observed mean values depending upon the element and depth strata. Future sampling should detect changes of 230 and 130 kg N ha−1 in the forest floor (combined O horizons) and 0‐ to 10‐cm stratum in the mineral soil respectively. Similarly, changes of 5.9 and 2.4 Mg C ha−1 should be detectable for forest floor and 0 to 10 cm pools respectively. Soil N content for the forest floor was 1300 kg N ha−1. For the mineral soil depth strata (0–10 cm, 10–20 cm, 20 cm to the bottom of the B horizon), N contents were 1600, 1200 and 3100 kg N ha−1 respectively. Total solum N content was estimated to be 7200 kg N ha−1. Soil C contents for the combined O horizons, 0‐ to 10‐, 10‐ to 20‐ and ≥ 20‐cm strata were 30, 32, 27 and 73 Mg C ha−1 respectively. The total solum C content was estimated to be 160 Mg C ha−1. Concentrations of soil N and C were positively correlated with elevation over the 240 m range studied, but soil pools of N and C were not correlated with elevation or soil mapping unit.